Information on European corn borer, field scouting and economic threshold worksheets, and degree-days.
European Corn Borer Moth Flights Approaching Peak First Generation Field Scouting Resources
Eileen Cullen, Extension Entomologist UW Entomology Department
European corn borer moth flights have been increasing over the last week. Black light trap catches are reported from cooperators throughout the state to the WI DATCP Wisconsin Pest Bulletin http://pestbulletin.wi.gov/ (click on “Corn” link at left for latest black light trap counts). Moth counts increased last week at Arlington (125 moths) and Marshfield (30 moths). Mazomanie, Sparta, ChippewaFalls and Manitowoc recorded slight increases over the previous week, but traps in these locations were below 20 moths per trap. Counts for the week ending June 16th will be posted to the Wisconsin Pest Bulletin this Friday June 16th at the link above. Thank you to Clarissa Hammond of the WI DATCP Pest Survey for coordinating and reporting the black light trap network.
European corn borers overwinter as 5th instar larvae in corn stalks, crib corn, and large-stemmed weeds. In spring larvae remain in these protected sites to pupate. After emergence in June, moths spend daylight hours in sheltered areas (weeds or grasses) within or bordering corn fields. Females deposit egg masses on the underside along the midrib of lower leaves of young corn plants.
Moths are attracted to the tallest corn for egg laying. Young corn plants produce DIMBOA, a naturally occurring plant compound that inhibits larval survival on the plant. Once corn plants reach an extended leaf height of 17-24 inches, this plant chemical is sufficiently diluted for larvae to feed and develop on the corn plant. Early planted field corn will be taller during the current first generation flight and provide an attractive oviposition site for female moths.
In central Wisconsin, under typical late June temperatures, it takes about 6 days for eggs to hatch.
First instar larvae will move to the plant whorl and begin to feed. As leaves lengthen, feeding results in “pin-hole” damage. There are five larval instars and two generations per year in Wisconsin. Field scouting for first generation larvae is important because by the 3rd instar, larvae will tunnel into the midrib of the leaves, eventually burrowing into the stalk of the plant.
Natural control plays a key role in moderating European Corn Borer populations as weather conditions, predators and parasitoids take their toll on populations. Warm, calm evenings are conducive to moth flight activity. Below normal temperatures will reduce flight activity, thereby reducing mating and egg-laying. High temperatures and low humidity can increase moth mortality. Heavy rains interfere with moth activity, but showers do not.
1. Field Scouting and Economic Threshold Worksheets
UW-Extension publication A1220 The European Corn Borer has been updated. You can download the fact sheet from UW Extension publications http://cecommerce.uwex.edu/. From the publications home page, click on the “Agriculture” link on the left of the page. Select “Crops and Forages”. Scroll down to publication A1220.
2. European Corn Borer Degree-Days
Moth flights are expected to peak at 631 DD after which point flight activity will decline. If economic threshold larval populations are reached (see UWEX publication A1220), the appropriate time to control first generation is during the period of 800 to 1100 degree days (above a modified base temperature of 50F). This window brackets the time during which larvae feed on outer plant surfaces prior to tunneling. Scouting during this time will indicate whether treatment is justified.
A visit to the WI-MN Cooperative Extension Agricultural Weather Page at http://www.soils.wisc.edu/wimnext/ will help you track first generation European Corn Borer degree-days for your area. From the main page, click on the “Corn” link. From the Corn Crop Product page click on “European Corn Borer” under the insect phenology section.
European corn borers do not reach economically damaging levels in many years. In fact, first generation flights in Wisconsin the past couple of years have been at or below average. However, because of population fluctuations between years, and the specified 800-1100 degree-day treatment window, scouting is important each year to determine whether the flight has resulted in economic threshold level larval populations and feeding damage.
European corn borer egg mass shortly before hatching
“Pin-hole” damage caused by first-generation European corn borer