We have been monitoring Asiatic garden beetle grubs (AGB, Maladera castanea) in Northwest Ohio since 2012. Typically known as a turf pest, the grub has caused varied economic damage to corn in Northwest Ohio since then. While 2014 remains the worst year for their damage to date, there were isolated outbreaks—including in soybeans--of the grub in 2015 but generally they had limited impact, perhaps due to weather related conditions. This year we noticed their presence as early as May 6th, after a period of warm weather in late April. Since then, limited root feeding and overall impacts on corn stand have not been seen like in previous years. What could be the cause? Most of Northern Ohio became cool and wet after the first full weekend in May when some corn was planted. However, the majority of corn was not planted until the 3rd or 4th weeks of May. Generally, we believe that the life cycle of the AGB was ahead of corn planting or growth to see negative impacts. We typically observe less AGB damage in later planted fields. Recent digs for the grub have turned up fewer, but more lethargic, grubs indicating possible earlier pupation or control from in furrow insecticidal treatments.
|A dead AGB grub (left) next to a healthy grub in the same dig.
Identification and scouting: This beetle has four life stages: egg, larva (or grub), pupa and adult. The grubs that are present now represent the third instar larva. 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. 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 ). AGBs are typically smaller and more active than other grubs and also have white, maxillary palps (bubble) near their mouth (CORN Newsletter 2013-15), see photo 1. If uncovered from the soil surface, the g+rubs try to move quickly back underneath the soil. Damaged fields often have gaps in rows, and affected corn often appears wilted and stressed.
Strategies for Control: While there are no perfect treatments for controlling AGBs, here are some thoughts to consider. The mis-matched timing of the AGB life cycle and later corn planting and emergence appears to be helpful this year. While there was no statistical difference in yield after using in-furrow insecticide in 2014 On Farm Research (https://agcrops.osu.edu/sites/agcrops/files/ofr_reports/2014%2520Fulton%2520AGBproducts.pdf), we can find dead or dying grubs when soil insecticides are used in furrow at planting (see yellowing AGB larva in photo 2). Fields with low to moderate pressure may benefit from an insecticidal seed treatment, although more data is needed for both control tactics. Finally, if stand loss occurs, consider replanting corn (See replant calculator: http://web.extension.illinois.edu/csrec/eb260/entry_6903/). If you have questions on this new pest, please contact Eric Richer (firstname.lastname@example.org), Andy Michel (email@example.com), or Kelley Tilmon (firstname.lastname@example.org).