Late blight threatens Carolinas tomatoes

07/18/2014 12:00 AM

07/18/2014 2:00 PM

Late blight, the dreaded disease that wiped out the East Coast tomato crop in 2009, has shown up again in North Carolina.

First identified in late June on potatoes growing in the Coastal Plain, it has also attacked a field of tomatoes in the mountains near Hendersonville.

Dr. Lina Quesada-Ocampo, plant pathologist with N.C. State University, warns that the late blight pathogen can travel long distances and lurk in gardens and fields until environmental conditions are right, then destroy crops virtually overnight.

“Time to protect your potato and tomato crops, no matter what part of the state you are in,” said Debbie Roos, sustainability agent for the Cooperative Extension at NCSU.

Late blight affects tomatoes, potatoes and other members of the nightshade family. It is caused by an oomycete. Once thought to be a type of fungi, oomycetes are now considered a distinct class of organisms related to algae and diatoms. They are responsible for a host of diseases gardeners love to hate, including “damping off,” which can wipe out whole trays of seedlings.

Notoriously, the late blight pathogen caused the Irish potato famine of the 1840s.

Quesada-Ocampo explained that nights in the range of 50 to 60 degrees Fahrenheit and days in the 80s, accompanied by rain and high humidity, are ideal conditions for late blight.

The disease typically starts with irregular, water-soaked lesions, sometimes with a “halo” along their edge, on green healthy leaves high on the plant. The disease can progress very rapidly, turning leaves brown and destroying fruit. It spreads readily via wind, farm equipment, irrigation water and other vectors.

These are among the steps Quesada-Ocampo, Roos and other experts recommend to control the disease on tomatoes:

• Don’t allow plants to remain wet for long periods. Instead of overhead sprinklers on your garden, use drip hoses.
• Keep weeds under control.
• Promptly remove infected plants and fruit. Put them in a closed plastic bag in the trash, not in the compost pile.
• Improve air circulation by training tomatoes up stakes or strings, and do not crowd plants.
• Grow resistant varieties when possible. “Mountain Magic,” “Mountain Merit” and other “Mountain” varieties developed by North Carolina agronomist Randy Gardner are good choices.
• Protect crops with fungicides.

Organic growers and home gardeners can use “fixed copper” products such as ChampION (available online) as a preventive measure. Apply them once or twice a week to cover the whole plant when conditions are favorable for the pathogen. Chemical users can apply Daconll or similar products in the same way.

In cases of heavy infection, you may have to destroy all your plants to limit the spread of the disease. Inform your county’s Cooperative Extension Service ( if you suspect a late blight outbreak.

Late blight does not affect fall crop varieties, so you can feel free to plant such cool-season vegetables as broccoli, beets, carrots and lettuce in any beds where you lose tomatoes to late blight. Remember, though, the clock is ticking: Plant for fall over the next four weeks.

Although you can start flats of lettuce seedlings now, some experienced growers say it is a little too late for broccoli and cabbage. Others would go ahead and risk it, but it still makes sense to be thinking of where to find good transplants in mid-August.

Try local farmers’ markets where some farmers sell their extra seedlings, as well as local nurseries such as Renfrow Hardware in Matthews, Whitener’s Greenhouse in Huntersville and Windcrest Farms in Monroe, a source of organic seedlings.

If you visit Asheville, check out Reems Creek Nursery in Weaverville, just north of Asheville’s downtown on Interstate 26. The cooler conditions in the mountains means strong fall seedlings are ready a bit earlier.

Another autumn item on your July garden to-do list is checking out the gardening classes offered in the fall by Central Piedmont Community College’s Corporate and Continuing Education Department. Enrollment is open now:

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