Grubs of the Asiatic garden beetle (Maladera castanea) have been making their presence known in Northwest Ohio corn fields since 2012. For a long time this grub has been a pest in the lawn and turf industry, but in past few years it has severely damaged corn. This beetle is similar to most in its life cycle having four stages of egg, larva (or grub), pupa and adult. Currently, the third instar larva are feeding on root systems, specifically the mesocotyl. Damaged fields often have gaps in rows, and affected corn often appears wilted and stressed.
In Ohio, damage appears to be most prevalent in sandier soils, which are concentrated in NW Ohio, but can also be found in isolated areas near sandy river beds.
This year we have been seeing them since approximately the third week of May, and now is the time to scout for this pest. Look for corn in sandy soils that appear to have uneven growth stages, are wilting, or with gaps in the row. Dig around the plant and look for the presence of white grubs (see the video here: http://www.oardc.ohio-state.edu/ag/pageview3.asp?id=3787 ) and photos here.
Asiatic garden beetles are typically smaller and more active than other grubs and also have a white “bubble” near the head. If uncovered from the soil surface, the grubs try to move quickly back underneath the soil. At this point in time, the grubs can be found within the first 1-2 inches of soil and often create tunnels around the root system of the corn—you may also find them in between rows. In the mid June we anticipate the larva to pupate and by July, adult beetles will begin emerging to lay eggs all over again.
While the turf and ornamental industry has dealt with these insects for some time, we have much to learn about this insect, its management and the thresholds for economic damage as they relate to growing corn. While there are some ways to trap for Asiatic Garden Beetle larva, at this point in time, it is just necessary to get out into your corn fields and dig for the larva in those sandier soils. We suggest starting with your no-tilled fields and fields without soil applied insecticide first. We are still making observations and at this time there doesn’t seem to be any “silver bullets” for controlling this pest. Many things are part of the discussion and research plots including tillage, seed treatments, insecticide, rotational programs and more. There are also no rescue treatments available besides replanting. Please conduct a stand count before considering replanting. It is suggested to use the re-plant calculator (http://web.extension.illinois.edu/csrec/eb260/entry_6903/), written by Emerson Nafziger and Bob Nielson, from Illinois and Purdue, respectively. If you have questions on this new pest, please contact Eric Richer (firstname.lastname@example.org) or Andy Michel (Michel.email@example.com).