Life cycle and description

• Adult stage: Fly with dark gray body, black legs, 5 – 7 mm. Similar to house fly, but smaller. Development time is variable.
• Egg stage: White, elongate, 1mm in length. Eggs hatch in 1 to 9 days.
• Larval stage: White/yellow/cream-colored maggot, pointed head, round tail, 5 –7mm, segmented (12). Development time lasts between two and three weeks.
• Pupal stage: Dark brown, 5mm.
• Development time lasts one week or more.

Confirmation

Seeds can be dug up and inspected for seedcorn maggot damage. Damage is characterized by the presence of maggot tunnels inside the seed or loss of the entire seed content. In addition, the cotyledons and first leaves of the seedling may be deformed and weak.

Problems with similar symptoms

Cutworms, white grubs and wireworms can also reduce germination, resulting in gappy stands.

Why and where it occurs

The eggs are deposited in crevices or surface soil close to seeds. Prevalence of seedcorn maggots is greatest in well fertilized or manured soil.

There are normally 4 to 5 generations of seedcorn maggot each year. The first two generations in the early planting season are the most destructive as maize seeds have usually not yet germinated.

Host range

Hosts include maize, beet, onion, garlic, lettuce, peas, cabbage, spinach, turnip, radish and sprouting potatoes.

Geographic distribution

Seedcorn maggots are found in North America’s temperate regions and tropical highlands.

Damage

• Mechanism of damage:Seedcorn maggots damage newly planted seeds by feeding on seed contents, causing poor germination and a gappy plant stand. Seedlings that do emerge are spindly with few leaves. Occasionally, seedcorn maggots tunnel seedling stems.
• When damage is important:Damage is most critical when severe infestation results in extensive loss of seed germination and very poor crop stands.
• Economic importance: If stand loss is severe, replanting may be necessary as responsive treatments are generally unsuccessful.

Management principles

• Insecticide treatment of seed will reduce damage. Thiamethoxam or Clothianidin are two seed treatment options. Other neonicotinoid insecticides should not be used within 45 days of planting seed treated with these insecticides. Soil-applied Diazinon could be broadcast before planting. It requires incorporation at once to a 2 inch depth. Drift and runoff should be avoided.
• Avoid planting in wet and cool periods, particularly where fields are well fertilized and manured.
• Shallow planting later in the season into well prepared beds encourages faster germination.
• Fields with heavy cover crops such as clover or alfalfa or high manure content attract egg-laying flies in the early planting season. Prevent this by plowing or turning over the field either at the end of the cropping season or two weeks before planting. Let manure age before turning it under.
• Reducing seedcorn maggot fly access to the seed row can be achieved by attaching drag chains to the planter machine.

References

Bessin, R. 2004. Seedcorn Maggots. ENTFact-309. University of Kentucky Entomology Cooperative Extension Service. http://www.uky.edu/Ag/Entomology/entfacts/veg/ef309.htm (7 November 2006).

Carter, C.C., K.F. Horn, D. Kline, J.R. Baker, J. Scott and H. Singletary. n.d. Seedcorn Maggot.  Insect and related pests of shrubs: Some important, common and potential pests in Southeastern United States.  Center for Integrated Pest Management, North Carolina State University. http://ipm.ncsu.edu/AG271/corn_sorghum/seedcorn_maggot.html (7 November 2006).

Chaney, W.E. and E.T. Natwick. 2007. Cole Crops: Seedcorn Maggot. UC IPM Pest Management Guidelines. UC ANR Publication 3442. University of California. http://www.ipm.ucdavis.edu/PMG/r108300211.html (16 November 2006).

Davidson, R.H. and W.F. Lyon. 1987. Insect Pests of Farm, Garden and Orchard. Hoboken, NJ: John Wiley & Sons.

Godfrey, L.D., S.D. Wright, C.G. Summers and C.A. Frate. 2006. Corn: Seedcorn Maggot. UC IPM Pest Management Guidelines. UC ANR Publication 3443. University of California. http://www.ipm.ucdavis.edu/PMG/r113300111.html (16 November 2006).

King, A.B. and J.L. Saunders. 1984. The Invertebrate Pests of Annual Food Crops in Central America. London: Overseas Development Admin.

Ortega, A. 1987. Insect pests of Maize: A Guide for Field Identification. Mexico, D.F.: CIMMYT.

Contributors: Gabrielle Turner, Biswanath Das