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Local extension office sounds disease alert
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Forsyth County News

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 disease and impatiens downy mildew.

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.

Late blight is a less common tomato disease, which doesn’t usually survive on dead plant material or over the winter in soil.

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

It 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.”

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