Twospotted Spider Mite in Alfalfa
Crop Injury: Several kinds of mites infest alfalfa, including the twospotted spider mite (Tetranychus urticae). Twospotted spider mites are a concern in alfalfa fields grown for seed. Twospotted spider mites cause leaf stippling, giving an overall yellowish or bronzing appearance to foliage. Defoliation, decreased vigor, and plant death can also occur. Pollinators and natural enemies can be adversely impacted by profuse twospotted spider mite webbing on plant tissue.
Pest Description: Twospotted spider mites are very small, wingless, and yellowish-green. They have two dark spots as adults. Depending on the developmental stage, they have either six or eight legs. Twospotted spider mites create webbing on foliage and live in colonies of multiple life stages.
Spider mites and webbing
Adam Sisson
Spider mites and webbing
Adam Sisson
Life Cycle: Twospotted spider mites hatch from eggs laid by overwintering females. Adulthood is reached after progression through multiple nymphal stages.
Scouting: Twospotted spider mites can be an issue particularly during hot and dry seasons and in dusty areas of a field. Look for mites on the lower leaf surface and for webbing on plant tissue; infestations generally progress upwards from the lower portion of the plant.
Management: Management includes appropriate pesticide application prior to middle and upper canopy infestation. Certain pesticides can reduce natural enemies, causing a mite “flare” within a field. Late season infestations may not require management due to plant maturity.
Prepared by the Alfalfa Pest Management Working Group.
Spider mites and webbing
Spider mites and webbing
Spider mites and webbing
Gallery images courtesy Adam Sisson
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