Rebel Roundup

For over 20 years, insecticides have been used to control soybean aphids (SBA) in Minnesota. “Keeping track of the available products has been something of a roller coaster ride,” says Dr. Bob Koch, University of Minnesota Extension soybean entomologist, “particularly as it pertains to chlorpyrifos.” Its tolerances were revoked in 2022; then in November, the order was vacated, allowing the Minnesota Department of Agriculture to conditionally register chlorpyrifos for 2024.

While chlorpyrifos is an effective tool, it’s also associated with health concerns. Koch warns against immediate, widespread use, but instead suggests using it in rotation with other effective insecticides.

Pyrethroid insecticides have also been used heavily to control SBA, resulting in an increase of performance failures. Lab assays with SBA have documented pyrethroid resistance, but they couldn’t necessarily predict product performance in the field. A comparison of insecticide field trials from 2005 to 2020 found that a pyrethroid effectively controlled SBA through 2014. However, control deteriorated rapidly after 2014, coinciding with the increase of lab-confirmed resistance.

As a result, Koch doesn’t recommend using a pyrethroid as the initial SBA control treatment. If aphids are resistant, not only would the insecticide be ineffective, it would kill the natural enemies that suppress SBA populations.

Can pyrethroid resistance be reversed? If aphids displayed a fitness cost when developing resistance, it might be possible for susceptible populations eventually to outnumber resistant ones if pyrethroid use ceased. Instead, the opposite occurred in Koch’s study. This suggests that even if pyrethroid inputs were reduced, it’s unlikely that populations could become susceptible again.

Managing insecticides to maintain efficacy is critical and cost-effective. In a regional study comparing seed treatments to scouting and using threshold-based recommendations, using the economic threshold (ET) of 250 aphids per plant provided a larger return on investment. Preventative applications are not only costly, they may affect beneficial insects and increase risk for insecticide resistance.

Soybean gall midge (SGM) is a newer pest in Minnesota found throughout much of the southwestern part of the state. The bright orange larvae feed under the outer layers of the stem tissue, causing dark lesions at the base of the plant. Damage can lead to plants breaking off, wilting and dying.

Nebraska entomologists have documented 100% yield losses on field edges and 17 to 31% losses in the field’s interior. Most Minnesota fields are nowhere near this level of infestation, but we need to watch for this pest.

Because the larvae feed within stem tissue and adult emergence occus over an extended period, spraying insecticides is largely ineffective. Other integrated pest management tactics are needed for SGM.

The University of Nebraska- Lincoln has identified soybean lines or varieties which appear to have some resistance that may lead to SGMresistant varieties. Furthermore, they found that hilling soybeans, which protects the stem from SGM, has shown positive results, but logistics of hilling are challenging.

Koch and colleagues identified ground beetles, those abundant beetles that scurry around on the soil, as a potential predator of SGM. They found the beetles did indeed eat SGM larvae both in the lab and field.

They also discovered a new parasitic wasp species associated with SGM. The female kills SGM by laying eggs directly into larvae. Koch estimates that 5 to 10% of the SGM population is killed by them.

Another new pest, the soybean tentiform leafminer, was detected in Minnesota in 2021. The heaviest infestations have occurred in western and northwestern Minnesota, but seem limited to field edges near trees. The pest status of this insect is being evaluated.

These tiny larvae move into the leaf and feed. As they grow, they hollow out the leaf leaving a blotch and eventually creating a tentiform mine. Insecticides with translaminar properties applied at the early larval stages provided good control, while there was almost no control at the late tentiform stage.

Like SGM, there may be some germplasm in current soybean varieties that could potentially provide resistance to this pest.

For more information from University of Minnesota Extension, visit extension.umn. edu/crop-production.

Thanks to the Soybean Research and Promotion Council and the Corn Research and Promotion Council for their generous support of this program.

For more news from U of M Extension, visit https://www. extension.umn.edu/news or contact Extension Communications at extdigest@umn. edu. University of Minnesota Extension is an equal opportunity educator and employer.

Showing Respect

We have been blessed with some beautiful weather and it feels like an early spring in our neck of the woods. With spring-type weather, students often become more restless, impatient and agitated. We have certainly seen a change in behaviors recently to go along with the warmer temperatures. It is a good time of year to review our school wide expectations of being Respectful, Responsible and Ready to Learn. In the month of February, we have been focusing on respect.

As a part of our school-wide PBIS (positive behavior interventions and support), we teach what respectful behavior looks like in the various areas of our building throughout the school day. Some of the respectful behaviors that we focus on include using an appropriate voice tone and volume level, using kind words, being patient, taking turns, respecting others’ property, keeping hands and feet to ourselves, and being honest. These behaviors help students to be successful in all areas of life. We ask you as parents and community members to help teach and encourage these behaviors in the home and community. Working together, we can build good habits that last a lifetime.

Studies have shown that the most important factor in workers’ career success is good social skills. It is important to teach tolerance, conflict resolution and emotional control at an early age. Parents are key in making this happen! It is also crucial for children to know that their parents and school are on the same page with behavior expectations. We are in this together. And when we support each other and expect the best from our children in all areas of their lives, we all win! Nikki Cheskie MCC Elementary Mental Health Coordinator