Alan
McNab
Professor of Plant Pathology |
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Blight
symptoms caused by cucumber mosaic virus (CMV), begin on
young inner leaves and later appear on outer leaves. Leaves
are mottled,
curled, and wrinkled; later they become yellowish and finally
die. Plants affected early are severely stunted. The virus
overwinters in many perennial weeds, builds up in many vegetable
crops (especially cucurbits), and is spread from infected plants
by aphids. Symptoms develop much faster at high temperature
than at low temperatures. |
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Blue
Mold (Downy Mildew), caused by the fungus Peronospora effusa,
affects only spinach. Initial symptoms are indefinite yellowish
areas on upper leaf surfaces. On the corresponding lower surface,
a gray to violet gray mold appears. Affected areas turn black
and die. The disease may affect entire leaves and plants. In
severe attacks, all plants in a field may be destroyed within
a few days. The blue mold fungus overwinters in soil, in seed,
and in spinach plantings. Fungus reproductive spores are spread
from plant to plant by wind. Disease develops best in cool moist
weather and is most prevalent in coastal areas. |
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White
Rust, caused by the fungus , is characterized by white blister-like
pustules, usually on the lower surface of leaves. The correstponding
upper surface leaves may be yellowish. |
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