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Corn+Soybean Digest

Start Monitoring for Western Bean Cutworm in June

Western bean cutworm (WBCW) was historically found in the western Corn Belt, where it was a common pest of dry beans and a sporadic pest of corn. Starting in the year 2000, economic damage from this pest was found on corn in Iowa and Minnesota. Since then, this pest has continued to rapidly spread eastward, reaching Ohio in 2006. The easiest way to monitor the presence of this pest is trapping of the adult moths. In 2006, three adults were caught, six in 2007, 150 in 2008 and over 500 in 2009. Most moths have been caught in the extreme northwest or west central portion of Ohio.

The adults emerge in late June-early July after fully grown larvae overwinter inside chambers in the soil 3-8 in. deep. The adults are mostly dark brown and black, with three characteristic markings that distinguish them from other moths: 1. a white stripe on the top edge of the forewing, 2. a light brown-tan colored dot and 3. a comma or crescent-shaped mark behind the dot. Mid-flight of the adults usually occurs in mid-July, with adult flight ending by mid to late August. There is one generation per year.

During the summer flights, adults mate and females lay eggs on the uppermost portion of the flag leaf. Eggs are laid in unevenly distributed clusters of five to 200, averaging about 50/cluster, and hatch within five to seven days. Eggs first appear white, then tan and then a dark royal purple. Once eggs turn purple, hatching should occur within 24 hours.

In pre-tassel corn, larvae will move to the whorl to feed on the flag leaf and unemerged tassel.

Once the tassel emerges, larvae move to the ear, while feeding on corn pollen, leaf tissue and silks. By the fourth instar, larvae will enter the ear through the tip, or seventh instar, larvae emerge from the ear and fall to the ground to overwinter in soil chambers. Pupation occurs in May, immediately before adult emergence.

Cornfields can be easily monitored through simple pheromone traps. Four windows from an empty gallon milk jug are cut, and the jug is tied to a post at least 4 ft. high. A bent paper clip is used to attach the lure to the inside lid of the milk jug and the cap is replaced to keep the lure in place. The bottom of the jug is filled with a 4:1 water-antifreeze solution, with a drop of dish soap added. Traps are placed on the edge of a cornfield; one trap per field is sufficient.

Traps should be inspected at least weekly. When the first adult is collected or when adults are collected on consecutive nights, scouting for eggs or larvae should begin. Lures can be purchased at either Great Lakes IPM, 10220 Church RD NE, Vestaburg, MI 48891, or at Gempler’s, P. O. Box 270, 211 Blue Mounds Road, Mt. Horeb, WI 53572. You can also contact your local Extension office for assistance.

While no eggs have been reported from WBCW in Ohio, a single larva and a single injured ear of corn were found in 2009 in the state. However, economic damage has been reported in Indiana and Michigan. Ontario is also reporting large adult collections for the first time. For now, scouting remains the growers’ best tool for managing WBCW.

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