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<P ecan Disease Research in Ala-bama
Agricultural Experiment Station, Auburn University/E. V. Smith, Director/Aubiurn, Alabang
-

."

I

4'

CONTENTS

Page
SC A B -- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - 3

Materials and Methods ----------Results and Discussion --------DOW NY SPOT----------------------

-5 -6
10
-

Materials and Methods -------Results and Discussion --------BROWN LEAFS POT-------------

-11
-11
- - -13

Materials and Methods -Results and Discussion-14
LIVER SPOT---------------

- - --

- - --

-

- -

-14

----

15

Materials and M ethods-------------------------------16 Results and D iscussion ------------------------------- 16
ZONATE LEAFSPOT-------------------------------------17

Materials and M ethods---------------------------

---- 18

Results and D iscussion-------------------------------18 OTHER DISEASES
LITERATURE ------------------------------------

19

CITED ---------------------------

-------- 23

FIRST PRINTING 4M, JUNE

1972

Pecan Disease Research in Alabama
A. J. LATHAM, U. L. DIENER, and F. E. GARRETT*

ISEASE IS A MAJOR limiting factor in the production of pecans, the most important horticultural crop in Alabama. Spraying pecan trees for disease and insect control has become standard practice, especially with owners of large orchards. Development of improved models of air-blast, mist-blower, and hydraulic sprayers and use of new, highly effective pesticides has resulted in increased yield and quality of nuts adequate to pay for equipment, labor, and chemicals and yield a profit. Increased yields are not due to pest control alone, but are also attributed to use of new knowledge from research on nutrition (fertilization), management, and mechanical harvesting. This publication summarizes results of research on major pecan diseases by Auburn University Agricultural Experiment Station.

D

SCAB Pecan scab is one of the major diseases encountered in producing pecans in Alabama. The causal fungus, Fusicladium effusum Wint., attacks most seedling and improved varieties. In the past, Stuart pecans showed good resistance to scab (5) whereas Success and Schley exhibited little. Scab has become widespread on Stuart in recent years (4,5) and little difference in susceptibility between Stuart and Success has been evident during the last 5 years. Apparently, physiological races of the fungus capable of attacking Stuart and Desirable have developed. Symptoms appear on new foliage as olive-brown lesions on the ventral (lower) leaf side and later on the dorsal (upper) surSAssistant Professor, Department of Botany and Microbiology; Professor, Department of Botany and Microbiology; and Alabama Department of Agriculture and Industries, respectively.

PO I

FIG.

1. Scab lesions (block spots) on pecan leaflets.

fatce. F-igure 1. Iiially lesions arc p~ii-p)oint ill size. buit soon enlarge to 3-5 mm10. diameiter and coailesce. Thosc Ion sliicks are small, b~lack, and circular, Figuire 2, mduO appear smuiki i as the ut-u lik c elarges. Enltirc shuck sillfaces of lhitll\ sulsceptile 's arictics mlay beomile blackenled Im\ coalesced seal) lesionis. I muinituure scabbI) anits ill such1 (li olitlioll fall jpieiiatuik el b efore lharn cst i fail to fill. Lesions~ miay dcelIop oi curren1 t-seasoni leaf petiloles and) econtribuite to leaf ab)scissioni. ''b priulnar\ Source of ms erwsiiiterilig iuioeoliii is scabbed leas es, shucks, ando ws.

4

"5,

P 4
'low,

FIG. 2.

Scab lesions (blackened

areas) on pecan shucks.

111

Materials and Methods

Research on scab control with fungicides has been conducted in Alabama since 1961 (4). Fungicides evaluated are listed in Table 1 by common and chemical names. Insecticides were applied throughout the season as recommended for insect control, usually in combination with a fungicide.
TABLE

1.

FUNGICIDES USED IN PECAN DISEASE CONTROL INVESTIGATIONS

Trade or proprietary name

Common name

Chemical name

________ not available ACX-77 50 W _________________ bnomyl l-(butylcarbamyl) -2-benzimidazole Benlate 50 W__________________ carbamate ________ triphenyltin acetate Brestan 60 W ___________________ Cyprex 65 Wi and n-dodecylguanidine acetate dodine Cyprex 80 W______________ chlorothalonil tetrachloroisophthalonitrile Daconil 2787 75 W_________ N- [1,1,2,2-tetrachloroethyl)-sulfenyl] ________ Difolatan 80 W 4F-------cis-4-cyclohexene-1,2-dicarboximide ________ coordination product of zinc ion Dithane M-45 80 W_______ and maneb ________ Du-ter 50 W i-------------------- triphenyltin hydroxide
Kocide 101 86 W_____________ _______ cupric hydroxide

Polyram 80 W____________

5.2 parts by weight ammoniates of [ethylene-his(dithiocarhamate) ]-zinc with 1 part by weight ethylenebis [dithiocarbamic acid] bimolecular and trimolecular cyclic anhydrosulfides and disulfides
------

TD-225 FS 75 W___________

thiophanateTopsin-M 70 W_____-_________ methyl ziram Zerlate 76 W--------------------Zineb 75 W
1'Registered -_____________________

pyrimidine 1,2-bis (3-methoxycarbonyl-2thioureido) benzene zinc dimethyldithiocarbamate
zinc ethylenebis

1-dodecyl-1,4,5,6-tetrahydro-2-methyl

zineb

(dithiocarbamate)

for pecan disease control.

