How to Manage Pests

UC Pest Management Guidelines

DESCRIPTION OF THE PESTS

Spider mites resemble tiny spiders, no larger than a pin head. Nearly identical in appearance, the carmine mite occurs on sugarbeets primarily in the Imperial Valley and the twospotted spider mite is more common in other beet-growing areas of California. When newly hatched, spider mites have three pairs of legs but as they mature, they develop four pairs. They vary in color from nearly transparent to yellowish, greenish, or even red. They have two darkly pigmented spots, one on each side of the body. While visible to the unaided eye, they are best seen and identified with the use of a 10X hand lens. Both species cause similar damage and are managed in the same manner.

DAMAGE

Mites feed on the undersurface of the leaf. They puncture cells on the leaf surface and feed on the sap from leaves, leaving them blotched with white or pale yellow spots, which range in size from mere specks to larger areas as the specks coalesce. The damage is visible on both the upper and lower surface of the leaf. Spider mites spin very fine webs over the surface that become prominent as the number of mites per leaf increases. Severe infestation can cause defoliation.

MANAGEMENT

Spider mites are usually controlled by predatory insects and mites. Outbreaks are often the result of plant stress or dusty conditions. Mature sugarbeets can tolerate dozens to hundreds of mites per leaf without significant reductions in yield or quality. Treatments may be necessary on early and mid-season sugarbeets although treatment thresholds have not been established.

Biological Control
Spider mites have numerous predators including lacewings, assassin bugs, damsel bugs, minute pirate bugs, bigeyed bugs, and sixspotted thrips. Predatory mites are often found attacking spider mites. Predatory mites can be distinguished from spider mites by their slightly larger size and a more flattened, pear-shaped appearance. Predatory mites are clear, lacking any spots or coloration. These natural enemies can keep spider mite populations in check and may bring spider mites under control. Always check for their presence when you find mites in your fields.

Cultural Control
Mites are more serious on stressed plants, particularly water-stressed or dust-covered plants. Outbreaks may occur as a result of foliar applications of organophosphates, carbamates, and pyrethroids used to control other pests such as armyworms. Avoid using these insecticides where possible and observe good cultural practices including adequate nutrition and irrigation.

Monitoring and Treatment Decisions
There are no economic thresholds for spider mites. If numbers continue to increase in spite of the presence of biological control agents and injury becomes severe, treatments might be necessary.

PUBLICATION

UC IPM Pest Management Guidelines: Sugarbeet
UC ANR Publication 3469
Insects and Mites
E.T. Natwick, UC Cooperative Extension Imperial Co.
Acknowledgement for contributions to Insects and Mites:
C. G. Summers, Entomology, Kearney Agricultural Center, Parlier
D. R. Haviland, UC IPM Program, Kern Co.
L. D. Godfrey, Entomology, UC Davis

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