Strategies for resistance management
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Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.
Pathogen resistance is a real threat to the most successful of disease management programs. In the laboratory, pathogen resistance can be seen on Petri plates when Botrytis or Phytophthora grows despite the addition of a fungicide. In the greenhouse, pathogen resistance can be seen when disease becomes uncontrollable despite the use of fungicides that have been previously proven to work. Another term for fungicide resistance is control failure. Control failure is the result of the fungicide no longer working and the resulting plant loss from disease.
To avoid control failure and keep effective fungicide tools working, keep the following in mind:
- When is the pathogen most vulnerable? Control should be aimed at the pathogen’s “weak link.”
- How
is the pathogen being introduced to the growing area? If the pathogen
is coming in as a hitchhiker, how is the pathogen being managed before
you receive it? There are lots of examples of a grower unknowingly
receiving a pathogen on a crop and then that pathogen is already
resistant to the key fungicides.
- What
fungicides have been proven to be effective in controlled studies?
Sometimes growers experience control failure and think they have a
pathogen resistance problem when the real problem is that they aren’t
using a proven effective fungicide.
- If
a fungicide isn’t working, the problem may not be fungicide resistance
but could be the wrong spray interval. Fungicides suppress the pathogens
for a period of time, after which the pathogen will resume its
destructive activity. If the interval between fungicide sprays is too
long, then the pathogen will not be limited and will continue to cause
problems.
- Alternate
fungicide sprays making sure that the active ingredients in each spray
differ enough so that the pathogen cannot readily adjust and overcome
one particular fungicide type. Relying only on your “favorite fungicide”
may give the pathogen ample opportunity to mutate resulting in a
pathogen that no longer responds to your fungicide program.
- Use
the labeled rates of fungicides. Using less than the labeled amount of
fungicide results in a sub-lethal dose that is thought by some to
condition a pathogen to tolerate the active ingredient that fungicide.
- Do
not over-apply fungicides. When disease is rampant and a crop is at
stake, it is tempting to overdo fungicide rates and the number of
applications. This tactic rarely works and tends to cause further
problems, including plant burn.
- Keep up-to-date on the newest fungicides as they become registered. If they’ve been proven to be effective, incorporate them into your fungicide rotation program if they offer a new and unique means of managing your pathogen problems.