Research was conducted in Autauga, Baldwin, Dallas, Macon, Mobile, and Montgomery counties on the Lewis, Mahan, Moore, Schley, Stuart, and Success varieties. Much of the research involved the Success pecan, however, since it scabs severely each year in Baldwin and Mobile counties where extensive plantings of large trees were available with cooperating growers. John Bean and Myers air-blast, Hurricane mist-blowers, and John Bean hydraulic sprayers were' used in pesticide applications (4,5, 6,15,16.) Data were taken from three to eight replicated single-tree plots per treatment each year between August 15 and September 4. Data were collected using 50 green nuts from each tree before shuck-split and recorded as: clean-no scab on shuck, or
[5]

0

1

2

3

4

FIG. 3. Nearly full-grown nuts of the Schley variety classed according to degree of scab infection: 0-clean, no scab on shuck: 1-trace to 10 per cent scab; 2-11 to 25 per cent scab; 3-26 to 50 per cent scab; and 4-51 to 100 per cent scab (USDA photo).

scabbed1 shuck-class I , trace to 10 per cenit: claiss 2, 11 to 25 per'' cei t, class :3, 26 to 50 per cci it: class 4., 51 to 100 pei cci t. Seal inices wX calciilat(( lox iiiiil)1 ing iiiiiiler of niuts init class (re the class iii iiocie claisses wX re siiiflm(( anid tihe total dix ided

bx byte

produlct of replicationis times 100. IPercitait~e fi(.'ures tidrlight scab~ inicidlence represenit asnnlit iarx of classes I anda 2. Ileax x ii cidence(. Figu re 3. represcints atsinnmarXv of classes :3 andio 4".

I )ata ol niut (flialitx of Suicc(ss pecans xx(ro collectedl 1o the follow ing procedures: Trees wxere sliaken an i raitdoim sam pie of 100 nttts coliected lb\ 1 ickiitr 12 niits aitei ht dlifici (-it places f101total r undi~er thi(tree. An ts Xx ore craickedl ;OiOd data r ecordi we (ighlts of No. I iiieats as pc)euitag(., XX (jht of aiiiiei s ais pcr((eltagc, ando the pr ice offeredl for the( cotiiiid~ meats iox i cioiii 1)ata we re s5tnni aired as mieanis foii ropli10 uk rcial shl(ller (4).
cationis of each t (;tiiitttt.

Results and Discussion

~st I I w ars. I )isease fax 1oabl for dliseaose (elex(ojictnt thela conitrol dlata fronm reseairch ini Ballxx in ain d M olil0' cotiles ale suimmiiarized illtalhs 2 ani 3. A sca) iiidil\ loss thi;ii 1.t) inits cates that ;opjroxiii itelx 90 pcr cent (of giee aniii ha~d 1(ss thanoi thoe irface cox erecl xxitlh scab: this eoi istitootcs 10 per cei it iof sili ck si
[I6 1

TABLE 2.

SUMMARY OF SCAB CONTROL ON SUCCESS PECAN WITH PLICATIONS AT 8-WEEK INTERVALS IN BALDWIN AND

COUNTIES, 1963-1969, 1971

MOBILE

FUNGICIDE AP-

Treatment and rate,

pounds! 100

gallons

Years tested No. 1 2 2 2 2 2 1 2 8 4 1 1 1 1 1 1 1 2

1

Scab index'
0.11

Scab incidence on shucks Clean Light Heavy Pct. Pct.
8.5
7.2 6.0 1.3 6.1 3.0 2.0

Pct.

ACX-77 50 W, 0.3 Benlate 50 W, .2 Benlate 50 W, .3 Benlate 50 W, .4 Brestan 60 W, .2 Brestan 60 W, .3 Brestan 60 W, .4 Cyprex 65 W, .75 Cyprex 65 W, 1.0 Cyprex 80 W, .8 Daconil 2787 75 W, 1.0 Daconil 2787 75 W, 1.5 Daconil 2787 75 W, 2.0 Difolatan 80 W, 1.0 Difolatan 4F, 1.0-------. Dif olatan 4F, 1.5-------. Dithane M-45 80 W, 2.0Du-ter 20 W, 1.5-------Du-ter 50 W , .2--------Du-ter 50 W , .3--------. Du-ter 50 W , .4--------Du-ter 50 W, .6--------Kocide 101, 2.0--------Zineb 75W , 2.0--------Polyram 80 W, 2.0-----TD 225 FS, 1.2--------Topsin-M 70 W, 1.0_---.
Check (unsprayed)

.10 .06 .02

91.5
92.8 94.0 98.7 92.8 97.0 98.0

----

.03 .02 .41 .11 .08 1.42 .90 1.70 .12

.11

1.1

78.0 91.4 93.0 17.8 38.3 8.0
89.2
90.0 89.0 92.0 96.8 92.6 97.1 95.3 94.0 62.6

16.4 8.2 7.0 64.7 56.7 71.3
10.8
10.0 11.0 7.0 3.2 7.1 2.9 4.5 6.0 29.7

5.6 .4 18.1 5.0 20.7

.17 .19

5
5 3 1 1 2 2 1 1 8

.10 .06 .09 .03 .05
.07

--1.0 .3 .2

.60
.58 1.59 1.47

-----

7.7

63.6 19.4 14.8
97.4 .7

28.0 59.0 72.8
2.6 30.5

8.4 21.6 12.4
68.8

------

2.91

.05

1 Rated

on scale of

0-4.

a high degree of control. Nuts in classes 3 and 4 were unmarketable and grouped under "scab incidence heavy," tables 2 and 3. Cyprex was the first fungicide to successfully control scab for periods up to 3 weeks between applications. This organic fungicide at a rate of 1 pound per 100 gallons has given excellent control during 8 years of use. It has been the standard for comparison of other fungicides in the evaluation program. Du-ter, which was developed a few years after Cyprex, also has shown excellent protective qualities for scab control. Applications of Du-ter at 0.3 and 0.4 pound per 100 gallons for 5 and 3 years, respectively, have been highly effective, Table 2. Du-ter treatments at 0.2 pound averaged 92.6 per cent scab-free shucks during 5 years of tests. However, this least effective rate of application may not result in commercially acceptable control when used by many applicators. Both Cyprex and Du-ter are registered with the
[7]

TABLE 3.

