|Panicle-Feeding Bugs: Rice Stink Bug, Oebalus pugnax (Fabricius); Southern Green Stink Bug, Nezara viridula (L.); Conchuela, Chlorochroa ligata (Say); Leaffooted Bug, Leptoglossus phyllopus (L.); False Chinch Bug, Nysius raphanus Howard|
Description and Biology:
Several species of true bugs, primarily stink bugs, may move in relatively
large numbers from cultivated and noncultivated host plants to sorghum
during kernel development. The bugs usually have a clumped distribution
in a field.
Symptoms and Damage: The bug species described above have similar nature and symptoms of damage. These bugs suck juices from developing sorghum kernels and, to a lesser extent, from other panicle parts. They may cause economic damage, depending on the number of bugs per panicle, duration of the infestation, and stage of kernel development when infestation occurs. The number of bugs that will reduce grain yield varies according to the species of bug and stage of kernel development when infestation occurs. Bugs cause more damage during early kernel development and less damage as kernels develop to the hard-dough stage. Both nymphs and adults can reduce kernel weight, size, and quality. Fungi often infect damaged kernels, causing them to turn black and be further deteriorated in quality. Damaged kernels rarely develop fully and may be lost during harvest with mechanized equipment.
Rice Stink bug
Southern Green Stink Bug
False Chinch Bug
|Monitoring: Accurately estimating numbers of panicle-feeding bugs per plant is affected by the tendency of these insects to congregate on sorghum panicles and within areas in a field. The beat-bucket technique described above for monitoring corn earworm can be used to estimate the average number of bugs per panicle. However, adult bugs will fly from the sampled plant and from the bucket. Plant leaves and weeds in the field also should be inspected for bugs. At least 30 plants from the whole field should be inspected to ensure reasonable reliability of sample estimates. Fields larger than 32 hectares should be subdivided for sampling into areas no larger than 32 hectares.|
|Management: Infestation in sorghum usually
occurs when other hosts become unacceptable or unavailable. Early planting
of sorghum helps avoid bugs migrating from other host plants. Not all species
of stink bugs found in sorghum cause economic damage. Several species prey
on harmful insects and, thus, are beneficial.
Sorghum kernels in the hard dough stage are usually not damaged by bugs. For most of the bug species, an infestation level per panicle of over sixteen bugs would be required to justify insecticide treatment at the hard dough stage of kernel development. The economic injury level for rice stink bugs ranges from four to nine and five to 13 at the milk and soft-dough stages, respectively. Insecticide applications would be justified when there are two to six or four to 11 per panicle at the milk and soft-dough stages of kernel develop, respectively, for southern green stink bugs, conchuela, or leaffooted bugs per panicle. The economic injury level for false chinch bug is 140 per panicle when infestations begin at the milk stage of kernel development.