Practical Aspects of Preventing Fungicide Resistance

Only a few diseases are likely to develop resistance:

Pathogens that reproduce prolifically, have a short life cycle, and have extended periods of favorable conditions for disease development.

Diseases that require numerous fungicide applications throughout the season.

Diseases that fit these characteristics include Dollar Spot, Anthracnose, Pythium and Microdochium Patch.

These four diseases are the most important to manage wisely to limit the chances of resistance.

Minimize inoculum levels:

This is a numbers game where the larger the inoculum level, the better the chances of a genetic alteration allowing resistance to develop.

Using only curative applications or long intervals between preventative applications allows tremendous build-up of Inoculum.

Make preventative applications for the four primary diseases most likely to develop resistance.

Apply fungicides at the appropriate rate and application interval to keep inoculum levels low.

Increase the frequency of applications and/or rates during high disease pressure.

Reduce the selection pressure:

Maximize cultural practices to limit disease pressure – dew management, air movement, regular mowing, rolling, etc.

Maximize application technique to improve control – increasing spray volume and decreasing droplet size will improve control of most fungicides.

Avoid repeated use of fungicides with the same mode of action.

Alternate between fungicides with different modes of action, not just different brand names.

Include multi-site contact fungicides in tank-mixes as often as practical.