The first reports of the adult moth of western bean cutworm being active this year were last week in Sandusky County and this week in Clark and Franklin Counties. This new pest was found in much larger numbers than ever in some parts of northern Ohio last year, so sweet corn growers should be on the lookout for it this year. The western bean cutworm has slowly but steadily been advancing into Ohio from the western USA over the past 12 years. It was found first in northwestern Ohio but has moved into north central and northeastern Ohio. It has not yet been detected at some southern Ohio sites. This pest is a caterpillar feeds on kernels of ears in both sweet corn and field corn. Feeding damage is usually at the tip end, but can be in the middle or butt end of the ear. There are often several western bean cutworm larvae in one ear, because this species is not cannibalistic; this makes it different than the corn earworm, which also feeds on kernels at the tip of the ear, but which typically is found as a single larva per ear because it cannibalizes its fellow corn earworm larvae.
Monitoring of western bean cutworm can be done in two ways. The adult moths can be monitored with a pheromone trap using a commercially available lure that lasts for 4 weeks. A bucket type of universal moth trap can be used, or a trap can be made from a one-gallon plastic milk jug with part of the sides removed, with an inch of dilute antifreeze solution in the bottom as a drowning and preserving agent. This pest has one generation per year, with adults usually first detected in late June, peak activity in late July, and moth activity ending by late August. Trap reports on western bean cutworm from several Ohio locations can be found using this link: https://docs.google.com/spreadsheets/d/10gh3rHahdxLKkXQapGyEPxWsjHYRmgsezOoFHnwtyEo/edit#gid=441280294 The second way of monitoring is scouting. This is particularly important on any farm where the moth of western bean cutworm is detected in traps. Scouting should be done to monitor eggs and hatching larvae. Scouting should concentrate on plantings in the emerging-tassel stage. Look at 20 consecutive plants in each of 5 random locations per field. Examine the flag leaf (the leaf below the tassel), where eggs are usually laid. Eggs are laid in masses. Eggs are white when fresh, then they darken to purple when ready to hatch. Hatch will occur within 24-48 hours once eggs turn purple. Our tentative threshold for sweet corn is to consider treatment if eggs or larvae are found on more than 1% of plants for fresh-market or on more than 4% of plants for the processing market. Insecticide applications must occur after egg hatch, or after tassel emergence, but before larvae enter the ear.
The newer BT sweet corn hybrids in the Attribute II series (from Syngenta) provide genetic control of the western bean cutworm, but BT sweet corn hybrids in the Performance series (from Seminis) and the older Attribute series (from Syngenta) do not control this pest.
Pictures and additional details on western bean cutworm can be found in our OSU fact sheet: http://ohioline.osu.edu/factsheet/ENT-40
-Celeste Welty, Extension Entomologist, OSU, Columbus OH