Description of the Pest
Ground mealybug is a small, whitish insect found on the roots of alfalfa and other crops. It is restricted to the heavier soils of the Sacramento Valley and is not found in the San Joaquin or Imperial valleys.
The ground mealybug has slender, waxy filaments that form a sort of netting over some individuals. The ground mealybug also secretes a small amount of wax, which can give the soil a somewhat bluish appearance when the mealybugs are abundant. There are three generations per year with numbers peaking in the early winter, spring, and mid-summer periods. The eggs, nymphs and adults all occur in the soil.
The ground mealybug feeds on alfalfa roots and can cause severe yield losses. Feeding interacts with stressful environmental conditions, resulting in greatly reduced plant growth that is particularly evident during summer. Infestations in alfalfa fields generally occur in "circular" patches and spread slowly, as the mealybugs feed on their hosts and move out from a central infestation point.
The best place to monitor for ground mealybug is right at the line between healthy and unhealthy plants. Look for bright white tiny insects that crawl around the roots, about 6-12 inches in the soil.
There are no thresholds or control measures for this pest. Crop rotation may help, but this pest appears to survive on several crop plant and weed species. Because there is differential survival across host species, rotation to a less preferred host may aid in management. In a greenhouse study, greatest survival was on potato, tomato, safflower, and alfalfa, followed by cotton, cantaloupe, dryland rice, sugarbeets, and wheat. There was only slight survival on field corn and kidney beans. However, there were no plant species without some level of survival.