MANHATTAN, Kans. - Warm weather often signals the emergence of twospotted spider mites (Tetranychus urticae), reports Raymond Cloyd with Kansas State University Entolomology, in a recent informative KSU Turf blog
, which contains excellent photographs of the mites and the damage they do.
Twospotted spider mite is considered a warm-weather mite because, in general, populations are mainly active from late spring through early fall. Summer temperatures allow twospotted spider mites to reproduce rapidly, so they tend to overwhelm natural enemy populations, which are able to regulate them under "moderate" temperatures. This article will primarily cover the management strategies that homeowners and professionals may implement in order to alleviate or avoid problems with twospotted spider mite.
Twospotted spider mite management involves maintaining plant health, implementing sanitation practices, and/or using pest control materials with miticidal activity (miticides).
First, avoid exposing plants to any type of "stress" by maintaining proper watering, fertility, and mulching as this may reduce any potential problems with twospotted spider mite populations. For example, inadequate moisture or overfertilizing plants, particularly with nitrogen-based fertilizers, may enhance development and reproduction of twospotted spider mites.
Monitor for twospotted spider mite populations regularly by knocking the spider mites off plant parts such as branches or twigs onto a white sheet of paper. This makes it easier to observe spider mites. Plant-feeding spider mites typically leave a green streak when crushed whereas predatory mites leave a red streak. A very effective and quick method of dealing with twospotted spider mite populations is applying a forceful water spray throughout the plant canopy at least twice per week during the season. This will dislodge eggs and the motile life stages (larvae, nymphs, and adults). Direct forceful water sprays at the leaf undersides where the twospotted spider mite life stages are located. The removal of plant debris and weeds eliminates overwintering sites. In addition, many broadleaf and grassy weeds are hosts for twospotted spider mites.
Clod, in the blog, also reports that pest control materials with miticidal activity available to professionals for regulation of twospotted spider mite populations outdoors include abamectin (Avid), acequinocyl (Shuttle), bifenazate (Floramite), etoxazole (TetraSan), hexythiazox (Hexygon), potassium salts of fatty acids (M-Pede), and petroleum or neem-based oils (horticultural or summer oil).
Read the label and follow label directions, and make applications before twospotted spider mite populations are extensive and causing aesthetic damage. In addition, rotate compounds with different modes of action in order to avoid twospotted spider mite populations from developing resistance.
Try to target "hot spots" or localized infestations of twospotted spider mites, which will also reduce the potential for the development of resistance. Twospotted spider mites reproduce by a combination of sexual and asexual means resulting in offspring that develop from both fertilized and unfertilized eggs. Therefore, within a twospotted spider mite population, males only have one copy of a resistant gene, whereas females have two copies (RR). This indicates that females are more tolerant to miticide applications or may develop resistance more rapidly than males.
Thoroughly cover all plant parts with spray applications; especially when using pest control materials with contact activity. Some products such as Avid and TetraSan have translaminar activity, which means that the material penetrates into leaf tissues and forms a reservoir of active ingredient within the leaf. This provides residual activity even after spray residues have dried. Mites that feed on leaves will ingest a lethal concentration of the active ingredient and be killed.
Be advised that many pest control materials used to suppress other insect pests encountered on horticultural plants may be harmful to the natural enemies of twospotted spider mite, which could lead to an inadvertent increase in twospotted spider mite populations or secondary pest outbreaks.