Cherry leaf spot: Save the leaves!

The current cherry leaf spot epidemic in northwest Michigan necessitates the frequent use of fungicides to protect remaining, healthy leaves to prevent an unprecedented early defoliation event.

A major cherry leaf spot epidemic is currently underway in northwest Michigan. Drive-by scanning of tart cherry orchards in Leelanau, Grand Traverse and Antrim counties conducted last week in addition to orchard scouting indicated significant numbers of yellow, cherry leaf spot-infected leaves with additional still-green, cherry leaf spot-infected leaves. This situation would be a concern in mid-August, but since this is only late June, we are at a critical stage for cherry leaf spot control and, ultimately, tree health.

The yellow leaves infected with cherry leaf spot will defoliate relatively soon or already have dropped. The more recent leaves with cherry leaf spot will turn yellow soon and also drop from the trees. However, trees are still producing new leaves and will likely produce more flushes of leaves in response to this early defoliation. These new leaves and uninfected leaves must be adequately protected with fungicides in the coming two months in order to maintain any type of foliage into late August and September.

With the current situation, there will be a tremendous amount of inoculum in orchards as spores are produced and disseminated from every cherry leaf spot lesion on all currently infected leaves. With all of this inoculum out there, growers will be challenged to protect new leaves, and the ultimate goal is to protect uninfected leaves.

Full-cover spray applications are needed to ensure the best leaf coverage. Spray intervals should be reduced to seven to eight days if there are intervening rains. Without rain, the interval can be lengthened, but the next protective application must be on prior to the next rain event.

The best (most efficacious) fungicide combinations for cherry leaf spot control at this time (June 2012) are as follows:

  • Chlorothalonil – Bravo Weather Stik at 4 pints/A
  • Copper at 1.2 lbs metallic copper per acre. Only use copper if high temperatures are predicted below 80 degrees Fahrenheit for the next several days.
  • Syllit at 24-27 fl. oz./A + Captan 50WP at 4 lbs/A
  • Luna Sensation at 5 fl oz/A + Captan 50WP at 4 lbs/A

Note: These four possible treatments are not listed in any particular order. Any of them should provide equivalent levels of disease control.

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

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