Cucurbit Family Plant Problems - Powdery Mildew and Downy Mildew
Powdery mildew on cucumber.
Powdery mildew - mold on leaf.
Downy mildew - top surface.
Downy mildew - bottom surface.
The topsides of leaves are covered with a
white powdery growth. Areas of the leaves and stems turn brown, wither, and
dry. Fruit may be covered with the growth.
ANALYSIS: Powdery mildew
This common plant disease is caused by either of two fungi (Erysiphe
cichoracearum or Sphaerotheca fuliginea) that thrive in both humid and dry
weather. The powdery patches consist of fungal strands and spores. The spores
are spread by the wind to healthy plants. The fungi sap the plant nutrients,
causing yellowing and sometimes the death of leaves. A severe infection may
kill the plant. Since powdery mildew attacks several different kinds of plants,
the fungi from a diseased plant may infect other types of plants in the garden.
Under conditions favorable to powdery mildew, infection can spread through a
closely spaced planting in a matter of days or weeks.
ANALYSIS: Downy mildew
This common plant disease is caused by the fungus Pseudoperonospora
cubensis. Irregular shaped yellowish to brown spots appear on the upper sides
of leaves, usually at the center of plants. Under moist conditions, a purplish
mildew develops on the underside of leaf spots. Leaves die as spots increase in
size. Spread is rapid from crown toward new growth. The causal fungus
overwinters in areas with relatively warm climate and can be introduced to
other areas by wind. Moist conditions favor disease development.
At the first sign of the disease, treat the plants with a fungicide
containing chlorothalonil. Continue treatment at intervals of 7 days for as
long as the disease is a problem. Grow varieties resistant to powdery and downy
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Text and images adopted from theOrtho
Last Updated: Fri Sep 06 10:30:00PM CST 1996
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