garden q&a: Grape vines need to be pruned
Q. I have a question about grape vines. For the second year now my grape leaves have developed some sort of disease. By mid summer the leaves develop brown spots which eventually cover the entire leaf. Then it dries up and falls off. I have sprayed with a copper solution as well as with oil-based solutions. I have also removed all the diseased leaves which then generates new healthy growth. Nothing has worked. I have planted new vines across the yard, and this year I saw some brown spots on these plants as well. Is this a common ailment or is there a possible deficiency in the soil? You expertise would be greatly appreciated.
A. There are many common foliar diseases of grapes, and I suspect that your plants have one or more of them. The only way to be sure exactly which disease your plants are battling is to send a tissue sample in to the folks at the Penn State Extension Service. You can contact them at 412-473-2540 to find out how to take and send a tissue sample.
But, regardless of exactly which disease is to blame for the defoliation of your grapes, there are several things you can do to stave off an onslaught during next year's growing season. First off, be sure your plants are properly pruned. In March, remove existing vines all the way back to their second growth node and dispose of them properly. Do not let them lie in the vineyard as they can serve as vectors to the disease organisms.
Secondly, be on the lookout very early in the season for signs of fungal issues. Wet spring weather promotes these issues, and when these conditions are present, there's a good chance that fungal diseases will become problematic. Getting on a regular organic spay program early in the season is key to keeping fungal issues at bay. Though copper products are often recommended for this, I prefer using a biological fungicide based on Bacillus subtilis. One common brand is Serenade. It is available as a wetable powder and as a liquid and it works to kill a large number of common fungal organisms on fruits, vegetables and vine crops. The rate and frequency of application depends on the targeted fungal organism, but all are listed on the product's label.
A few items to keep in mind:
• Properly spaced plants are less prone to these issues as good air circulation allows the foliage to dry more quickly. Keep that in mind when siting any new plants.
• Some grape varieties are more prone to certain diseases than others. Be sure to plant resistant varieties whenever possible. The extension service can provide a list of suggested varieties.
• A summer pruning, timed when the fruits are about a quarter-inch across, also increases air circulation. To do this, remove any vines covering the developing fruit clusters, as well as those shooting up and away from the plant.
Horticulturist Jessica Walliser co-hosts “The Organic Gardeners” at 7 a.m. Sundays on KDKA Radio. She is the author of several gardening books, including “Grow Organic” and “Good Bug, Bad Bug.” Her website is www.jessicawalliser.com.
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