CONTROL OF SCAB ON SUCCESS PECAN WITH FUNGICIDE APPLICATIONS

AT 4-WEEK INTERVALS IN BALDWIN AND MOBILE COUNTIES, 1966, 1967, 1970

Treatment and rate, pounds/100 gallons

Years tested

Scab index'

Scab infection on shuck
Clean Light Heavy

Pct. Pct. Pct. 8.0 _ Benlate 50 W, 0.4 ----------------------'70 0.04 92.0 Brestan 60 W , .2 ---------------- 69.5 ----- '67 .41 29.3 1.2 94.2 5.8 _--'67 Brestan 60 W , .3 ----------------- .06 Brestan 60 W, .4 '66 .44 73.7 23.3 3.0 Cyprex 65 W , 1.0 ----------- .16 '66,'70 86.8 11.2 2.0 Cyprex 80 W , 1.0 -----------------------'70 .05 91.0 9.0 81.0 19.0 '70 .13 Difolatan 4F, 1.0 -------- -------------3.6 .37 74.6 21.8 '66,'67,'70 Du-ter 50 W , .2 --------------------------Du-ter 50 W , .3 -------------------------- 86.2 '67 .18 13.4 .4

---------------------------

___ Du-ter 50 W, .4--------------

.

'66,'67,'70

.08

90.8 35.0 .0

9.2 37.5 15.3 27.5 84.7

Kocide 101 86 W, 2.0 ---------------'66 1.55 Check (unsprayed)-- _-------------'66,'67,'70 3.34 1 Rated on scale of 0-4.

Environmental Protection Agency (EPA) for pecan scab control1 . Benlate (4 years) and Brestan (3 years) both performed well throughout these tests. Difolatan provided good control of scab (1 year's data) and ranked between Du-ter and Zineb in effectiveness. Daconil 2787, Kocide 101, Zineb, Polyram, and TD225FS have given poor scab control in the 3-week schedule. Daconil 2787 was first tested in 1964 at 2.0-pound rate; ineffectiveness was attributed by the manufacturer to partial loss of fungicidal activity during storage. Subsequently, the fungicide was retested at 1.0- and 1.5-pound rates with similar results in
1968, Table 2. Unsprayed pecans showed 69-85 per cent heavy

scab infection, and most of these were unmarketable. ACX-77 and Topsin-M were effective in first-year evaluations (1971) and warrant further investigation to determine optimum rates of application. These two fungicides are not registered for use on pecans. A comparison of data in tables 2 and 3 shows that a 3-week spray interval resulted in consistently high percentages of clean shucks. When the spray interval was extended to 4 weeks, Table 3, disease control decreased (6). Extending the spray interval to 4 weeks may prove disastrous under environmental conditions favoring high disease incidence, since the fungicide
1

Refer to Table 1 for

information

about registration of fungicides used in these

investigations, and for common and chemical names. .[8]

on pecan shucks or foliage may be weakened to a concentration ineffective to prevent fungal infection and scab development. Rainy weather, spray machinery breakdown, sprayer operator health conditions, or other extenuating circumstances may on occasion extend the spraying date several days beyond the desired 21st day. During such situations the rate of 0.3 or 0.4 pound Du-ter or 1.0 pound Cyprex still has been effective. However, the marginal rate of 0.2 pound Du-ter was only partially effective in 1966, with 47.5 per cent of the shucks remaining uninfected (data not presented.) The overall 3-year average was 74.6 per cent scab-free shucks from the 0.2-pound rate as compared with 86-90 per cent for 0.3- and 0.4-pound rates. A 4-week schedule was followed in 1970 to maintain vigorous, disease-free foliage and promote maximum crop potential for 1971, since the trees had sustained severe damage from Hurricane Camille in 1969. Plant tissues associated with floral initiation and development were damaged by strong winds of the hurricane. In 1970, poor nut set was followed by prolific new vegetative growth; subsequently, many nuts that set fell prematurely and left few nuts to provide test results. Data in Table 4 show that disease control prevented losses in quality and price of pecans, as well as yield losses, from premature drop. With a more susceptible variety, such as Mahan or Schley, the return from effective scab control in both yield and quality might be far greater, since unsprayed orchards of these two varieties averaged 75 to 90 per cent losses. This investigaTABLE 4. RELATION OF PECAN SCAB CONTROL WITH FUNGICIDES TO NUT QUALITY
SUCCESS VARIETY IN BALDWIN COUNTY, ALABAMA, 1961 AND PRICE OF

Green nuts Treatment
and rate, pounds/ 100gal.
DisShucks

Grade at harvest
Total Wt. of
t

d Of To Wt. of scab- Nuts/ Nuts/ ease bed lb. Pops wt. No. 1 of fered e lb. index 0-10% meats meats bers price loss No. 17.2 16.4 16.8 18.0 21.2 1.5 Pct. 89.4 88.0 58.8 6.2 4.8 No. 50.7 50.0 54.2 58.6 56.7 4.5 No. 4.3 5.0 6.1 4.5 7.2 4.4 Pct. 49.38 44.7 47.5 46.4 44.5 3.7

Of-.drop,

mrePreture

Dodine, 1 Dodine, 1/2 and 12 Zineb, 2 -.--.... Ziram, 2_....... 3 Check LSD, 1%.......

0.70 .67 1.46 2.78 3.57 .5

Pct. Pct. Cents Pct. 9.0 10.3 19.4 34.5 10.8 35.5 11.9 35.5 10.8 29.2 15.2 6.3 5.4 17.0 17.9 17.9 15.1 2.6 _ 2 10 30

1 Rated on scale of 0-4.
- First four sprays at 1/2 -pound, last four

at 1-pound rate.

' Insecticide only.

