Landscape and Nursery - Two Spotted Spider Mite Season

Spider mite season is upon us. Although these mites are more of a problem in dry weather, they can still be a problem in some plants in a wetter year. The following is some information.

The list of host plants for the Two Spotted Spider Mite, a warm season mite, is considerable. A partial list includes many perennials, winged euonymus, and occasionally juniper and dwarf Alberta spruce. Typically conifers are not the preferred hosts of two-spotted spider mite species. These mites can have an entire generation occur in less than 7-8 days if temperatures exceed 85° F. It is possible for 15 generations of two-spotted spider mites to occur during the summer. Typical symptoms include stippling damage and webbing. Affected foliage yellows, then turns brown and dies if mites are not controlled. Damage does not recover, so early detection and timely control is the best management technique. Monitor with a beating tray (or white clipboard) by rapping foliage on the board and looking for the tiny mites that drop off. A hand lens can be used to note what life-stage is present (on the underside of foliage), but this is slower than the use of the beating tray. Very fast predatory mites may be seen, with light colored bodies and long legs. If predators are noted, keep monitoring to be sure they are reducing the spider mite population, and that the mites don’t overwhelm the predators.

Control with horticultural oil (check the label for weather conditions and make sure the plant is not under drought stress) in order to kill eggs and active forms, as long as mites are contacted (on the underside of foliage). Hexythiazox (Hexygon) is a miticide that kills immature mites and eggs and prevents adults from laying eggs. Abamectin (Avid) provides a quick kill and a long residual (may need 2 applications since they only control active mites. Florimite is a miticide that can also provide excellent results. The list of effective miticides is extensive. Note that imidacloprid (Merit) is not a miticide.

Information from the June 28, 2007 edition of the Plant and Pest Advisory, Landscape, Nursery and Turf Edition, Rutgers University.