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Black Rot

July 31, 2014
grapes

If you have grapes, then you should be on the lookout for black rot.  Black rot impacts grape production every year.  It is a fungus that infects young canes, flowers, tendrils, leaves, and fruit.  Most individuals do not notice they have black rot until they see the dark, mummified grapes on their vines.

Initially, black rot symptoms appear as minute, round, reddish-brown spots on the leaves.  On the shoots, petioles, and tendril symptoms appear as irregular, sunken, tan to brown lesions.  Black rot initially appears as soft, light brown spots on the fruit, but later on it turns into a shriveled black, wrinkled mummy fruit.  The mummified fruit will often remain on the vine, but occasionally it will fall off.  If the mummified fruit remains on the vine, then you should remove it.  Leaving the mummified fruit allows for the fungus to overwinter and impact next year’s production. 

Black rot is caused by two different fruiting bodies.  These fruiting bodies can overwinter in mummified fruit, fallen leaves, and stem lesions of infected plants. Plants are primarily infected with black rot when the plant surfaces remain wet long enough for the fungus spores to germinate and penetrate plant tissue. 

Due to the fact the fruiting bodies of this fungus can overwinter, it is important that all grape producers practice good sanitation.  Good sanitation includes removal and destruction of diseased plant tissues.  Destruction of disease plant tissue should occur away from where the grape vine is growing.  You should also disinfect your trellis.

Another way to help control black rot is by purchasing and growing resistant cultivars.  Some of the resistant cultivars include: Cayuga White, Mars, Marquis, Norton, and Traminette.  In addition to purchasing resistant varieties, you can decrease your chance of having black rot by selecting a site to grow your grapes that has good air circulation, is well (or somewhat well) drained, using high trellises, and removing all weeds from the base of the grapes.  Those four steps will help prevent the plant material from being wet and the spores that cause black rot from germinating.

If you have black rot, then you could use a fungicide.  Fungicide should be used at the beginning of the bud break and continue through berry maturity.  If you decide to use a fungicide please read and follow all label instructions including harvest restrictions. 

As always, if you have any questions or would like information on any agriculture, horticulture, or natural resource topic, then please contact your local Purdue Extension Office at 448-9041 in Clay Co. or 829-5020 in Owen Co. or reach me directly at smith535@purdue.edu Purdue University is an equal opportunity/equal access/affirmative action institution.

Upcoming opportunities available to you through Purdue Extension include:

July 12-18 – Clay County Fair

July 26— Herbs & Flower Arranging, 10-10:45 am, Owen Co. Public Library

August 1-17 – Indiana State Fair

 

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