Hayden Schug, Agriculture Agent | hschug@umd.edu
University of Maryland Extension, Charles County
As soybean planting gets underway across Maryland, it’s important to watch for early-season pests that can impact stand establishment and ultimately yield potential.
Seedcorn maggots are a common problem in freshly tilled fields, especially those with high organic matter or recent manure applications. Maggot feeding can destroy the sprouting seed, leading to weak stands or gaps in rows. An insecticide seed treatment containing neonicotinoids (such as thiamethoxam or clothianidin) can protect against seedcorn maggot. Additionally, monitoring soil temperatures and avoiding planting into cool, wet soils can help minimize risk.
Slugs are another concern in no-till and cover-cropped fields. They thrive in moist, heavy residue environments and can cause heavy feeding injury to cotyledons, stems, and young leaves. Good furrow closure at planting is critical, open seed furrows can create a pathway for slugs to reach seeds and seedlings before emergence. Slug baits containing iron phosphate or metaldehyde can be applied if damage is severe, but results are often variable. Managing residue to reduce slug habitat and scouting early are important preventative steps.
Bean leaf beetles may also move into emerging soybeans, feeding on cotyledons and early leaves. While light feeding typically does not justify treatment, heavy populations can reduce stands. Insecticide seed treatments should provide adequate protection, however, if high populations persist, foliar insecticide applications labeled for bean leaf beetle, such as pyrethroids, can be used if defoliation thresholds, 30% for vegetative growth, are met.
Timely scouting is critical. Examine plants as they emerge, especially in fields with a history of early pest issues, cover crops, or heavy residue. Focus on stand counts and visible injury, and determine if replanting or other action is needed based on stand loss and defoliation thresholds. A pest timeline for common soybean insect pests is found in the figure attached.
