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Problem: Black Rot on Grapes
Host Plants: Grape
Description: Black rot affects both leaves and fruit, although the most dramatic damage occurs on the berries. Look for developing berries that begin to turn dark purple or black. The infected berries eventually will shrivel but will tend to cling to the cluster. If you look carefully you will see the tiny black fruiting structures (pycnidia) dotting the surface of the shriveled berry.
Recommendations: Black rot is difficult to control once the fruit rot phase has developed. Try to manage the vines (tie up drooping vines, remove leaves next to fruit clusters) such that there is good air movement. Routine fungicide applications are necessary to inhibit further infection. Start control measures when the new shoots begin to emerge from the vine. During wet weather, don’t stretch out the application interval to more than 10 days or so. There are many fungicides labeled for black rot. Some of the more effective products include Nova (sold as Immunox for homeowners), Bayleton, Elite, Ferbam, Procure, Rubigan, Abound, Sovran, and Flint. Mancozeb is also effective but the waiting interval (66 days to harvest) precludes precludes its use except early in the season.
References:
1. Plant Pathology Pest Alert #14, June 26, 2001, K-State Research and Extension, http://www.oznet.ksu.edu/path-ext/Alerts/2001 alerts/Alert 14.asp
Last Update: 05/31/2005
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