Field Corn XI-16

Two Spotted Spider Mite

Frank B. Peairs

Two-spotted spider mite

Identification (and life cycle/seasonal history)

Adult two-spotted spider mites (TSM) 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 80E 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 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

Banks grass mite and two-spotted spider mite respond differently to miticides.  Thus, in areas where a mixture of Banks grass mite and two-spotted spider mite occurs, the only effective chemical treatment seems to be an application of bifenthrin 2ER, HeroR, Comite II or Oberon 4SC as described for Banks grass mite control.  Dimethoate is registered, but not recommended for this situation.

RRestricted use pesticide.

Categories: Field corn, Insects, Two-spotted spider mite

Date: 5/16/2008