Phytotoxicity of Revus Top on Concord grapes

Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.  

Recent applications of the new fungicide Revus Top (mandipropamid and difenoconazole) have led to phytotoxicity symptoms on Concord grapes in New York, Pennsylvania and Michigan. Symptoms were not seen on Niagara or any other grapes. Based on previous trials with Revus Top on Concord grapes, which did not indicate any problems, this is an unexpected and worrisome development. Phytotoxicity symptoms appeared like brown necrotic areas (fingers) between the vines, much like an oil burn. The reason for the phytotoxicity symptoms is not clear, but applications were mostly made during hot weather (high 80’s and low 90’s).

In addition, tank-mix partners, including foliar fertilizers and/or oil-based insecticides may have played a role. Applications of the same tank-mixes to Niagara grapes showed no symptoms. We know that Concord grapes are more sensitive to certain fungicides (e.g., Flint, Pristine) than Niagara grapes. The other factor that may have played a role is that rapidly growing plant tissues have a thinner wax layer than slow-growing shoots and leaves. This could have also made the leaves more sensitive.

At this point, growers should stop making applications of Revus Top to Concord grapes until further notice. The product can still be applied to other grapes, including Niagara and other grape varieties. A residue tolerance is still in effect as well, so there is no problem with harvesting the grapes.

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