Gem fungicide for stone fruit

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.

Gem is a new fungicide from Bayer available in 2006 for the stone fruit market in Michigan. The active ingredient of Gem is trifloxystrobin, the same active ingredient as in Flint. The concentration of trifloxystrobin in Gem is 25%, which is lower than the concentration of trifloxystrobin in Flint (50%). Gem is a replacement product in the stone fruit market for Flint and is only labeled for use on stone fruit.

The use of Gem fungicide should be targeted towards control of cherry leaf spot and powdery mildew. Label rates of Gem are 4.0 to 8.0 oz per acre with recommended rates of 4 to 5 oz per acre under conditions of low infection severity and 6 oz per acre under conditions of higher infection pressure. Disease control ratings in the 2006 Michigan Fruit Management Guide for Flint (2 to 4 oz acre) at the cover spray timings for leaf spot and powdery mildew control are excellent for both diseases, and we would expect similar results with Gem.

As with other strobilurin fungicides, there is a risk of fungicide resistance developing. Therefore, Gem should not be used more than twice consecutively or more than four times per season. My recommendation is that Gem not be used more than twice per season.

Think “protectant mode” when applying Gem or any other fungicide for stone fruit disease control. We do not have data on after-infection activity of fungicides for leaf spot control. Resistance management strategies focus on killing pathogen inoculum and preventing spore germination. Fungicides applied preventively at the correct rates and with good coverage will accomplish the goal of killing pathogen inoculum and preventing spore germination.

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

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