HPIPM:Two Spotted Spider Mite FC
Author: Frank B. Peairs[1]
Identification (and life cycle/seasonal history)
Adult two-spotted spider mites (TSM), Tetranychus urticae Koch, are minute, 0.5 millimeter (1/50 inch) long, greenish colored arthropods with eight legs and a rounded body. TSM have dark pigmentation concentrated in two spots on either side of their abdomen. Females may lay five to six tiny spherical eggs per day. These can be seen with the aid of a hand lens. Mites have four life stages: egg, larva, nymph, and adult. The eggs hatch into six-legged larvae. Larvae pass through two additional stages as eight-legged nymphs before becoming adults. The only difference between these nymphal stages and the adult stage is size. The mite life cycle may be as short as six days during hot, dry weather (greater than 80 degrees F and less than 50% relative humidity).
Plant Response and Damage
TSM are barely visible with the naked eye but are usually noticed as a result of their damage and webbing on leaf surfaces. Mites damage corn and other plants by piercing plant cells with their mouthparts and sucking the plant juices. An early sign of mite feeding is the appearance of yellowish dots on the topside of the leaf. Later, whole leaves, leaf tips and margins will turn brownish-yellow and dry up. Spider mite populations are worse during hot, dry weather.
Management Approaches
Resistant Varieties
Spider mite resistant corn hybrids are not yet available. Although they are not resistant, longer season hybrids tend to develop fewer mite infestations than do those with earlier maturities.
Biological Control
There are 35 natural enemy species from 15 families of predatory insects, mites, and spiders associated with mites on corn. Preservation of beneficial insects and mites is critical to proper management of spider mites in corn. Some of the most important are the predatory mite, Amblyseius fallacis, and a small black lady bird beetle called Stethorus.
Cultural Control
Three key cultural practices may help reduce the probability of mite outbreaks: (1) proper irrigation to avoid drought stress; (2) late planting; and (3) the use of full-season hybrids.
Chemical Control
Treatment guidelines for two-spotted spider mite and Banks grass mite are similar. Banks grass mite and two-spotted spider mite respond differently to miticides. Effective treatments include those listed for Banks grass mite (see Banks Grass Mite), with the exception of dimethoate.
The information herein is supplied with the understanding that no discrimination is intended and that listing of commercial products, necessary to this guide, implies no endorsement by the authors or the Extension Services of Nebraska, Colorado, Wyoming or Montana. Criticism of products or equipment not listed is neither implied nor intended. Due to constantly changing labels, laws and regulations, the Extension Services can assume no liability for the suggested use of chemicals contained herein. Pesticides must be applied legally complying with all label directions and precautions on the pesticide container and any supplemental labeling and rules of state and federal pesticide regulatory agencies. State rules and regulations and special pesticide use allowances may vary from state to state: contact your State Department of Agriculture for the rules, regulations and allowances applicable in your state and locality.
