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Two stem borers are sporadic rice field pests: the rice stalk borer (Chilo plejedellus) and sugarcane borer (Diataea saccharalis). Rice stalk borer adult moths are about 1 inch long with pale white fore and hind wings tinged on the edges with metallic gold scales. Front wings are peppered with small black dots. The larvae hatch from eggs laid on leaves and crawl down the leaf toward the stem, where they may feed for a short time on the inside of the leaf sheath before boring into the stem. Larvae are pale yellow-white with two pairs of stripes running the entire length of the body. This distinguishes them from sugarcane borer larvae, which have no stripes. Larvae are about 1 inch long. Sugar cane borer moths are straw-colored with a series of black dots, arranged in a V-shaped pattern, on the front of the wings. The adults are about 1 inch long. After hatching, the larvae crawl down the leaf and bore into the plant stem, where they move up and down and feed for 15 to 20 days. Larvae are pale yellow-white in the summer with a series of brown spots visible on the back. Overwintering larvae are a deeper yellow and lack the brown spots. Though both begin egg laying as early as May, most injurious infestations don’t occur until late summer.
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The adults (Lissorhoptrus oryzophilus) are grayish-brown snout beetles about 1/8 inch long with a dark brown V-shaped area on their backs. In the spring, the adults leave overwintering sites in ground litter and bunch grasses and migrate to rice fields during early evenings. Females lay eggs in the stems of submerged rice. The larvae, sometimes called maggots, are white, legless and C-shaped. They range from 1/32 to 3/16 inch long. After feeding on the leaf sheath for a short time, they drop through the water to the soil and begin feeding on the roots. One larva per plant can reduce yields by 80 pounds an acre, according to data collected in Texas.
Rice is attacked during the seedling and tillering stages before flooding. Caterpillars hatch from egg masses deposited by female moths (Spodoptera frugiperda) in the field or move into rice from adjoining areas. Larvae are light tan to greenish to brownish and about 1 1/2 inches long when fully grown. They have three yellowish-white, hair-like stripes on the back, a conspicuous inverted "Y" on the head and prominent black tubercles from which hairs arise. Small larvae are hard to detect. Older larvae feed on leaf blades and can severely reduce plant stands. The action threshold is about 25 percent defoliation or when stands are threatened.
Adult rice stink bugs (Oebalus pugnax) overwinter near the ground in heavy grasses. In the spring, the straw-colored, 3/8- to 1/2-inch long adults become active. A sharp spine on the shoulder helps distinguish this pest from other stink bugs. Females lay two rows containing 10 to 50 cylindrical light green eggs on foliage of heading grasses. The nymphs - which at first have a bright red abdomen with black head, thorax and legs - lack wings. Rice stink bug feeding reduces both the quantity and quality of grain. Adults and nymphs have piercing-sucking mouth parts, which they use to feed on the kernel. Rice stink bug feeding causes kernel discoloration, called pecky rice. But not all pecky rice is caused by stink bugs. Pecky rice is more apt to break during milling than undamaged rice.
Chinch bugs (Blissus leucopterus) overwinter in grasses or leaf litter as adults that are about 1/8 to 1/6 inch long. Females are larger than males, and both are black and about three times longer than they are wide. Each wing has a triangular black spot near the outer margin. Newly emerged rice is most susceptible to damage. Symptoms include striping, stippling and yellowing of leaves. An average of one chinch bug per seedling can cause mortality, reduction in height and delay maturity in surviving plants. Inspect rice frequently from emergence until three weeks later. Look for adults on foliage and behind leaf sheaths, inspect the stem and probe the soil around the plant.