Have you ever cracked open a pecan from your landscape or orchard and have seen black spots on the kernel? This was more than likely caused by stink bugs, or leaf-footed bugs. The damage occurred when the pecan was forming and was in the developmental stage.
The southern green stink bug, Nezara viridula; the brown stink bug, Euschistus servus; and the leaf-footed bug, Leptoglossus phyllopus are three species that feed on the kernel of the pecan. These insects are part of the Hemiptera order of insects. Stink bugs and leaf-footed bugs overwinter as adults in weedy areas along fence rows and ditch banks. They may also overwinter in leaf litter and under the bark of trees. They become active I the spring as temperature start to rise.
The southern green stink bug is shield-shaped. This insect is approximately one-half to three-fourths of an inch in length and is light green in color.
The brown stink bug is similar in size and shape to the southern green stink bug. The main difference is the color is brown to gray. The outer parts of the body may be outlined with light to dark markings.
The leaf-footed bug is about one-half inch long and is a narrow insect. The leaf-footed bug is brown in color and has flat, leaf-like structures on the hind legs. Infestations of stink bugs or leaf-footed bugs usually occur from September through shuck split.
Stink bugs and leaf-footed bugs suck the sap from developing nuts. Black pits occur when the stink bugs feed prior to the shell hardening of the pecan. Nuts with black pit will drop from the tree prematurely. Kernel spots occur after the shell hardens. Kernel spot is the dark brown to black spots on the kernel. It is most likely not detected until after the pecan has been cracked or shelled. This black spot is often bitter tasting.
Weed control in and near the orchard is helpful to suppress the populations. Some plant trap crops, which lure the stink bug and leaf-footed bugs away from the pecan orchard in September through November. Planting rows of peas, including blackeye, purple hull and crowders, along the outer rows of the orchard in July or August produces a good trap crop for these insects.
Once the crop of peas stops blooming or setting pods, some will apply an insecticide to the trap crop to kill stink bugs and leaf-footed bugs. This controls the bugs before they fly and infest the pecan orchard.
In pecan trees, many late-season pest control insecticides used to control pecan aphid, shuckworm and pecan weevil may also be effective in stink bug and leaf-footed bug control. Products like bifenthrin, carbaryl and permethrin also may be effective for control of these insects in pecan or other areas.
Stink bugs and leaf-footed bugs also infest a number of other crops. Many fruits, nuts and vegetables may be affected by these insects. The economic impact to your crops will warrant control. Be sure to read and follow all label directions when applying any product to mitigate a pest species in your orchard, landscape or garden.
As with any pest, monitor the crops and trees to determine how severe the infestation is. When most insects become adults and begin flying, they are usually more difficult to control. Most insect pest species are much easier to control, in most cases, when they are young and immature.
Copies of an Extension publication, “Homeowner’s Guide to Pests of Peaches, Plums and Pecans,” by Allen Knutson, Kevin Ong, James Kamas, Bill Ree and Dale Mott are available upon request from our office.