7/2/2013 - By Matthew Shultz

With temperatures now climbing above 90 degrees F on a daily basis, growers will start pulling out the miticides from their chemical storage, and using them in their spray rotations. The Two Spotted Spider Mite or Tetranychus urticae is the most prolific pest to nursery growers through the summer months. This pest overwinters either as fertilized eggs, or as dormant adults in more temperate climates. Eggs of the Two Spot are perfectly round, and can be used for quick identification in the field with a hand lens.

Once temperatures start to creep above 85 in the spring, mites will become increasingly active. Mites thrive in dry, dusty and hot environments, and when conditions are optimal an egg can develop into a sexually mature adult in less than one week. Females typically lay about 10-15 eggs daily for a couple of weeks under optimal conditions, before dying off.

The two spot gets its name from the two black spots that can be seen under a hand lens, and is an important identification trait. In outbreak situations, colonies of the mites will produce webbing, which some speculate is to protect egg masses against natural enemies. Spider mites feed on the undersides of leaves by inserting a stylet into the leaf tissue and sucking out the plant’s fluid.

Mites are easy to control with preventative sprays, but once populations get out of hand, two spot can be extremely difficult to eradicate. Most registered miticides won’t target all life stages, so it is good to recommend mixing an ovicidal miticide with a miticide that acts on juveniles and adults, for example, Hexygon (good residual control of eggs and immatures) + TetraSan (good residual/translaminear activity for adults). Other reliable miticides include – Avid, Tame, Akari, Floramite, Sanmite, SuffOil-X.

There are some naturally occurring predators of these insects, and most of the chemicals listed are relatively safe to these biologicals. Water stressed trees and shrubs are usually more susceptible to mite outbreaks, so keeping plants healthy and relatively stress free is an important control method to use. Mites thrive in dusty environments, so use irrigation to keep dust down as well.

By Matt Shultz, Horticultural Tech Support Specialist and Sales Representative, Harrell’s LLC and Marshall Horsman, Technical Services Manager, Harrell’s LLC.