Summary Content
This project, which marked its 11th year in 2024, used field survey data to inform farmers and other agricultural professionals of pest and disease issues in-season. Three IPM scouts traveled western Minnesota, visiting 469 soybean fields, looking for old and new pests and diseases using a set protocol. In each field, soybeans were growth-staged and insects including grasshoppers, soybean aphid (SBA) incidence, severity and parasitic wasp infestation, soybean tentiform leafminer, soybean gall midge and presence and feeding injury caused by Japanese beetles, two-spotted spider mites, bean leaf beetles and foliage-feeding caterpillars scouted. Incidence and severity of frogeye leaf spot, Cercospora leaf blight, Alfalfa mosaic virus and Phytophthora root and stem rot symptoms were also scouted.
Findings
SBA incidence increased from 0 to 81-100% of plants infested over a two-week period in July, eventually leading many fields to reach treatments thresholds (250 aphids per plant on 80% of plants with populations increasing) and be treated with an insecticide. It is theorized that the mild 2023-24 winter led to 2024 being a “good” SBA year, meaning that the even milder 2024-25 winter may be setting Minnesota soybean producers up for another ‘good’ SBA year in 2025.
Cercospora leaf blight was observed throughout much of the scouting area, with symptomatic fields as far flung as Big Stone and Roseau Counties.
Economic Benefit to a Typical 500 Acre Soybean Enterprise
With the knowledge that 2024 was going to be a SBA management challenge, PIs were able to share with farmers how best to manage this pest, given current labeled pesticides. For example, with pyrethroid-resistant soybean aphid populations still widespread, an understanding of how using premixes with active ingredients from two different insecticide groups may impact both in-season management and the insecticide-resistance profile of the larger population is essential. Premixes have multiple active ingredients combined often at lower than the label rates of each active ingredient (a.i.) on their own. When one of the a.i.’s is a pyrethroid, the other tank mix partner is working from a position of vulnerability. Lower rates of a single effective active ingredient puts tremendous selection pressure on the SBA population to select out those individuals capable of surviving what would now be two different classes of insecticides. Having effective pesticides from multiple insecticide classes to control this damaging insect is essential for long-term, high-yielding soybean production in Minnesota; thus, they’re priceless.
