111r 111111
School ot Forestry Depatmental Series No. 14
Auburn University Auburn University, Alabama
Alabama Agricultural Experiment Station
L owell T Frobish. Director September 1994
1111
Il '1
CONTENTS
INTRODUCTION ................................................................................................................ I
CONCERN FOR NITRATES IN GROUNDWATER ........................................................................ I
Nitrogen Use in the U.S................................................................................................ 2
Nitrogen Use by Forest Industry ........................................................................................ 2
Nitrogen Use in Tree Nurseries.......................................................................................... 2
Nitrogen Harvested with A Loblolly Pine Seedling Crop ......................................................... 3
Nitrogen and Cover-Crops............................................................................................. 3
Rationale for Nitrogen Fertilization in Nurseries................................................................... 3
Nitrate Levels in Nursery Well Water ................................................................................. 5
CONCERN FOR PESTICIDES IN GROUNDWATER....................................................................... 6
Soil Fumigation.......................................................................................................... 6
Herbicide Use in Nurseries............................................................................................... 6
Weed Management ...................................................................................................... 8
Insecticides.................................................................................................................. 9
Insect and Mite Management ............................................................................................ 10
Fungicides ................................................................................................................ 11
Disease Management................................................................................................... 11
TYPICAL NURSERY REGIME................................................................................................ 11
MODELLING RUNOFF AND LEACHING AT THE ASHE NURSERY................................................. 12
MEASURES TO REDUCE AGROCHEMICAL CONTAMINATION OF GROUNDWATER ..................... 13
MITIGATING PRACTICES FOR NITROGEN ............................................................................... 13
SUMMARY .......................................................................................................................... 14
LITERATURE CITED............................................................................................................ 16
Information contained herein is available to all pers ons regardless of r ace, color, sex or national/ origin. First Printing 2M, September 1994.
ACKNOWLEDGMENTS
The author expresses apprecijation to Drs. Ken McNabb, Eric Vonce and Harold Walker for their coimioents on earlier drafts. This
work was funded in part by the Auburn University, Southierni Forest Nursery Cooperative and the National Council for the Paper
Ind/ustry for Air and Stream lIprovemient.
Managing Pesticides and Nitrogen in Southern
Pine Nurseries and Some Ways to Reduce the
Potential for Groundwater Contamination
DAVID B. SOUTH
1
INTRODUCTION
In the southern United States, chemicals are an in-
tegral part of the management of bare-root nurseries. The
rationale for using chemicals is based on economics as
they can reduce hand labor, improve the use of valuable
seed, and increase seedling performance. The cost of all
chemicals associated with loblolly pine seedling produc-
tion averages less than 0.2 cent per seedling. The cost of
nitrogen (N) fertilizers (including usage for cover crops)
is less than 0.01 cent per seedling. The most expensive
chemical treatment (fumigation with methyl bromide and
chloropicrin) costs about 0.15 cent per seedling. The to-
tal cost of producing a bare-root loblolly pine seedling is
usually less than 2.5 cents, due in part to increased effi-
ciencies provided by chemicals. In 1993, one nursery con-
tracted to grow loblolly pine for as little as 1.8 cents per
seedling (excluding seed cost).
The cost of southern pine seedling production can
be tripled when nursery managers do not use pesticides
and inorganic fertilizers. Hand labor requirements would
increase dramatically, seed costs would likely double, and
the average production goals per nursery would be low-
ered. A reduction in mean nursery production would re-
quire establishment of additional nurseries or a reduction
in levels of artificial reforestation. Due to an increase in
frequency of catastrophic losses, some of the money spent
on preparing sites for outplanting would be wasted in years
where there is an unexpected shortage of plantable seed-
lings. The standards for a plantable seedling would also
likely be lowered (accepting smaller seedlings and some
with evidence of disease). At some nurseries, oak trees
would need to be eliminated from the surrounding area,
perhaps 600 acres or more, in order to reduce the prob-
ability of infection from fusiform rust. An increase in me-
chanical cultivation would probably increase the consump-
tion of gasoline and might increase the output of carbon
dioxide. The latter are a few of the esoteric reasons for
using chemicals in nursery management. However, there
is little doubt that ceasing the use of chemicals would de-
crease the economic efficiency of tree nurseries in the
South.
CONCERN FOR NITRATES IN GROUNDWATER
Although the use of chemicals has increased the effi-
ciencies of crop production, the general population is in-
creasingly concerned with potential environmental effects.
Groundwater contamination is one of these concerns. For
example, nitrates and pesticides (to a lesser extent) can be
found in well water. Between 1988 and 1990, the Envi-
ronmental Protection Agency (EPA) sampled approxi-
mately 1,300 wells for the presence of pesticides and ni-
trates. They found that nitrates were five to 13 times more
likely to occur in drinking water wells than contamination
from pesticides (U.S. EPA 1990).
On a region-wide basis, the production of forest
tree seedlings appears to be inversely related to nitrate
concentrations in drinking water wells. For example, Ne-
braska produced only 3.6 million seedlings in 1990 and
had more than 30 percent of the drinking water wells with
more than three mg/1 of nitrate-N. In contrast, South Caro-
lina produced more than 230 million seedlings and had a
very low percentage of drinking water wells that exceeded
three mg/1 of nitrate-N (Table 1). The reason for this ap-
parent correlation is in part due to the percentage of land
covered by forests. States with a low population density
and a high percentage of land in forests generally have low
levels of nitrates in the drinking water. In contrast, states
with a high population density or a high percentage of land
in row crops tend to have high levels of nitrates in well
water. The ratio of croplands to timberlands has even
proven useful when modeling nitrates in watersheds
(Osborne 1988). Therefore, regions that harvest planta-
tions and replant nursery seedlings will have fewer prob-
lems with nitrates in groundwater than regions that con-
vert to row crops or residential areas after harvesting.
iSouth is a professor in the Auburn University School of Forestry.
2 ALABAMA AGRICULTURAL EXPERIMENT STATION
TABLE 1. EXAMPLES OF THE MAXIMUM MEASURED
NITRATE-N IN GROUND WATER BY STATE AND THE
AMOUNT OF TREE SEEDLINGS PRODUCED IN 19901
Wells with over 1990 seedling
State 3 mg/L of nitrate-N production
Pct. Thousands
States With High Nitrate
Rhode Island.......... 45.1 195
Kansas ................... . 54.2 175
Arizona ............ 38.3 0
Oklahoma .............. 35.9 72,845
New York ............ 40.3 7,300
California ............ 32.6 54,613
Delaware ................. 34.6 0
Nebraska ............. 32.7 3,611
Pennsylvania .......... 30.3 3,261
States With Low Nitrate
Georgia .............. 4.8 174,983
Florida ................ 4.3 111,052
New Hampshire..... 4.3 500
South Carolina ....... 4.1 237,655
Michigan ............. 3.9 16,489
Virginia ............... 3.4 75,806
Louisiana ............... 2.4 60,923
Mississippi ............. 1.8 79,315
'Source: Fedkiw 1991; Mangold et al. 1991.
Nitrogen Use in the U.S.
Farmers use most of the N fertilizer in the U.S.
For example, approximately 23 billion pounds of N were
sold in 1985. Of this amount, an estimated 0.2 percent
(45 million pounds of ammonium nitrate, diammonium
phosphate, urea, etc.) were used by the forest industry in
the South for pine plantations and nurseries.
It has been estimated that forests in the United
States contribute approximately 780 million pounds of N
each year as non-point sources of water pollution (Sands
1984). However, this amount is much higher than the
10,300 million pounds of N applied to forests in the South
(a 75-1 ratio). Apparently, much of the N in the EPA es-
timate comes from natural processes and little is due to
inorganic fertilization. For example, N will sometimes
flush from a watershed that has been clearcut (Krause
1982). Even so, the EPA has estimated that the forests'
contribution to N pollution is one-sixth that of the natu-
ral background levels of N (U.S. EPA 1978). In fact, some
suggest farmers should plant trees in riparian zones to re-
duce the potential of nitrates contaminating groundwater
(Licht 1992).
Nitrogen Use by the Forest Industry
Nitrogen fertilizers are used by the forest indus-
try to improve growth of pines both in pine plantations
(Allen 1987) as well as in nurseries. In 1988, the area of
pine plantations fertilized with N exceeded 66,000 acres
(NCSFNC 1989). The amount applied in one application
usually varies from 115-210 pounds N per acre. The
amount of N applied to loblolly and slash pine plantations
exceeded 10 million pounds in 1988. In contrast, the
amount of N applied to 1.9 billion southern pine seedlings
in 1988 is estimated to be 0.6 million pounds. A 1992 sur-
vey of southern pine nurseries reported that 168,000
pounds of nitrogen was used to produce 503 million seed-
lings. Therefore, the amount of N applied to southern pine
plantations is more than 16 times that applied in southern
pine nurseries.
The recovery of applied N in crop trees is higher
in forest nurseries than in forests. In loblolly and slash
pine nurseries, about 50 percent of the amount applied is
utilized by the crop. Often 150 pounds N per acre are ap-
plied during the growing season and 75-80 pounds N per
acre are removed at harvest (Boyer and South 1985). In
comparison, less than 30 percent of fertilizer N applied to
conifer stands is recovered in the above-ground tree bio-
mass (Pritchett 1979; Ballard 1984). The efficiency can
be 23-26 percent in 13-15 year-old slash pine plantations
(Pritchett and Smith 1974; Mead and Pritchett 1975). The
efficiency may only be 9-14 percent if the fertilizer is ap-
plied at time of outplanting (Baker et al. 1974).
Recovery of fertilizer N in the above-ground por-
tions of grain crops seldom exceeds 50 percent and is of-
ten lower (U.S. Congress 1990). For example, when ap-
plying 134-178 pounds N per acre to corn, the efficiency
may only be 35-40 percent. The efficiency is higher in
conifer nurseries because nursery managers use frequent
applications of N (five to 12 per year), higher plant den-
sities, and harvest both roots and shoots.
Nitrogen Use in Tree Nurseries
With regards to N fertilization, there are several
differences between plantations and nurseries. In planta-
tions, 115-210 pounds N per acre might be applied in a
single application. However, in southern pine nurseries,
150 pounds N per acre might be applied in five or six ap-
plications over one growing season. Typically, 30 pounds
N per acre would be applied every two weeks beginning
the first week in June and ending around the middle of Au-
gust. Sources predominantly used are ammonium nitrate
and ammonium sulfate while southern pine plantations are
treated mainly with urea and diammonium phosphate.
Nursery managers in other regions of the world
apply 17-100 percent more N to conifer seedlings than in
the southern U.S., where a common rate is 150 pounds N
per acre per crop. For example, in Australia, slash pine
is fertilized at 192 pounds N per acre (Donald 1991).
Bare-root nurseries in the Pacific Northwest typically re-
quire twice as much N per seedling crop than do nurser-
ies in the southern United States. It may take two years
or more to produce a plantable seedling in the Northwest
compared to one year in the South. In the Northwest, the
amount applied during the first year may be 155 pounds
N per acre (45 pounds N per acre applied pre-sowing and
MANAGING PESTICIDES AND NITROGEN 3
110 pounds N per acre applied as top-dressing). In addi-
tion, approximately 160 pounds N per acre are applied as
top-dressings during the second year (van den Driessche
1984). This average of 315 pounds N per acre per crop
is about double the amount often applied to a crop of pine
seedlings in the South.
Nitrogen Harvested with a Pine Seedling Crop
If one defines the desired weight and nutrient con-
tent for the "target seedling," then one can also calculate
the amount of N removed by a crop of seedlings. For ex-
ample, when growing 600,000 trees per acre, the amount
of N removed would be 80 pounds N per acre (assuming
each seedling contains 60 mg of N: 40 mg in foliage; 10
mg in stem; 10 mg in root). Since N fertilization in coni-
fer nurseries is about 50 percent efficient, about 160
pounds N per acre would need to be applied in order to
not lower the base level of N in the soil. If we only ap-
ply 75 pounds N per acre and removed 80 pounds N per
acre, we would be relying on organic matter, N fixation,
air pollution, and soil reserves to provide the extra N. This
may actually work during the first few years, but the sys-
tem would not be sustainable. After several harvests, suc-
ceeding seedling crops would begin to suffer. This may
have occurred in the past when nursery managers produced
several seedling crops without applying sufficient amounts
of fertilizer. In order not to "mine" the soil, some re-
searchers recommend applying 150 pounds N per acre to
loblolly, slash, shortleaf, and sand pine seedlings that are
grown at a density of 20-23 seedlings per square foot.
However, higher rates would be required with higher den-
sities or when fertilizing with the objective of improving
height growth in the field.
Nitrogen and Cover-Crops
Nitrogen is used in nurseries to promote the
growth of both seedlings and cover-crops. Typically, about
half of the seedbed area is sown to cover crops each year.
Due to potential buildup of disease (Hamm and Hansen
1990) and insects (Dixon et al. 1991), legumes are not of-
ten used as cover-crops. Cover crops sown in the spring
are usually monocots. These include a hybrid of sorghum
and sudan grass, millet, and corn. Nursery managers typi-
cally apply about 75 pounds N per acre to their cover crop
unless they are adding woody materials (i.e. sawdust, bark,
chips, etc.) as an organic amendment. In that case they
usually add about 215 pounds N per acre. The most com-
mon rotation is two years of monocots to two years of
seedlings. Therefore, some nursery managers apply about
one pounds N to a cover-crop for every two pounds N that
is used on the seedling crop.
The rate of N fertilization used for pines will
range widely depending upon species, soil texture and
nursery manager. The rate can range from 21 pounds N
per acre at some to 300 pounds N per acre at others
(Larsen et al. 1988; Dierauf 1991). The amount applied
often varies depending on the nursery manager's philoso-
phy (in some cases researcher's philosophy). To a lim-
ited extent, N rates are based on results from nursery and
field trials (Switzer and Nelson 1963; Hinesley and Maki,
1980; Duryea 1990; Blake and South 1990; Diearuf 1991).
Rationale for Nitrogen Fertilization in Nurseries
There are several reasons why N is applied in
nurseries. These include: (1) producing a healthy cover-
crop to reduce soil erosion; (2) producing a healthy green-
manure crop to improve soil organic matter; (3) reducing
the cull percentage of the seedling crop and thereby in-
creasing seed efficiency; (4) improving the root growth po-
tential of the seedling crop; and (5) improving the perfor-
mance potential of the seedling crop.
One way nursery managers could reduce the use
of N would be to cease using N for cover-crops (used to
prevent soil erosion) and green-manure crops (used to im-
prove organic matter). Using N fertilizers only for the
seedling crop could reduce total nursery consumption by
approximately one third. However, biomass produced by
the monocots would be reduced and this would decrease
their utility. This could be overcome to some extent by
applying organic amendments such as pine bark or
composted sawdust.
Some suggest that legumes be used as cover-
crops. However, use of beans as a cover-crop would in-
crease the likelihood of increasing pathogens such as
Fusarium and Macrophomina which can reduce seed ef-
ficiency (Hamm and Hansen 1990; Dixon et al. 1991). In
addition, herbicides are sometimes used to control weeds
in legume crops. However, alachlor can leach and has
been detected in groundwater. Although legumes were
once commonly used as cover-crops (Wakeley 1954), it is
now realized that cover-crop selection is an important con-
sideration for an effective integrated pest management pro-
gram (Dixon et al. 1991).
Some pathologists recommend leaving areas fal-
low and not using any cover-crops (Sutherland 1991).
However, fallow areas are often subject to excessive soil
erosion in areas with heavy thundershowers. A major rea-
son why nurseries use cover-crops in the South is to re-
duce soil erosion.
Inorganic N is applied to tree seedlings for eco-
nomic reasons. If inorganic N fertilizers were not applied,
nursery managers would use more expensive sources such
as chicken manure, horse manure and cow manure. Al-
though these sources are usually not expensive at the
source, transportation costs usually make them more ex-
pensive on a dollar per pound of N basis. One pound of
N is contained in three pounds of ammonium nitrate or 145
pounds of horse manure (Pritchet 1979). The delivered
cost of fertilizer can vary with year and location. How-
ever, at a delivered cost of $210 per U.S. ton of ammo-
nium nitrate, the cost of N would be about 32 cents per
pound.
4 ALABAMA AGRICULTURAL EXPERIMENT STATION
Improved seed efficiency is one major economic
reason for using N. Seed efficiency is defined as the num-
ber of plantable seedlings produced per pure live seed
sown (South 1987). Losing one plantable seedling per
square foot of bed will usually mean a loss in nursery in-
come of $870 per acre (when seedlings sell for $30 per
thousand). In contrast, fertilizing with 150 pounds N per
acre will cost approximately $48 per acre. In effect, the
break-even analysis indicates that one could afford to fer-
tilize with N even if the loss in seedling production
amounted to only 1,600 seedlings per acre. There is no
doubt that ceasing to use N would result in a substantial
loss in production of much more than 1,600 plantable
seedlings per acre.
In one study (Duryea 1990), applying 100 pounds
N per acre to slash pine seedbeds produced 13 percent
culls. Applying an additional 50 pounds N per acre in Au-
gust resulted in 10 percent culls (this was not a statisti-
cally significant reduction). However, if a single appli-
cation of 50 pounds N per acre ($16 per acre for ammo-
nium nitrate and $10 per acre application costs) could pro-
duce an additional 21,780 plantable seedlings per acre (3
percent increase in plantable seedlings), then the increase
in crop value could amount to $653 per acre. If a nurs-
ery had 30 acres in production, this could equate to an ad-
ditional net income of $18,810. This level of economic
return provides a strong incentive for nursery managers not
to reduce the level of N fertilization.
Root growth potential (RGP) is an indication of
the ability of seedlings to produce new roots after
outplanting. It is often measured by counting the number
of new roots produced under controlled conditions in ei-
ther a greenhouse or in growth chambers. The applica-
tion of N in the nursery has been shown to increase the
RGP of pine seedlings (Donald 1988; Switzer 1962; South
et al. 1989). Chlorotic pine seedlings will usually have
lower RGP values when compared to seedlings that are not
deficient in N.
Researchers have debated how much N should be
applied to a crop of loblolly pine seedlings. One reason
for the debate is due to different management objectives.
Some researchers have short-term objectives while others
have long-term objectives. Those with long-term objec-
tives believe the rate should be increased since the N con-
tent (mg N per seedling) can be positively correlated with
field growth (Switzer and Nelson 1963; Landis 1985;
Cubic ft../tree
I150 Ibs. N/A
10.5%
7.7%
Study 3 Study 4
300 lbs. N/A
7.7%
Study 5
Figure 1. The effect of applying extra nitrogen in the nursery on increasing individual tree volume
after 12-16 years (adapted from Autry 1972.)
6.3%
9.5%
6
5
41-
3
21-
1
0
Study 1 Study 2
MANAGING PESTICIDES AND NITROGEN 5
Number of nurseries
8 - Well 
[ Surface
7
6
5 
.
4
3
Aw
2
o/i
.13 .18 .22 .27 .31 .36 .40 
.44 .49 .53 .56 .62 .67 
.71
mg/I nitrate-N
Figure 2. Nitrate-N levels (refers to the nitrogen 
content of nitrate) in irrigation water from
southern tree nurseries during the 1980's.
Larsen et al. 1988; van den Driessche 
1991). Published
studies have demonstrated that field 
growth can be in-
creased by applying additional N in the 
nursery (Switzer
and Nelson 1967; van den Driessche 1991; 
Duryea 1990;
Hinesley and Maki 1980). Five studies 
in Mississippi
(Autry 1972) demonstrated that average tree growth 
14 to
16 years after planting can be increased by applying 
300
pounds N per acre in the nursery instead 
of 150 pounds
(Figure 1). These results are supported by 
studies with
other pines. For longleaf pine (Hinesley and 
Maki 1980),
applying an extra 150 to 300 pounds N per acre 
in the fall
improved volume growth after eight years 
in the field.
Duryea (1990) found that applying an additional 
150
pounds N per acre in August increased average 
slash pine
volume by 15 percent after three growing 
seasons.
Some researchers ignore data demonstrating
growth gains and make recommendations based 
on short-
term objectives. For some, the objective 
is to keep seed-
lings short so that top-pruning is not required. 
Therefore,
they recommend applying about 75-80 
pounds N per acre
to a crop of pine seedlings. However, 
Duryea (1990) con-
cluded that cutting back on N in the nursery 
may not be a
beneficial way to control height since top 
pruning was a
non-detrimental method of controlling height 
and pro-
duced a uniform crop of seedlings. Duryea 
found that
seedlings with reduced foliar N contents 
grew less during
the year after transplanting. This debate among research-
ers will likely continue until they agree that 
long-term per-
formance is more important than the short-term 
appearance
of pine seedlings.
Nitrate-N Levels in Irrigation Water
During the 1980s, the Auburn University 
South-
ern Forest Nursery Management Cooperative 
sampled ir-
rigation water from 42 tree nurseries 
in the South.
Twenty-six samples came from wells and 
15 came from
surface waters. Water was analyzed by the 
Auburn Uni-
versity Soils Laboratory for nitrate-N. 
The nitrate-N lev-
els in samples from wells ranged from 0.14 
to 0.66 mg/1
(refers to the nitrogen content of nitrate). For 
surface wa-
ter samples, the range was from 0.19 to 0.47 
mg/1. None
of the samples exceeded three mg/1 of nitrate-N 
(Figure
2). Most wells used for irrigation at nurseries 
are deep
wells. The EPA estimates that 1.2 percent 
of community
water wells and 2.4 percent of rural 
domestic wells have
nitrate-N contents exceeding 10 mg/1.
Water samples collected from 11 Forest 
Service
nurseries (most in the West) showed a wide 
range of ni-
trate-N levels in the vadose zone, which 
is the soil above
the groundwater but below the surface 
soil. A majority
of samples were between 0 and 50 mg/1 
(Landis et al. 1992).
6 
ALBAMAAGRIULTRAL XPERMENTSTAI
CONCERN FOR PESTICIDES IN GROUNDWATER
The EPA National Pesticide Survey of 1,300
drinking water wells found low levels of nitrate common
in well water, but presence of pesticides was much less
common. For example, no pesticide residues were de-
tected for more than 65 compounds. Some nursery pesti-
cides not detected in the survey included acifluorfen, car-
baryl, carbofuran, chlorothalonil, diazinon, diphenamid,
EPTC, fenamiphos, hexazinone, methiocarb, metolachlor,
napropamide, prometryn, pronamide, triademefon, and tri-
fluralin. However, residues from 14 pesticides were de-
tected. With respect to Maximum Contaminant Levels
(EPA standards for public water systems), 0.8 percent of
the community water wells had pesticide contamination
that exceeded the Maximum Contaminant Level and 0.6
percent of rural domestic wells had levels that exceeded
this value.
DCPA (acid metabolites) and atrazine were the
two most commonly detected pesticides in well water
samples from the EPA survey. Also found were the her-
bicides - dinoseb, prometon, simazine, alachlor, bentazon;
the insecticides - lindane, chlordane, 4-nitrophenol (a
breakdown product of parathion); the fungicides -
hexachlorobenzene, ethylene thiourea (a breakdown prod-
uct of EBDC fungicides); and the nematicides - ethylene
dibromide and dibromochloropropane. Most of these pes-
ticides are not used in southern pine nurseries. However,
a few managers use mancozeb (an EBDC fungicide) and
some use atrazine which is occasionally used to control
weeds in cover crops. DCPA has been used in Federal tree
nurseries in Washington and Oregon (Landis and Campbell
1989). Although the parent compound is considered to
have a low leaching potential (Landis et al. 1992), the acid
metabolites can leach into groundwater.
Soil Fumigation
Methyl-bromide and chloropicrin are the most
commonly used pesticides in conifer nurseries and cur-
rently account for 95 percent (by weight) of the pesticides
used in southern tree nurseries (Table 2). These fumigants
are used to kill weed seed, soilborne pathogens, nema-
todes, and insects. Mixtures containing 2 percent chlo-
ropicrin are commonly used to control perennial weeds
(e.g. nutsedge), nematodes and easy-to-kill fungi. Mix-
tures containing 33 percent chloropicrin are used when dif-
ficult-to-control disease fungi occur.