[9]

thu

lii

cidal

0 iostrate(I thle \ Jiie of peiut~I scall olitrol xx II fI I iit spraites i mereaisilig re'turn, b.loth ill u(iialitx and( total pro-

\ll a(I(ed hlelefit f 10111 annu~al spratX ing for co1ntrol of dliseases and( inlsects has been olbscers(( ill reduled~ alternjate lleirini~r. faiirly moodI erop of pecanIs occurrfed (ach)yea (in tihl test orcha8rds. Thc~sc results conltrastedl w~ithi uulspi ax (( p)ori\n uih tg(l or-

elhards xxhIere ia beax v crop) mlighit occur on I cx (Fx other xear. It is recogizedl that fertilizationi and( properl mlanaguent a1l(o en ter inito the mX erall p rob ilm of alteritate hiu)(i Il. rotectix c actix dxv xxas correlated with the thorapl~)ication . A pecan blranich or 1lm) "miusseti byte spraN xx ias readlilx detected byIthe amuotunt of scalb an(d foliagec diseases at bars\ 't. A fIuluiie xill serx e its iltIt(gici(Ie oiu~rcss of
1

f 1h~iticihl(

pilrpose oly wxhen the pecan tree is thoroiughix spray ed wxithl ani alielfiate dosagec at the prescrib ed timie iiiteixal. FLxperieiiu' gailled fr1om1 resear~ch ini cooperatinlg (groxx rs' orchlardis has shoxx i that x igiorolls Ill sprax (d trees wxith hi gh (liseash scab) ilicidielle and( (defoliation ullav be sprax ed tihe boy lo ig~ crar with C(ApI x or I)ii-ter and( seal) controlled 94 per cent 01 1better (1(6). When(1 peechu foliage an d nut shacuks wxere adeq uatck\ coy crel wit it a [n~licidle scab) vv as conitrolled 9() per ((lit or b~etter thro()tllit theseI im stigationi . Con t rol wias aehicex d dei\ spite the area's plex uiliiighigil hidl~ity, wh ich is hlgh ilta r81111 for seal) dic(1111 Inct.

DOWNY

SPOT
funiigus1
miost

1)1 ux Ii s pot, L8aused 1bI thi(
1)ciiiaree and~ Cole, attacks

AIiju )sjIlClr('IIU

((Iry/gi(n

pecan x arieties, Mionex miaker

FIG.

4. Downy

spot lesions (frosty, white spots) on underside

of pecan

leaflets.

[It)]1

and Stuart being the most susceptible (17). Downy spot lesions interfere with photosynthesis during summer, resulting in lower nutrient availability for the current season nut development and subsequent crop initiation (3). Lesions first appear in early summer as white tufts or "frosty" spots approximately 1/8 inch in diameter on the lower sides of leaflets, Figure 4, caused by sporulation of M. caryigena. Later in the summer the spots become greenish-yellow on both leaf surfaces, then change to brown in the fall. As the season advances, diseased areas die and some premature defoliation occurs. Leaflet abscission from the leaf rachis may begin in early September. The fungus overwinters in the diseased leaves where its life cycle is completed. During rainy periods in spring, new leaves are infected by fungal spores disseminated from fruiting bgdies of the pathogen in old leaves (3).
Materials and Methods

The efficacy of fungicides Benlate, Cyprex, Difolatan, Du-ter, and Zineb for control of downy spot in Alabama was determined. Each fungicide was applied with a Myers air-blast sprayer to five Stuart pecan trees. In 1968, evaluations were made on blocks of trees sprayed on a 2- or 3-week schedule starting with a pre-pollination application when leaves showed 12 to 3/4 inch growth (April 11). Evaluation of a third block of trees was initiated postpollination (May 2). In 1969 and 1971, experiments were designed to evaluate disease control when spraying was begun prepollination (April 20) or post-pollination (May 22, 1969, and May 10, 1971). Since applications in 1970 did not begin until April 28, pre-pollination protection sprays were omitted. Leaf disease severity was determined on 12 compound leaves that were collected from each single-tree plot at a height 6 to 12 feet from the ground. Three leaves were collected from each of four equidistant stations per tree. The fourth leaf from terminal bud was collected during September of each year. Leafspot data were analyzed statistically (11,12).
Results and Discussion

Infections by the fungus continued to increase throughout the 1968 season. Leaves sprayed with Difolatan exhibited a "bloom" of infections that were too numerous to count as definite leafspots on September 18; only definite leafspots that occurred early in the season could be counted. Fungicides applied on a 2- or
[ 11 ]

TABLE 5.

CONTROL OF DOWNY LEAFSPOT ON STUART PECAN WITH FUNGICIDES IN

MACON COUNTY, ALABAMA, 1968

Treatment and rate, pounds/100 gallons 2-week interval
C yprex, --------1.0-----------------------------

1 Spotsper compound leaf July September No. No.

4.8 a

6.1 a

Difolatan, 1.0---------------D u-ter, .4-------------------------------------Zineb, 2.0------------------------3-week interval Cyprex, 1.0----------------------------------------------------------------Difolatan, 1.0-D u-ter, .4-------------------------------------

33.5 bC 11.6 ab 16.3 ab 13.2 ab 46.2 c 18.4 ab 50.1 c 87.1 d
e

35.6 abc

11.8 a 28.0 abc 18.1ab
50.6 bc

Zineb, 2.0------------------------------------Zineb (PPSO)', 2.0--------------------------------163.2 Unsprayed -------

22.9 ab 58.4 c 101.1 d
206.2 e

Means followed by the same letter are not significantly different at the 1 per cent level according to Duncan's Multiple Range Test. 2 PPSO pre-pollination spray omitted, Zineb applied post-pollination only.

'

_--

3-week schedule were effective in controlling leafspot, Table 5. at However, Cyprex was significantly better than 2-week intervals and both Cyprex and Du-ter were better than Difolatan at 3-week intervals. Effectiveness of Zineb was equal to Du-ter at 2-weeks, but leafspotting at 3 weeks was nearly three times greater. Statistically signfficant differences that occurred between preand post-pollination applications illustrate the benefit of prepollination applications for preventing early leaf infection by M. caryigena. Some variability in disease control among Ben-

Difolatan

late, Cyprex, and Du-ter treatments was observed each year in

pre-pollination applications. Leafspot incidence per compound leaf was so small, however, that differences may have been u-important to overall photosynthetic activity of the foliage, Table 6. When post-pollination applications in 1969 were delayed until May 22, pronounced differences between Cyprex, Benlate, and Du-ter were recorded. These results emphasize the importance of making three pre-pollination applications on a 2-week schedule beginning as leaves first emerge, followed by the 3-week spray schedule until September. This prevents scab and foliage diseases through the growing season. The high incidence of downy spot lesions on unsprayed trees in September, tables 5 and 6, does not show all leaf spots that
developed during the season, since many

leaflets

had already

abscissed. Whole compound leaves were difficult to find at this [ 12 I1

TABLE 6.

