|Chinch Bug: Blissus leucopterus leucopterus (Say)|
|Description and Biology: Nymphs of chinch bug are pale yellow when hatched but soon become red except for the first two abdominal segments are remain pale. Subsequent instars become darker red but retain a pale yellow band across the front part of the abdomen. The last nymphal instar is black and gray with a conspicuous white spot on the back between the wing pads. The 4.2-mm-long adult chinch bug is black, with reddish yellow legs, and conspicuous white forewings, each of which has a black triangular spot at the middle of the outer margin. Chinch bugs overwinter as adults in bunch grass. In spring they migrate from overwintering sites to small grains where they lay eggs of the first generation. Nymphs of this generation migrate to sorghum and other hosts such as corn. In south Texas, adults may move directly from overwintering site to sorghum without first infesting small grains. Chinch bug eggs are laid behind lower leaf sheaths of host plants, on roots, or in the ground near hosts. The life cycle is completed in 30 to 40 days. A second generation disperses within host crop fields, and in south Texas there may be an additional generation.|
|Symptoms and Damage: Adult and immature chinch bugs damage plants by withdrawing large amounts of plant juices from stems or underground plant parts. Young plants are highly susceptible to damage. Older plants withstand more chinch bugs than smaller plants, but they, too, become reddened, weakened, stunted, and frequently lodge. Chinch bug outbreaks are favored by dry weather.|
Monitoring: Chinch bugs coming from small grains or directly from wild host plants infest sorghum in early spring. Careful examination of plants, especially behind leaf sheaths, and the soil around plants is required to locate chinch bugs. Examine at least five plants at random sites per field. Because chinch bugs often feed on small plants below the soil surface, especially in loose, dry soil, carefully examine bases of plants below the soil surface. On large plants, chinch bugs are most commonly found behind the leaf sheaths. Insecticide should be applied when two or more adult chinch bugs are found on 20% of seedlings less than 15 cm tall. On taller plants, control may be warranted when there are four to five immature and adult bugs per plant. Generally, one chinch bug per seedling sorghum plant results in approximately 2% grain yield loss. Fifteen chinch bugs per plant can cause as much as 33% reduction in crop value.
Management: Cultural practices that stimulate dense, vigorous sorghum stands are recommended because these conditions are less favored by chinch bugs and injury is reduced. Sorghum should be planted as early as possible. Chinch bugs sometimes are difficult to control with insecticide. Systemic insecticide applied to seed or at planting for soil insect pests will control chinch bugs. In fields with a history of economically damaging infestations of chinch bug, treatment with at-planting, soil-incorporated insecticide may be justified. Granular products must receive about 13 mm of rain after application to be effective in suppression of early season chinch bug infestations. If infestations after plant emergence reach the economic threshold, post-emergence insecticide treatment may be justified. When using ground application equipment, insecticide should be applied in at least 93.5 liters of water per hectare through nozzles directed at the base of plants. Satisfactory control seldom is obtained on plants in the boot stage or later. Aerial insecticide application seldom is effective and is not recommended.