In 1945, weeds, disease and soilborne insects
caused a high degree of seedling mortality because nurs-
ery managers were not using pesticides. To produce one
plantable seedling, it was often the case that three good
seeds were sown (resulting in a seed efficiency of 33 per-
cent). Production levels were limited and a total of about
50 million seedlings were grown in the South in 1945. It
was initially believed that methyl bromide fumigation was
too expensive but nursery managers soon learned that fu-
migation reduced weeding times and produced more
plantable seedlings. As a result, seed efficiencies in-
creased to 66 percent after the 1950s. By 1975, approxi-
mately 77 percent of the nurseries in the South were us-
ing methyl bromide/chloropicrin on an operational basis.
By 1987, almost all nurseries were using these fumigants.
A single nursery today can produce in excess of 50 mil-
lion seedlings. By integrating several pest control prac-
tices and cultural techniques, seed efficiency now is of-
ten greater than 80 percent. These fumigants are now con-
sidered the backbone of a nursery manager's pest manage-
ment program.
Although mixtures of methyl bromide and chlo-
ropicrin are restricted use pesticides (because of their toxic
properties), they usually do not persist in the soil for long
periods of time. In fact, tree seed can be sown within a
day or two after the plastic tarp has been removed and the
soil has been sufficiently aerated. After the tarp has been
removed, any gas which remains generally moves up into
the atmosphere, not down into groundwater. As a result,
groundwater contamination by methyl bromide and chlo-
ropicrin have not yet been detected in the United States
(Parsons and Witt 1989).
There is concern that man-made sources of me-
thyl bromide could act to deplete the ozone layer. Since
this fumigant will be removed from the marketplace, al-
ternatives such as 100 percent chloropicrin will become
more common. Without the use of methyl bromide, some
nursery managers may decide to control nutsedge tubers
with herbicides like alachlor, atrazine, and bentazon. Un-
like methyl bromide, these herbicides have been detected
in domestic wells. There is little doubt that use of other
pesticides will increase when methyl bromide is withdrawn
from the market.
Although fumigation may cost $1,100 per acre,
the practice commonly increases crop value. This increase
can result simply from an increase in seed efficiency (even
when chronic levels of pathogens are not present). In
other words, fumigation often results in increasing the
number of plantable seedlings enough to pay for itself. An
increase of 37,000 plantable seedlings per acre is usually
enough to pay for fumigation (Table 3). For a density of
740,000 seedlings per acre, this would equate to a 5 per-
cent increase in plantable seedling production for a 1:1 ro-
tation (where soil is fumigated prior to sowing each pine
crop). For a 2:2 rotation, an increase of 2.5 percent a year
would be required (where soil is fumigated once for two
consecutive pine crops).
Herbicide Use in Nurseries
Southern tree nurseries use a relatively small per-
centage of herbicides applied annually in the United States
(Table 4). The total amount of herbicides used in 1989
amounted to 394 million pounds (U.S. Congress 1990).
6 ALABAMA AGRICULTURAL EXPERIMENT STATION
MANAGING PESTICIDES AND NITROGEN 7
TABLE 2. THE AMOUNT OF PESTICIDES USED TO PRODUCE 503 MILLION SEEDLINGS IN SOUTHERN TREE
NURSERIES IN 1992, THE ESTIMATED TOTAL USED ASSUMING AN ANNUAL PRODUCTION OF
1.2 BILLION SEEDLINGS, AND THE RESPECTIVE SOIL SORPTION COEFFICIENTS
Pesticide Trade Amount used Total estimated Soil sorption
names in nurseries used in 1992 coefficient
Lb. a. i. Lb. a. i. ml./g
Fumigants
Methyl bromide ......................................
Chloropicrin ..........................................
Dazomet ........................................... Basamid
Herbi
Oxyfluorfen ................................... Goal
Sethoxydim .................................. ..... Poast
Glyphosate ......................................... Roundup
EPTC ........................................ ..... Eptam
Atrazine ........................................ .... Various
Fomesafen .............................. Reflex
Lactofen ........................................ .... Cobra
Napropamide ...................................... Devrinol
Fluazifop ............................................. Fusilade
Alacllor ........................................ .... Lasso
Others ................................................
TOTAL ...............................................
Insect
Chloryrifos ......................................... Dursban
Diazinon........................Diazinon
Phosmet ....................................... Imidan
Esfenvalerate.................................. Asana
Malathion...................................... Various
Dimethoate.................................... Cygon
Acephate....................................... Orthene
Others............................................ .-
TOTAL ........................................... --
Fung
Triadimefon ................................... Bayleton
Benomyl....................................... Benlate
Captan .......................................... Captan
Chlorothalonil................................. Bravo/Daconil
Thiram......................................... Gustafson
Mancozeb ..................................... Manzate
Metalaxyl...................................... Subdue/Ridomil
Others............................................ .-
TOTAL .......................................... .-
13 1,309
25,966
6,000
305,400 E
1
60,400 B
13,900 B
22
62
102
iicides
ticides
gicides
1,560
688
330
156
134
80
77
42
23
17
54
3,163
1,413
359
298
187
171
75
44
41
2,588
496
1,132
1,188
1,038
244
85
66
56
4,305
100,000 B
24,000
200
100
60
10,000
400
5,700
170
7,300E
6,000 E
10,300 E
6,070
1,000
-3
5,300
1,800
20
2
1,000
1,900
200
1,380
670
2,000
50
'E = estimated.
2
Soil sorption coefficient for methyl isothiocyanate.
'Unknown.
From a survey of southern tree nurseries (43 percent of
total production surveyed), it is estimated that 7,300
pounds of herbicides were used in 1992 (Table 2). This
means that southern tree nurseries use less than 0.002 per-
cent of the herbicides used in the United States. Typically
forest nurseries in the South use about 1.8 pounds active
ingredient (a.i.) per acre to control weeds while farmers
often use three pounds to control weeds in corn. Nursery
managers commonly use oxyfluorfen, glyphosate and
lactofen. These herbicides have high soil sorption coeffi-
cients (Table 4) and are not considered to have a high po-
tential for leaching (Landis et al. 1992). Their relative
leaching potential index is greater than 2,000 (Hornsby
1992). Those that do have a high potential for leaching
include atrazine and fomesafen (sodium salt) but it is es-
timated that southern pine nurseries used less than 220
pounds of these herbicides in 1992. Atrazine use was
in cover-crop areas while most of the fomesafen was used
in pine seedbeds in Georgia.
8 ALABAMA AGRICULTURAL EXPERIMENT STATION
TABLE 3. THE INCREASE IN PLANTABLE SEEDLINGS RE-
QUIRED TO EQUAL THE COST OF A SINGLE PESTICIDE
APPLICATION (ASSUMING 30 DOLLARS PER THOUSAND).
Pesticide Application Cost 
No. plantable
trees needed
Dol./a.
Chloropicrin....... Fumigation 1,100 
36,666
Triadimefon ....... Seed treatment 2 66
Triadimefon ...:... Foliar spray 
22 733
Oxyfluorfen ....... Preemergence 35 
1,166
Oxyfluorfen ....... Postemergence 11 
366
Diazinon ............ Postemergence 9 
300
Weed Management
Weed management is potentially one of the most
expensive steps in the production of tree seedlings. 
In the
past, cost of handweeding could exceed 25 percent 
of the
total production costs (Boyer and South 1984). 
Prior to
1947, southern pine nurseries were weeded almost 
entirely
by hand or in combination with mechanical cultivation
(Wakeley 1954). Weed populations were high 
and the time
required to handweed often exceeded 1,000 
hour per acre
per year. During the 1950s, methyl bromide 
use was
evaluated at several nurseries. At nurseries with 
high weed
populations, fumigation reduced handweeding times 
by
50-66 percent (South and Gjerstad 1980). Today, nursery
managers employ efficient weed management systems 
and
several have reduced handweeding costs to less than 1 
per-
cent of production costs.
Weed control techniques
have improved dramatically since
1947. To document the changes
in weed management practices, a
questionnaire was sent to nursery
managers in 1988. A total of 39
nurseries responded to the ques-
tionnaire. Four nurseries did not
keep a record of handweeding
times and therefore their data are
not included. Some nurseries did
not report the cost of methyl bro-
mide fumigation and therefore a
cost of $1,000 per acre was as-
sumed. Cost of a herbicide appli-
cation (one tractor-trip) was as-
sumed to be $5 per acre.
