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Extension sounds alert for impatiens, tomato disease
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 Signs of tomato late blight disease

  • Dark, irregularly shaped blotches on leaves
  • Curled edges on leaves
  • Dark lesions on stems
  • Green fruit turning brown and soft from stem to blossom end
  • White, cottony fungus on underside of leaves and stems

Report any signs of late blight to the Hall County Cooperative Extension Office, 734 E. Crescent Dr., Suite 300, Gainesville, or 770-535-8293

Two plant pathogens have been confirmed in Forsyth County this month, according to officials with the Forsyth County Extension Office.

In a news release, the office issued a warning to gardeners to be alert for signs of tomato late blight and impatiens downy mildew disease.

The latter has existed for some time, but was first reported in Georgia last month, said Heather Kolich, extension assistant.

Kolich said it can be introduced into landscapes by purchased plants infected with a fungus-like organism called Plasmopara obducens. It reproduces and spreads in mild, wet conditions.

"Wind can carry the spores long distances to infect other plants," she said. "Impatiens afflicted with downy mildew will have yellowing leaves and a white or grey fuzzy appearance on the undersides of the leaf.

"Affected plants become stunted and drop their leaves. High humidity and wet leaves foster development of downy mildew."

Kolich said to avoid overhead watering and irrigate early in the morning on dry, sunny days and to remove infected plants, seal them in a plastic bag and dispose of them.

Fungicides are not effective at eliminating the disease.

Gardeners should replace the impatiens with a different type of plant in the infected bed this season and for next year.

The other disease is a much bigger problem.

Tomato late blight caused by Phytophthora infestans has been tracked over a large portion of the eastern seaboard with North Carolina experiencing a particularly heavy hit. Florida, Pennsylvania and New York also have reports of late blight.

Late blight is a less common tomato disease, which doesn’t usually survive on dead plant material or over the winter in soil. It is also the same disease that caused the Irish potato famine of 1845 and can spread to eggplants as well.

The bigger implications for late blight are for farmers of organic tomatoes and the home gardener, but consumers could see the impact at the supermarket if large quantities of crops are affected.

Kolich said University of Georgia plant pathologist Elizabeth Little refers to the disease as a water mold.

The recent weather in Northeast Georgia isn’t helping the situation either. Late blight spreads rapidly in mild, wet weather and can kill plants within a few days.

Leaves of plants afflicted with late blight have dark, irregularly shaped blotches.

These blotches often originate at the leaf edge and spread inward.

"Petioles, stems and fruit may show dark brown lesions," Kolich said. "Under humid conditions, you may see white fungal spores on the leaf undersides and on lesions on the stem.

"Fungicides containing copper or Mancozeb will help control late blight."

That’s not much help, however, for many organic farmers.

But take heart. Cultural controls will also help prevent the disease, including keeping plants dry by using soil-level irrigation.

The Hall County Extension Office reports only a few cases of late blight and advises gardeners to bring in samples if they are suspicious of infection on their plants.

According to the USAblight project backed by the USDA, "Yield losses caused by late blight and the cost of control measures have been estimated to exceed 6.7 billion dollars annually and the disease is a major threat to food security worldwide."

Track blight infections with the USAblight project at usablight.org.

Kelly Ivors, associate professor of plant pathology and North Carolina Cooperative Extension specialist, advises "once plants show signs of late blight, the best option may be to harvest the fruit, even if it’s green, and learn how to make fried green tomatoes."

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