How to Manage Pests
UC Pest Management Guidelines
DESCRIPTION OF THE PESTS
Stink bugs and other plant bugs occur throughout California, but only reach damaging numbers sporadically. Although they may differ in color and size, stink bugs all have the same overall shield-shaped body. The consperse stink bug is the most commonly found in all pear districts.
Adult consperse stink bugs have gray brown to green bodies with yellow to orange legs, and antennae that have darkened tips. The body and legs are covered with small black specks and the undersurface of the body varies from gray to green. Consperse stink bug eggs are barrel-shaped, pearly white when first laid, turning pink before hatching, and laid in clusters on twigs and leaves. The conchuela is a large, grayish black stink bug with a reddish marginal border and a reddish spot in the middle of the back that distinguishes it from the bordered plant bug. Redshouldered stink bugs are green or brown and may have a red line across the shoulder. Leaffooted plant bug adults are about 0.75 inch long, yellowish brown and have yellow bands across the middle of the back. The back is flat and the hind legs have distinctive, leaflike enlargements.
Stink bugs damage the crop directly by feeding on fruit. Early season feeding results in dimples or irregularly depressed areas on mature fruit. If the feeding occurs after maturity, there is little external evidence other than excrement, which appears as small, brown, tear-shaped drops. Internally, stink bug feeding produces white, pithy areas that turn brown when fruit is peeled. If the spots are the result of stink bug feeding, these pithy areas will be concentrated near the stem end of the fruit. If they resulted from lygus bug feeding, they may be located anywhere on the fruit surface. In pears, these pithy areas are too deep to be removed by ordinary peeling practices and the fruit is unsuitable for canning or fresh market.
Adult stink bugs move from tree to tree and can puncture large numbers of fruit. If they are migrating into the orchard, fruits on trees in outside rows will show the most damage. Frequently, damage by these pests is limited to specific areas in the orchard.
Stink bugs and plant bugs may become more important pests in orchards where mating disruption is used for codling moth control. Infestations of stink bugs depend on the type of vegetation in and adjacent to the orchard. Most infestations occur in orchards with ground covers or adjacent to uncultivated areas; stink bugs move to ground covers in orchards when weeds in uncultivated areas dry. Consperse stink bug is rarely a pest in clean-cultivated orchards surrounded by cultivated lands, unless the land is planted in crops stink bugs favor: wheat, tomatoes, berries, alfalfa, or corn. Monitor weeds in spring and trees in early summer to determine need for treatment.
Reduce weed host plants, listed below, both within and adjacent to the orchard to minimize stink bug problems.
Organically Acceptable Methods
Biological and cultural controls are organically acceptable methods of controlling these pests.
Monitoring and Treatment Decisions
If stink bugs are observed, monitor during the cluster stage in March or April by inspecting host plants located inside and along borders of sampling blocks. Spend about an hour checking the bases of plants for overwintered adult bugs. Favored host plants are mullein, mustard, and dock. If these are not present, bugs may be found on plantain, milkweed, mallow, morningglory, thistles, vetch, velvetgrass, beardgrass, bush berries, everlasting peas, and other broadleaf plants.
If more than five stink bugs are found during the hour, apply a ground spray to the weeds immediately. Depending on the distribution of the bug population, a spot treatment may be adequate. If two to five bugs are found, and if bug damage has been experienced previously in the orchard, a ground spray might be advisable. If fewer than two bugs are found, resample in 7 to 10 days.
Consperse stink bugs can also be monitored beginning in early April with double cone traps baited with an aggregation pheromone. Place traps just outside the edges of the orchard to determine if adults are migrating into the orchard. (For more information, see PHEROMONE TRAPS.) Cut fruit is attractive for feeding. Beginning in May, place cut fruit at the edge of the orchard next to unmanaged or alternate hosts. Check and replace weekly.
In June and early July spend about 30 minutes sampling for adults starting from the edge of the orchard and working your way inward. Also inspect fruit for feeding damage. Examine fruit on the tree for the presence of bugs, excrement, or visible damage. To verify that damage is caused by stink bugs, peel the fruit. If more than three fruits per half-hour of inspection show feeding damage, spots of excrement, or active bugs, treatment probably is required to avoid economic loss by end of harvest. Be sure to take into account preharvest intervals when choosing the treatment material, and apply this treatment to the trees. (For information on sampling stink bugs in conjunction with other pests at this time, see SAMPLING DURING FRUIT DEVELOPMENT.)
Harvest fruit sample
At harvest, assess program by monitoring fruit in the bins for stink bug and other plant bug damage. Sample 200 fruit per bin from 5 bins per orchard (or 20-acre block in large orchards). (For more information regarding this sample, see HARVEST FRUIT SAMPLE.)
UC IPM Pest Management Guidelines:
Insects and Mites
L. G. Varela, UC IPM Program, UC Cooperative Extension, Sonoma County