While many poinsettia growers come to expect pests like whiteflies and fungus gnats in their greenhouses, most are not on the lookout for mites. However, the Lewis mite (Eotetranychus lewisi) has begun to crop up around poinsettia operations in recent years, and can develop a major infestation before detection. Because this is a relatively uncommon pest, we have compiled all the information you need to know about the Lewis mite, and how to safely combat an infestation using beneficial insects.

The Lewis mite has a generally similar appearance to the two-spotted spider mite (Tetranychus urticae), but is smaller (0.25-0.36 mm long) and has multiple spots (instead of the signature two spots on the spider mite). Eggs are round, and white to light orange in color. Females will lay 60-90 eggs in the span of about a month. It takes 12-14 days to cycle from egg to adult at 70° F.

Lewis mites feed on the underside of leaves by piercing the surface and removing the contents of the cell. This results in a stippled appearance, along with yellowing of the leaf. This early damage can sometimes look like nutrient deficiency, so it is important to scout the underside of the leaves for an infestation. After an increase in Lewis mite population, the damage can include the upper foliage turning brown and falling off, and webbing around the growing points (although the webbing will not be as abundant as the two-spotted spider mite’s webbing).

The damage typically occurs late in production (usually October, but sometimes as early as August or September). Unfortunately, Lewis mites are not attracted to yellow sticky cards, so an active scouting program must be utilized to detect early damage. Once an infestation is detected, it is important to remove those plants, as well as surrounding ones, from the greenhouse to be treated separately. The infested plants should be able to be saved with applications of Amblyseius fallacis. Fallacis should also be released in the greenhouse on the plants surrounding the original infestation. We suggest releasing 2 mites per square foot or 100,000 per acre once the infestation is found. While we suggest using bush beans to monitor and/or trap the two-spotted spider mite, this technique will not work on the Lewis mite, as it will choose the poinsettia over the beans (unlike the spider mite).

Although an uncontrolled infestation of Lewis mites can lead to major crop loss, it is manageable by using applications of fallacis at first detection. If you have more questions about scouting for or treating a Lewis mite infestation, feel free to contact us at order@evergreengrowers.com!

Sources:

British Columbia Ministry of Agriculture (http://www.agf.gov.bc.ca/cropprot/mites.htm#lewis)

FloriBytes Digital Newsletter (http://www.oardc.ohio-state.edu/floriculture/images/FloriBytes0911_pest-_Lewis_Mite.pdf)

Greenhouse Product News (http://www.gpnmag.com/managing-lewis-mites-poinsettia)

University of California (http://ucanr.edu/blogs/blogcore/postdetail.cfm?postnum=4380)

Brian Spencer, Applied Bio-nomics (http://appliedbio-nomics.com/)