University of Nebraska-Lincoln

INSECT MANAGEMENT GUIDE FOR SORGHUM

Updated May 15, 2000 by ZB Mayo

Index:

Chinch Bugs
Corn Leaf Aphids
Greenbugs
Soil Cutworms
Seed-Attacking Insects

Chinch Bugs

For further information, refer to NebGuide G86-806-A, Chinch Bug Management.

Sorghum Adjacent to Ripening Wheat Field


Chinch Bug Life Stages	Damage to Seedling Plants

Preventing chinch bug damage to sorghum by cultural practices is more reliable than chemical controls. Do not plant sorghum into wheat stubble, or adjacent to winter wheat. Chinch bugs do not feed on legumes, so soybeans are an alternative to sorghum in fields with a high probability of chinch bug infestation.

Research in Nebraska and Kansas indicates that under high infestations, soil insecticides are not highly effective and may need to be supplemented with foliar sprays. Also, these sprays may need to be repeated during migration.

Insecticides for Chinch Bug Control in Sorghum

Corn Leaf Aphids

For further information, refer to NebGuide G96-1284-A, Cereal Aphids.


Corn Leaf Aphid Wingless Adult	Corn Leaf Aphid Infestation in Whorl

Corn leaf aphids rarely cause economic damage to grain sorghum in Nebraska. This bluish-green aphid is narrow-bodied with solid black legs, antennae and cornicles ("tail pipes"). Treatments seldom result in a yield increase that would pay for the cost of treatment - except in times of severe drought stress after heading.

Greenbugs

For further information, refer to NebGuide G87-838-A, Management of Greenbugs in Sorghum

and NebGuide G96-1284-A, Cereal Aphids.

Occurrence and Management

Greenbug Colony and Feeding Damage

Greenbugs are frequent pests in Nebraska sorghum. These small insects are light green, with a darker green stripe down the back. The tips of the legs, cornicles, and most of the antennae are black. Typically they feed on the underside of leaves on larger plants; however, greenbugs may be found in the whorls of seedling sorghum. Resistant hybrids reduce greenbug damage, but sometimes even resistant hybrids will require insecticide treatment.

Although seedling sorghum can be treated at planting time with soil systemic insecticides, or seed treatments, these applications are not suggested. These treatments do not usually prevent mid-to-late season buildup, which normally peaks in late July or early August. Seedling sorghum occasionally is infested with greenbugs in late May or early June. Unless plants are threatened in the seedling stage, it may be best to withhold treatment until greenbug colonies are better established but still small. Foliar treatments have given good control and often have prevented mid-season damage.

The following table summarizes greenbug treatment guidelines at various sorghum growth stages:

Growth stage	Treatment Guidelines
Seedling (0-5 leaves)	Greenbug colonies present on 10-20 percent of plants; visible yellowing or spotting on leaves.
Plants six inches tall to boot	Greenbug colonies beginning to cause red or yellow leaf spotting on leaves of most plants, and before any entire leaves are killed, and if parasite numbers are low (less than 20 percent of greenbugs are mummies.)
Boot to heading	Treat if greenbug colonies are present on most plants and have killed one lower leaf, and if parasite numbers are low (less than 20 percent of greenbugs are mummies.)
Heading to hard dough	Treat if greenbug colonies are present on most plants and have killed two normal-sized leaves, and if parasite numbers are low (less than 20 percent of greenbugs are mummies.)

These guidelines are based more on damage than on greenbug numbers, therefore, they apply to both greenbug resistant and greenbug susceptible grain sorghum hybrids. They are not hard and fast rules. Resistant lines should tolerate greenbug damage better than susceptible lines. Older plants will tolerate more greenbugs, while small or stressed plants will generally tolerate fewer greenbugs.

Forage Sorghum

Forage sorghum is typically planted in early July following harvest of small grains, and runs greater risk of serious greenbug infestation in the seedling stage. For infestations on larger plants, treatment may be justified when 25 percent of the lower leaves have greenbug colonies and are showing signs of feeding damage.

Insecticides for Greenbug Control in Sorghum

Soil Cutworms

For further information on soil cutworms, refer to NebGuide G93-1153-A, Corn Cutworms.


Black Cutworm	Plant Cut Below Ground

Soil cutworms are occasional pests of seedling sorghum. The most common species involved is the black cutworm. This pest is a greasy black or gray worm with a brown head. The cutworm may be over 1 inch long when feeding is completed. Black cutworms feed primarly at night and will hide under debris or in the soil during the day. Young black cutworms feed on above-ground portions of plants while older cutworms cut plants at or below the soil surface.

Insecticides for Soil Cutworm Control in Sorghum

Seed-Attacking Insects

For further information on seed-attacking insects, refer to NebGuide G91-1023-A, Insects That Attack Seeds and Seedlings of Field Crops.


Wireworms	Seedcorn Maggots

For wireworms, seedcorn maggot, and seedcorn beetle, use a planter box seed treatment with lindane or Gaucho-treated seed. Follow label directions for amounts and restrictions.