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Problem: Two-spotted Spider Mites - Tetranychus urticae
Hosts: Too numerous to mention. However, most conifers not usually bothered.
Description: Though at first the spherical eggs of this mite are colorless and transparent, they become opaque as they age and become a greenish-yellow color as they near hatching. Both nymphal stages resemble the adult with the female being more oval than the male. Body color varies from yellow to pale green but is never reddish like the morphologically identical Tetranychus cinnabarinus. There is usually a dark spot on each side of the dorsal midline; hence the name.
Adult females overwinter and may turn an orange color in late fall. As the weather warms in the spring, the female will begin laying eggs. Parthenogenesis (reproduction without fertilization) is common. Newly hatched eggs give rise to the larvae which in turn give rise to two stages of nymphs. The adult follows the second nymphal stage. This whole process will normally take from 10 to 14 days during the summer with individual females living an average of two months. There can be 10 to 12 generations per year.
If mites are suspected, hold a sheet of white paper beneath a branch and tap the branch. Mites will be dislodged and can be seen as tiny specks on the paper that move about.
Mites primarily feed on lower leaf surfaces. Using their piercing mouthparts to stab epidermal cells, they withdraw the cellular contents which cause the cells to collapse. Chlorotic spots occur where damaged adjacent cells coalesce. A stippling appears on upper leaf surfaces. Severely damaged leaves may die.
Recommendations: Spider mites tend to be a yearly problem in Kansas. Kelthane has been one of our standard recommendations for a number of years but is now labeled only for certain vegetable, fruit and nut crops. On ornamental plants, commercial applicators often use Talstar and Capture for mite control. The active ingredient of both products is bifenthrin and can be found in homeowner packaging in Ortho's Rose & Flower Insect Killer. Note that it is not to be used on edible crops. Other effective miticides for commercial use include deltamethrin (DeltaGard) and Scimitar (lambda cyhalothrin). Lambda cyhalothrin is now packaged for homeowners under the name of Spectracide Triazicide and is labeled for a wide range of ornamentals as well as a number of the brassicas (cabbage, broccoli, cauliflower,
etc.) and tomatoes. All of the above materials kill predatory mites as well as those you seek to control. Predatory mites feed on the mites that feed on plants and therefore provide a natural control.
Horticultural oils can also be an effective control of moderate infestations. Adequate coverage is essential. Horticultural oils help suppress all three life stages eggs, immatures and adults and they are kind to mite predators.
A couple of additional follow-up treatments applied three to
four days after the initial treatment may be required to clean up mites escaping initial
treatments, or mites that emerged from eggs present at the time of the initial treatments.
References:
1. Insects and Mites Associated With Shade Trees and Woody Ornamentals, pg 14, K-State Research and Extension Pub S-85
2. “Insects That Feed on Trees and Shrubs”, Cornell University Press, pg 419
3. Life Histories of Common Insects, Mites and Nematodes Infesting Ornamental Plants in Missouri, Missouri Department of Agriculture, pg K-1
Last Update: 08/08/2005
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