How to protect plants from fungus and weevils

The Pittsburgh Post-Gazette features Dick Till, assistant district manager of Davey's South Pittsburgh office, in this article about fungus and weevils.   

Posted: July 25, 2015 

By Doug Oster 

Gently brushing a basil plant in the garden releases the aroma of summer. Unfortunately, the herb is under attack from a disease that thrives in recent wet conditions. Tomatoes are also struggling with fungal diseases and weevils are bedeviling poplar, magnolia and sassafras trees. 

Denise Schreiber, greenhouse manager for Allegheny County Parks, bemoans the effect basil downy mildew is having on her harvest. “I use handfuls, handfuls of basil to make my sauce,” she says with a sigh.

The disease started to take hold about a decade ago in the South and has moved north over the last two seasons, infecting plants through both airborne and soil-borne spores.

“First the leaves turn yellow, then you’ll see little black spots,” Mrs. Schreiber says. Under close inspection, the undersides of the leaves reveal fluffy, gray spores.

She’s harvesting what she can from the upper parts of the plant. Though the infected leaves are technically edible, “they probably don’t taste very good,” she adds. Seeds of the plant can also be infected and there’s no way to tell if they are tainted.

Mrs. Schreiber has fielded many distressed calls from friends and other gardeners. Once basil is infected, nothing can be done to save it.

“The plants need to be thrown away,” she says. “Don’t compost them.” A compost pile would be the perfect place for the spores to overwinter.

If plants succumb to the disease, you can plant a new crop, but in another bed away from the infected soil. Look for healthy plants at the nursery and give them plenty of space for good air circulation, Mrs. Schreiber says. But that is no guarantee the downy mildew won’t return since wind can carry the spores from one area to another. She’s even seen basil for sale in grocery stores infected with the disease.

Breeders are trying to find resistant varieties, she says, and there’s some good news in that red and lemon varieties seem to fight off the disease better than the standard Genovese basil. But that’s no help for Mrs. Schreiber.

Click here to read what Dick Till has to say about the yellow poplar weevil. 

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