Powdery mildew control in tart cherries

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.

Powdery mildew (PM) can be a problem in tart cherry orchards, particularly in young orchards. This pathogen can also cause defoliation during mechanical harvest, if the infection is severe. However, the biggest issue for powdery mildew control is when growers do not control this disease early in the season, because by the time they see the white mycelium on the leaves at harvest-time, it is too late for control. We currently do not have fungicides that will eradicate powdery mildew, so growers need to control this disease before they see it by using protectant products.

Research conducted in winegrapes at Cornell University showed that controlling powdery mildew early greatly reduces the potential for infected fruit. Based on that work, we know that efficacy of fungicides to control powdery mildew may be impacted by the timing of application. Sprays of Pristine, Gem, and wettable sulfur were applied to a block of 13-yr-old Montmorency tart cherry trees at the Northwest Michigan Horticultural Research Station. This experiment was primarily designed to test the timing of Pristine sprays in the control of leaf spot, brown rot, powdery mildew.

Spray dates and respective growth stages were as follows:

  • May 13 (chlorothalonil on all treatments at bloom)
  • May 20 (petal fall)
  • June 3 (shuck split)
  • June 13 (first cover)
  • June 23 (second cover)
  • July 3 (third cover)
  • July 14 (fourth cover)

Leaf spot, brown rot and powdery mildew infection were initially evaluated on July 25; leaf spot and powdery mildew leaf infection were evaluated a second time on August 21.

The best control of powdery mildew leaf infection with a Pristine program was achieved with five to six consecutive sprays. Similarly, control of powdery mildew fruit infection with a Pristine program was best with four to six consecutive sprays. Six sprays of Gem gave disease control similar to six sprays of Pristine. The sulfur program with six total sprays was less effective than six sprays of Gem and Pristine. However, the most important aspect is to apply these products earlier in the spring for good season-long powdery mildew control.

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