Corn earworm activity is beginning in Michigan sweet corn fields

Operate your own pheromone trap if you grow sweet corn to be able to detect the activity of corn earworms earlier.

The corn earworm is generally the most serious pest of sweet corn in Michigan and it also infests a range of other crops, such as tomatoes, green beans and peppers. The adult moth prefers to lay eggs on fresh, green silks and those fields that have fresh silks should be monitored with a pheromone trap at this time.

Since larvae move down the silk and subsequently feed protected in the ear, the only chance to prevent larval damage is during the journey of the larva from the silks to the ear. Protectant insecticide sprays are, therefore, necessary so that the silks are covered with fresh residue when eggs hatch. This increases the likelihood that the small larvae contact a lethal dose of insecticide before they reach the protected region within the ear. Because the silks grow rapidly when its hot, frequent insecticide applications may be necessary. The spray applications should be started only after moths are caught in the pheromone traps, and the following decision guide is recommended.

  • Catch is less than 10 corn earworms per night in the pheromone traps: Moths probably will not lay enough eggs to justify control.
  • Catch is greater than 10 corn earworms per night in pheromone traps: Moths are laying enough eggs to warrant treatment.

The determination of the spray interval depends on the value of the crop, cost and effectiveness of the insecticides. In general, if greater than 50 to 100 moths per night are being caught in the pheromone trap, the spray interval should be two to four days. With fewer moths caught per night the spray interval should be seven days.

Some of the more effective insecticides in sweet corn for control of corn earworms are Warrior, Capture and Mustang Max, which all contain pyrethroid as the active ingredient. Effective alternatives to the pyrethroids are Coragen and Radiant, but these insecticides do not control corn rootworm, so if this pest is present, a pyrethoid insecticide may still be needed. To find out more about the application rates of insecticides, check out the E-312 MSU Bulletin, 2012 Insect, Disease and Nematode Control for Commercial Vegetables.

For more on sweet corn insect management, read Purdue University Extension’s Managing Insects in Commercially Grown Sweet Corn.

To buy traps and lures:

  • The Hartstack wire trap can be purchased from Bob Poppe, Route 1, Box 33, Lexington IL, 61753 (about $250/trap). These traps last for many years.
  • Instead of the Hartstack wire traps, the Heliothis traps can be used.
  • Lures can be purchased from Great Lakes IPM (800-235-0285) and should be changed every two weeks.

Michigan State University is not supporting the use of any particular insecticide brand. When using pesticides, always follow the label recommendations.

To learn more about corn earworm biology, trapping and management, see the recent MSU Extension News articles:

Dr. Szendrei’s work is funded in part by MSU‘s AgBioResearch. 

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