BIG BEND HORTICULTURAL LABORATORY
Big Bend Hort. Lab. Mimeo Report BBL 67-3 February 22, 1967
SCAB AND FOLIAGE DISEASES OF PECAN AND THEIR CONTROL
by J. R. LARGE, Associate Plant Pathologist
Pecan scab, Fusicladium effusum Wint., is the disease which causes the great-
est loss of the nut crop in North Florida. There are eight diseases in addition
to scab of economic importance on pecan trees,
Scab and the four leaf diseases listed below can be controlled by the regular
spray schedule(l). Most seasons it pays to control leaf diseases on non-scabbing
varieties. Two spray applications of bordeaux, Tri-phenyl-Tin hydroxide, or
Cyprex in May and June will usually control the leaf diseases. The other diseases
1. Downy Spot, Mycosphaerella caryigena, Demaree and Cole.
2. Pecan Leaf Blotch, Mycosphaerella dendroides Cke, Demaree and Cole.
3. Brown Leaf Spot, Cercospora fusca Rand, is a disease of minor importance.
4. Gnomonia Leaf Spot, Gnomonia dispora, Demaree and Cole.
5. Nursery Dieback, Botryosphaeria berengeriana de N., is controlled by
pruning out the dead stems and twigs in the Fall. Repeat pruning in the Spring
to remove any remaining infection.
6. Nursery Blight, Elsinoe randii, Jenkins and Bitancourt, is often severe
in nurseries and is of minor importance in mature orchards. It is controlled by
using the standard bordeaux spray schedule starting about the 5th of April.
7. Powdery Mildew, Microsphaera alni Wint., is of minor importance in
Florida. Control is obtained on non-scabbing varieties by two applications of
6-2-100 bordeaux applied in June and July.
8. Pink Mold, Cephalothecium roseum Corda., appears in late summer or Fall
as pinkish fungus growth on hulls and in kernels. The fungus enters the nuts
through scab or injuries. The scab control schedule will check this disease.
9. Crown Gall, Agrobacterium tumefaciens (E. F. Smith and Town) Conn., is
a bacterial disease which causes wart-like growths at soil level. Do not plant
diseased nursery trees. On orchard trees cut out the galls and paint wounds with
a mixture of 1 part creosote to 3 parts coal tar. Do not cultivate or harrow
close to infected trees as the machine will infect healthy trees.
PECAN SPRAY SCHEDULE
The pecan spray schedule consists of 5 or 6 sprays made at approximately
three week intervals beginning about April 10 and continuing until August 15. Do
not spray unless you carry out a complete cultural program. The cost of a complete
program for a 25 year old tree in 1965 was estimated to be about $9.00(2). This
included all costs with 6 scab sprays. This program will increase the yield of
nuts from scab susceptible varieties 50 pounds or more per tree. Use the April
insecticide spray and the May and June insecticide applications on scab resistant
varieties(l). One of the least expensive spray chemicals for control of Pecan
scab is bordeaux mixture in April, May, June and two July applications.
The most promising fungicides developed in the past 50 years are Tri-phenyl-
Tin hydroxide (Du-Ter), and N-dodecyl guanadine acetate (Cyprex). Du-Ter will
control all diseases except powdery mildew. Add Sulfur W/P 2 lbs./100 or Kara-
thane 1 lb./100 to the July and August applications if Mildew is present. Use
Du-Ter 50 W at 4/10 lb./100 gallons. In very wet weather use 1/2 Ib./100.
The second most promising fungicide is Cyprex 2 lbs./l0. Cyprex cannot
be used in the April and May applications on the Moore and Van Deman varieties
as the early applications cause marginal burning and necrosis of the young foliage.
Excellent scab control was obtained in 1966 on the Big Bend Horticultural Labor-
atory pecan trees using alternate applications of Du-Ter and Cyprex applied with
a speed sprayer. See pecan spray schedule Big Bend Hort. Lab. mimeo report
Varieties which appear to be Scab susceptible varieties:
Curtis Mahan Frotcher
Elliott Pabst Van Deman
Russell Moore Mobile
Farley scabs some, but Desirable started scabbing badly
appears to be somewhat near Cairo, Georgia in 1953.
resistant. Stuart is scabbing severely in
Alabama and Mississippi.
1. Large, J. R., John Van Duyn and H. W. Young 1967. Pecan Disease and
Insect Control Suggestions. Big Bend Hort. Lab. Mimeo Report BBL 67-4.
2. Seale, A. D., Jr. 1966. Cost and Return for a Pecan Enterprise.
Proc. Southeastern Pecan Growers Association 59: 15-34.