Dealing with pesticide resistance

May 24, 2019

Pesticide resistance is when a pest is no longer affected by a pesticide type. Resistance most often occurs when repeated applications of the same or similar pesticides are made during the growing season or on an annual basis.

Resistance begins to develop when not all of the targeted pests are killed by a pesticide. Those not killed typically have a genetic change or mutation that allows them to deal with a pesticide without dying.

When these pests (insects, diseases or weeds) reproduce, they pass onto their offspring the ability to deal with that type of pesticide. The cycle can continue until the pesticide is no longer harmful to that pest population.

As we move into the growing season, pesticides need to be used more responsibly to help avoid pest resistance, harm to non-targets like pollinators and harm to the environment.

A pesticide should not be applied until the true cause of the problem is positively identified. Is it a pest? If so, what type of pest and does that pest cause long term harm or short term cosmetic injury? Does the pest even need to be controlled? Is the pest population high enough to cause damage?

If control is needed, what is the best control method or combination of methods to use? Pesticides are an important tool in pest management, but they should be one of the last control methods turned to.

There are cultural controls like planting resistant plants, replacing a plant that has a chronic issue, using a tall mowing height to reduce weed seed germination, and the correct use of mulch to shade out weed seed.

Another form of control is mechanical. Examples include hand-pulling weeds before they go to seed, pruning or pinching off a diseased plant portion, or hosing mites off plants with a strong stream of water.

If it is determined a pesticide application is justified, select a low risk pesticide but one that will be effective and apply it at the correct time in a pest’s life cycle, which may not be when symptoms are first noticed.

Always use the recommended label rate for a pesticide. If you use less than the recommended rate, the targeted pest may recover and this helps build resistance.

If you use more than the recommended rate, the plant itself may be damaged, money wasted, and there are likely to be higher environmental or human risks.

If a pest issue requires frequent pesticide applications, such as the use of preemergence herbicides for crabgrass and other annual weeds, rotate the type of pesticide used.

Pesticides have different modes of action or chemistries which is how they kill a pest. For example, some insecticides are stomach poisons, some act on an insect’s nervous system, and others prevent molting which halts metamorphosis.

If you use a different pesticide but it has the same mode of action or chemistry as the previous pesticide, such as two different organophosphates, this will not work to reduce pest resistance. Rotate chemistries used to help reduce resistance.

This can be challenging for homeowners. Read label directions about active ingredients closely and ask when buying a pesticide. Also, avoid repeat applications for preventive purposes only unless you are absolutely sure they are needed. Annual insecticide applications for white grubs are one example.

Kelly Feehan is a community environment educator for Nebraska Extension-Platte County.

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