Should you use a neonicotinoid seed treatment in soybean? If you no-till in a northern state, the answer is probably no — and if you do, the effects may be more harmful than beneficial, says a research paper jointly published by universities in Indiana, Iowa, Kansas, Michigan, Minnesota, Missouri, Nebraska, North Dakota, Ohio, Pennsylvania, South Dakota and Wisconsin.

According to the paper, “The Effectiveness of Neonicotinoid Seed Treatments in Soybean,” neonicotinoid seed treatments only provide a maximum of 3 weeks protection after planting. However, they can be useful for managing early-season pests in targeted, high-risk situations, such as:

  1. Fields transitioning from pasture, Conservation Reserve Program land or grassland to soybean production, as they tend to have higher populations of long-lived soil pests that can’t be controlled with foliar insecticides.
  2. Fields with recently incorporated animal manure, green cover crops or weeds, as seedcorn maggot females lay eggs in rotting organic material.
  3. Double-cropped soybeans or specialty (food-grade or seed) soybeans. In double-cropped soybeans, soybean aphids may migrate from mature soybean plants to colonize later-planted plants. In food-grade or seed soybean, early-season pests may carry diseases that affect crop quality.

But these high-risk scenarios are uncommon in northern states, as seed and seedling pests like wireworms and seedcorn maggots rarely reach economically damaging levels in most soybean fields.

One pest that is a major threat for northern states is soybean aphid, which is listed on labels for neonicotinoid seed treatments, the paper says. However, soybean aphid populations typically increase to threshold levels after the 3-week protection period neonicotinoid seed treatments offer.

The paper says research has repeatedly demonstrated that using foliar insecticides to treat soybean aphids populations that meet the threshold of 250 aphids per plant is the most effective and economical approach for soybean aphid management.

Not only does using neonicotinoids in soybeans in northern states typically have little effect on yield or profits, they also pose risks to non-target organisms and threaten resistance development in target pest populations.

The study found some organisms like slugs can become “toxic” by ingesting neonicotinoids and pass it to their natural enemy, the ground beetle, disrupting the biological control of slugs. That same study found that soybeans grown without neonicotinoid seed treatments produced higher populations and yields than the soybeans that were treated.

The authors conclude that when pest problems occur, the best management approach is an integrated one, which can include crop rotations, conserving natural enemies, using soybean varieties resistant to pests or disease, and applying insecticides when populations have reached their established thresholds.

For more information, you can download the paper from Purdue University Extension’s website.