Downy Mildew Confirmed in North Carolina

Downy mildew is a widespread, serious disease of grapevines. Initial leaf symptoms are light green to yellow spots, called “oil spots” because they may appear greasy. Under humid conditions, white, downy spore masses can be seen on the lower leaf surface. These spores are wind dispersed. The lesions eventually turn brown as the infected tissue dies. Severely infected leaves drop prematurely, which can reduce winter hardiness of the vine. Infected flower clusters dry up or become covered with white spores under humid conditions. Infected berries turn a mottled dull-green or reddish purple and readily fall from the cluster. Although berries become resistant to infection within three weeks after bloom, the rachis remains susceptible for several weeks longer.

Downy Mildew was confirmed on cucumbers in Columbus County late last
week (5/27) and in Duplin County early this week (6/1). It is probably
scattered all over NC even if symptoms have not been observed yet.

For commercial growers:
General recommendation is to spray on a 5-7 day schedule with high
pressure and enough water volume (25-50 GPA depending on canopy size) to
obtain coverage. Presidio and Ranman are the top tier products for
efficacy. Previcur Flex, Gavel, and Tanos would be the second tier.
Presidio, e >S9 E n @ lA dJ}AQ Pq 1yP A m fungicide to
be tank mixed. Ranman requires a surfactant and Gavel can be used alone.
Bravo, Mancozeb products (Dithane, Pencozeb), Curzate, and copper
fungicides are good tank mix partners. Post harvest interval should be
consider when selecting products. Gavel and mancozeb products are a 5
day PHI while all others are 3 or less.

For home gardeners:
Spray a chlorothalonil product (Bravo, Daconil) every 7-14 days.
Alternate each week with a mancozeb product before harvest, then use
only the chlorothalonil product through harvest. Mix fixed copper in
with either product 2 or 3 times a season. Good thorough coverage is
important for control. In rainy periods, spray at least every 7 days.

More information about downy mildew forecasting, identification, and
control, is available at the Downy Mildew Forecasting website which can
be found at http://cdm.ipmpipe.org.