Fungicide resistance makes it more difficult for growers to manage important crop diseases. Although fungicide resistance may be perceived as less urgent than other day-to-day challenges of growing a crop, this issue has become increasingly important and steps must be taken to delay the onset for as long as possible.
The use of fungicides is becoming increasingly common in production of our agronomic crops like corn, soybeans and even cotton. Most of the fungicides used belong to only a few at-risk classes of chemistry. Important fungicides, e.g., azoxystrobin and tebuconazole, are now available as “generic” products. The availability of generic fungicides often leads to a reduction in cost, which can result in overuse of a product. This increases the risk of fungicide resistance.
It is becoming increasingly difficult to bring new fungicides to growers, especially fungicides in new classes. Protecting the efficacy of fungicides in the strobilurin, triazole, SDHI and benzimidazole classes has never been more critical.
Implementing management strategies to reduce the risk for development of fungicide resistance are critical for the future of crop protection, but may be less convenient or more expensive than a grower’s current preferred practices. However, overcoming such immediate concerns is a small price to pay when one considers the immense costs associated with resistance.
While resistance to herbicides, insecticides and fungicides is perhaps inevitable, growers can take steps now to push the onset far into the future.
There are six basic strategies to minimize early development of fungicide resistance:
- Always use at-risk fungicides in combination with chemically unrelated fungicides (different modes of action) which are preferably at low risk to resistance. This can be achieved by alternating applications of fungicides and by incorporating tank-mixes of unrelated fungicides into a spray program. Growers can insure fungicides belong to unrelated classes by comparing the FRAC codes found on the front of the label.
- Restrict the number of fungicide applications and/or total amount applied per season, and to apply fungicides only when necessary.
- Maintain manufacturers’ recommended application rates, even if you believe that satisfactory control can be achieved with lower rates.
- Avoid post-infection use. Fungicides are most effective when applied before infection has occurred.
- Practice integrated disease management by deploying tactics such as crop rotation and use of disease-resistant varieties to reduce the immediate need of fungicides.
- Maintain chemical diversity in a disease management program. It is tempting not to do this when less-expensive fungicides within a single class are available; however this can have significant consequences for the future.