Several Problems Reported With Emerging Corn

Keep scouting fields for cutworms and other corn problems. Rod Swoboda 

Published on: May 15, 2006

Farmers need to continue to scout emerging corn for signs of black cutworm and flea beetles this week. In addition, many farmers are trying to figure out what to do with fields that have a lot of weeds growing along with the corn.

"There are several things you should be looking for when corn is emerging and when the plants are still small and have recently emerged," says John Holmes, Iowa State University extension crop specialist at Clarion, in northern Iowa.

Check for sidewall compaction in the seed furrow. Also, check for signs of root feeding from seedcorn maggot, seedcorn beetles, wireworm and white grub. Cutworm feeding will first show up as leaf feeding. Search for the cutworm and determine if it is a black or a dingy cutworm. "Black cutworms will be very small," says Holmes. "Dingy cutworms will be three-quarters of an inch or larger."

Cutworm feeding on corn in central Iowa

West Central Cooperative agronomist Bill Heaning reported finding black cutworm larvae feeding on corn west of Scranton on May 12. Bill says larvae were feeding on V1-V2 stage corn, both above and below the soil surface. He reported seeing fields with 10 to 15% damage.

ISU Extension Entomologist Marlin Rice predicted black cutworm feeding would begin on May 11. It appears that the predictions were pretty accurate. Rice is advising farmers to scout fields for cutworm feeding. Watch for leaf feeding initially followed by plant cutting and stand reductions. Insecticide treatments should be considered if cutworms are three-fourths inch or less in length and 2% to 3% of the plants are wilted or cut. For more information see "Black cutworms return, cutting dates predicted" in ISU's May 1 ICM newsletter.

Did planter perform as you would like?

Flea beetle survival was probably higher than normal due to the warm weather this past winter, so watch for flea beetle feeding on young corn plants. "As you take your stand counts, notice the plant spacing. Also, note the planting depth. Did your planter perform as anticipated?

Also watch for weed problems, such as leafy spurge. "Last week I noticed 8 to 10 inch tall leafy spurge in a ditch in Webster County," says Holmes. "The bracts were already yellow. At a glance the leafy spurge looked like wild mustard. The key characteristics to identify leafy spurge are long narrow leaves that resemble kochia, milky sap and yellow bracts."

If you find leafy spurge, let your county extension director know. "We are still trying to document where this weed is located in Iowa," says Holmes.

Be on lookout for bean leaf beetle

"This pest - bean leaf beetle - is out there and is waiting for soybeans to emerge," notes Holmes. "A number of agronomists and farmers have said they've seen bean leaf beetle on volunteer beans, in ditches and in alfalfa. Keep a close eye on emerging soybeans. Treatment with insecticide often is not necessary because bean stands aren't significantly reduced by early season feeding."

If the beans are being grown for seed, it's important to treat as soon as beetles are found in the field. That prompt treatment with insecticide spray will prevent the transmission of a disease called bean pod mottle virus.

"The beetles will be back this spring. We are finding them now on alfalfa, but their populations appear to be small in the Ames area," says ISU's Marlin Rice. "Based on this past winter, we predict that the survival of overwintering bean leaf beetles was very similar to what we've seen the past couple of years. In otherwords, great conditions for the beetles throughout most of the state except for the northwest corner of Iowa."