Corn silks and soybean foliage are on the menu for Japanese beetles. And Eric Maupin is making sure they don’t get to order.

Maupin, who grows corn, soybeans and wheat in Newbern, TN, sometimes battles earworms, stinkbugs and other insects. He scouts every field to determine infestation levels and chooses the right insecticide for the situation. He’s ready for one of the newest insects to start invading western Tennessee.

“We’ve seen a few Japanese beetles, we know they’re more apparent in our area and we’ll be looking for them in 2011,” says Maupin.

“We sprayed pyrethroids Karate and Lambda/cy for worms and stinkbugs last year (2010). We’ve used Baythroid and Warrior in the past. We feel these and other pyrethroids will work against the beetles, if needed," he says.

They weren’t needed for light infestations last year, where Maupin saw some soybean fields with 20% defoliation from the ambitious beetle. The economic threshold for spraying Japanese beetles is about 30% defoliation, says Scott Stewart, University of Tennessee entomologist in Jackson.

Unfortunately, he sees greater infestations of Japanese beetles across corn and soybeans fields in west Tennessee and he doesn’t expect the problem to go away. “This insect was accidentally introduced into the northeastern U.S. almost a century ago and has been making its way our direction ever since,” Stewart says.

He adds that they are a frightening sight. “It’s a big, showy insect that is scary to growers,” says Stewart. “There can be eight or nine beetles per ear of corn with every silk eaten off. It’s an ‘oh-my-gosh’ situation.”

The economic threshold for the beetles in corn is three or more beetles per ear during tasseling and silking when pollination is not complete, says Mike Gray, University of Illinois Extension entomologist. He notes that growers sometimes mistakenly apply insecticides too early; in the wake of bad experiences they’ve seen from damage in the past. 

He encourages growers not to spray for beetle control before pollination. “If soil moisture is not in short supply, silk growth can often keep pace with clipping,” says Gray. “In general, ½-1 in. of silk tissue protruding beyond the ear tip is adequate for pollen reception.

“Under drought conditions, silk clipping will need to be monitored much more carefully. If applied too early, an insecticide may not have enough residual effect to control the beetle adults that may fly into cornfields later. A well-timed single application could work as well as two applications," Gray says.

Scouting for insects is vital to Maupin’s corn and bean program. “I scout and find our biggest problem, then look for insecticide that will cover everything,” he says. “We saw some Japanese beetle defoliation in our area but didn’t see enough of a threshold.”

Stewart reminds growers that the beetles often occur at much higher numbers on the edges of cornfields. “You really need to check the whole field and not base decisions on the outside rows,” he says, adding that silk clipping can certainly influence pollination.

“But our data show it takes continual feeding over days to impact yield. We experimented by clipping silks for 15 straight days once silking began and it had no impact on yield.”

He says growers have sprayed for Japanese beetles in some soybean fields, especially in middle Tennessee and other areas. “If treatment is needed in soybeans to prevent excessive defoliation, most pyrethroids do a good job controlling them,” he says.

Stewart points out several insecticides approved for corn and soybean control of Japanese beetles: Asana XL, Baythroid XL, Brigade, Declare, Fanfare, Mustang Max, Karate or Warrior. He encourages growers to follow the labels.

 

February 2011