Sanitation key to avoid black rot

Q. My grapes on my arbor have a blight. They’ve had it for three years. How do I get rid of this?

Hazel from North Jackson

A. Your grapes don’t have a blight, but it is a disease. The disease is called grape black rot. For anyone with grapes in their backyard, you probably know this disease. Each August – just before the grapes ripen – you suddenly notice that the bunches of green grapes turned into raisins in just a few days. You were looking forward to an excellent harvest, but your plans were foiled!

Grape black rot is the most devastating grape disease in Ohio. This year’s warm and wet summer helped this disease grow and take many backyard crops where control methods were not implemented.

The disease starts as yellowish spots on the leaves. These spots turn reddish brown as summer progresses. If you look at the spots closely, you’ll see small black dots. These are the fruiting bodies of the disease. If you take a close look at those “raisins” you found where the grapes used to be, you’ll see black to grey spots on them.

This and other diseases are the reason we push fall clean up in the yard and garden. Sanitation is the most important thing you can do to reduce infection of next year’s leaves and grape crop. Right now, you should be removing all grape leaves from the area. Pick those “raisins” off the vine and remove them from the area. Rake any tendrils, bark and other plant debris off the ground. Get rid of it all!

Any plant parts left in the area can release spores during next year’s growing season and reinfect your grape vine.

Another common mistake is location and trellis design for back yard grapes. Grapes need to be grown in open, sunny areas with good air circulation to dry off leaves as the sun rises in the morning. Overhead trellis structures are a bad idea, as the grapes are shaded.

Controlling weeds by using mulch under vines will improve air circulation and shortens the time it takes for leaves to dry.

There are fungicides which can be used in the home garden. Using fungicides is a time-consuming process and must be done regularly. Thus, it is difficult to keep on schedule if you have just a few vines. So, stick to the basics.

Most backyard grape vines will do quite well if you simply follow good sanitation practices and do a good job keeping vines properly pruned for increased air movement through the plant.

To learn more about this disease, visit http://go.osu.edu/blackrot. For photos and details on pruning your grapevines, visit http://go.osu.edu/pruninggrapes.

Eric Barrett is OSU Extension educator for agriculture and natural resources in Mahoning County. Call the office hot line at 330-533-5538 to submit your questions. Regular clinic hours ended Oct. 31, but you can still call and submit questions. Hours vary throughout the winter season.