RESEARCH UPDATE
1992
PEANUTS
White Mold Affected by Crop Rotation
Crop rotation has always been
among the most effective tools for man-
aging disease and nematode pests of
peanuts. Information on the value of
crop rotation in fighting peanut dis-
eases, particularly white mold, was
gathered in tests on 16 Alabama farms
in 1991. Fields, selected on the basis of
past cropping history, fell into one of
the following categories: poor - 3 or
more years continuous peanut pro-
duction, including unplowed summer
fallow; average - 1 year peanuts behind
1 year of another crop or clean sum-
mer fallow; good - 2 or more years
between peanut crops; best - peanuts
following bahiagrass pasture. White
mold damage was assessed in plots
within 2 days of digging and yields
were taken.
As expected, the least white mold
damage was seen in the best rotation
category where peanuts followed
bahiagrass pasture, see table. Numbers
of white mold hits in these fields was
only about 4 percent of those found in
fields in the average rotation category.
White mold was much more common
than expected in those fields in a good
rotation. Fields in the average category
where peanuts were grown every sec-
ond year suffered the heaviest white
mold damage. In one field, nearly 28
percent of the plants in the untreated
control plots were killed by the white
mold fungus before harvest. Surpris-
ingly, fields in continuous peanut pro-
duction suffered no more white mold
damage than fields in the good rotation
category.
Yields were not closely tied to the
level of white mold damage, see table.
Highest yield was recorded in fields in
the best or bahiagrass rotation. Despite
considerable differences in white mold
damage, yield of peanuts in the good
and average rotations was roughly the
same. Root-knot nematodes, not white
mold, were largely responsible for the
poorer yields seen in the non rotated
peanuts. Root-knot nematodes did not
substantially reduce yield in the other
three rotation categories.
The occurrence of Rhizoctonia
limb rot was not affected by crop rota-
tion. Minor limb damage was seen in at
least one field in all but the poor rota-
tion categories. The impact of Rhizocto-
nia limb rot on yield was 
minimal,
when compared to white mold, in the
fields checked in 1991.
A.K. Hagan, J.R. Weeks, and K.L. Bowen
IMPACT OF CROP ROTATION ON THE OCCURRENCE OF
WHITE MOLD AND YIELD OF PEANUT IN 1991
Rotation 
White mold
hits #/100 ft.
Poor ................
Average ............
Good ...............
Best ...............
Yield
Lb./a
3,222
3,608
3,692
3.859
Submodel of AU
Pnuts Effective in
Disease Forecasting
Research on the disease control
submodel of AU-lLnuts, a peanut pest
control model, began in 1989, but only
in one location. A direct comparison
was made to the Envirocaster comput-
erized predictor and to the standard 14-
day program commonly used by grow-
ers. In the original test, the spray pro-
gram started at initial 
signs of disease,
with subsequent applications made
when three rainfall events (of 0.1-inch
or more) were recorded or predicted
following a protection period of 10days.
The AU-Pnuts model, disease sub-
model, as it was called, outperformed
the Envirocaster and the 14-day pro-
gram on both Florunner and Southern
Runner cultivars. AU Pnuts used one
spray less than the 14 day 
program,
and one spray more than the En-
virocaster.
During the very rainy 
year of 1991,
trials were conducted on nonrotated
and rotated Florunner and Southern
Runner peanuts. Again, the Auburn
model saved one to two sprays with
improved disease control and in this
particular season, it improved yields
over the 14-day program. These tests
validated the fact that the AU model
was just about right vwith the rules de-
veloped for its disease submodel and
continued on page 2
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Vacuum Seeder Has Little Impact On I
nut Yields
In 1991, weed scientists at Auburn
compared the planting accuracy of a
new air, or vacuum, planter to a tradi-
tional planter. This was done at stan-
dard (90 to 110 pounds per acre), mar-
ginal, and substandard seeding rates.
