March 18, 2011 Brown Wheat Mites Hit Area Wheat Fields
Brown wheat mites are developing into a major concern in the Rolling Plains and West Central regions of the state. Dr. Todd Baughman, Extension Agronomist for the Rolling-Plains, reports that no rust or disease is currently visible in Rolling Plains with the main issue being drought and brown wheat mites. Army cutworm has been problem in some fields. Aphids have not progressed to significant levels but dominated by bird cherry oat aphid which could lead to heavy barley yellow dwarf virus later in the season.
Tom Royer with Oklahoma Extension notes in his weekly newsletter that Brown Wheat Mites are also showing up in SW Oklahoma. Many area producers have made the decision to spray, but many others have questioned if the lack of moisture makes that a profitable decision.
The prolonged La Niña drought has set the stage in the winter wheat crop for greenbugs and brown wheat mites to develop. Royer notes that producers need to remain alert to these problems so that their wheat does not suffer dual effects from dry growing conditions plus brown wheat mites.
The mite is small (about the size of this period.) with a metallic brown to black body and four pair of yellowish legs. The forelegs are distinctly longer that the other three pair. Brown wheat mites can complete a cycle in as little as 10-14 days. They attach their eggs to soil particles and will undergo up to three generations each year, but have probably already completed at least one or two by now. Increasing populations will lay red-colored eggs, but spring populations begin to decline in mid-late April when females begin to lay white-colored “diapause” eggs.
Brown wheat mites cause problems in wheat that is already stressed from lack of moisture. They feed by piercing plant cells in the leaf, creating a fine stippling that gives infested leaves a grayish cast. As injury continues the plants turn yellow-bronze, then dry out and die. These mites feed during the day, so the best time to scout for them is in mid-afternoon. They do not produce webbing and will quickly drop to the soil when disturbed.
Brown wheat mite numbers can build up and cause yield loss under dry conditions. Producers should scout fields by direct counts; tap plants over a white sheet of paper and count dislodged mites to get more accurate counts. According to Royer an insecticide treatment is warranted if your field inspection reveals 25-50 brown wheat mites per leaf in wheat that is 6-9 inches tall. An alternative threshold is “several hundred” per foot of row. However, make sure you check your field before deciding to spray, especially after a good rainfall, as this pest is just one hard driving rain away from being killed off.
When wheat prices have been $2.50 to $3.00 per bushel controlling Brown wheat mites typically do not justify the cost of treating. Extension Entomologist Dr. Ed Bynum notes in the current Panhandle Pest Update that our current market prices for wheat may provide opportunities where control is justified. Control decisions will still be dependent on realistic yield potential, control costs (insecticide plus application), and anticipated market value.
Commonly used products include those based on Chlorpyrifos and Lambda-Cyhalothrin. Follow all label directions when using pesticides.