Biology Reference
In-Depth Information
Scab
Diseases characterized by an overgrowth of tis-
sue in a limited area are commonly called scab.
The hyperplastic scablike lesions correspond to
the necrotic or dead areas of leaf spots and can-
kers. Diseases called scab caused by
Elsino ¨
or its
anamorph,
Sphaceloma
, are treated under Spot
Anthracnose.
scattered, with tissue drying and falling out, leav-
ing circular holes.
Control
The brown-rot spray schedule should
also control scab, a sulfur spray 4 to 6 weeks
after petal fall being especially important.
A fungicide can be combined with an insecticide
spray for curculio.
Cladosporium caryigenum
Pecan Scab
,
Leaf
Spot
, general on pecan, and hickory. Scab is
perhaps the most important limiting factor in
pecan production in the Southeast. All varieties
are somewhat susceptible, even those, like Stuart,
that have been quite resistant in the past. Crop
losses may reach 75 to 95 %.
The fungus attacks rapidly growing tissue in
leaves, shoots, and nuts; mature growth seems to
be immune. On Schley and other highly suscep-
tible varieties, primary infection shows in elon-
gated olive brown lesions on veins and underside
of leaves. With secondary infection leaves appear
almost black, as a result of coalescing of spots;
defoliation follows. On more resistant varieties,
such as Moore and Stuart, infection is of ten
delayed until the leaves are nearly mature, and
so scab spots are confined to nuts. Nut lesions are
small, black, circular, slightly raised at first, then
sunken. Spots may be so close together that the
entire surface turns black; the nuts drop prema-
turely or remain attached to shoots indefinitely.
Infection is correlated with spring and early sum-
mer rainfall, continuous moisture for 6 to 8 hours
being required for the spores to germinate and
enter the host. First lesions appear in 1 or 2 weeks.
Cladosporium
Blotch Diseases
.
Cladosporium bruneo-atrum Possible cause
of russeting of citrus fruit hitherto attributed
solely to citrus mite.
Cladosporium carpophilum (Syn.
Fusicladium carpophilum
), apparently
a different strain from peach scab fungus.
Almond Scab
. Water-soaked symptoms on
young shoots turn brown; leaves turn black,
drop prematurely; circular, olivaceous spots coa-
lesce on fruit.
Cladosporium carpophilum
Peach Scab
, gen-
eral on peach, widespread on apricot, nectarine,
cherry, and plum. The form on cherry and Euro-
pean plum has been attributed to
Venturia
cerasae
(
Cladosporium cerasi
). Small, round,
olive black spots appear on infected fruits about
6 weeks after petals have fallen. These are usually
on upperside of fruit, and cracking may follow.
Twigs show nearly circular yellow-brown
blotches with gray or bluish borders; cambium
may be killed and twig die. Leaf spots are brown,
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