The intent was to determine if the re-
ported extra accuracy of the air planter
would allow for a reduction in seeding
rate. Both planters were adjusted by
AAES personnel to meet manufactur-
ers specifications to achieve desired
seeding rate. The exact spacing be-
tween individual seedlings was deter-
mined soon after crop emergence and
yield data was taken at harvest.
At a standard seeding rate, both
planters were equally successful in
getting most of the seedlings spaced
out very close to the (theoretical) per-
fect spacing. As seeding rate de-
creased, spacing variation tended to
increase, and below 70 pounds of seed
per acre the variation in spacing in-
creased dramaticall\. Appa
these lower seeding 
rates,
insufficient seedlings to "cra
the soil, thus a portion of s
have germinated never emer
Across all seeding rates, 
t
tion in seedling spacing w
equal between the two types
ers. Yield was influenced b\
rate, in that yields decreas
seeding rates dropped below 9
per acre. However, this trend
tical for both planters. Yield
influenced by planter. Due to
100 percent seed germination
ling losses due to disease a
pests, there will always t
variation in stand uniformit
modification 
in planter desigr
to completely eliminate this v
These results are based oi
results. The tests well be rel
the 1992 growing season.
Tillage for Peanuts Following Bahiagr
Acreage for peanut-bahiagrass
rotations have increased throughout
the Wiregrass. Research conducted by
the Alabama Agricultural Experiment
Station has shown the beneficial effects
of bahiagrass rotations. Nematodes
and soilborne diseases are drastically
reduced and root restricting layers,
such as plowpans, are penetrated by
bahiagrass roots and thus left more
permeable for the following crop.
Two on-farm experiments were
established in I lenry County in fields in
which bahiagrass was grown for five
consecutive years. In the late fall and
early spring, test areas were
with RoundupR to kill bal
Treatments consisted of corn
(disk, moldboard, disk, and d
diskings, and rototilling. The
had tines removed so that on
wide strips were tilled. Two
centered over the tilled stri]
attached to the rototiller. T-
one pass was necessary with
tilled treatment.
The first experiment indi.
totilled strips gave lower yic
conventional tillage or diskin
tillage treatments, sound ma
TILLAGE EFFECTS ON PEANUT YIELD AND GRADE FOLLOWING BAHIAGRASS
Conventional Rototilled
No Gyp Gyp No Gyp Gyp No Gyp Gyp
Yield per acre, Ibs.
Experiment 1 ....................... 4,280 4,150 4,080 3,990 
3,640 3,690
Experiment 2 ...................... 1,150 3,045 3,525 4,080 3,760 3,710
Sound mature kernels, pct.
Experiment 1 ...................... 77 78 78 78 77 
76
Experiment 2 .................... 74 74 74 73 
74 73
Pea- Submodel of AU Pnuts, continued
no corrections were needed. A second
result of the 1991 season was that the
rently at rules 
used with the disease 
submodel
there are were capable of controlling an early
ck open" 
leafspot epidemic 
(most 1991 
fields
eeds that were predominately affected by early
ge. leafspot 
while previous 
years were
tie varia- dominated 
by late leafspot).
as about 
Ten grower 
trials were 
conducted
of plant- during 1991 in five 
Alabama counties.
These trials were supported by the Na-
Sseeding tional Weather Service, which pro-
ed when
vided a special 5-day forecast. This
0 pounds 
information 
was transferred 
to growers
was iden- via 
a toll-free 
telephone 
number. 
In
was not 
these trials 
the two most 
frequently 
en-
less than 
countered problems 
involved failure 
to
and seed- 
initiate the 
AU-Pnuts 
program 
when
nd other 
sprays were 
called for and 
spraying too
be some 
close to harvest 
when a spray 
was not
/, and no 
indicated.
n is likely 
Growers planting 
in April often
ariation. had 
to spray as early 
as 23-26 days into
n 1 vear's the season 
because of frequent spring
eated in rains. Often 
growers did not believe 
the
program, and would delay initiation.
