EPA 24(c) Special Local Need registration for Indar for brown rot control

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.

A Special Local Need [EPA 24(c)] registration has been granted for the use of increased rates of Indar 2F for brown rot control. The basis for this request was from our observations that populations of the American brown rot fungus (Monoliniafructicola) are shifting in Michigan towards decreased sensitivity to sterol inhibitor fungicides. Note: this special registration only applies to Indar 2F.

Fungal sensitivity/resistance to sterol inhibitor fungicides acts in a quantitative manner, meaning that a fungus with a decreased sensitivity to one rate can be controlled by a higher rate of the same fungicide. Results from an orchard survey conducted by Erin Lizotte indicated that there was clear shifting in the American brown rot population, and that some orchards harbored American brown rot isolates that were close to the resistance threshold.

The use of higher rates of a sterol inhibitor fungicide acts as a hedge against resistance development. The higher rates are effective against fungal isolates that show decreased sensitivity; controlling these isolates then decreases the chance of further shifting to resistance.

Currently, the use of Indar 2F at the original label rate of 6 fl. oz. per acre should provide excellent control of American brown rot in most orchards. However, as a hedge against further shifting of the American brown rot population in most orchards, my suggestion is to use a rate of 8 fl. oz. per acre in 2009 for control of fruit infections. Growers whose American brown rot orchard populations are closer to the resistance threshold should consider using a 9-10 fl. oz. per acre rate.

It is essential, especially this year after the heavy American brown rot infections observed in 2008, that fungicide coverage is excellent. This will ensure a uniform exposure of the fungus to the higher rate of fungicide.

The 24(c) registration allows as high a rate as 12 fl. oz. per acre. A maximum of 48 fl. oz. per acre is allowed per season, i.e., no more than eight applications at 6 fl. oz. per acre or four applications at 12 fl. oz. per acre. Do not graze livestock in treated areas or feed cover crops grown in treated areas to livestock. Do not apply Indar 2F through any type of irrigation system.

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

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