Stealthy Mites in Poinsettias
Lewis mite is back with a few reports in poinsettias this fall. These small spider mites generally feed on leaf undersides causing a faint stippling easily overlooked as a nutrition issue or normal color break as bracts start. Overlooked, that is, until mite levels have become very high and it’s clear something else is going on. The timing unfortunately often coincides with dense foliage, closely spaced plants, expanding bracts and longer stems that easily break. Many years ago we ran a couple of trials comparing several miticide treatments. Avid and Akari (low rates) were among the most effective, followed by Floramite and Shuttle O (lowest label rates). Hexygon (low label rate) was much less effective in this trial; it is normally best used early in an infestation. Higher labeled rates for these would likely provide better control. Pylon (low and high label rates for mites) didn't work quite as well as expect, a surprise since the latter is known to be very effective against a range of different kinds of mites. Several other miticides worthy of evaluation haven’t been tested in our trials but may be effective rotation options. Growers have sometimes commented on less-than-expected results with treatments including those we’ve seen work well in the past. Issues in some cases include difficulty in getting good coverage, extremely high mite populations to start with, and possibly low label rate used. Check under leaves several days after application, comparing areas with best coverage to other areas, using good magnification to look for dead and live mites. When mite levels are extremely high, as they often are when detected, repeat applications and short rotation intervals using higher rates and products with different modes of action are usually necessary, but note label restrictions on numbers of applications per crop cycle. Incidentally, we found Lewis mites surviving on cuttings after rooting under mist, despite the constantly wet conditions that usually disfavor spider mites. (Image shows Lewis mite stippling on poinsettia leaves)
Dan Gilrein
Entomologist, Cornell Cooperative Extension of Suffolk CountyDan Gilrein is the Extension Entomologist with Cornell Cooperative Extension of Suffolk County at the Long Island Horticultural Research and Extension Center, Riverhead, NY since 1995 and previously served there as IPM Specialist with Cornell from 1987. In his current position he conducts applied research on control of arthropod pests in food crops and on ornamental plants, provides diagnostic services to the horticultural industries, and conducts educational programs and presentations for industry, government officials, civic groups and the public on pests and pest management.
