(Colletotrichum lagenarium), the most destructive
disease of watermelons, serious also on cantaloupe and cucumbers,
occasional on squash and pumpkin. Reddish brown or water-soaked areas
on leaves turn black or brown; leaves shrivel and shatter; stems have
elongated tan cankers. If pedicels are affected, young fruit shrivels and
dies. Older fruit is first bumpy, then has circular, black, sunken depressions up to 2 inches in diameter, 1/2 inch deep. Fruit is bitter and tough.
The fungus winters on seed and in crop refuse.
Control. Treat seed with Arasan or Spergon. Spray or dust with Dithane
Z-78 or Parzate, starting when vines begin to run and repeating at 10- to
14-day intervals. Variety Black Kleckley is quite resistant.
(Gnomonia platani), serious in wet seasons on
native American sycamore, less severe on London plane. Young
leaves are entirely black and shriveled, looking as if hit by late frost,
older leaves have dark-brown or black blotches, mostly along the veins.
The fungus progresses down the petioles resulting in nearly complete
defoliation in rainy springs. Small twigs killed back for 6 inches or more
give a witches' broom effect. The fungus winters in old leaves on ground,
producing perithecia in spring whence spores are blown up to new
growth overhead. Slime spores produced on leaves and twigs are splashed
by rain to other branches.
Control. In normal seasons spraying three times with bordeaux mixture
(8-8-100) or with Puratized Agricultural Spray, 1 pint to 100 gallons water,
starting at bud break and at 10-day intervals, gives reasonable control. In
very rainy springs the amount of control may not justify the expense of
spraying, and in very dry seasons the disease is negligible. Raking up
alien leaves is supposed to reduce inoculum for the next season, but
here is some overwintering on twigs.
(Gnomonia quercina). The fungus is closely related
to that causing sycamore anthracnose, but the disease is seldom as
serious. White oaks are most affected, with a tan scorching between
veins. Maple and linden anthracnoses are occasionally important in unusual
SPOT ANTHRACNOSES are chiefly characterized by bird's-eye spots
with raised borders.
BRAMBLE SPOT ANTHRACNOSE (Elsinoe veneta), common on dewberries,
black raspberries, and many red raspberry varieties. Symptoms are
circular spots, first raised, then sunken, with gray centers and purple
margins, on leaves and canes. Cane spots may coalesce to form large
cankers. Leaves fall prematurely, and fruits dry up. The fungus winters
in old canes.