328 
Joumal of Agricultural Research 
Vol. XXVIII, No. 4 
DIFFICULTIES ENCOUNTERED IN ENDEAVORS TO CONTROL PECAN SCAB 
Those attempting to control pecan scab encounter several perplexing difficul¬ 
ties. In addition to the problems arising in the control of other deciduous fruit 
diseases, even more perplexing ones appear. The problem of spraying the tops and 
centers of some of the larger pecan trees is not an easy one. Despite the youth¬ 
fulness of the cultivated pecan industry, some of the older cultivated trees have 
attained the height of 50 to 60 feet with a spread of 40 to 60 feet. The usual tower 
and spray rods are not practicable to use when spraying trees of such dimensions 
and resort must be had to the high-power spray outfits and spray guns. Most 
of the spray guns used by the writer are not capable of carrying the desired misty 
spray to the tops of the taller trees. It is hoped that horticulturists will devise 
some system of pruning that will tend to reduce the height of the trees and open 
up their centers so as to facilitate spraying operations. 
The pecan nut is susceptible to the attack of the scab pathogen from the time 
it is first formed, which is ordinarily during the latter part of April or the first 
part of May, until it has completed its growth. Any meristematic tissue seems 
to be subject to infection, necessitating, in case of the very susceptible varieties, 
frequent applications of spray from the first of May to the middle of August. 
Another difficulty in controlling pecan scab is due to the susceptibility of cer¬ 
tain varieties such as Delmas to twig infection. Since there is ample evidence that 
large numbers of spores are produced on infected twigs in the early spring, one 
can readily see how easily the unfolding leaves situated in such close proximity 
to these sources of infection may become infected. Twig infections on the cur¬ 
rent year's growth also serve to propagate the fungus during the summer. 
The rainy season through the central and southeastern sections of the pecan 
belt usually begins about the middle of June, and normally extends over a period 
of approximately three months. The average number of rainy days for June» 
July, and August at Thomasville, Ga., according to the United States Weather 
Bureau is 12, 15, and 14, respectively. Then, normally, rain may be expected 
on an average of almost every other day during those three months. Occasionally 
the number of rainy days greatly exceeds the average, as for example, July, 1921, 
had 27; July, 1922, 18; June, 1923, 24; and July, 1923, 21. 8 It is often difficult 
and occasionally impossible, on account of boggy soil, to apply spray at the times 
one thinks it should be put on during June, July, and August in the Coastal Plain 
region. 
Coincident with the rainy period, the pecan trees put on a new growth of twigs 
and foliage, which greatly complicates spraying operations on account of the 
extreme susceptibility of the new foliage. 
SUMMARY 
Excluding rosette, pecan scab, caused by Fusicladium effusum Wint., is the 
most important disease affecting the pecan. 
The disease is known to exist in all the Southern States bordering the Atlantic 
Ocean and Gulf of Mexico and in Arkansas. 
At the present time there is known to be a wide variation in the degree of 
susceptibility of the different cultivated pecan varieties to the scab disease. 
Some varieties are very susceptible while others are almost immune. 
The disease is known to attack the nuts, twigs, leaves, dormant buds, and 
catkins. Very little, if any, damage is done to the buds and catkins. Qonsider- 
8 The Weather Bureau indicates a rain measuring less than 0.01 of an inch as a trace. Days having only 
a trace of rain are included in the number of rainy days herein reported. The author feels justified in includ - 
ing the days when the precipitation indicates only a trace, as a misty, cloudy day, when the actual precipi¬ 
tation measures less than 0.01 of an inch may be much more favorable to spore germination and infection 
than a heavy shower followed by bright sunshine. 
