Thursday, May 01, 2014

White Grubs and Wireworms in Wheat Fields Require Special Treatment to Defeat

Contact: Jill Scheidt, agronomy specialist
Headquartered at Barton County Extension Center
Tel: (417) 682-3579

LAMAR, Mo. – A wheat field east of Carthage was scouted on April 30 by Jill Scheidt, agronomy specialist with University of Missouri Extension.

According to Scheidt, white grub and wireworm damage was seen in corn at the two and four-leaf stage. “Anywhere from five to 10 percent damage was only on the three outside rows on the edge of the field I scouted,” said Scheidt.

According to Scheidt, wireworms will eat on roots then bore through the base of corn plants and seeds. Wireworms are about one-half to one and one-half inches long, segmented, shiny and wire like, ranging in color from yellow to reddish brown.

White grub feeding is similar to black cutworm feeding, look for clipped plants. A bronze colored head and a white body help identify white grubs; they normally curl into a “C” shape.

“White grubs chew roots and seeds causing wilting of leaves and stunting of plants. No threshold levels or post-emergence or rescue treatments are available for either pest, as they usually do not cause significant yield loss,” said Scheidt.

At this point, only pre-plant, at-plant and seed treatments exist. Both pests occur in fields that were previously sod or near grassy areas.

Scheidt found no damaging freeze injury; wheat heads look healthy and white to light green when the stem is split open.

“I have not seen any diseases in wheat to warrant a fungicide. If fields have wet spots or low places with prolonged moisture look for root and crown rot diseases,” said Scheidt.

Scheidt found about 15 to 20 bird cherry oat aphids per foot of row in wheat. The threshold level for bird cherry oat aphids is 12-15 per foot of row. Bird cherry oat aphids have a red band around their rear and are olive green colored; they vector barley yellow dwarf virus which can cause stunting and sometimes severe yield loss.

According to Scheidt, Mustang Max and Warrior II are the most effective insecticides to use for aphid control in wheat. Temperatures need to be above 60 degrees to spray an insecticide.

The weekly field scouting report is sponsored by University of Missouri Extension and Barton County Extension. For more information on this scouting report, or to learn how to receive it a week earlier by telephone, contact the MU Extension Center in Barton County, (417) 682-3579.


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