FEBRUARY
2007

 

 

 

By
B. Rosie Lerner
 
Purdue
Extension
Consumer Horticulturist

 

 

 

 

 

02-01-07

Question and Answer

Q. Could you please tell me what I can do for my concord grapes? When they start ripening, they rot, or something like that.

A. I'd place my bets on a fungal disease called "black rot." There are some grape cultivars that are resistant to grape rot, but, unfortunately, ' Concord ' is highly susceptible.

According to Purdue Plant Pathology publication BP-36 "Grape Black Rot" http://www.extension.purdue.edu/extmedia/BP/BP-36.html, this is one of the most common and serious diseases of wild and cultivated grapes. The fungus attacks canes, tendrils, leaves and fruit. The disease is most destructive in warm, humid weather.

Symptoms of black rot first appear on leaves as small, yellowish spots that continue to enlarge and eventually become reddish-brown with tiny black dots. Lesions may also appear on young shoots, cluster stems and tendrils. These lesions are purple to black, oval in outline and sunken. Fruit symptoms often do not appear until grapes are half grown and begin as round, light-brownish spots, which then soften and become sunken. The spots enlarge quickly, rotting the entire berry in a few days. The diseased fruit shrivels and becomes small, hard, black, wrinkled and coated with raised, black, spore-producing structures of the fungus. The shriveled, infected fruit, commonly referred to as "mummies," usually remain attached to the fruit cluster.

Sanitation is absolutely critical to control black rot. Destroy mummies, remove diseased tendrils from the wires and, when pruning, leave only healthy fruiting canes without lesions. If only a few leaf lesions appear in the spring, remove the affected leaves immediately. Vines that are in sunny open areas with good air movement are less likely to develop black rot. Ruthless annual pruning will help keep the plants in check and allow for better air circulation.

There are some fungicides labeled for use in protecting grape plantings. However, fungicides can only prevent healthy plant tissue from getting the disease; they can't cure existing infections. You'll need to apply on a regular schedule, starting when new growth is 4 to 6 inches long and continue every 7 to 10 days until berries start to change color. Fungicides commonly available to backyard growers for control of black rot include Immunox, Captan and multi-purpose fruit spray. Be sure to read and follow all label instructions before you apply. For further information, refer to Purdue publication ID-146,"Managing Pests in the Home Fruit Planting," available at http://www.entm.purdue.edu/Entomology/ext/targets/ID/ID146pdf/ID-146.pdf.

Q. Every year something eats on our sweet potatoes. Do you know what eats on them, and if there is anything we can do to prevent it?

A. You didn't mention whether it is the foliage or the root or both that is being eaten. Wireworms are the chief suspects if the damage is primarily on the roots. Wireworms are more likely to infest new gardens that were previously in turf grass or had many grassy weeds. But rodents, grubs, flea beetles and even cucumber beetle larvae are also possibilities. The control/prevention of damage depends on correctly identifying the pest. If the problem continues this year, bring some specimens to the Purdue Extension office in your county to see if they can help diagnose the problem. You'll find contact information for all 92 Purdue Extension county offices at http://www.extension.purdue.edu/counties.html.

 

Writer: B. Rosie Lerner
Editor: Olivia Maddox,