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If I were to make a guess, I would say that 80% or more of the soybean seed sold today is treated with both a fungicide and insecticide. In the case of some individual seed companies it may be near 100%, because they want to treat all soybean seed going out the door.

I can see a seed company’s concerns from their perspective—growers are reducing seed rates to lower seed cost, as most realize that a final stand of 100,000 to 110,000 plants, evenly distributed, will optimize yield. Yet those same growers are planting earlier, and often in harsher soil environments that slow and challenge germination. So naturally, they want companies to treat seed to protect their investment and give every seed a chance to germinate and emerge.

At the same time university pathologists are telling us that seed treatments often don’t pay and that continued use of a fungicide and/or insecticide will bring about pesticide resistance. We all know that dependence on glyphosate, a single mode of action, has created weed control challenges today.

Seed treatment fungicides make sense because of their ability to help ward off seemingly plentiful soil pathogens and ensure the seed and seedling have time to germinate and emerge. Today’s seed treatments usually come with 2 or 3 modes of action to cover a broader spectrum of diseases to protect your investment.

But, is the insecticide necessary and does it really add significant value at a time when insect risks are small? Generally, the insecticides claim efficacy on seed corn maggot, early bean leaf beetle and aphid infestations. While the dosage is probably sufficient initially, as the seedling grows the protection quickly dilutes out as the plant gets bigger. And, most insect problems often don’t show up until July.

But there are times when insecticide treatments make sense in soybeans:
1. Transition from grass or CRP when insect risks can be high.
2. High probability that a soil-borne insect, such as bean leaf beetle, will vector a disease such as pod mottle virus.
3. High probability of soil-borne insects that are nearly impossible to scout and sample for.
4. Risk of seed corn maggot infestation, particularly after manure use or grass.
5. Growing seed or food grade soybeans when the seed coat and product quality can be impacted.
6. Isolated fields or fields planted early that are magnets for bean leaf beetle.

I agree that automatic use of insecticides as part of soybean seed treatments may be questionable. But it may be difficult to get seeds treated without it and it is a good risk management tool. However, the downside is the risk of developing insect resistance that accompanies overuse.

Soybean agronomist Daniel Davidson, Ph.D. posts blogs on agronomy-related topics. Feel free to contact him at djdavidson@agwrite.com or ring him at 402-649-5919.