All nurseries surveyed
were using methyl bromide fumi-
gation in combination with
oxyfluorfen (Table 5). Many
nurseries also were using
sethoxydim to control grasses.
Fall fumigation was used by 13
nurseries, and spring fumigation was used 
at 10 nurser-
ies. Managers at 16 nurseries fumigate some 
of their land
in the fall and some in the spring. The median
handweeding time was 10 hours per acre 
per year. Only
four nurseries reported handweeding times greater 
than 35
hours per acre per year. The nursery with 
100 hours per
acre per year produced mainly 2-0 white 
pine and used
only two applications of oxyfluorfen per crop. The nurs-
ery with 77 hours per acre per year had a high population
of sicklepod, morningglory, and 
nutsedge. Research by the
Auburn University Southern Forest Nursery Management
Cooperative determined that frequent postemergence 
ap-
plications of oxyfluorfen (at 0.125 pound 
a.i. per acre)
have proven more effective than two or three applications
at 0.5 pound a.i. per acre (Blake and South 1987). This
research resulted in an improvement in weed control with-
out increasing the total amount of 
herbicide used per year.
Nurseries that apply only two applications of oxyfluorfen
per crop are likely to have higher handweeding costs. For
these reasons, the number of herbicide applications 
per
pine crop usually exceeds 10 per year (Table 5).
The use of herbicides sometimes becomes a 
po-
litical issue as evidenced by the U.S. District Court 
Or-
der of 1984 that temporarily banned the use of herbicides
on National Forest lands in Washington and Oregon. The
consequences of ceasing the use of herbicides in a nurs-
ery weed management program can be documented 
by ob-
serving the effect this ban had on weed management costs
at the J. Herbert Stone Nursery (Figure 3). Even with the
use of methyl bromide/chloropicrin fumigation and me-
chanical cultivation, handweeding cost in one-year-old
TABLE 4. ESTIMATED PESTICIDE USE ON U.S. FIELD CROPS IN 1989
AND ESTIMATED PESTICIDE USE IN SOUTHERN TREE NURSERIES IN 1992 1,2
Crops Acres Herbicides Insecticides 
Fungicides
Lb. Lb. Lb.
Corn .............. 72,800,000 219,000,000 
27,100,000 60,000
Cotton ........... 10,500,000 16,000,000 15,600,000 
160,000
Grain
sorghum ....... 11,900,000 11,000,000 1,900,000 
0
Peanuts............1,700,000 6,000,000 
1,300,000 6,190,000
Soybeans ...... 61,300,000 108,000,000 
9,500,000 60,000
Tobacco..............700,000 1,000,000 
2,700,000 350,000
Barley &
oats..............21,400,000 5,000,000 
200,000 0
Rice.................2,800,000 12,000,000 
500,000 70,000
Wheat............76,700,000 16,000,000 
2,200,000 88,000
(Avg. use rate per acre 1.5 0.2 
0.03)
South. tree
nurseries................4,000 7,300 
6,000 10,300
(Avg. use rate per acre 1.8 
1.5 2.6)
'In addition to the above, nursery managers in the South used an estimated 
380,000 pounds of
fumigant in 1992.
2
U.S. Congress, Office of Technology Assessment 1990.
MANAGING PESTICIDES AND NITROGEN 9
TABLE 5. WEEDING TIMES, FUMIGATION AND HERBICIDE COSTS AT SOUTHERN PINE SEEDBEDS IN 
1987
State Handweeding /A Fumigation Herbicides Approximate
time cost cost area rate goal post tractor cost for weed
treated trips management
Hr./yr. Dol. Dol./a.
NC ........... 4
SC ........... 6
AL ........... 6
AL .......... 7
AR ........... 8
FAL ........... 8
AL ......... 102
FL ......... 15
TX ......... 19
LA ......... 12
FL ......... 15
TX ......... 19
GA ......... 20
MS ......... 24
MS ......... 25
NCGA ........ 26
ALMS ........ 307
MS ........ 320
NC ......... 51
AL ......... 77
MS .......... 0
AL ........... 2
GA
2 
......... 4
VA ........... 4
GA .......... 8
VA ........... 8
LA ........... 8
GA ........ 10
TX ......... 13
AL ......... 21
GA ........ 22
GA
2 
...... 30
GA ........ 37
VA ....... 100
21
48
30
34
75
64
90
35
80
89
90
90
67
163
116
145
104
121
300
347
0
9
14
22
56
27
40
40
75
113
193
172
10
222
500
660
800
700
1,000
1,000
920
900
1,000
1,000
900
1,200
980
900
1,100
1,000
1,060
600
1,000
545
1,000
1,050
1,100
889
1,000
950
889
925
1,090
850
1,000
1,000
950
889
900
1,000
Pct. Lb./a.
Methyl Bromide with 2%
62 380
100 375
84 320
100 400
2 400
100 350
100 350
49 350
65 425
69 325
40 350
45 400
70 350
0 400
80 350
31 400
16 400
70 400
100 350
65 450
Methyl Bromide with 33%
100 400
100 400
9 400
39 350
16 350
58 400
56 350
72 375
100 275
58 350
100 350
58 350
100 400
25 350
53 350
Dol./a. Dol./a. No./yr Dol. a./yr. Dol./1,000
1
Chloropicrin
19
70
32
38
64
58
61
58
64
49
64
66
52
64
75
46
72
35
43
75
15
30
15
0
76
30
30
25
40
30
15
30
0
20
20
30
20
20
46
30
Chloropicrin
81
60
46
64
17
52
64
64
46
75
23
49
61
43
19
25
0
81
0
16
60
25
45
20
20
15
25
10
0
15
8
17
9
6
9
14
11
17
17
10
10
21
11
17
17
12
17
13
13
17
16
8
19
13
4
15
15
8
11
17
5
11
17
9
4
504
1,033
710
1,102
280
1,142
1,136
693
919
1,118
699
732
804
332
1,096
610
394
941
999
1,537
1,236
1,209
316
541
261
730
722
974
976
863
1,256
852
1,055
535
1,084
0.69
1.55
1.10
1.72
0.50
2.37
1.70
0.50
1.45
1.80
0.83
1.56
1.63
0.47
1.10
0.73
0.50
1.48
1.53
2.08
3.91
2.18
0.56
0.70
0.47
1.58
0.91
1.76
1.63
1.10
1.62
1.36
1.76
0.65
2.05
'Cost per thousand plantable seedlings produced.
2
Includes cost of mineral spirits used in 1987.
seedbeds was five times greater than the total weed man-
agement costs prior to the ban in 1983. In addition, seed
efficiency at the Wind-River Nursery was reduced to the
point where 25 percent more seed was required to produce
the same number of plantable seedlings. In contrast, seed
efficiency can often be greater than 80 percent with the
use of effective herbicides and soil fumigation (South
1991a). Ceasing the use of herbicides in forest nurseries
not only increases the cost of seedling production, but
could also reduce the number of seedlings available for
reforestation.
Insecticides
Most (85 percent) of the insecticides used in the
United States are applied to corn, cotton, and soybeans
(U.S. Congress 1990). The total amount of insecticides
used in 1989 amounted to 61 million pounds. Tobacco
farmers often use 3.8 pounds (a.i.) of insecticide per acre
while nursery managers use less than half that rate (Table
3). Southern pine nurseries use a very small percentage
of this amount (approximately 0.01 percent). From a sur-
vey of southern pine nurseries, it is estimated that 6,000
10 
ALABAMA AGRICULTURAL EXPERIMENT STATION
pounds of insecticides were used in 1992 (Table 4). In-
secticides used included chlorpyrifos, esfenvalerate, and
acephate. These insecticides are not considered to have a
high potential for leaching into groundwater. However,
dimethoate and diazinon are considered to have a medium
potential for leaching (Landis et al. 1992).
Insect and Mite Management
Pests that can be troublesome for nursery man-
agers include sucking insects and mites (southern red
mite, scale insects, aphids, fire ants, tarnished plant bugs);
defoliating insects (pine webworm, redheaded pine saw-
fly); stem feeders (Nantucket pine tip moth); and root
feeders (white grubs, mole crickets, cutworms, lesser corn-
stalk borer). Nursery managers usually apply non-chemi-
cal methods to try and prevent high populations from oc-
curring (Dixon et al. 1991), and where deemed necessary,
apply chemicals to control high populations (Bacon and
South 1989).
