Leaf blotch disease is caused by the fungus _Mycosphaerella dendroides_
(Cke.) Demaree and Cole. The disease occurs mainly in trees of poor
vigor, which may be due to neglect, infertile soil, rosette or
overcrowding. Nursery trees are particularly susceptible to the disease.
The fungus overwinters in fallen leaves. In the early spring, large
numbers of spores produced in the old leaves on the ground are carried
by wind currents to the young leaves in the tree, where they germinate
and rapidly invade the tender leaf tissue.
The disease symptoms first appear on the undersurface of mature leaves
in early summer, as small olive-green velvety spots. By midsummer black
pimplelike dots become especially noticeable in the leaf spots after the
surface spore masses have been removed by wind and rain, giving the
diseased areas of the leaves a black, shiny appearance. When the disease
is severe, infected leaflets are killed, which causes defoliation of the
trees in late summer or early fall and results in reduced tree vigor and
increased susceptibility to disease and insect attack.
_Control._—Leaf blotch disease can be controlled effectively in the
early spring by disking under old fallen leaves that harbor the fungus
pathogen.
In areas where a spray program for the control of scab disease is
carried out, leaf blotch usually is not a damaging disease. In
localities where leaf blotch disease occurs in the absence of other
pecan diseases, two applications of fungicide will control the disease
effectively. The first spray should be applied after pollination when
the tips of the nutlets have turned brown and the second spray
application should be made 3 to 4 weeks later. See spray schedule, page
4.