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Alert: August 07, 2006 |
| Black Rot of Grape Vines |
| Disease Highlights |
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Corn Growers Should Be Wary of Potential Aflatoxin Problems Aflatoxin is a toxic metabolite produced by the ear rotting fungus Aspergillus flavus. Aspergillus infection and development is favored by hot, humid and droughty conditions during the grain fill period. Historically, southeastern Kansas has been a hot spot for aflatoxin development in summers such as the one currently in progress, but high aflatoxin level samples can come from anywhere in the state. Symptoms of Aspergillus ear rot are masses of yellow-green spores on or between the kernels. Often times only a few kernels per ear may be infected. Although any part of the ear may be infected with the fungus, the tip is the most common site. |
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The Kansas Grain Inspection Service, Inc. offers aflatoxin tests. They have offices in Topeka and Hutchinson and can be reached at 785-233-7063. (Jardine)
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Black Rot of Grapevines Symptoms of black rot are appearing our ripening grape clusters. Black rot is caused by a fungal pathogen, Guignardia bidwellii. The pathogen infects leaves and causes small leaf spots, but the most important damage is to the fruit. The fungus infects young fruit which slowly start to turn brown. The brown color starts at the infection zone and spreads its way around the berry (see photo). Finally, the infected berry shrivels up, turns black, and small, round spore-producing structures are formed. The fungus survives the winter in these “mummy fruit”. |
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In the spring, during warm, wet weather, the mummies produce spores that infect the newly emerging leaves and young fruit. Research in recent years has shown that grape berries are susceptible until about 6 weeks after bloom. Black rot has a long latent period. That is, by the time you see symptoms on the berries, they might have already been infected for up to 5 weeks. So, there is nothing you can do about the fruit that are infected with black rot now. You can start to get things under control for next year, though. During winter pruning cut off the mummy fruit and either remove them or at least drop them to the ground and get them out of the trellis (where they would be right next to susceptible growth in the spring). Use pruning and trellising to open the canopy, too. Increased air flow will help prevent the moisture build-up that favors this disease. If you have a history of black rot and spring weather is wet, then fungicide applications might be necessary to manage this disease. Fungicide applications are most important when the flower and fruit clusters are young, from immediate prebloom until 5 or 6 weeks after bloom. One possible schedule would be to apply a chemical immediately before bloom, and then 2 or 3 more applications at 2 week intervals. Fungicides for home grape growers include captan and myclobutanil products (ex: Immunox). Commercial growers have more options, including several strobilurin fungicides (ex: Abound, Flint, Pristine (which also includes Boscalid), Sovran), DMI fungicides (Elite, Nova, Bayleton, Rubigan), mancozeb, ferbam, and ziram. Again, there’s nothing you can do about the black rot in your grapes right now but as you plan ahead for next year be sure to consider sanitation, pruning, airflow, and if you are going to use chemicals use them in that critical window from prebloom until 5-6 weeks later. (Kennelly)
Disease Highlights
Leaf Scorch & shedding due to hot/dry
weather- Elm, pine, maple, *sycamore*, sweetgum
Contributing Authors: Doug Jardine
jardine@ksu.edu
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Web updated 9/01/06 |