In the past many seedlings were lost due to in-
sects when chemical methods were either ineffective or not
used. Nursery managers in Florida and in the Carolinas
lost 25-40 percent of their crop due to white grubs feed-
ing on the roots of pine seedlings (Wakeley 1954). If nurs-
ery managers stopped using fumigants and insecticides,
there is no doubt that, at some nurseries, white grubs
would once again cause significant seedling losses.
From the 1950s through to about the end of the
1970s, a mixture of xylene and mineral spirits was applied
to pine seedlings two or three times a week for weed con-
trol. The frequent use of these chemicals also resulted in
suppressing various above-ground insect pests. In general,
tip moths and mites were not a problem until after the
spraying of mineral spirits ceased in the fall. Since min-
eral spirits are essentially no longer used, injury from these
pests and others have become more frequent. In particu-
lar, injury from two plant bugs has greatly increased
(South 1991b; South et al. 1993). Prior to the initiation
of an insecticidal program, some nursery managers were
culling 10 percent of their crop due to injury from these
insects. For a 30 million tree nursery, this resulted in a
loss of $90,000 which is equal to three million seedlings.
Since insecticides are relatively inexpensive (about $9 per
acre for the chemical plus application), it only requires
$/acres
5,000 
-
First year D Second year
4,000 -
3,000 -
2,00 -
1,000 -
,000
------- -.- ....
1983 1985 1986 1987 1988 1989 1990 1991 1992
Figure 3. The cost of weed control in 2+0 seedbeds at the J. Herbert Stone Nursery in Oregon
in 1983 when herbicides were used and from 1985 to 1992 when herbicides were banned (but
methyl-bromide and chloropicrin were used.)
\ l--rlr ~I.C)VUS ~LIV~V VIIV~~VL~Vj) V~AL ~~V-C~ILU~ J-VVUVI VVI~I yvu~u rrlru v~ll~
10 ALABAMA AGRICULTURAL EXPERIMENT STATION
MANAGING PESTICIDES AND NITROGEN 
11
saving about 300 seedlings per acre to justify applying in-
secticides (Table 3). At some nurseries, this is equivalent
to only three linear feet of nurserybed. This is the eco-
nomic justification used by nursery managers who are
willing to apply insecticides to protect their crop.
Fungicides
About 80 percent of the fungicides in the United
States were applied to peanuts (U.S. Congress 1990). On
average, a peanut farmer might treat with 3.6 pounds (a.i.).
Although the total amount of fungicides used in 1989
amounted to 7.8 million pounds, southern pine nurseries
used only a small percentage (approximately 0.13 percent).
From a survey of southern pine nurseries, it is estimated
that 10,300 pounds of fungicides were used in 1992 (Table
2). On average, a nursery manager may treat with only
2.6 pounds of fungicides per acre. Commonly used fun-
gicides were captan, chlorothalonil and triadimefon. These
fungicides are not considered to have a high potential for
leaching into groundwater. However, a breakdown prod-
uct of mancozeb (ethylene thiourea) has been found in well
water and benomyl and metalaxyl are considered to have
a high potential for leaching (Landis et al. 1992).
Disease Management
In the past, many seedlings were lost due to dis-
ease when fumigation and fungicides were not used. There
are many studies that show large increases in seedling pro-
duction when chemicals are used to prevent diseases such
as damping-off (Boyd 1971, Clifford 1963, Foster 1961, Hill 1955,
Hodges 1962, Shoulders et al. 1965, Sutherland and Adams 1965).
In addition to chemicals, nursery managers use
various non-chemical methods to reduce the likelihood of
disease problems. Some nursery managers attempt to keep
the soil more acidic than pH 5.5 to aid in reducing the
chances of damping-off. Although tile drainage is expen-
sive, it is used by some managers to remove water from
the nursery and improve soil aeration (this reduces the
likelihood of microaerophilic pathogens). Many manag-
ers avoid the use of legumes as cover crops in order to
lower the potential risk from disease. Nurseries are often
placed on sandy (more than 75 percent sand content), well
drained sites (diseases are more likely on fine-textured
soils that are wet due to poor drainage and a lack of macro-
pores). If nursery managers ceased using fumigants and
fungicides, there is no doubt that significant losses would
result due to damping-off and infection by fusiform rust.
In 1975, a nursery manager typically would ap-
ply carbamate 28 times or more to control fusiform rust
(a total of 28 pounds a.i. per acre per crop). By 1986, only
four applications of triadimefon were needed for rust con-
trol (totaling two pounds a.i. per acre per crop). Nursery
managers began to treat seed with triadimefon after re-
search indicated it eliminated the need for the first
postemergence application. In 1986, researchers again rec-
ommended using less fungicide and this cut the rate of
triadimefon in half. By 1989, some nurseries would ap-
ply only a seed dressing and two applications of
triadimefon (a total of 0.63 pound a.i. per acre per year).
Researchers have made great strides in the South in greatly
reducing the number of pounds of fungicides applied to
control fusiform rust (U.S. Forest Service 1993).
TYPICAL NURSERY REGIME
Nursery crops are managed differently according
to management objectives, pests and environmental con-
ditions. At some nurseries, reducing operating costs is an
overriding concern. At others, high seed efficiency is very
important, because they use valuable genetically improved
seed. Some nurseries have high populations of nutsedge
while others may have problems with tarnished plant bugs.
Tables 6 and 7 illustrate examples of the chemi-
cal use at a hypothetical southern pine nursery. This nurs-
ery is located on a Troup soil and is managed on a 1:1 ro-
TABLE 6. FIRST YEAR PESTICIDE AND NITROGEN USE AT A HYPOTHETICAL NURSERY IN THE SOUTH
Month Crop Irrigation Rain Choloropicrin Goal Post Bayleton Asana Am. nitrate
In. In. Lb./a. Lb./a. Lb./a. Lb./a. Lb./a. Lb./a.
Jan ............ Pine 0 4.5 0 0 0 0 0 0
Feb .......... Fallow 0 4.0 0 0 0 0 0 0
Mar .......... Fallow 0 6.0 0 0 0 0 0 0
Apr .......... Sorghum 0 4.5 0 0 0 0 0 50
May .......... Sorghum 0 4.0 0 0 0 0 0 0
Jun ............ Sorghum 0 3.0 0 0 0 0 0 25
Jul ............ Sorghum 0 5.0 0 0 0 0 0.1 0
Aug .......... Sorghum 0 3.5 0 0 0 0 0 0
Sep .......... Sorghum 0 3.0 0 0 0 0 0 0
Oct .......... Fallow 0 2.0 300 0 0 0 0 0
Nov ......... Oats 0 3.5 0 0 0 0 0 0
Dec .......... Oats 0 4.2 0 0 0 0 0 0
TOTAL .... 0 47.0 300 0 0 0 0.1 75
MANAGING PESTICIDES AND NITROGEN
11
TABLE 7. SECONDYEAR PESTICIDE AND NITROGEN USE AT A HYPOTHETICAL NURSERY IN THE SOUTHERN UNITED STATES
Month Crop Irrigation Rain Chloropicrin Goal Poast Bayleton Asana Am. nitrate
In. In. Lb./a. Lb./a. Lb./a. Lb./a. Lb./a. Lb./a.
Jan. ......... Oats 0 4.9 0 0 0 0 0 0
Feb. ....... Oats 0 4.4 0 0 0 0 0 0
March ....... Fallow 0 5.9 0 0 0 0 0 0
April......... Sow 2 4.4 0 0.5 0 0.01 0.2 0
May ....... Pine 3 4.0 0 0.24 0 0.3 0.2 0
June ......... Pine 3 3.4 0 0.48 0.15 0.3 0.2 50
July ......... Pine 2 4.7 0 0.48 0 0 0.1 50
Aug ........ Pine 2 3.4 0 0 0.15 0 0 50
Sept ........ Pine 1 3.2 0 0 0 0 0 0
Oct ......... Pine 1 2.5 0 0 0 0 0 0
Nov ........ Pine 0 3.4 0 0 0 0 0 0
Dec ......... Pine 0 4.2 0 0 0 0 0 0
TOTAL .... -- 14 48.0 0 1.7 0.3 0.6 0.7 150
tation (one year pine to one year cover-crop). The soil is
fumigated in the fall with 300 pounds per acre of chlo-
ropicrin. Ammonium nitrate (25 pounds N per acre) is ap-
plied to the pine crop on the following dates; June 7, 20,
July 4, 18, August 1, and 15. Oxyfluorfen is applied
preemergence on April 10 at a rate of 0.5 pound a.i. per
acre. Postemergence applications of oxyfluorfen are ap-
plied (0.12 pound a.i. per acre) on the following dates;
May 23, 30, June 6, 13, 19, 27, July 3, 10, 17, and 24.
