Everything you need to know about seedcorn maggot

Seedcorn maggot integrated pest management considerations.

For decorative purposes.
Photo by Chris DiFonzo, MSU.

Michigan State University Extension has received several calls about seedcorn maggot in soybeans. The following is a quick refresher on seedcorn maggot, plus an example of a current infestation in southern Michigan. On another note, black cutworm cutting is something else to watch for, especially in fields where heavy winter annual weeds were present but recently sprayed (larvae move from the dying weeds and concentrate on the corn).  

Seedcorn maggot life cycle 

  • Adult flies overwinter. 
  • Late March to mid-April: Adults emerge. Adults are attracted to fresh decaying stuff for egglaying. 
  • Late April to mid-May: Larvae feed and develop on the decaying material, also damaging seeds planted early into the same locations. 
  • Mid-May: Pupation (first round of damage is over). 
  • Mid- to late May: First generation adults emerge. In cool, wet seasons, a repeat infestation cycle could occur in later planted fields. 

Enviroweather seedcorn maggot model 

  • Go to Enviroweather. Choose corn in the crop list, then select seedcorn maggot. 
  • See the following for an example of how to use this model: Using the seedcorn maggot model on MSU Enviroweather. 
  • The overwintering generation lays eggs in fields planted in April. Their larvae are responsible for the damage we see in mid-May. 

Maggot risk formula: Tillage + freshly decaying green stuff + slow emergence (April planting, cool conditions, seeds planted too deep) 

Ranking of agronomic situations, which are attractive for seedcorn maggot egglaying and infestation 

(Wisdom from Ron Hammond, PhD, former maggot expert at Ohio State University) 

  • High risk: Tilling in alfalfa, another legume, living green grass cover, heavy winter annual weed growth. 
  • Moderate (some) risk: Tilling in soybean or corn residue (usually too dry to be attractive). 
  • Very low risk: Tilling bare soil. 
  • No risk: “No-till anything, I have never seen a problem, period!” said Hammond. 

Limitations of seed treatments 

  • The clock starts ticking on an insecticidal seed treatment when the seed goes in the ground. 
  • Below-ground, protection can be overcome by high pest pressure (too many maggots). Above-ground, expect at most 30 days of protection (like for soybean aphid).  
  • Note that the rate of insecticidal seed treatment differs by crop. Example, thiamethoxam (e.g., Cruiser) rate per acre is 0.083 pounds for soybean and 0.16 pounds for corn. During the seed treating process, this rate gets divided per seed resulting in 0.075 milligrams per soybean and a variable 0.25 – 1.25 per corn kernel. Thus, the lowest rate of thiamethoxam per kernel is about three times the rate per soybean. 

Replanting maggot-ravaged fields 

  • Attractive decaying green stuff is dried up and seeds emerge fast under warm soil conditions. 
  • Recommendation: Don’t waste more money on an insecticidal seed treatment. 

The Michigan State University Extension field crops team has many ways of informing farmers and agriculture professionals with pest pressure updates, including the Fast Fonz Facts that Chris Difonzo emails out to subscribers. To subscribe to Fast Fonz Facts, email difonzo@msu.edu. Virtual options are watching the Field Crops Virtual Breakfast Series at 7 a.m. on Thursdays, Central Michigan updates from Monica Jean on Wednesdays, wheat watcher updates from Jenna Falor and southwest Michigan updates from Nicolle Ritchie, both published on Thursdays.


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