Apr. 26,1924 Pecan Scab and Sources of Early Spring Infections 
325 
Twig lesions formed during the latter part of the summer or early autumn develop 
black more or less hemispherically shaped, sporulating stromata on their surfaces 
(PI. 2, B). The author considers the sporulating stromata thus formed as very 
important sources of the early spring infections. They have frequently been 
observed producing conidia abundantly during April and May at the time the 
new leaves were unfolding and extremely susceptible to scab infection. Pecan 
twigs infected as illustrated in Plate 2, B, when collected at various times during 
the winter and spring months and placed in damp chambers for 48 hours, have 
almost invariably produced conidia from the stromata in great profusion. Spot6 
on twigs that have been killed by a severe attack of scab during the previous 
season also serve to carry the disease over winter. 
Primary infections from such sources as those just described are the most 
difficult to prevent. Pecan leaves are very susceptible to attack of the scab 
pathogen during the time they are unfolding. During this period, young pecan 
leaves are also very susceptible to sjyay injury, thus increasing the difficulty of 
preventing early leaf infections. Pecan leaves unfold over a period of several 
days, during which time an application of spray may do great damage to the 
foliage and serves only to protect those pinnae already unfolded and exposed. 
OLD NUTS AS SOURCE OF PRIMARY INFECTIONS 
Nuts that have been killed by the scab fungus during the previous summer 
are, as a rule, important sources of the early spring infections. All such nuts, 
however, seem not to carry the fungus through the winter, but only those that 
have attained one-half size or more before being killed by the disease. The nut, 
illustrated in Plate I, E, is a good example of this type of the primary infection. 
The dark blotches, seen on the stem-end of such nuts will produce conidia during 
the early spring weeks. Frequently, nuts are slightly spotted with scab during 
late summer. Infections taking place at this time may cause no damage to 
the nuts since the kernel develops and matures normally. These late infections 
usually form the sporulating stroma and serve as a means of carrying the disease 
through the winter. Either empty shucks or late season infected nuts are quite 
noticeable as sources of the early infection when they remain on the trees over 
winter and become the center of a number of scab-infected leaves the following 
spring. 
LEAVES AS SOURCE OF PRIMARY INFECTIONS 
Scab spots that have formed on the smaller'Veins of the leaflets or those that 
have formed within the network of the vascular system do not form sporulating 
bodies and are, therefore, not believed to harbor the fungus through the winter. 
Lesions on the mid-veins of the pinnae, rachises and petioles, especially those 
that form near the base of the petiole duce the hold-over stroma, and con¬ 
sequently serve as sources of the primary infections. 
CONTROL MEASURES 
During the pioneer days of the cultivated pecan industry, the variety Georgia 
was thought to be the most susceptible to pecan scab. The growers early realized 
the seriousness of the disease on this variety and promptly top-worked the Georgia 
to varieties considered at that time as being resistant or immune. Mistakes 
were made during this period of varietal changing, owing to the then apparent 
resistance of some varieties now known to be exceedingly susceptible. For 
instance, the Georgia variety was top-worked to Delmas. Later, Delmas orchards 
were top-worked to the variety Schley. The last-named variety is now known 
to be very susceptible in some localities. While many growers are still discarding 
the susceptible varieties by top-working to the more resistant ones, this method 
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