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Agronomic Crops Network

Ohio State University Extension


On Our Watchlist: Seedcorn Maggot and Alfalfa Weevil

There are two insect pests in particular that we’re wary of at the moment:  Seedcorn maggot (in corn and soybean) and alfalfa weevil. 

Seedcorn maggot is most likely to be a problem in fields where cover crops or other green vegetation has been disked in, or manure applied, a handful of days previous to planting.  The nice rotty smell attracts the adult flies to lay eggs in the soil, which hatch into the maggots that can feed on seeds and seedlings of corn and soybean.  Insecticidal seed treatments typically provide good protection against the maggots.  However, if these crops were planted early into cold soils the seeds will be slow to germinate and there is a greater likelihood that the seed coating will wash off before germination.  These products are very water-soluble which is how they work – they are taken up by the germinating seed and transported through the fluid transport system of the plant to be incorporated into the new growth.  But if the seed sits in the soil too long before germinating, much of the product may be lost into the surrounding soil instead of being incorporated into the plant for its protection from maggots and other early season pests.  Stubbornly cold soil temperatures in April may have delayed germination for early plantings, which is why we Seedcorn maggot is on our watchlist.  There is no rescue treatment once damage begins, but replanting is always an option if stand loss is severe enough.

Alfalfa weevil is on our watchlist too.  Cold temperatures last week may have slowed feeding but the temperatures haven’t been cold enough to kill the weevil larvae.  We are concerned that as soon as it warms they will speed up their feeding again with a vengeance.  Scout your fields now, not when excessive feeding grabs your attention.  Keep in mind that at a certain point, early harvest is preferable to treatment.  General scouting and management information was provided in last week’s newsletter:



Crop Observation and Recommendation Network

C.O.R.N. Newsletter is a summary of crop observations, related information, and appropriate recommendations for Ohio crop producers and industry. C.O.R.N. Newsletter is produced by the Ohio State University Extension Agronomy Team, state specialists at The Ohio State University and the Ohio Agricultural Research and Development Center (OARDC). C.O.R.N. Newsletter questions are directed to Extension and OARDC state specialists and associates at Ohio State.