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Let’s talk crops! talks about the effects of the 2021 drought on pests and what this means for 2022 – Crookston Times - Energy And Water Development Corp

Let’s talk crops! talks about the effects of the 2021 drought on pests and what this means for 2022 – Crookston Times

University of Minnesota Extension

Insects and other arthropods that feed on crops are cold-blooded animals whose growth, development and population dynamics are largely driven by their environmental conditions. On March 2, 2022, Bruce Potter, University of Minnesota Extension IPM specialist, Drs. Ian MacRae, UMN Extension entomology specialist, and Seth Naeve, UMN Extension soybean agronomist, joined UMN Extension educator Angie Peltier for a wide-ranging discussion of how the 2021 drought influenced pest pressure and how 2021 population dynamics may influence 2022 pest pressure. This was the ninth episode of the 2022 Strategic Farming: Let’s talk crops! webinars in this series.

Dr. Seth Naeve shared with the audience that “if the soybean plant is unable to keep up with water demand, the crop will begin to change its cellular composition, changing the solute content within cells to begin to take more water into the leaves through osmosis. The plants are doing a lot of adjustments to work best under water-limiting conditions, before we see any sign of this in the field.”

One of the first visual symptoms related to drought that one can observe are stunted plants that roll their leaves, in the case of corn, or flip their leaves over to expose the lighter, lower leaf surface to the sun, in the case of soybean, in an effort to reduce water loss from foliage. These above-ground indications of water stress tend to occur each day when the water usage rate outpaces the ability of the plant to take up sufficient soil moisture. After some time with insufficient water availability, loss of yield potential occurs after the crop slows the rate of leaf expansion and shuts off photosynthesis beginning in the afternoon, said Naeve.

Bruce Potter shared that “Knowing what insects are going to do in reaction to a drought is a lot easier to predict than the drought itself.” Dr. MacRae added, “Insects are cold blooded, so all of their physiological processes are driven by ambient temperature. The warmer it is, generally the faster the physiological processes will run. Generally speaking, higher ambient tempera tures will result in shorter generation times and more egg laying.” Insect population densities can also be affected by how dry the previous fall was as the dry 2020 fall likely helped to set the stage for grasshopper populations reaching treatment thresholds in 2021.

Of additional concern during drought years is that insecticide efficacy can be negatively affected. If insecticide applications take place during very hot temperatures and periods of low relative humidity, some of the active ingredient never makes its way onto the leaves, but is rather lost to volatilization.

The weather yearround can also impact the insect pests that plague Minnesota crops. Soybean aphid eggs spend the winter in Minnesota and so are exposed to our low relative humidity and harsh winter air temperatures. Insects such as spider mites are not as affected by winter air temperatures once there is considerable snow cover noted Potter as they tend to move back to perennial plants after harvest where they are insulated from temperature extremes by snow. “Aphids that infest small grains such as English grain aphid and bird cherry oat aphid, tend to spend their winters in the southern US and so weather conditions there will affect their survival and numbers as they make their way north to Minnesota this spring” said Potter.

One unexpected guest, Seth Dibblee, who works for the U.S. EPA in Chicago on pesticides and initially joined the Strategic Farming: Let’s Talk Crops! webinar as a member of the audience, was pulled into the discussion to share information regarding the fate of chlorpyrifos for managing Minnesota insect and mite pests in 2022 and beyond. Mr. Dibblee shared that the tolerance of chlorpyrifos on food and feed crops has been revoked as of February 28, 2022, meaning that food and feed crops in commerce can no longer have detectable chlorpyrifos residue. According to Mr. Dibblee, the typical process for ending a registration of a specific active ingredient starts by canceling the use the active ingredient. This is so that treated food- and feed-crops have some time to cycle out of the marketplace before the residue tolerance is revokved. According to Mr. Dibblee, in this instance, the process happened in reverse order due to a federal court ordering the US EPA to revoke tolerances before all crops that were treated legally in 2021 had finished cycling through the marketplace. The US Food and Drug Administration has recently issued guidance to food buyers and processors regarding how to handle crops in this situation. There is currently a lawsuit that has been filed by industry groups asking the court to stay the chlorpyrifos ruling, and it seems likely that little will change without another court ruling.

Potter, MacRae and Naeve answered many more audience questions about plant growth and development under drought stress, how multiple stressors can work together, adjusting treatment thresholds for multiple simultaneously occurring pest populations, the insect population dynamics under drought stress and what crop producers can expect of pests going into the 2022 cropping season, particularly when growing soybean after soybean. For those that missed this session, it is now available to view on YouTube at https:// For more information and to register to attend other weekly session through the end of March, visit

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