Managing cherry leaf spot in poor spraying weather
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.
With an almost constant barrage of wind and rain, getting into the orchards has been difficult to say the least. When managing cherry leaf spot, conventional wisdom has shown that protectant management strategies that keep leaves protected during infection periods are the most effective treatments. The key to controlling cherry leaf spot is to minimize infection and disease spread early in the season in order to help the trees retain leaves until later into the fall. Unfortunately, it has been almost impossible for growers to get their sprays on when necessary. Due to the weather, there have also been a lot of questions regarding how often to apply fungicides, how long the fungicides are providing protection when exposed to rain and what to apply if an application was missed.
The fungicides Gem (strobilurin) and Pristine (strobilurin and boscalid) are excellent options for application at the first cover timing. These products are often used at first cover because they control both cherry leaf spot and powdery mildew. Both fungicides are rain fast within two hours and move locally within leaves. This means that if you applied a strobilurin two hours before rainfall then the leaves are protected despite the rain. If you are applying a strobilurin on alternate rows then the spray interval should be tightened by two to three days, as long as the rainy warm weather continues.
If a spray was missed because of high winds or rain, there is little compelling evidence that post infection treatments are effective. The best shot at getting any back action against cherry leaf spot is a full cover of Syllit FL (27 oz), tank mixed with Captan (3-4 lb). This should be followed by an application of Pristine or copper (1.2 lbs. metallic copper per acre) for the next cover. The cool weather this season has provided a good opportunity to try copper on farms where phytotoxicity has been an issue.