tl ..IG BEND HORTICULTURAL LABORATORY
Si ii~ J- MONTICELLO, FLORIDA
Big BenJfrr 1b1 Mimeo| Report BBL 67-8 April 10, 1967
BRESTAN 60* (TRIPHENYL-TIN-ACETATE) A PROMISING FUNGICIDE FOR PECAN SCAB CONTROL.
by John R. Large
Associate Plant Pathologist
Brestan 60 (Triphenyl-Tin-Acetate) was included in the experimental fungicides
tested for control of Pecan scab on Mahan pecan trees in the Monticello Nursery or-
chard in 1966, and compared favorably with Du-Ter 50W and Cyprex 65W.
The spray experiments were started April 10 in a block of Schley trees. Obser-
vations May 10, indicated a very light set of nuts on these trees, therefore, the
tests were moved to the Monticello Nursery orchard of Mahan trees about May 12th.
In April, the Mahan trees had a good crop of nuts set on the trees, but the crop was
further reduced by an early brood of casebearer. In spite of this early infestation
and the fact that the first fungicide was applied May 16 enough nuts remained on the
trees for nut scab infection counts for each fungicide tested. The orchard was
sprayed four times: May 17, June 21, July 19, and August 11. Insecticide was added
to the May and August applications. The dilute spray was applied with a hand gun on
a hydraulic sprayer at 450 psi. There was a shortage of rain in March and April
with ample rain in May, June, July and August. The total rainfall for these seven
months was 33.31 inches. The monthly rainfall in inches was as follow: March 2.72;
April 0.99; May 6.92; June 6.69; July 5.70; August 5.12; and September 5.17. There
were 49 days of rain during the 154 days, and the humidity remained high most of the
time, providing excellent conditions for scab development.
Scab infection counts were taken August 23rd from green nuts on the trees using
the method of Diener and Garrettl. The scab index figure (range 0 to 4) was cal-
culated from data taken on 50 nuts from each of 4 single tree replications for each
treatment. Data were recorded as scabbed shucks: Class 0 clean, no scab infect-
ion on the shuck; Class 1 trace to 10%; Class 2 11 to 25%; Class 3 26 -
50%; Class 4 51 to 100%. The number of nuts in each class was multiplied by the
class number. The resultant figures were summed and divided by the number of nuts
to give the scab index for each tree. The mean of 4 replications was calculated for
each treatment (Table 1). These data are also presented as the percentage of nuts
with heavy, light, or no (clean) visable scab infection. The figures under light in-
fection represent the means of the data from classes 1 and 2 and under heavy infest-
ation from classes 3 and 4. The nuts with heavy infestation are essentially worth-
less and frequently drop before harvest. Nuts with light infection are usually
lighter in weight and of poorer quality than nuts free from scab.
The results of the 1966 experiments are shown in Table 1.
Grateful acknowledgement is made to the Monticello Nursery Company for providing
the orchard, and to the several Chemical Companies for experimental materials.
*Brestan is not approved for use by the U. S. Food and Drug Administration.
Even though the April prepollination sprays were omitted on these Mahan trees
this season good commercial scab control was obtained with Brestan 60W, Du-Ter 50W
and Cyprex 65W. For each of these fungicides the scab control was better than the
control on bordeaux sprayed trees. The scab control with DAC 2787, Geigy 14986B
and Kocide 101 was not as good as the control obtained with bordeaux mixture.
Dark green foliage remained on the trees sprayed with Brestan or Du-Ter until
frost. Trees sprayed with Geigy 14986B were observed to be severely defoliated on
the first of November.
Further investigation of Brestan 60 is warranted to determine the minimum
effective dosage, and phytoxicity on pecan varieties. No phytotoxicity was noted
on the Mahan variety.
1. Diener, U. L. and F. E. Garrett. Control of Pecan Scab in 1964 in South-
west Alabama. Southeastern Pecan Growers Association 58: 73-74, 1965.
TABLE 1. SUMMARY OF NUT SCAB INFECTION ON MATURE MAHAN PECAN TREES,
MONTICELLO NURSERY COMPANY ORCHARD. COUNT MADE AUGUST 23, 1966.
Fungicides listed according to percentage clean, scab free nuts.
1. DuIe Flow4 &
1. Du-Ter Flow
2 lb./1 gal.
2- Du-Ter 50W
3. Du-Ter 50W
4. Cyprex 65W
5. Brestan 60W
6. Brestan 60W
7. Du-Ter Flow.
9. Cyprex 65W
10. Cyprex 65W
11. Du-Ter 50W
12. Daconil 2787
13. Kocide 101
14. Geigy 14986B
4-1 then 6-2
Percent Nut Scab Classi-
Clean Light Heavy
0 1 L ?9 u