DOWNY LEAFSPOT INCIDENCE ON STUART PECANS SPRAYED WITH FUNGICIDES IN MACON COUNTY, ALABAMA, 1969-71

Treatments and rate,
pounds/100 gallons 19691

Spots per compound leaf
1970
19712

No.

No.

No. 6.3 b 1.8 a 7.1 b

Pre-pollination'
Benlate 50 W, 0.4 ........... Cyprex 65 W, 1.0 -Du-ter 50 W, .3--Unsprayed Post-pollination' Benlate 50 W, .4 ............. Cyprex 65 W, 1.0------------

-

1.1 3.9 5.9 81.8

a a a b

--

23.6 a 126.6 b

7.2 a 8.0 a

8.4 bc 11.3 cd

Du-ter 50 W, .3 Unsprayed _

--------

30.4 a 8----153.0 c

15.7 a 205.1 b

11.9 203.0

d

1 Means of 60 compound leaves; number followed by same letter not significantly different at 1 per cent level according to Duncan's Multiple Range Test. 2 Means of 60 compound leaves; number followed by same letter not significantly different at 5 per cent level according to Duncan's Multiple Range Test. ' Significant differences between pollination times at 1 per cent, according to "F" test for significance.

late date on some heavily infected trees. High disease incidence caused some leaflets to fall from the rachis when the leaf was picked or jarred loose. Some leaves with high lesion counts may remain on the tree, but become of little value in supporting nut production. From a grower's viewpoint it would be practical if the fungicide selected for scab disease control also controlled foliage diseases. Commercial control of downy spot was obtained with Benlate, Cyprex, and Du-ter on a 3-week schedule in these experiments. In the past, Stuart pecan possessed some resistance to scab; thus growers delayed spraying until scab was evident. Such practices permitted high scab development on shucks and extensive downy leafspot incidence, resulting in loss of nutrients required by the tree for nut production. BROWN LEAFSPOT Brown leafspot is caused by the fungus Cercosporafusca Rand. Leafspots first appear in June or July on mature leaves of Stuart and other varieties. Symptoms on leaflets appear as circular concentrations of reddish-brown angular flecks on the leaf surface. These flecks may coalesce into a consolidated necrotic region with an irregular margin 10 to 20 mm. in diameter, Figure 5. If uncontrolled, the disease causes early defoliation and complete
[13]

FIG. 5. Brown leafspot lesions (diffuse and concentrated necrotic areas) on underside of pecan leaflet.

loss of lea s b-' Oc ()tober. The brow l~ Icafsp~ot Iii1o;us tcrs ini n(crotic tissue of old( leas cs.
Materials and Methods

05 (r\5 11-

1 11 \lontgoiie\ Comiity,. Cx pi (\ 1)i- ter, aid~ line ) wsere appliedl to Lewsis p~ecan trees 05th a mist bhm cre of a 1)nhtll schedule frm j 1ie to September 1965. 1)ata for 1 (OSSn leafspot see oiitx wSerc ealcu latedl from1 the peren tage of leas es iifeetecl on 10 to 20 terniia and as era ed fol fix e sili k-tree re1 )li ms

cationis ().

1Fun1 iilles sx ev applIied wsith a \e rs air-b last sp)rayXer to Stuart pecans ill M acon Co it gini in'tF April 20 and em tinuiit on a :3 55 (el schiedule thirough Angnst 19(59. 1)111iia 1971 , spray inn wsas iniitiatedl on April 20 w5ithi add~itionlal app)lication~s

for b rosw n leaf spot

we re recordled as fo d0(oss leaf spot, i.e., y Irom 12 comlpouhld~ leas Sper tree and fis e replicationis per treatiielit (11.12).

Results and Discussion

Ii \tontronierx (ionit, ll)u-ter

('as

the biest conitrol of bros

i

leafsfot, ss lreas /ine (1d(id not control tihe (disease f5 ). Contr ol
fplolbalbl\vs oiilo has o been better ifspr as iu ad eeni initiatedl i(l (arlier th ani J1l1 c. Applications oif IBeilate, C\ precv auid 1)o-ter pies (intedl (le ecloploent of bross leaf spot in the \lacon County research plots. liu ss as lwgui aid iln Baldswin and other conties sshere spl as early as April 2t). i each eclcriunent. (\tellsise ss inptil x
1 pression and (lefoliatioln of trees ss obser 5 (d in adljoining as sprav-ed or chards, Table 7.

n-

['4]

1'lCAN~~itFI0-, "t lGI0imN CouN

1965) 1)971 .-

k

r:A

1965
Pt.

19)69
\o.

1911
\o

9 nltc 50 \\ 1) 04 (: prex 65 XX 1.0
Ion-lt
I1o-lii

0
8.6 1.2 29.4 55.4 averagitd lot fiv
leaf lit ft rm 1 (1
0 I)

( 1

50(1

', .6

501 XX' ..

Ziwit 75 WX, 2.0) lospt itd cheek

12-I
replicaitonsx
compou nd leave

74.2
(trees) for five relicationst'.

