Managing Botrytis Fruit Rot Resistance to Fungicides

This post is primarily about managing resistance of botrytis fruit rot to fungicides. Before we get into it, please remember that chemicals to control diseases, or any pests, are just one of tools producers can and should use. Before spraying, make sure you make efforts to manage pathogens with cultural tools. For example, effective pruning strategies will help to improve air flow through the foliar canopy of your berry planting, (which will reduce the amount of time that the fruit and foliage are wet and potentially reducing the likelihood of a botrytis infection) (thereby reducing the level of botrytis spores and therefore damage from fruit rot). Similarly, dropping pruned branches into the alleys doesn’t necessarily eliminate pathogen fungal spores, and discing the pruned material doesn’t necessarily bury and kill spores either, but it may reduce the amount of spores present in the field. Although cultural methods will not by themselves control botrytis fruit rot, good cultural management does help, and should be used.

While some fungicides have post-infection activity, as a general rule, all fungicides should be applied prior to infection. Botrytis is a difficult disease to control and there are not a lot of new chemicals coming. So, we must manage the ones that are available well so that we do not lose the products that we have. Raspberry and strawberry growers have more products available for botrytis when compared to blueberry growers, but in general there are very few products available for botrytis control in berry crops.

What causes resistance to fungicides? The largest factor determining the presence of resistant fungal spores is the specific fungicide use history on your farm. To over-simplify it, the heavier the use of one or several fungicides, the higher risk of fungicide resistance. The only way to put off development of resistance is by rotating fungicides, between chemicals from different classes or groups (FRAC Groups). While using different, potentially more expensive products may cost more, loss of disease control will be more expensive in the long run.

Most of the products available for Botrytis management fall into 1 of a few groups of products, most of the new products that are being registered are within 1 of 2 groups either 7 or 9. Use this chart to help choose chemistries to rotate between and help postpone resistance. Note that some chemical brands contain ingredients from more than one group. This is intended to increase the product’s activity and reduce development of resistance.

*FRAC Group: Fungicide Resistance Action Committee chemical groups. Products within a group have similar chemistry and therefore mode of action. Rotate between products in different groups in order to postpone development of resistance. If you are interested in learning more about fungicide resistance you can check this link.

DISCLAIMER: The information and recommendations in this blog are presented in good faith and for general information only. The information is believed to be correct as of the date presented. However, neither TerraLink Horticulture Inc. nor any of its supply partners makes any representation or warranty as to the completeness or accuracy of any of the information. The reader assumes the entire risk of relying on the information.