Stink Bug Management Presents Late-Season Challenges for Producers
Of the major late-season nut pests, I feel that the stink bug/leaf-footed bug complex is the most difficult and challenging to understand and control for several reasons. Control difficulties are centered on that there are no treatment thresholds; the difficulty in scouting large trees; damage can occur up to and during harvest, and these insects are strong fliers and can easily move into orchards from surrounding host plants.
The kernel-feeding true stink bugs do not reproduce on pecan so adults have to move in surrounding areas. Given these management obstacles, producers need to be a detective to understand the species involved, where they are coming from and time of movement into the orchard.
In Texas, this kernel-feeding pest complex consists of the green, Chinavia hilaris (Say); southern green, Nezara viridula (L.); brown, Euschistus servus (Say); dusky, Euschists tristigmus; and Concheula, Chlorochroa ligata (Say) stink bugs, and the leaf-footed bugs, Leptoglossus phyllopus, L. opposites and L. zonatus.
The characteristic damage caused by this group will be nut drop during the water stage and black spots on kernels at harvest. Unfortunately, most producers do not realize the kernel damage until harvest and unfortunately, this is too late. For producers that sell wholesale, this damage can result in a reduced price for the crop, and for producers who retail, it can result in unhappy customers.
Although a difficult group to manage there are several things that producers can do.
Management of orchard floor vegetation
Although stink bugs and leaf-footed bugs are strong fliers and damaging populations can and do move into orchards during the late season from other host plants, it is still important to manage weeds and orchard floor vegetation to prevent population build up within the orchard. I feel this is especially important for larger orchards. During the early season mid-summer it is easy to find the brown stink bug and the leaf-footed bug L. phyllopus on Gaura parviflora (sometimes called Gaura, Lizard’s tail or Velvet weed). These insects feed on a wide range of plants and will utilize many different hosts during the season. In the book “Stink Bugs of Economic Importance in American North of Mexico” by J.E. McPherson and R.M. McPherson, over 200 plants are listed as hosts for various stink bug species.
Treatment of border rows
In some situations when movement of adults into an orchard can be anticipated such as when row crops are harvested in the area, treatment of the border rows with an insecticide can help suppress populations.
Trap cropping is where an alternate desirable host plant is planted outside the orchard to draw adults away from pecan and into the trap crop; trap crops are then treated with an insecticide as needed. There are various plants that can be used as a trap crop; work in Texas has been with purple hull peas, soybeans and pearl millet. When using trap crops, the idea is to time the trap crop to be attractive just prior to and during the harvest season (September – October). However, there may be some exceptions to this. For example, if a field of early maturing soybeans that will be harvested in early August is near the orchard, then the planting time of the trap crop will need to be timed so it is attractive at the time of harvest.
Insecticide selection for this pest complex will have to be one of the pyrethroid-based insecticides. One important aspect of insecticide selection will be the pre-harvest interval or PHI since these insects can cause damage up to and during harvest. PHI’s for the various pyrethroid compounds can range from 21 days for bifenthrin to as close as 3 days for fenpropathin (Danitol). If livestock is grazing, then neither of these products can be used but the lambda-cyhalothrin base products do have a grazing clearance and a 14-day PHI.