Tell Spider Mites to Bug Off
Spider mites flourish in warm, dry conditions so water plants regularly to safeguard against infestation.
Image courtesy of Clemson University - USDA Cooperative Extension Slide Series, Bugwood.org
Although they are less than a millimeter in length, spider mites are among the most formidable garden pests, feeding on nearly 200 varieties of plants, including fruit trees, ornamentals, grapes, corn and roses. Puncturing epidermal cells of leaves with sucking mouthparts to extract sap, the damage they cause is readily evident as leaves become discolored and wither. When an infestation is severe, plants stress can be severe and lead to plant death. Because spider mites, a member of the Acari family, are so tiny, their presence often goes overlooked and damage to trees and crops is already underway. Spider mites reproduce quickly, in some cases, like that of the common two-spotted mite, spider mites can lay as many as twenty eggs a day, with offspring reaching reproductive maturity in less than a week.
Laying their eggs and also feeding on the underside of leaves, many spider mites produce webbing used to protect eggs and feeding colonies from predators and shifting weather conditions. When a spider mite population is high, the silky threads found on leaves are an indisputable indicator of an infestation.
Spider mites have numerous predators, including lady beetles, big-eyed bugs and spiders. In many cases, an extreme infestation of spider mites may be the result of the overuse of chemical pesticides, which can severely reduce the presence of beneficial insects and leave a spider mite population to grow without intervention. When a growing spider mite infestation reflects a dwindling predator presence, discontinuing the use of chemical insecticides may restore balance to a garden space. The return of beneficial insects takes time, however, and this strategy for spider mite management should be considered as a long-term solution.
Spider mites flourish in warm dry conditions. In areas where problems are likely to emerge, making sure plants are watered regularly is an early safeguard against infestation. In circumstances where an infestation has already been established, affected plants may be watered using a hose with a spray nozzle and directing the stream directly at plant leaves can dislodge eggs, feeding adults and wash away supportive webbing.
Inspect plants daily for eggs and mites, giving special attention to the underside of leaves. Prune any leaves that show extreme damage or heavy active infestation. In some cases, it may be necessary to cull entire plants. Any leaves or plants removed as a result of a spider mite occupation should be submerged in soapy water or sealed in an airtight container and removed from the site.
In cases where other management techniques are not sufficient to control an expanding spider mite infestation, chemical intervention should be considered. Many insecticides are ineffective against spider mites and may worsen conditions as beneficial insects lost to treatment. Select miticides specifically for the control of spider mites and follow manufacturer instructions. Although appropriate miticides will eradicate nymphs and adults, eggs will not be affected and multiple applications will be needed to interrupt a cycle of reproduction.