Ashleigh M. Faris
Cropping Systems Extension Entomologist
Department of Entomology & Plant Pathology
Oklahoma State University

Wheat producers in central Oklahoma are reporting the presence of the greenbug, Schizaphis graminum, in winter wheat fields. Greenbugs are one of the most important insect pests of wheat in the southern Great Plains and can occur from fall through spring. These aphids feed on plant sap and inject toxins into wheat plants, causing characteristic leaf discoloration and plant injury.

Early detection through field scouting is essential to determine whether populations are increasing and if an insecticide treatment is justified.

Greenbug Identification & Biology

Key identifying characteristics of greenbug (Figure 1):

• Small aphids (~1/16 inch long)
• Pale to lime-green body
• Dark green stripe down the middle of the back
• Dark tips on antennae and legs
• Found in colonies on the underside of wheat leaves

Greenbugs reproduce rapidly under favorable conditions (between 55° F and 95° F) and often occur in patches within fields rather than evenly distributed populations. During periods of cool weather, the greenbug may increase to enormous numbers, due to the absence of natural enemies, which develop significantly slower compared to greenbugs at such temperatures. On the other hand, cold weather can also influence aphid populations. However, this latest cold snap is not enough to eliminate greenbugs. It takes average temperatures below 20° F for at least a week to kill a substantial number of greenbugs in wheat.

Greenbug Damage in Wheat

Greenbugs damage wheat in two ways, through direct feeding and injection of toxic saliva. Greenbugs may also transmit barley yellow dwarf virus (BYDV), which can further reduce yield potential.

Typical early symptoms include small, reddish or copper spots on leaves (Figure 2) and yellowing around feeding sites. Advanced infestations will result in leaves turning yellow or orange, dead leaf tissue, stunted plants, and expanding patches of dead wheat. Heavy infestations may kill seedlings and reduce tillering, particularly during drought stress.

How to Scout for Greenbugs

The Glance-N-Go™ sampling system developed by Oklahoma State University can help determine whether aphid populations exceed economic thresholds. Download the Greenbug Glance N’ Go Sampler app for your smartphone. You will then input the control cost ($/Acre), crop value ($/Acre), and the Spring sampling window. Use a zig-zag or W-pattern (Figure 3) to scout your field, checking undersides of leaves at three tillers per stop for greenbugs and brown mummies. Use the app to record the numbers of these insects and sample until the app tells you to stop sampling or tells you treat. As temperatures warm, continue to scout regularly as greenbug populations may build.

Scouting recommendations without the Greenbug Glance N’ Go Sampler app:

1. Walk a W or zigzag pattern across the field.
2. Examine 10–20 plants at each stop.
3. Check:
   • Underside of leaves
   • Leaf midrib
   • Base of tillers
4. Record:
   • Aphids per tiller
   • Presence of aphid mummies (Figure 4)
   • Beneficial insects

Beneficial Insects

Natural enemies frequently control aphid populations. While scouting for greenbug you should also look for lady beetles, lacewing larvae, hoverfly larvae, and parasitized aphids (“mummies”) (Figure 4). If beneficial insects are abundant, aphid populations may decline without insecticide treatment. Where there are one to two lady beetles (adults and larvae) per foot of row, or 15 to 20 percent of the greenbugs have been parasitized, control measures could be delayed until it is determined whether the greenbug population is continuing to increase.

Based on current wheat scouting, it appears that parasitoid numbers are low this 2026 season so continuing to scout for greenbug will be critical in responding to populations that go unchecked by beneficials.

Economic Threshold Guidelines

The simplest way to determine if action needs to be taken against greenbugs is to utilize the Glance-N-Go™ sampling system developed by Oklahoma State University. Approximate guidelines historically used in Oklahoma wheat can be found in Table 1 below.

Thresholds are influenced by:

• Wheat growth stage
• Crop value
• Cost of treatment
• Presence of beneficial insects

Insecticides Labeled for Greenbugs in Wheat

Aphid feeding and insecticide performance are strongly influenced by temperature. Greenbugs tend to move higher on wheat plants during warm conditions but may move lower on the plant or below ground during cold weather, reducing exposure to insecticides. As a result, damaging populations are most often observed in late winter and early spring. Insecticides generally perform best when temperatures are above 50°F, and control may occur more slowly in cooler conditions (e.g., control at 45° F may take roughly twice as long as at 70° F). If applications must be made under cooler temperatures, use the highest labeled rate. Wheat grown under irrigation can typically tolerate higher greenbug populations than dryland wheat.

Always follow pesticide label directions, application sites, and rates. Be sure to read and follow the label for preharvest intervals (PHI) and restricted-entry intervals (REI). Use a minimum of 10 GPA by ground and 3 GPA by air (if labelled for aerial application) to ensure adequate coverage.

For assistance with aphid identification or treatment decisions, see OSU Fact Sheet EPP-7099 Small Grain Aphids in Oklahoma and Their Management, or contact your local OSU Extension office.

Cropping Systems Extension Entomologist Dr. Ashleigh Faris.