Cherry leaf spot observed on June 1

Growers need to tighten intervals and use full cover sprays if cherry leaf spot has been observed. Scout for cherry leaf spot as soon as possible.

This week, cherry leaf spot has been observed in many Montmorency blocks. In the past, when we have seen symptoms of cherry leaf spot this early in the year, it quickly rises to epidemic levels and causes premature defoliation and reduced fruit ripening. Fruit ripening is of particular concern this season with the big crop of fruit that has set throughout the state. Traditionally, we observe cherry leaf spot in the tops of trees and the fungus releases spores that move the infection “down” through the canopy. This year, the symptoms are throughout the tree canopy and we hypothesize that this infection is due to fungicide wash-off rather than a coverage issue.

We are recommending that growers get out and scout their orchards for cherry leaf spot as soon as possible.

Although this recommendation is time-consuming, it is imperative that growers determine the levels of infection in their individual blocks. We have received variable rainfall across the region, and in turn, orchards will have varying amounts of fungicide residue as a result of the amount or duration of precipitation and the timing of applications. If a cherry leaf spot infection is observed in a block, growers should apply a full cover of chlorothalonil (Bravo or generic brands) prior to the onset of shuck split as this material is highly effective against cherry leaf spot, but can only be used at this time and post-harvest. This chlorothalonil application will not eliminate the current infection. Rather, the intent of this spray is to protect tissue from the onset of spores from the existing infections. This protectant strategy will need to be used with other fungicides through harvest and beyond.

If cherry leaf spot symptoms are present, a half side of a fungicide is not recommended at this time. With full cover sprays, we are intending to minimize the impacts of this fungal disease by reducing the potential of a cherry leaf spot epidemic this season.

Following shuck split, fungicides used for cherry leaf spot control, such as Pristine, Gem, Adament and Syllit, should be tank-mixed with Captan. This serves both as a resistance management tool and will also provide more efficacious fungicide to deal with the increased inoculum load of the pathogen.

Dr. Sundin’s work is funded in part by MSU’s AgBioResearch.

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