Mites
Description: Spider mites are often lumped into the "pest insect" category. In fact, they are not an insect, but rather an arachnid with eight legs as opposed to the usual six. They also differ from most insects in that they do not have wings, and must rely on crawling from plant to plant or aerial dispersal by the wind.
There are several mite species. Some are pests, but most are beneficial. Of the most common pest mites, the species most likely to attack our roses is the Two-Spotted Spider Mite. This character is about 0.4 mm long, pastel green, amber or yellow, and is characterized by two black spots (sometimes four) on its back. Their appearance in your landscape is usually noted by the damage they cause and the presence of thin webs many, but not all, of the species produce.
Biology: The mite lifecycle, from egg to adult, can vary from 5 to 20 days depending on temperature and season. Generally speaking, mites enter diapause (an insect version of hibernation) during the fall when temperatures and sunlight decrease and host plants become scarce. They seek crooks and crannies in structures, in the soil, under the bark, or on your plants for the winter. When spring arrives, the mites mate and produce as many as 100 offspring within their short lifespans. Their preference is warm, dry weather. If temperatures get too warm, however, they will again enter diapause until such time as the weather cools. This means your roses are most likely to be attacked in late spring/early summer or late summer/early fall. In temperate, semi-tropical southern zones, they will continue to feed and reproduce, however, even through the winter.
Damage: When the Two-Spotted Spider Mite attacks your rose, it pierces the epidermis and apparently injects some of its saliva in the process. After feeding, two minute chlorotic spots appear as the leaf tissue collapses. During severe infestations, the entire plant may turn yellow and die. Mite damage may also appear as shortened internodes and petioles, failure to bloom, and twisted or distorted new growth.
Control: Because of their size, determining the presence of this pest is, at best, a challenge. (To put this in perspective, imagine a critter the size of a dot on a this page.) If infestation is suspected, first check the interior of the rose where stems join together. Often, small webs will be seen. These webs will commonly have debris in them, and are easily distinguished from the webs of beneficial spiders because the latter keep their webs very neat and tidy. If possible, take a cutting of the suspect area and tap it over a sheet of plain, white paper. What falls to the paper may appear as flecks of ground black pepper. If the "flecks" start crawling away, you've got spider mites!
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