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.

Tomato Blights are coming to a Garden Near You!

The North Carolina Cooperative Extension office here in Murphy has already received information that late blight (Phytophthora infestansin) in tomatoes has been detected in the states of Kentucky, Pennsylvania, Florida, Louisiana, and Maryland. It has not “officially” been reported in this area yet, but it is very likely to show up here before summer is over. This same disease will also destroy Irish Potatoes.

Late Blight is one of many diseases that can infect tomatoes and potatoes, but is probably the most devastating. Once the disease first starts on a plant, it can completely destroy the whole plant in a couple of weeks.

How does this disease end up in my garden? This disease, unlike Early Blight, usually does not overwinter here. Spores get caught up in upper air currents and are deposited in rainfall. However, it can overwinter in stored potatoes from an infected crop the year before.

Now that you are aware of the possibility of your garden getting infected by different diseases, the big question is what to do about it. One thing to keep in mind is how disease happens. Three things need to be present for any disease to develop. You have to have a pathogen (disease), a susceptible host (plant) and moisture. Take away any of the three, no disease.

With all diseases, the most important thing to do is prevention. Always purchase disease free plants and certified seed. Look for varieties that have resistance to certain diseases. Never work with plants when they are wet. Space plants out as much as possible for good air circulation. Dip tomato stakes in a 10% solution of bleach for 10 minutes. This will kill early blight spores and other bacterial diseases from the year before. Always rotate tomatoes and potatoes to a different location in the garden. Never follow one with the other. We have a list in our office or on the website of what vegetables should not follow other vegetables.

If you have done all of the prevention measures, you are still likely to get diseases. You now have to make a decision on whether or not to apply a preventative fungicide. Most of all fungicides the home gardener can purchase are preventative, not curative. Once a disease is present, the best you can do is try to slow down its development. For a fungicide to work, it has to be on the plant before the pathogen gets there. This means you have to apply the fungicide early, often (at least once a week) through out the season, reapply after rain wash off and get good coverage over the whole plant. It is best to alternate with different fungicides if possible to prevent diseases from getting resistant.

For those that choose not to spray a fungicide, you need to keep the plant as dry as possible. Do not water the whole plant, just the ground. Some commercial organic growers use “hoop houses” or high tunnels that are plastic coverings to keep rainfall and morning dues off plants. They also spray approved copper products to help with prevention. You can modify planting dates by planting very early hoping to harvest some fruit before the disease takes the plants out.

If you need more information on these diseases, visit our website or Blogs, http://cherokee.ces.ncsu.edu/. We have good pictures of these diseases and detailed information posted there or call the office at 837-2210 or email keith_wood@ncsu.edu