Tcn to 20 terinals~I'
Spots couted~t pet

III Aliabama, browXil leaf spot has eaulsedl the mi ost wXidlespreadl dlefoliation of any tgal disease. Other diseases, 'auchi as Zon ate x Jeafspot, are more sporadic and cause hi ghly local ized diefoliationt . Althou gh brown leafspot iniencette and(1(I el ts nltv he i ta seX ere, it has been the easiest foliagte d1isease to conttrol. LIVER SPOT s (lwmmoini (U rt/a) var. t inl orchards ini en tral Alab am a. f ithtest inclid(encie wXas ob1 serXe ('Ion seedilin g pecats ini M acot Count x. Thbe disease has n ot been ob sers ed iln BaldwXin or Biutler etoutnties (10). TwXo trees wer lftu tlinf tiectedi near Granid B~a, MoItbile Comity . Acco~trdling to) Colte (1), live (spo)tt dotes not occutr in regions o~f high huidtl)ity~, such~l as alongt the Gulf Coast. 1
Lax (1 spot disease, eauisedi by pccantae Cole, has been found1(

the itgu

FIG. 6. Liver spot lesions on a pecan leaflet (USDA photo).

[

I5]

Leafspots appear in June as dark brown circular areas, 5 to 12 mm. diameter, on the lower surface of leaflets. As the summer progresses, lesions may be observed on both lower and upper surfaces with leafspots exhibiting the liver color during late summer, Figure 6. Acervuli (fungal fruiting structures) appear as minute blisters on the lower leaf surface. Conidia (spores) from these structures are further spread by air currents in the orchard. It overwinters and completes its life cycle in fallen leaves where more spores are produced to infect succulent young leaves the following spring. Materials and Methods Tests were conducted in Macon County to determine the value of Benlate, Cyprex, and Du-ter for liver spot control. Each fungicide was applied to five Stuart pecan trees with a Myers airblast sprayer. Spraying was begun in 1969 and 1971 on April 20, with subsequent applications made every 3 weeks until September. During 1970, pre-pollination applications were omitted since spraying could not start until April 28. Twelve compound leaves were collected from each single-tree plot for leafspot counts. Three leaves were collected from each of four stations around the tree. The fourth leaf from terminal bud was collected in September of 1969 and 1971 and in July of 1970. Leafspot data were analyzed statistically for differences among treatments and times of applications. Results and Discussion Significant differences were observed in 1969 and 1971 between pre- and post-pollination applications, according to the analysis of variance "F" test. Thus, a significantly lower incidence of liver spot occurred when applications started during the pre-pollination period than later, Table 8. The incidence of liver spot was low with all of the fungicides used. However, some distinct differences were noted, e.g., five liver spot lesions were counted on each compound leaf sprayed pre-pollination with Du-ter, whereas ony 7 of 10 compound leaves sprayed with Benlate had lesions, Table 8. Benlate thus appeared slightly better than Cyprex or Du-ter in 1969 and 1971. These differences among Benlate, Cyprex, and Du-ter may have been of small consequence to the photosynthetic capacity of the leaves. The overall effectiveness of these fungicides was especially apparent when compared with unsprayed checks
[16]

TABLE 8.

INCIDENCE OF LIVER SPOT ON STUART PECAN FUNGICIDES, MACON COUNTY, 1969-71

SPRAYED WITH

Treatments and rate, pounds/100 gallons

19691

Spots per compound leaf 1970 No.

19711 No. 0.70 a 1.50 a 5.22 a .93 a 4.57 a 2.97 a 45.58 b

No. Pre-pollination2 Benlate 50 W, 0.4 .......... 0.17 a Cyprex 65 W, 1.0 .20 a Du-ter 50 W, .4 ....-......... .68 a Post-pollination' Benlate 50 W, .4____________ .55 a Cyprex 65 W, 1.0 .58 a Du-ter 50 W, .4............ 1.03 a Unsprayed (check) ........... 59.23 b

....

1.273 1.28 .17 4.78

1 Means followed by same letter are not significantly different at 1 per cent level according to Duncan's Multiple Range Test.
2

Significant differences occurred between pre- and post-pollination sprays acNo significant differences among treatments and check.

cording to "F" test for significance at 1 per cent level of probability.
3

in which 59 lesions (1969) and 45 lesions (1971) occurred per compound leaf. Disease incidence of such proportions caused abscission of leaflets from the compound leaf rachis and premature defoliation. ZONATE LEAFSPOT Zonate leafspot, caused by Cristulariella pyramidalis Waterman and Marshall, was reported first in Alabama and Georgia in 1967 (8,14). Symptoms on pecan were similar to those described on maple and other hosts (2). The appearance of leafspots on the dorsal side of pecan leaves was grayish brown with concentric ring formation less distinct than from the ventral view. Leafspots viewed from the ventral side appeared light brown to tan in the center, becoming darker brown toward the periphery. Small lesions were characteristically circular with the pronounced concentric rings formed in the leafspot of the larger irregular-shaped necrotic tissue, Figure 7. A few cone-shaped, tan, fruiting bodies (conidiophores) of C. pyramidalis were observed on the lower leafspot surface with the aid of a hand lens. Conidiophores were not observed on small lesions (7-10 mm.); however, on large lesions (15-20 mm.) the conidiophores were erect and occurred somewhat randomly over the leafspot. Leaves with extensive lesion development became desiccated, curled upward from the margins, and fell from the trees. De[17]

FIG. 7. Zonate leafspot (circular lesions and concentric rings in lesions) on pecan leaflet.

foliationi occuirred ill (al K kiitrst 1971 foIlowXiiiw. (\tcnskj e leaf in feion01 (1.3). D~iseas( inceiden ce vv as clos(ly relat((d to wca(thier coliditionis. Xccor(Iinur to l)axt ?), zoniate lcafsIpot onl maple is cciirred sporadically and t\ pically f oll(cd an iuinisualix mioist and oo p 0!~Ol oliiiuring lat( summ1!I er. Tihe i IidienceA of ioiiato leaf s1 ot in iAlaliia appears to foIloXX this pjatterni. Puire cuilture isolations made fronii leaf spots and~ from Coidliophlores of C. pylramhidolks diPX l0op(l XX ite nixcelia and brownish-la ck scle,)otia 1- nun. (dialmeter on V-S flutec agar. Tlhe fiili 4i1 has lbeeni cultuired oni a1u plait(s am)(l~endl xxitl ita arictX of Carb)ohyd rates, \ i [aliil s.andi( natula mil(dia, boilt eollid~iopholres (did not forIm ini th)se Culltures. Sc lejotia form11d wXitllhin 3 (laxs onl C/apck's miedliuml 5111 pllecltcl X itli yeast ex\tract or N\-S Nomie formli(d on pi otatoi dextrose agar. juice and XX tbiii 4 dais
po0(, 1)n cirnmlieal, i)(anl
01 litrienit

afar (9).

