PECAN SCAB WITH SPECIAL REFERENCE TO SOURCES 
OF THE EARLY SPRING INFECTIONS 1 
By J. B. Demaree 
Assistant Pathologist , Fruit Disease Investigations , Bureau of Plant Industry, 
United States Department of Agriculture 
INTRODUCTION 
Owing to the extensive development of the cultivated pecan industry through¬ 
out the southeastern United States during the past 15 or 20 years, the economic 
importance of those diseases which materially decrease production has assumed 
a prominent position. Excluding rosette, which is apparently caused by, or at 
least associated with, unfavorable soil conditions, scab caused by Fusicladium 
effusum Wint., is preeminently the most important pecan disease. 
DISTRIBUTION 
Though the pecan is indigenous along the several rivers in Texas, the Missis¬ 
sippi, and its tributaries, as far north as central Illinois and southern Indiana, 
scab is known to exist only in the Southern States bordering the Atlantic Ocean 
and Gulf of Mexico, and in Arkansas. These facts indicate that high humidity 
as well as high temperature may be essential for its maximum development. 
In the southeastern United States pecan scab was until recent years of serious 
economic importance only within a distance of 50 to 100 miles from the coast 
line, but now it seems to be extending its range of distribution inwardly. This 
condition is thought to be due largely to the increased number of plantings and 
to the frequent summer rains of the past few years, which have favored the 
rapid spread of the disease. The apparently rapid spread of scab in the central 
section of the southern pecan belt 2 may also be accounted for by the fact that 
the cultivated pecan industry is comparatively new and many orchards are young, 
having only recently come into bearing. A young orchard composed of one of 
the very susceptible varieties, such as Delmas, even when situated near the 
coast, may produce two or three crops of disease-free nuts before the scab fungus 
has become so well established as to reduce the yield of nuts. Even now the 
disease is of a less serious nature and fewer varieties are attacked 150 miles from 
the coasts than at points within 50 miles of them. Certain varieties, such as Van 
Deman, Schley, and Pabst, are very susceptible when grown near the Gulf and 
southern Atlantic coasts, but are at present only slightly attacked at points 100 
miles from these coasts. 
Not considering the natural agencies favoring the spread of pecan scab, the 
growers in many instances are partly, if not largely, responsible for the presence 
of the disease in its most accentuated form. This condition is brought about 
by the occasional neglect of orchards that have become unprofitable due to the 
loss of the crop by scab. Some growers' think there will be a return of weather 
conditions, totally unfavorable for the development of the disease, which will 
permit their trees again to become productive. During this interval of neglect, 
1 Received for publication Feb. 27, 1924. 
* The southern pecan belt is fairly well confined to that portion of the South in which cotton grows. . 
Journal of Agricultural Research, 
Washington, D. C. 
(321) 
Vol. XXVJII, No. 4 
Apr. 26,1924 
Key No. Q-391 
