Managing Fungicide Resistance in Blueberries

Fungicide Resistance refers to an acquired reduction in sensitivity of a fungus to a specific fungicide. Fungicide resistance often develops due to repeated application of fungicides from the same Group on a particular crop. This is why we need to know which Groups the fungicides belong to and how to rotate them in order to better manage resistance.

Growers in British Columbia have been following a good rotation of fungicides from several groups. As a result, we have been able to keep older products viable longer than most markets. As products age, it becomes more important to tank mix the products that attack a specific site on the fungus with products that are multisite attack oriented. For example, Captan, a multi-site product that is still efficacious, should be tank mixed with older products like Switch and Pristine.

Group 7 fungicides are a very important tool in botrytis (fruit rot, grey mold) management in British Columbia. TerraLink, alongside its crop protection partners and growers, have been vigilant in their ongoing use of integrated resistance management strategies, including rotations of chemistry. There have been concerns raised to the performance of Group 7 fungicides in blueberries in the Pacific Northwest of the USA. In British Columbia, the situation is being monitored closely.

For 2019, the newly introduced Group 7 fungicide Kenja is an important addition, and like all other fungicides, we need to manage its lifespan as well. Kenja operates on a different site of the fungus than the other Group 7 products but it needs to be used in a rotation program right out of the gate just like the older products.

Regalia Maxx is a biofungicide derived from plant extract to induce the plants’ natural defense mechanisms against certain fungal and bacterial diseases and registered on Botrytis, Anthracnose and Alternaria in blueberries.

Preserving the life span of key fungicides is only possible if all growers fully cooperate to manage resistance by rotating Group 7 products, not using them consecutively in sequence and not more than twice in a season.

To maintain the efficacy of Group 7 fungicides, we recommend growers to continue a proactive resistance management strategy:

• Apply fungicides preventatively at early bloom and thereafter, being careful to time sprays well.
• Use premixes or tank-mixes with multiple modes of effective action against botrytis.
• Rotate effective modes of action.
• Practise good sanitation.
• Continue to use other acceptable cultural practices.

A good fungicide management program takes into account the use of the right groups of fungicides as well as the spectrum of disease control needed. Rotate fungicides to avoid using the same groups back to back. For eg. Use fungicide from group 7 followed a fungicide from another group.

The following is a list of fungicide products for blueberries in alphabetical order: