Pest Management
Insects
Monitor for wireworms, seedcorn maggot and cutworms from May to June. Insecticide seed treatment protects against wireworms and seedcorn maggot only. Assess the need for protection on a field-by-field basis. Scout weekly for soybean aphids from R1 to R5. See Soybean Aphids: Identification, Scouting and Management. Scout for leaf and pod feeding insects such as grasshoppers, green cloverworm and corn earworm from R1 to R6. See Soybean Insect and Disease Identification Guide.
Weeds
Soybean seedlings are poor competitors against weeds. Yield potential is maximized when weeds are controlled until at least the V3 stage.
Glyphosate-resistant kochia has been confirmed in several Manitoba municipalities. A proactive, integrated weed management strategy is recommended to prevent herbicide-resistant weeds. This may include diverse crop rotations, improved crop competition via narrower row spacing and higher plant populations, herbicide tank mixes, rotating modes of action and field or site-specific weed management. Herbicide options vary by production system and caution must be taken to prevent herbicide drift. Volunteer canola is the most abundant weed in soybean crops, according to the 2016 provincial weed survey. The action threshold (5% yield loss) for volunteer canola control is 2.5–3.2 plants/m2.
Diseases
Soybeans are susceptible to the root rot complex, including Fusarium spp., Rhizoctonia solani, Pythium spp. and Phytophthora root rot (PRR). Fungicide seed treatment can offer protection against these diseases for up to three weeks after seeding. Scout for early-season diseases in June. Fusarium spp. and PRR are the most common seedling diseases in Manitoba.
Scout for foliar and stem diseases from July to September. Common foliar diseases include bacterial blight, brown spot and downy mildew, although these are not generally of economic importance. Soybeans are susceptible to Sclerotinia (white mould), but are more tolerant than canola, dry beans and sunflowers.
The occurrence of stem rot, stem canker, anthracnose, frogeye leaf spot and bacterial pustule is being studied in Manitoba. Soybean cyst nematode (SCN) was first identified in Manitoba in 2019. Since SCN has only recently established itself in the province, cleaning the soil off of equipment, vehicles, soil sampling equipment and clothing will reduce the risk of introduction or spread.
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