Q. I have white powdery mildew on my green, table
grapes. This has not been a problem in
the past. What now? Is this related to
the cool, moist weather?
grapes. This has not been a problem in
the past. What now? Is this related to
the cool, moist weather?
 |
| Grapes should have air movement around them to prevent powdery mildew and bunch rots. In the hot desert we have to be careful about giving them full sun throughout the day because of sunburn to the fruit. |
A. Yes, powdery mildew on grape is seldom seen here
because of our very dry and hot weather. This very cool spring, higher humidity
and recent rains has made powdery mildew, as well as early blight on tomatoes a
problem. Powdery mildew will disappear when it gets hot and dry.
because of our very dry and hot weather. This very cool spring, higher humidity
and recent rains has made powdery mildew, as well as early blight on tomatoes a
problem. Powdery mildew will disappear when it gets hot and dry.
 |
| Horticultural oils can help reduce powdery mildew problems |
One thing that really helps
control powdery mildew forming on grape bunches is improved air movement around
grape bunches as well as sunlight during the morning hours. Sunlight on grape
bunches in the late afternoon can cause sunburn on the berries so be careful
about giving the fruit too much sun late in the day.
We can usually prevent powdery
mildew by removing the leaves around grape bunches for better air movement and
keeping bunches dry. Once powdery mildew has started, you may have to apply a
fungicide to keep it at bay or eradicate it.
mildew by removing the leaves around grape bunches for better air movement and
keeping bunches dry. Once powdery mildew has started, you may have to apply a
fungicide to keep it at bay or eradicate it.
One of the best organic controls
of powdery mildew on grape are the horticultural oils. Horticultural oils are
mixed with water and sprayed on grape bunches in the early morning hours. There
is a precaution in using oil sprays and not to apply it when temperatures are
high. However, I have had no problem applying oils during the cool early
morning hours.
of powdery mildew on grape are the horticultural oils. Horticultural oils are
mixed with water and sprayed on grape bunches in the early morning hours. There
is a precaution in using oil sprays and not to apply it when temperatures are
high. However, I have had no problem applying oils during the cool early
morning hours.
Insecticidal soaps labeled for
disease control have also given some control as well as dusting dry bunches
with sulfur dust.
disease control have also given some control as well as dusting dry bunches
with sulfur dust.