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| Reducing disease pressure in grapes with dormant fungicide applications |
| current > reducing diseas pressure |
| Update October 2005 from Annemiek Schilder, Dept. Plant Pathology, Michigan State University
Dormant applications of crop protection chemicals are typically applied in the fall or spring when no green tissue is present on plants. The purpose of dormant sprays is to eradicate pathogens and insects that are overwintering on the plant. Lime sulfur (a mixture of calcium polysulfides formed by boiling slaked lime with sulfur) has long been used as a dormant spray in tree fruit and brambles. Copper formulations are also used, particularly for control of bacterial diseases. These products kill mainly through direct contact, so applications must be applied with maximum coverage. Lime sulfur, while effective, is smelly, corrosive to farm equipment, and can be phytotoxic to green tissues. While lime sulfur used to be relatively inexpensive, the price has gone up significantly in recent years and can be as high as $100 per acre if applied at higher rates. In grapes we have done several years of trials with dormant fungicide applications, including less expensive alternatives, such as sulfur and copper products. Below a graph showing the efficacy of a single dormant spray at budswell against Phomopsis rachis infection in Niagara grapes at harvest. The following products were tested: Microfine Sulfur (powdered sulfur), Sulfur 6L (liquid sulfur), Kocide 2000 (copper hydroxide), and Cuprofix (basic copper sulfate). No other fungicides were applied during the season. ProPhyt applied on a seasonal schedule was included for comparison. We also found that dormant applications of sulfur and copper reduced black rot infection of fruit, and that dormant copper reduced downy mildew infection. In general, dormant sprays significantly reduce disease pressure of a range of diseases. The effects of dormant sprays on powdery mildew infection will be investigated in 2005. |
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It is important to note that Concord is sulfur sensitive. While we have not seen any phytotoxicity in previous trials, we have not specifically tested whether a dormant application of sulfur or copper can hurt the newly emerging green tissues through redistribution of the product. So as a safeguard, we do not recommend sulfur compounds at this time on Concord, even as a dormant spray. Niagara is not sulfur sensitive. Both cultivars are considered slightly sensitive to copper. At this time, Cuprofix is considered a good option for broad-spectrum disease control and is specifically labeled for dormant application. The label rate is a bit higher (2.5-6 lbs) than what we tested. Dormant sprays should not be used as a stand-alone measure of controlling diseases. However, in 2004, we tested a reduced spray program in Niagara grapes (a dormant application of Sulfur 6L, an immediate pre-bloom mancozeb spray, and one postbloom Abound spray). This program provided control of Phomopsis that was equivalent to a full-season spray program. This suggests that when a dormant spray is included, seasonal sprays may be reduced. The amount and timing of possible fungicide reductions will be further investigated during the 2005 season. |
in collaboration with MSU Extension and the Michigan Agricultural Experiment Station.
Updated11/15/07 Contact: J.N. Landis.