With this regime, it is very doubtful that measurable traces
of chloropicrin, oxyfluorfen, sethoxydim, or triadimefon
would leach into groundwater. Nitrate could leach into
groundwater when soil water moves downward due to
heavy rains that saturate the soil profile. However, this
management regime will likely result in a reduced poten-
tial for nitrate loss via leaching when compared to an ir-
rigated corn crop. This is because pine seedlings receive
multiple, small applications of ammonium nitrate which
increases nutrient use efficiency (U.S. Congress 1990).
MODELLING RUNOFF AND LEACHING AT THE ASHE NURSERY
Several risk assessments were conducted by
Labat-Anderson Inc. for forest nurseries owned by the
USDA Forest Service. The GLEAMS model was used
to predict the runoff and leaching potential of various
pesticides used at the Ashe Nursery in Mississippi. An
outline of the methodology is provided by Weiss (1992).
The GLEAMS model was used to analyze movement of
pesticides away from seedbeds in the form of (1) runoff,
(2) soil erosion (eroded sediment), and (3) leaching. Es-
timates of the relative leaching of various pesticides are
given in Table 8. Even under a worst case scenario, this
model predicts very little leaching of pesticides like
oxyfluorfen, sethoxydim, chlorothalonil, and thiram.
However, the model predicted that 10-14 percent of the
triadimefon would leach. In contrast, samples from
lysimeters at the Ashe Nursery indicate less than one part
per billion of triadimefon. Either the half-life of
triadimefon is less than that used in the GLEAMS model,
or the model has overestimated the potential for this fun-
gicide to leach. This suggests a need to verify predic-
tive models with actual field tests.
TABLE 8. ESTIMATED PCT. OF APPLIED PESTICIDE LEAVING
THE FIELD WITH RUNOFF, SEDIMENT, AND LEACHATE
Runoff Sediment Leachate
Longleaf Crop Followed by Loblolly
Benomyl .............. 0.41 0.10 0.09
Captan ................... 0.00 0.00 0.00
Chlorothalonil ....... 0.64 0.37 0.00
Diazinon ............... 1.34 0.05 1.85
Glyphosate ........... 0.46 0.04 0.43
Oxyfluorfen .......... 0.31 0.76 0.00
Sethoxydim ........... 0.39 0.03 0.01
Thiram ................. 0.00 0.00 0.01
Triadimefon .......... 0.85 0.03 14.39
Loblolly Crop Followed by Loblolly
Benomyl............... 0.07 0.02 0.05
Captan ................... 0.00 0.00 0.54
Chlorothalonil ....... 0.12 0.17 0.00
Diazinon .............. 0.28 0.02 1.48
Glyphosate ........... 0.05 0.01 0.33
Oxyfluorfen .......... 0.06 0.33 0.00
Sethoxydim........... 0.00 0.00 0.02
Thiram ................. 0.00 0.00 0.00
Triadimefon .......... 0.04 0.00 9.94
1
From Weiss 1992.
20.10 = One-Tenth of One Percent.
ALABAMA AGRICULTURAL EXPERIMENT STATION12
MEASURES TO REDUCE AGROCHEMICAL CONTAMINATION OF GROUNDWATER
There are numerous political strategies which, if
enacted, could reduce the usage of water soluble agro-
chemicals. Several propose that taxpayers pay farmers to
reduce the use of agrochemicals on sensitive areas that are
under croplands (U.S. Congress 1990). A few proposals
would promote tree planting with its associated nutrient-
scavenging and carbon storage benefits. "The potential
benefits in reduced agrochemical use with respect to pro-
tection of national (e.g. groundwater) or global (e.g., at-
mosphere) resources may argue for increasing payments
for those acres planted to trees" (U.S. Congress 1990).
There are various options that the forest industry
could choose to reduce the potential for groundwater con-
tamination from use of agrochemicals in forest nurseries.
One option would be to reduce the demand for seedlings
by outplanting fewer trees per acre. Currently about 1.2
billion pine seedlings are grown each year in the South.
Typically, many companies in the South plant 650 to 750
trees per acre. A few companies plant more than 1,000
trees per acre. In comparison, 350 trees per acre are fre-
quently planted by forestry organizations in the Northwest.
However, when no-thinning regimes are used, planting 300
to 500 trees per acre can be more profitable than planting
900 or more (Conrad et al. 1992; Caulfield et al. 1992;
Dean and Jokela 1992). If companies that plant 1,000 or
more trees per acre in 1993 decided to plant only 500 trees
per acre in 1994, then the use of agrochemicals at their
nurseries could be cut in half without changing any nurs-
ery management practices. However, good planting su-
pervision as well as good seedling performance would be
needed to ensure stocking uniformity and high seedling
survival. Some companies might not want to change their
management approach and would rather spend money on
overplanting to ensure adequate stocking.
Nursery managers do not have control over po-
litical issues or outplanting densities, but they do choose
which chemicals to purchase. Fortunately, nursery man-
agers in the South tend to choose pesticides that have a
low potential to leach. Oxyfluorfen, lactofen, and
fluazifop-p-butyl have chemical properties that cause them
not to leach. In general, the soil sorption coefficient for
these materials are very high (Table 4). In contrast, her-
bicides that could leach in sandy soils include atrazine,
bentazon, DCPA (acid metabolites), dicamba, and
fomesafen. A list to aid managers in selecting pesti-
cides to minimize water quality problems could be de-
veloped for all pesticides likely to be used in southern tree
nurseries (Hornsby 1992). This list could be distributed
to nursery managers so that they can make an informed
decision on which pesticides have both low soil sorption
coefficients and moderate persistence in soil.
One way to reduce the use of chemical pesticides
would be to increase the use of biological pesticides. Cur-
rently, there are only a few biological pesticides on the
market. Bacillus thuringiensis is currently registered and
is specific to lepidoptera larvae. However, lepidoptera are
not usually a problem in conifer nurseries. B. popillae or
B. lenomorbus are available for use in controlling white
grubs while a virus is labeled for use on redheaded pine
sawfly larvae (Dixon et al. 1991). Biological control of
weeds has been researched for several years. Currently,
the U.S. Forest Service in Pineville is hoping to control
prostrate spurge with Amphobotrys ricini. However, to
date, only two biological pesticides have been registered
for use on weeds (Te Beest et al. 1992).
MITIGATING PRACTICES FOR NITROGEN
It is apparent that for southern pine nurseries, use
of N fertilizers is more likely to result in groundwater con-
tamination than use of pesticides. There are several ways
to lower the potential for leaching of nitrates in bare-root
nurseries.
An important factor in attempting to reduce move-
ment of nitrates into groundwater is proper irrigation man-
agement. A problem that sometimes results is a lack of
irrigation uniformity. When this occurs, nursery manag-
ers may over irrigate some areas in order to provide
enough irrigation on the dry spots. This problem can of-
ten be remedied by recommendations from extension spe-
cialists. For windless tests, an irrigation system should
have a coefficient of uniformity of 0.80 or greater.
The amount of irrigation water applied can vary
greatly by nursery. For example, some managers that
use mulches will use less irrigation water than those that
use only soil to cover seed. However, the amount applied
can vary with nursery manager. Some use tensiometers
to assist in irrigation scheduling but many still use the
"one inch a week" guideline (Wakeley 1954) in conjunc-
tion with the touch and feel method. New nursery man-
agers are often not given enough instruction on how to
monitor soil moisture and therefore tend to over-irrigate.