Materials and

Methods

\ Ixcelia! dIiscs :3 1h111. ill diamieter X (r( lplacedl (l pecai leax os. b l )1 i The leaX 'cX leX (1111(lemdi pimhinit root canla file tlhro1i the nliXcelia! (isc anid leaf fiX timles. In fectioni XXas cX idllceccl by\ tineX ooloielit (of a light caramiel ibr)X I lesio OliX thill 12 1hours inicubiationl ill a miist chamuler. (Aouidiio)hiores XXole t al s1) (lr((l to at petal leaf, an d inciiibatedl ilnia lhuidiity heliali lso. liiiigicide tests XX(.rc establishil l replicated l )ots ini 1965 ill th( orciiardl XX11 r zoiiate leafspiot ottIinred dllril(r 19617. 131 ostali Cx ple\, aiid I )ii t(r XXore (Xaltiatcd.
Results and Discussion P~ecai

scedllilig leaa

05

iuiilled
!,rvI I

XXith

iiixcelia!

dlists of C.

onntiu pl/relmidulis~~~~

(a

clp

tpclznt

leafspot symptoms in glasshouse tests. Development of zonation in the leafspots was more pronounced under the fluctuating temperature of the glasshouse than in laboratory tests where temperatures were relatively constant (8). Conidiophores formed readily on leaves incubated in a humid environment. Conclusive evidence for development of a secondary cycle of infection with conidiophores was demonstrated by using these fruiting bodies as a source of inoculum (8). The effectiveness of specific fungicides for control of zonate leafspot is unknown. Fungicide evaluations were negative during 1968, since zonate leafspot did not recur in the orchard where it was first discovered. Low incidence of zonate leafspot was observed during 1969 in the orchard where first observed in 1967. During 1970 and 1971, zonate leafspot was severe in Dallas and Perry counties; nearly total defoliation occurred on several trees in Perry County. Incidence of zonate leafspot is apparently increasing. OTHER DISEASES Powdery mildew, caused by the fungus Microsphaera alni Wint., appears as a white powder on leaves and nut-shucks in midsummer. The powdery appearance is caused by the white superficial fungal growth. Nut-shucks that are infected early in the season split prematurely, resulting in shriveled kernels. Sulfur 90 per cent W at 2 pounds per 100 gallons water was shown to prevent this disease. Pabst pecans are especially susceptible to it. Sooty mold is caused by an unidentified species of Capnodium, a fungus that grows in aphid secretions on the pecan leaf surface. The fungal growth is entirely superficial, but often so abundant that it may injure the plants by significantly reducing the photosynthetic area. Du-ter at 0.6 pound per 100 gallons and Cyprex at 1 pound per 100 gallons prevented sooty mold, but Zineb treatment made no difference in sooty mold incidence as compared with unsprayed pecans (5). The best procedure for control of sooty mold has been through elimination of aphids with applications of Dimethoate, 3/4 pint per 100 gallons. Zinc deficiency in pecan trees is characterized by a rosette appearance of foliage. Leaves become mottled and yellowish, and leaflets are narrow and crinkled in advanced stages of the disease. New shoot growth is checked, internodes are short, and the foliage appears bunched or rosetted. In the final stage, shoots
[ 19]

dlie
no(

etirrett Year s

Ixack frFont the tips; this dlie-ILack is tisullI contfinled to the growxth. Affe eted trees 1 ear po)(orly, filled] nuts ot*
pcant trees w~ith

ntuts, dlep~endintg oin seXverity of the dhisease.

/linc (deficiencex sx tptoins maX sulfate per acre app~lied to the

he treatedl wXith 150) pountds inic soil. Foliage spraX s of 4f potltos

\u Zinc per 100) gallonts should also 1)e atpplied duirinig the first three sprays in the first 2 g ars, and( 11 in )5bs flio t Xears as symflptomts p)(rsist.

ear (little leaf) is ait iitritioid disease. S\ iptolts w Xere l t sev eral seedIlintg tre(s ando occasionualX oil b~raniches of Schle\ ill ia large orchtaro(f imtprovXedl Xarieties near Iltr tslo
Mouse ob~serve

ill \lacon Cotyt~. Primtiary s's iptots are, blunlt roundtoeo leaflet tips5 wXhere tissue has failedl to d(leX op. Figl1ire S. Leoaf tissues are pale-greetn to y ellow wXith soe niecrosis at the leaf let tip. Aff ected leav es may 1 e con sidlelal\ redulcedl in size, and1( the tipf of the ii(-X eill oftent protrudes l)eyond( the( leaf nuarriu. The i OtCertaitn branchles of somie trees. dlisease miay' be foundol ( iio' th of nuts oit sever(elys affe(ctedl trees is great ly ret ardedl or prevenuted. The mlouise cat condl~ition is cau sedl b\ a dleficiencye of miaulganlese . Spra~iutg trees XXith 1 01r 2 per cenit miantganese poundcs tiiagise sulfate to the soil sulfate or applx itig ? to 4f und ter matu re trees has beetn reportedl to promtote ia5() per eel t recoX erX of' affected trees inl 2 Xears (7)