G.R. Wehtje Additionally, 
three of the 10 growers
used an unnecessary spray at the end
of the season.
ass Even with errors, seven 
of the 10
growers did better than the 14-day pro-
sprayed gram 
with AU-Pnuts, 
two did about the
hiagrass. same, 
and in one case the conventional
ventional was better 
(this grower, however, 
made
isk)r,-vo several 
major deviations from 
AU-
rototiller Pnuts). 
Total fungicide applications
ly 1-foot- were reduced only 
by about 1/2 spray
planters, each for the 10 growers, and 
that only if
ps, were the three unnecessary end-of-season
hus, only sprays are removed.
the roto- 
P. A. Backman
cated ro- nels (SMK) werenot different. Also soil
Ilds than test values for the check plots (no gyp-
g. In all sum) were not different and no nutri-
ture ker- ents were determined as deficient.
In 1990, the results were different
from the first experiment. The disked
and rototilled strips had equally high
yields while the conventional tilled
treatment produced the lowest vield.
In the disked and rototilled treatments,
the addition of calcium, as gypsum, did
not increase yield or SMK, but gypsum
did increase yield in the conventional
tillage treatment.
continued on page 3
IlL
New Fungicide Performs Better On Most
Common Peanut Rotations
A recent survey of Alabama pea-
nut growers indicates that a majority
use crop rotations considered to be
poor to fair by the Alabama Coopera-
tive Extension Service. Only about 5
percent used a good rotation and only
1.5 percent used the best rotation
(peanuts behind bahiagrass), as shown
in table 1. Nematode damage and leaf-
spot defoliation generally got worse as
the frequency of peanut production in-
creased, table 2.
Using these same rotations, re-
searchers found that Moncut ,, an ex-
perimental fungicide with excellent
activity on white mold and Rhizoeto-
nia-related diseases of peanuts, in-
creased yield more in fields kept in poor
and fair rotations than in those in which
good and best rotations were followed.
In a peanut-corn-peanut 
rotation,
which was considered fair, one ap-
plication of Moncut increased peanut
yields in two fields severely dam-
aged by white mold by
1,700 pounds. How-
ever, yield gains were
much lower in fields
with light white mold
pressure. Peanuts in
poor rotations (con-
tinuous peanuts)
showed little yield re-
sponse to Moncut,
due to surprisingly low
white mold damage.
Moncut is not la-
beled for use on pea-
nuts. If the product
were available, and
performed at the levels
TABLE 1. CLASSIFICATION OF PEANUT ROTATIONS USED BY ALABAMA FARMERS
Best rotation = longterm pasture, followed by peanuts
Good rotation = 2 to 3 years of cotton or corn, followed by peanuts
Fair rotation = 1 year of cotton or corn, followed by peanuts
Poor rotation = peanuts followed by peanuts
TABLE 2. EFFECT OF PEANUT ROTATIONS ON LEAFSPOT DEFOUATION AND
NEMATODE POPULATIONS
Rotation Rootknot 
Leafspot
No./100 cc of soil defoliation
Pct.
Longterm bahiagrass + peanuts. 5.5 65.1*
Cotton + cotton + peanuts .......... 0.0 30.0
Peanuts + corn + peanuts .......... 10.6 35.0
Peanuts + peanuts. .................. 1,521 41.5
* High due to defoliation by velvetbean caterpillars
recorded in the 1991 tests, it would
increase the value of Alabama's peanut
crop dramatically, but this improve-
ment would be heavily dependent on
the rotation, according to the Auburn
tests. If this product, and similar fungi-
cides now in development, were
labeled and used on everv peanut acre
in the State in which poor to fair rota-
tions are used, it is projected that it
would increase the dollar value of
Alabama's crop by $24 million.
A.K. Hagan
Predicting LCB Larval Numbers From Adult Flush Counts
Lesser cornstalk borers (LCB) are
an economic pest of a number 
of crops,
including peanuts, in the Southeast.