There are essentially four different irrigation re-
gimes used during the growing season. The first is dur-
ing the germination phase. Usually, this requires frequent
irrigations to keep seed from drying out. Most nursery
managers do not over-irrigate during this period because
they need to shift irrigation frequently. The second regime
is during the "growing" phase and begins when the tap-
root reaches about six inches and ends usually in Septem-
ber. Some nursery managers apply too much irrigation
water during this phase. They often try to keep the soil
surface moist instead of observing the soil moisture in the
root zone. Use of tensiometers can aid nursery managers
during this phase of growth (Retzlaff and South 1985a,b;
Dierauf and Chandler 1991). At one nursery in Georgia,
MANAGING PESTICIDES AND NITROGEN
13
14 
ALABAMA AGRICULTURAL EXPERIMENT STATION
switching to use of tensiometers (in addition to switching
to pine bark mulch) reduced annual water consumption.
There is no doubt that some nursery mangers could ben-
efit by scheduling irrigation during the growing phase,
based on readings from tensiometers.
The third irrigation regime is used during hot days
to cool the seedlings. Each field is irrigated for about 15
minutes (about 0.06 in.) and irrigation is shifted as quickly
as feasible (since most irrigation systems can not irri-
gate the entire nursery at once). Much of this water
evaporates and little actually reaches below the soil sur-
face.
The fourth irrigation regime is used during the
"hardening" phase. Traditionally, irrigation is reduced or
withheld during the fall to "harden-off" the seedlings.
However, if the seedlings are put under too much stress,
root growth potential could be reduced as well as root
growth (Williams and South 1988; South et al. 1988). This
stress is more likely to happen at sandy nurseries than at
silt loam nurseries.
Although sandy soils often require more irri-
gation water than fine textured soils, this does not neces-
sarily mean that the amount of water reaching the water
table is greater. In some nurseries, a dry zone soil may
develop in the lower soil profile and irrigation water may
penetrate only the upper soil horizons. Applying an inch
of irrigation water a week (0.25 in. on Monday, Wednes-
day, Friday, and Saturday) would not be enough to cause
the entire profile to be saturated. Agrochemicals will
move into groundwater only if there is no break in the soil
water column. On sandy soils, it is usually not irrigation
per se, but saturating rains that penetrate deep into the soil
profile and cause agrochemicals to move to levels be-
low three feet.
Most N is applied in conventional granular form
(as ammonium nitrate, diammonium phosphate, ammo-
nium sulfate, or calcium nitrate). Slow release formula-
tions are sometimes used in container nurseries but are
generally not used in bare-root nurseries even though they
have been evaluated for three decades (Anonymous 1964;
Benzian et al. 1967). Slow release formulations have an
advantage when compared with just a single application
of a conventional fertilizer. However, since an optimum
nutrient management can be obtained with split applica-
tions of conventional fertilizers (Oertli 1980), there is not
much growth advantage in using slow release formula-
tions. In fact, once applied, the nursery manager looses
some control over nitrogen release. However, the main
reason slow release formulations are not used in bare-root
nurseries is due to their relatively high cost.
Nitrogen fertilizers are applied by one of four
methods. Granular fertilizers are usually applied with 5
or 4-foot-wide hoppers (centered over the bed) or with an
oscillating spreader. The oscillating spreader covers the
entire ground and is favored by some managers because
they can treat more beds per mile (4-foot hoppers when
mounted three in line, only treat three beds per mile).
However, the oscillating spreader applies fertilizers to the
tractor paths as well as the seedbed. A 17-25 percent re-
duction in the use of N could be accomplished if nurser-
ies with oscillating spreaders switched to using 5 or
4-foot hoppers.
The third method involves applying fertilizers
through the irrigation system. Several nursery managers
have applied fertilizers through the common riserline ir-
rigation system. Most found the results less than satis-
factory and have gone back to using tractors to apply fer-
tilizer. One reason for using fertilizer spreaders is due to
the lack of uniformity in irrigation. However, relatively
uniform irrigation can be achieved with a center pivot sys-
tem. Currently there are three southern pine nurseries that
use a center pivot system.
The fourth method involves applying liquid fer-
tilizers as a tank-mix with herbicides (typically
oxyfluorfen). Nurseries in Alabama, Florida, Texas, and
Virginia are currently using this technique. This method
holds some promise for increasing nutrient use efficiency
because multiple, small applications of fertilizer generally
promote better plant uptake (U.S. Congress 1990). How-
ever, if the number of applications were doubled by ap-
plying liquid fertilizer on a weekly basis, as opposed to
every two weeks as is typical with granular N, then nutri-
ent use efficiency might increase slightly. A particular ad-
vantage to this system is that the nursery manager can
eliminate five or six tractor trips each year. Since the her-
bicide oxyfluorfen is often applied on a weekly basis, com-
binining fertilizer in the mix would, in effect, eliminate the
need for additional fertilization trips. This system has
been in use in Virginia for several years.
Tile drainage systems are currently used at some
nurseries to remove excess water and to improve soil aera-
tion. This system could also be used to reduce the poten-
tial for groundwater contamination of nitrates (Landis et
al. 1992). To install this system costs approximately
$1,000-2,000 per acre (depending on the spacing between
pipes). The system can be installed in both new nurser-
ies and existing nurseries. Experience indicates the sys-
tem can work well in sandy nurseries. A large reservoir,
with an impermeable bottom, would be needed to retain
runoff. The runoff could be recycled for irrigation, thus
reducing the drain on groundwater reserves.
One final way to reduce the movement of agro-
chemicals is to abandon the bare-root system and switch
to producing seedlings at a container nursery with a wa-
ter-recovery system. A prototype water-recovery system
has been developed at an ornamental nursery at Eustis,
Florida (Rackley 1992). This system involves covering
the soil with a ground cloth and a 6-mil polyethylene and
constructing a catchment pond to hold the runoff. This
system retains 50-75 percent of the irrigation water. The
14 ALABAMA AGRICULTURAL EXPERIMENT STATION
MANAGING PESTICIDES AND 
NITROGEN 
15
rest is retained by the crop and lost to the atmosphere. In-
stallation of this system costs an additional $8,000-10,000
per acre. The runoff from the pond is reused as irrigation
water. Currently, the price of container-grown loblolly
pine seedlings can be four times that for bare-root seed-
lings. If one assumes that a container nursery could pro-
duce nine million seedlings per acre before the tarp would
need replacing, then the cost would add about $1 per thou-
sand (assuming it cost $8,000 to replace the tarp). There-
fore, the cost of installing this system for a container nurs-
ery would not greatly increase the overall cost of produc-
tion. The major deterrent to switching from a bare-root
nursery would be the higher cost of producing container-
grown stock. Some container nurseries sell pine seedlings
for $120 per thousand as compared to $30 per thousand
for bare-root stock.
SUMMARY
Nursery managers in the South currently use rela-
tively small amounts of the following herbicides: atrazine,
simazine, DCPA, bentazon, prometon and alachlor. Ceas-
ing the use of these herbicides would not significantly af-
fect the economics of producing southern pine seedlings.
Therefore, it is recommended that nursery managers cease
using these six herbicides as well as any use of lindane,
dibromochloropropane, hexachlorobenzene, and
mancozeb. When appropriate, nursery managers should
continue to use the EPA approved pesticides that have a
low probability of leaching (e.g. oxyfluorfen, lactofen,
fluzifop-p-butyl).
Nitrogen is used in nurseries to increase seed ef-
ficiency and to increase height growth after outplanting.
Although several practices can be used to reduce nitrate
leaching, growing legumes as cover-crops or reducing the
total amount of N applied to pine seedlings are not rec-
ommended. Managers of bare-root nurseries should first
consider the following to reduce the potential for leach-
ing nitrates:
(1) Check irrigation uniformity and make adjustments if the coefficient of uni-
formity is less than 0.80.
(2) Schedule irrigation during the "growing" phase to avoid saturating the soil. At
some nurseries, managers may not need to water until the soil tension reaches 30 kPa.
(3) Avoid applying N to tractor paths.
(4) Increase nutrient use efficiency by applying N on a frequent basis.
(5) Apply ammonium sulfate when soil acidification is needed.
(6) When feasible, reduce the amounts of N applied to cover-crops.
(7) Where tile drainage exists, consider building a reservoir to store effluent to use
as an irrigation source.
MANAGING PESTICIDES AND NITROGEN 15
16 
ALABAMA AGRICULTURAL EXPERIMENT 
STATION
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