Mildew - Cucurbits
Powdery mildew is caused by the fungi (in vine crops by Sphaerotheca
fulginea & Erysiphe cichoracearum) that appear as a white
powdery growth on the stems and leaves. It affects cucumbers,
pumpkins, melons, ornamental gourds, squash, and other vegetables.
The pathogen can be introduced by wind from areas with relatively
warm climate where it overwinters. Disease development is very
fast in three days and nights that are hot and dry during the
day and the nights are cool with a high relative humidity. The
pathogens attack the vines and lower surfaces of the leaves first.
Small patches of white thin thread-like masses of mycelium appear
on the infected areas. These spread and eventually cover the
whole leaf surface or vines with white powdery looking fungus.
The affected leaves turn yellow and finally dark brown causing
an early death of the leaves, which affects fruit development.
It does not affect the petioles. The disease tends to be a problem
from late July to early September.
Plant resistant varieties of cucumbers, pumpkins, and
muskmelons; follow a regular spray schedule with recommended fungicides
in your state; rotate vine crops with non-cucurbit crops; and use
cultural practices that avoid overcrowding, too much shading, and
poor air circulation.