August 10, 2007

Sorghum leaf with active greenbugs and showing damage from greenbugs.

One of the greenbug's natural predators, the greenbug parasite, develops internally in the greenbug, eventually causing its exoskeleton to swell and change to a tan color.

Greenbugs have been observed and are increasing in numbers in some central Nebraska sorghum fields. They should be monitored closely for the next couple of weeks in case economically damaging populations develop. Predator populations, particularly lady beetles and greenbug parasites, have been found in many fields. The greenbug parasite is highly effective in controlling greenbugs if it gets started early.

The adult parasite is a small wasp that lays eggs inside greenbugs. The immature stage (larva) of the parasite develops internally and ultimately kills the greenbug. Just before completing development, the larva causes the greenbug exoskeleton to swell and change to a tan color. This is the parasite pupal stage, called a mummy. The wasp will emerge from the mummy in 1-2 days.

Because parasites and predators can be highly effective in controlling greenbugs, delay use of insecticides until economic thresholds are reached (see Table 1).

For more information on greenbug management refer to University of Nebraska–Lincoln Extension NebGuide G838, Management of Greenbugs in Sorghum. Most insecticides registered for greenbug control usually provide excellent control. Insecticide resistant greenbugs have occasionally been present in Nebraska but there have not been any recent reports of insecticide failure in Nebraska.

Bob Wright
Extension Entomologist

Table 1. Treatment Thresholds

Plants 6 inches tall to boot stage: Treat if greenbug colonies are beginning to cause red or yellow leaf spotting on most plants; before any entire leaves are killed, and if parasite numbers are low (less than 20% 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% 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% of greenbugs are mummies).