Ashleigh Faris, Cropping Systems Entomologist, IPM Coordinator
Department of Entomology & Plant Pathology,
Oklahoma State University

Following a period of dry weather, wheat growers in central Oklahoma are reporting activity of the Brown Wheat Mite (BWM). Unlike many other wheat pests, BWM thrives in drought conditions, and its damage can often be mistaken for moisture stress or nutrient deficiency.

Identification

The Brown Wheat Mite is small—about the size of a needle point—but is generally easier to spot than the Wheat Curl Mite because it is active on the leaf surface.

• Appearance: BWM has a dark red to brownish-black, oval-shaped body (Figure 1).
• Distinguishing Feature: Its front legs are significantly longer than its other three pairs of legs.
• Behavior: They are most active during the day, particularly in the afternoon, and will quickly drop to the ground if the plant is disturbed (Figure 2).

Figure 1. Brown wheat mite (BWM).

Figure 2. Brown wheat mites (BWM) on wheat. Image courtesy L. Galvin, OSU Extension.

Biology and Life Cycle

BWM populations consist entirely of females that produce offspring without mating (parthenogenesis), allowing for extremely rapid population growth under dry conditions. The BWM has a unique life cycle in that it can lay two types of eggs. Environmental conditions dictate when these two types of eggs are laid:

• Red Eggs: Laid during the growing season and hatch in about a week when conditions are favorable.
• White (Diapause) Eggs: Laid as temperatures rise and the crop matures. They are highly resistant and allow the population to survive the summer heat, hatching only when cooler, wetter weather arrives in the fall.

Damage

BWM damage is caused by the mites piercing plant cells and sucking out the plant nutrients.

• Symptoms: Initial damage appears as “stippling” (fine white or yellow spots) on the leaves. As feeding continues, leaves take on a silvery or bronzed appearance (Figure 3).
• Tipping: Heavy infestations cause the tips of the leaves to turn brown and die.
• Weather Interaction: Damage is most severe when plants are already under drought stress. Because both BWM damage and drought cause yellowing/browning, it is essential to confirm the presence of mites before treating.

Figure 3. Brown wheat mite (BWM) damage.

Scouting

Because BWM is highly mobile and drops when disturbed, careful scouting is required:

• Timing: Scout during the warmest part of the day when mites are most active on the upper leaves.
• The Paper Test: Gently but quickly shake or tap wheat plants over a white piece of paper or a white clipboard. Look for tiny dark specks moving across the surface.
• Economic Threshold: While thresholds vary based on crop value and moisture stress, research suggests a treatment threshold of 25 to 50 brown wheat mites per leaf in wheat that is 6 inches to 9 inches tall is economically warranted. An alternative estimation is “several hundred” per foot of row. If the wheat is severely stressed, the lower end of that threshold should be used.

Management Recommendations

• The “Rain” Factor: A significant, driving rain is often the most effective control for BWM. Rain can physically knock mites from the plant and promote fungal pathogens that naturally reduce the population.
• Chemical Control: If populations exceed the threshold and no rain is in the forecast, chemical intervention may be necessary. Know the cost of the treatment and value of your wheat so you can determine if an application is a worth return on investment.
  • Effective Ingredients: Organophosphates (such as Dimethoate) have historically provided better control than many pyrethroids, as the latter can sometimes result in mite “flaring” or simply fail to provide adequate residual control.
  • Coverage: High water volume is critical to ensure the insecticide reaches the mites, especially if they have moved toward the base of the plant.
  • Pre-harvest Intervals & Grazing Restrictions: Always read and follow the label guidelines. For more on acaricides that can be applied in wheat see the Oklahoma State University Fact Sheet “Management of Insect and Mite Pests in Small Grains” (CR-7194).
• Cultural Practices: Since BWM thrives in dry, dusty conditions, maintaining good soil moisture and vigorous plant growth can help the crop tolerate feeding. Here’s to hoping for some rain soon in the forecast; we could really use it for lots of reasons in Oklahoma.