Several species of stinkbugs feed on and dam- age wheat during flowering and grain fill, including the rice stinkbug, southern green stinkbug, several species of brown stinkbugs, and in West Texas, the conchuela stinkbug (Fig. 32). Stinkbugs have pierc- ing-sucking mouthparts that penetrate the develop- ing kernel. The insects’ feeding on immature grain can reduce germination, kernel weight, and baking quality. The periods most susceptible to stinkbug feeding and damage are the flowering and milk stages. Once the grain is in the soft dough stage, it is less susceptible to damage from stinkbugs.
In a research study, one rice stinkbug per 10 wheat heads (spikes) during the milk stage signifi- cantly reduced germination and kernel weight. During the soft dough stage, no significant reduc- tion in germination or kernel weight was found until at least three rice stinkbugs per 10 heads were present. Similar results were observed for southern green stinkbug. These results suggest that if rice or green stinkbugs average one or more per 10 heads during the flowering or milk stage, apply an insec- ticide to protect the crop from damage. During the soft dough stage, consider treatment if infestations average 3 or more per 10 heads. An infestation of 1 stinkbug per 10 heads is a high infestation. Stink- bugs are usually not distributed uniformly within a field. Instead, they are often more abundant in local areas, often near field margins. To accurately assess the infestation before deciding on treatment, scout several areas of the field.
Fully developed beet armyworm larvae (Spodop- tera exigua (Hübner)) are 1¼ inches long. They are light green with a conspicuous black spot on each side of the thorax above the second pair of tho- racic legs (Fig. 33). Damaging populations are most likely to occur in late summer or early fall when hot, dry conditions inhibit the growth of preferred hosts, forcing the moths to deposit egg masses on young, small grains.
Compared to other caterpillar pests, beet armyworms are more difficult to control with insecticides. Choose an insecticide that lists beet armyworm on the label. Fields planted after mid- October usually escape beet armyworm infestation.
Chinch bug and false chinch bug
Adult chinch bugs (Blissus leucopterus leucopterus (Say)) are about 1⁄8 inch long. The body is black, but the wings are mostly white with black triangular spots at the
middle of the outer margin (Fig. 34).
Young chinch bugs are shaped like the adults. They are red at first but turn darker as they mature. They have a white band across the abdomen (Fig. 34).
In early spring, chinch bugs move into small grains from bunch grass, where they overwinter. Young and adult chinch bugs feed on small grains, and very heavily infested plants may be stunted or killed. Infestations are usually confined to small, well-defined spots. When a damaging infestation occurs on the field border, prompt treatment may prevent infestation of the entire field.
Adult false chinch bugs (Nysius raphanus (Howard) are 1⁄8 inch long, narrow, and a dull yellowish gray (Fig. 35). 35). The wing tips are transparent and extend beyond the end of the abdomen. These insects often increase in the spring on weedy plants in the Mustard family and then migrate in large numbers to other crops, including small grains.
False chinch bugs suck sap from the stems and heads of small grains. This feeding may cause poorly filled heads and shriveled grain, but the extent of their damage is not well documented. Before applying insecticide, consider the per- centage of the field infested and make sure that these bugs are feeding on the small grains and not just migrating through.
Several species of grasshoppers are occasional problems in Texas small grains (Fig. 36). Most damage occurs in the fall when these pests migrate into fields.
Before planting, check the areas around the wheat fields for heavy infestations. Treat them before the planted wheat emerges. Some insec- ticides applied as seed treatments are labeled for grasshopper control.
Flea beetles (Phyllotreta cruciferae (Goeze)) are black, shiny, and about the size of a pinhead (Fig. 37). They jump readily when approached. In the fall, these beetles may infest the borders of a field and gradually move across it, feeding on and killing plants as they go. They skeletonize the leaves, giving injured plants a bleached appearance before they wilt and die.
Fields and field borders that have been kept clean of weeds during the previous season are less subject to flea beetle damage.
Wheat Stem Maggot
The second-generation wheat stem maggot (Meromyza americana Fitch) produces adult flies that emerge in the spring and lay eggs on the leaves of barley, oats, rye, wheat, and other grass hosts.
The developing larvae, or maggots, feed on the stem just above the last stem joint, cutting the flow of moisture and nutrients to the head (Fig. 38). The head turns from green to tan to white, but the leaf sheath and stem below where the maggots have tunneled remain green. These white heads are eas- ily pulled from the plant.
Because the infested tillers seldom exceed 1 per- cent of the wheat, insecticide treatments are rarely, if ever, necessary.
Pale Western Cutworm
The pale western cutworm (Agrotis orthogonia Morr.) is a subterranean cutworm that feeds almost entirely on the stems of the wheat crown just below the soil surface. The larvae prefer loose, sandy, dry, or dusty soil.
Evidence of caterpillar feeding includes wilted leaves, thinning stands, and dead tillers (Fig. 39). When the infestation is severe, the larvae can destroy a field in a matter of days.
In late summer and fall, the adult moths emerge and deposit up to 300 eggs per female in cultivated soil. Although some eggs may hatch in the fall, most hatch in late winter or early spring. After developing in the spring, the mature larvae (Fig. 40) burrow into the soil to transform into a pre-pupa. This stage over-summers until pupating in August. Because dry weather favors the survival of pale western cutworms, outbreaks may follow dry springs.
Consider treating if you find one larva per square foot when the potential for yield is good, and 2 larvae per square foot when the potential for yield is low.
Sometimes during dry weather in late fall, the aster leafhopper and other leafhopper spe- cies migrate in large numbers into fields of small grains. These pests apparently increase on wild hosts and move into small grains to feed on succulent plants. Leafhoppers suck sap from the leaves. When infestations are large, the fields can look silver. Infestations often decline after freezing tem- peratures. Insecticide recommendations have not been developed for leafhoppers infesting wheat.