Scouting for Seedcorn Maggot

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Seedcorn maggots prefer cool, wet spring weather when emergence is delayed, and heavy textured soil that retains moisture.  They also like soil that has recently had manure applied as well as freshly buried green residue in conjunction with a deep planting depth.  They primarily target soybeans and edible dry beans but can also target corn.

Adult seedcorn maggots look like small elongated houseflies are 5 to 6 mm long and a pale grey to yellowish colour.  The larvae are 6 to 10 mm long and are a yellowish-white headless, legless maggot.  The body tapers to the front with two small protracting mouth hooks.

The pupal stage overwinters in the ground at a depth of 7 to 13 cm, and the adults are active at temperatures between 16 and 29°C.  The eggs are laid in the crevices of wet soils that emit a decomposing organic matter odour and on weeds or weedy areas.

Young larvae penetrate germinating seeds to feed on internal tissues and can also finish their growth on decomposing organic matter.  The larvae enter summer diapause when temperatures are 29°C or higher.  Peak adult activity is in the early spring and again in the fall when it is cooler.

Scout from April to mid-June and look for symptoms such as poor emergence, tunneling and scarring.  There are no available rescue treatments, plant stands should be assessed to see if replanting is required.

To prevent seedcorn maggot, plant later in good soil conditions to ensure rapid seedling emergence.  If manure or green residues are incorporated, wait at least two weeks before planting.

 

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 Photo Source: Pest and Disease Image Library, Bugwood.org. 

 

 

Sources:
Grain Farmers of Ontario. Guide to Early Season Field Crop Pests. (verified May/15)
Pest and Disease Image Library, Bugwood.org.