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Tips for Improved Fungicide Resistance Management

The Tomato Magazine
August 2005

By Sally Miller
Department of Plant Pathology
Ohio State University

Fungicides have been categorized into groups based on their mode of action against plant pathogenic fungi. These groups are numbered and contain all fungicides with similar modes of action, whether or not they are in the same chemical class. Pathogens that develop resistance to one fungicide in a group are likely to be resistant to all fungicides in that group. Therefore, most label instructions for fungicides at risk for resistance development require alternating such fungicides with fungicides with a different mode of action. The fungicide group number is provided on the label and is shown in the table below.

When deciding on which fungicides to use in alternation, choose fungicides that are: 1) effective against the diseases of concern, and 2) have different Fungicide Group numbers. Some products are a mixture of fungicides from two different groups, e.g. Groups 11 and 27 (Tanos); Groups 9 and 12 (Switch); and Groups 7 and 11 (Pristine). Nonetheless, label instructions for these products require alternation with additional fungicides.

Fungicide group number and risk of resistance development for some fungicides commonly used in vegetable disease management. Adapted from FRAC Fungicide List (1) (2003) (http://www.frac.info/publications/frac_list02.html). Not all fungicides labeled for use on vegetables are included, and not all are labeled for use on tomatoes. Check the label for permitted uses.

Editor’s Note: Dr. Sally A. Miller is a professor, Department of Plant Pathology, Ohio State University. She can be contacted by phone at
(330) 263-3678 or by e-mail at miller.769@osu.edu.

© 2006 Columbia Publishing

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