Louisiana soybean producers are experiencing a new type of stink bug that is as damaging as but more difficult to control than green stink bugs and brown stink bugs.
The new stink bug threat (Piezodorus guildini) is referred to as the red-shouldered stink bug, although that's not the correct common name for this species. It acquired the misnomer because of its appearance. Adult Piezodorus guildini have a reddish-orange band across the back, right behind the head (a characteristic also common to another stink bug species). Piezodorus guildini are light green and about a third smaller than a southern green stink bug.
Piezodorus guildini is an established pest of soybeans in South America, especially in Brazil. Research from South America indicates it is as damaging (if not more) as the southern green stink bug. Piezodorus guildini damages soybeans by reducing yield and quality, and it can cause leaf retention.
Piezodorus guildini is not new to Louisiana but it has, until now, never been a major pest of soybeans here. This stink bug was first observed in 2000 in light numbers on south Louisiana's St. Gabriel Research Station.
Populations of Piezodorus guildini first became high enough for insecticide testing in 2002 and 2003. The results were not alarming, but they did show it is more difficult to control than the southern green stink bug.
Heavy populations were first reported this year from south and southeast Louisiana, where early-maturing soybean fields required multiple applications for at best mediocre control. Populations of Piezodorus guildini have since spread into the southwestern soybean parishes and into the lower Delta parishes of northeast Louisiana.
Environmental conditions conducive to an epidemic year and the pest's general tolerance to most insecticide treatments are probably the causes for this stink bug becoming a major pest in 2004.
LSU AgCenter research in 2004 indicates that acephate is the most effective insecticide for control of Piezodorus guildini. Because of the large acreage of late-planted soybeans in some areas of the state, a crisis exemption under Section 18 was declared for the use of acephate on soybeans between Sept. 3 and Sept. 19.
Methyl parathion at high rates also gives good initial control of this species, but lacks any effective residual control.
Jack Baldwin is professor and Extension entomologist with the Department of Entomology, LSU AgCenter.