FIG. 8. Mouse ear disease symptoms (rounded leaf-tips) an pecan leaflet. 20') I

Shuck disease, also kn ow\ itas "tulip)discasc" or "pops." is iai\ears b)\ poor filliiig of niits fromi the embryo\ . No this disease anod the p~arasitic organism has b~een ilup1 licatcd ini siltrue cause is nmknowi. Shucks oj)(H pleuoatoorel\ anto 1 ill houiette, the opening shucks alod m111p~resenut the appear-auee of
fest in sonic0

properly filled xx hem .ajcn lpfoeFgr nuotuirc anidisiltesn ntormoalily. lse n~e opeut \\ci fm fectedl nuts aore cracked, oulx a shrix cl((. dlrx eluibnI o is founmd:
h a hay, ()ceurremlce of the problemo such mouts are kuuoxvu as .pops., ult ith success eali bI th e dlisease heelsi associatedl primly also has b~een olbser edl out occasmomi "xith the \hahan amnd sehlex soils exhmihit this xarieties. Success pecants growxin g illheitx problemf to an appreciab~le exten t. Wtater relaticonls mia\ I ax e ii pr oper o t fillinout soiiii Ho it

FIG. 9. Shuck disease symptoms; note and adjacent green unopened shucks.

"tulip" configuration of opened

shucks

f1 1

LITERATURE CITED
(1) COLE, J. R.

Gnomonia caryac pecanac nov. var. J. Agr. Res. 47:869-881.

1933. Liver Spot Disease of Pecan Foliage Caused by

(2) DAVIS, T. C. 1963. Zonate Leafspots on Various Hosts Caused by
Cristulariellapyramidalis. Plant Dis. Reptr. 47:983-985. (3) DEMAREE, J. B. AND J. R. COLE. 1932. The Downy Spot Disease of Pecans. J. Agr. Res. 44:139-146. (4) DIENE+R, U. L. 1962. Control of Pecan Scab in Alabama in 1961 and Its Relation to Nut Quality. Plant Dis. Reptr. 46:232-235. (5) ---------------------- AND F. E. GARRETT. 1967. Control of Scab and Other Diseases of Pecan in Alabama. Plant Dis. Reptr. 51:185-188.
(6)

---------------------A. J. F. E.
,

LATHAM, AND

CARRETT.

1968.

New Fungi

(7)

(8) (9) (10) (11)

(12)

cides for Control of Pecan Scab in Alabama. Highlights of Agr. Res. Auburn Univ. (Ala.) Agr. Exp. Sta. 15(1):9. GAMMON, N., JR., AND R. H. SHARPE. 1956. Mouse Ear a Manganese Deficiency of Pecans. Amer. Soc. Hort. Sci. 68:195-200. LATIAM, A. J. 1969. Zonate Leafspot of Pecan Caused by Cristalariella pyrarnidalis. Phytopathology 59:103-107. -----------------------. 1969. Zonate Leafspot of Pecan in Alabama and Georgia. Proc. Southeastern Pecan Growers Assoc. 62:86-87. -----------------------. 1970. Liver Spot Disease of Pecan in Alabama. Plant Dis. Reptr. 54:408. . 1970. Efficacy of Selected Fungicides for Control of -----------------Downy Spot on Pecans in Alabama. Plant Dis. Reptr. 54:725-727. ----------------------- . 1971. Fungicidal Control of Pecan Downy Leafspot.
Highlights of Agr. Res. Auburn Univ. (Ala.) Agr. Exp. Sta.

18(1): 6.

(1.3) ------------. 1972. Some hosts of Cristulariella pyramidalis in Pecan Orchard Hedgerows. Plant Dis. Reptr. 56:176-177.

(14) -----------

AND H. J. AMLING. 1968. A New Leafspot Disease of Pecan Incited by Cristulariella pyrarnidalis in Alabama and Georgia. Plant Dis. Reptr. 52:747. AND

(15) ------------

F. E.

GARRETT.

Alabama during 1968. 62:90-95. Alabama during 1969. 63:40-43. (17) OSBURN, M. R.,
KENKNIGHT.

Proc.

1969. Control of Pecan Scab in Southeastern Pecan Growers Assoc.
1970. Control of Pecan Scab in

(16) ------------------------------.

Proc. Southeastern Pecan Growers Assoc.

USDA Agr. Handbook No. 240.

'1966.

W. C.

PIERCE, A. M. PHILLIPS, J. R. COLE, AND G. F. Controlling Insect and Diseases of the Pecan.

[23]

A%3K

.Ue ; JaI

L tXiEK M

i

:

a e iOinU 5YSTEM

OF ALABAMA'S LAND-GRANT UNIVERSITY

With an agricultural

research unit in every
major soil area, Auburn

h

i

0

University serves the
needs of field crop, livestock, forestry, and hor-

ticultural producers in

each region in Alabama. Every citizen of the State has a stake in
this research program, _

I
r
i r io 4

since any advantage from new and more
economical ways of producing and handling, _

,

farm products directly
benefits the consuming

public.

Research

Unit Identification

1. Tennessee Valley Substation, Belle Mina. 2. Sand Mountain Substation, Crossville. 3. North Alabama Horticulture Substation, Cullman. 4. Upper Coastal Plain Substation, Winfield. 5. Forestry Unit, Fayette County. 6. Thorsby Foundation Seed Stocks Farm, Thorsby. 7. Chilton Area Horticulture Substation, Clanton. 8. Forestry Unit, Coosa County. 9. Piedmont Substation, Camp Hill. 10. Plant Breeding Unit, Tallassee. 11. Forestry Unit, Autauga County. 12. Prattville Experiment Field, Prattville. 13. Black Belt Substation, Marion Junction. 14. Tuskegee Experiment Field, Tuskegee. 15. Lower Coastal Plain Substation, Camden. 16. Forestry Unit, Barbour County. 17. Monroeville Experiment Field, Monroeville. 18. Wiregrass Substation, Headland. 19. Brewton Experiment Field, Brewton. 20. Ornamental Horticulture Field Station, Spring Hill. 21. Gulf Coast Substation, Fairhope.