Population outbreaks typically occur
in hot, dry years, and in peanuts grown
in well-drained soils. Yield losses in
peanuts can exceed 70 percent in severe
outbreaks, and predicting such out-
breaks would provide a valuable man-
agement tool for Alabama growers.
It is the larval stage of the LCB that
causes feeding damage on peanuts.
H owever, sampling for LCB larvae is a
time consuming and laborious 
process,
because the larvae are underground.
Adult lesser cornstalk borers are small
moths that rest on peanut foliage or on
the soil surface, making them much
easier to sample. Estimating the abun-
dance of crop-damaging larvae by
sampling adults would be a valuable
tool for both researchers and 
growers,
and recent AAES tests indicate this is
possible.
The abundance of larvae and
adults of lesser cornstalk borers was
monitored in conventionally tilled and
planted Florunner peanuts for 3 years
at the Wiregrass Substation in Head-
continued on page 4
Tillage for Peanuts, continued
If soil-test calcium is less than 300
pounds per acre, yield increases can be
expected with supplemental calcium
applications. Soil-test data showed
that the check plots had 160, 310, and
320 pounds per acre of calcium for con-
ventional, disked, and rototilled treat-
ments, respectively. This supports the
idea that the moldboard plow turned
the soil, in which calcium was accumu-
lated in the top few inches, to depths
beyond that of the pegging zone of
peanuts. Plowing also brought to the
surface calcium deficient soil that re-
quired supplemental calcium. This
shows that tillage can be a factor in
maintaining soil calcium within the
pegging zone.
Both experiments showed that
disking bahiagrass resulted in high
yields. Planting in the disked area was
not hindered by excess sod or clods
since bahiagrass had been sprayed
with Roundup the previous fall and
again that spring. On the 
other hand,
the appearance of the field was not as
nice as the conventional tillage. Of all
the treatments, the biggest problem
was evident during the digging of the
rototilled treatment. Tractor speed must
be slower and plov points on the digger
were subject to damage going through
soil between the tilled strips for the
rototilled treatment.
J.F. Adams and D.L. Hartzog
Predicting Larval Numbers, continued
land. Larval abundance was moni-
tored by weekly soil sieving through-
out the growing season. The abundance
of adults was monitored weekly by
flushing moths from roxws. Regression
was used to determine if adults in
week "i" can explain the variation in
larval abundance in week "i + 1", over
the 3 years of observation. The mean
number of larvae from week "i + 1"
increased linearly with an increase in
adult flush counts from week "i", in-
dicating that larval density could be
N ew Herbicide
Effective on
Hard-to-Control
Peanut Weeds
Pursuit?, a new herbicide from
American Cyanamid, made its debut
in peanuts in 1991. This herbicide can
be applied either to the soil (preemer-
gence through ground cracking) or
postemergence. It offers control of
several weeds, such as bristly starbur,
coffee senna, small flower morning-
glory, and both vellow and purple nut-
sedge, which are only marginally
controlled with other herbicides regis-
tered for use on peanuts.
In evaluation trials in 1991 by the
Alabama Agricultural Experiment Sta-
tion, one herbicide program that per-
formed well was a treatment of para-
quat plus Pursuit (0.032 pounds per
acre) applied at ground cracking, fol-
lowed by a postemergence treatment
of paraquat plus 2, 4-DB plus
Basagran?. This program provided a
good balance between the economy
of the older herbicides and the efficacy
of this new material.
Another Pursuit-like herbicide,
called Cadre@, is also under develop-
ment by American Cyanamid, and is
being tested by the AAES. It appears
to be similar to Pursuit, but it is much
more active on Florida beggarweed.
Cadre is expected to be registered in
1993 or 1994.
G.R. Wehtje
predicted by adult abundance. The
resulting equation indicated that
about 13 larvae per yard can be ex-
pected to be found 1 week later for
each adult per yard flushed.
This equation could be a signifi-
cant addition to management of the
lesser cornstalk borer, because the use
of adult flush counts allows for the
prediction of damaging and difficult-
to-sample larval populations before
they occur.
T.P. Mack
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