Greenbug numbers remain relatively light to moderate in most fields of early planted wheat (October through the first half of November) or plants ranging from 3 to 6 inches in height. Heavier greenbug numbers have been detected in a few fields, but in most fields numbers are light and sporadic, with the exception of injury to smaller plants that emerged later in tractor tracks.
Greenbugs reproduce rapidly at temperatures between 55 and 95 degrees Fahrenheit and their natural enemies reproduce slowly when temperatures are below 65 degrees. Consequently, the lower temperatures have greatly slowed beneficial insect activity and, with greenbugs unchecked, their numbers can increase rapidly. Therefore, producers should continue to monitor fields for this insect.
Late planted fields or those in which wheat emergence was delayed by dry conditions are more of a concern at this time, since lower numbers of greenbugs can cause economic injury. Inspections should be made at five different sites per 20 acres while walking diagonally across a field. Each inspection site should consist of 1 linear foot of row and the number of greenbugs estimated/recorded at each site. Producers should check fields during the warmest part of the day, when greenbugs are more likely to be exposed on the upper parts of the plant. During the morning hours, colonies of greenbugs are being detected near the base of the plant at or just below the soil surface.
Yellow or brown plants caused by greenbug feeding in spots in the field may indicate a need for treatment. Occasionally, colonies of 25 to 50 greenbugs per foot of drill row can cause economic injury to very small plants. Treatment on larger plants, 3 to 6 inches in height, should be made when greenbug numbers reach 100 or more per linear foot of row. Plants of 4 to 8 inches in height should be treated when 200 or more are found per linear foot of row.
Some insecticides include Lorsban 4E or Nufos 4E at 0.5 to 1 pint/acre, Dimethoate 4E at 0.5 to 0.75 pint/acre, Proaxis at 3.84 ounces/acre, Warrior at 3.84 ounces/acre, Mustang Max at 3.2 ounces/acre, Malathion (5 pounds) at 1.5 pint/acre and Methyl parathion (4 lb.) at 0.5 to 1.5 pint/acre.
Malathion has a seven-day waiting period between application and grazing. Lorsban, Nufos, Dimethoate and Mustang Max have a 14-day waiting period between application and grazing. Methyl parathion requires a 15-day waiting period between application and grazing. Proaxis and Warrior require a 30-day waiting period between application and grazing.
Low temperatures slow the activity and effectiveness of most insecticides. It may take twice as long for an insecticide to kill at 45 degrees Fahrenheit as it would at 70 degrees. For best results, apply insecticides when temperatures are above 50 degrees Fahrenheit.
If an application must be made when temperatures are lower, use the highest rate recommended.
Glen C. Moore is the county extension agent for integrated pest management and entomology.