The insidious two-spotted spider mite
By Ralph E. Mitchell
Tiny, but terrible, the two-spotted spider mite is the bane of many ornamental and edible plants. Only one-fiftieth of an inch in length, when working in groups, this plant pest mite sucks the sap from leaves causing decline and damage. You can thwart their plans however, with some simple management techniques.
The two-spotted spider mite is a spider relative and not an insect. As such, it has eight legs, is more or less oval in shape, and translucent orange to greenish-yellow in color. There are also two distinct dark spots visible on its body giving this arachnid its classic name. Amazingly, these spots are really just stored waste kept within the mite’s translucent body. The life cycle goes from egg to larva, and from larvae to nymph to adult in no more twenty days, and adults can live up to a month. Two-spotted spider mites do best in dry, hot weather, so be on the lookout now.
As mentioned earlier, two-spotted spider mites use needle-like mouthparts to puncture and suck plant juices from the undersides of leaves. One of the telltale signs of an infestation of mites is an abundant accumulation of very fine webbing. As these are spider relatives, they can produce and use strands of silk. As the population of spider mites increases, the infested foliage will turn yellow, gray or have a bronzed cast. Multiple feeding sites even give the leaf tissue a bleached appearance.
What types of plants are likely to be infested with spider mites? Two-spotted spider mites are known to attack over two-hundred plants. Locally, I have seen them on ornamentals such as roses, viburnums, and red cedars. They also are common on tomatoes, eggplants and cucumbers. Beyond the feeding damage called stippling and the webbing, you can monitor for mites by taking a white sheet of paper and placing it under the suspected infested branch or leaf. Then, tap the infested plant part. The mites will drop onto the paper where they can be detected. While not microscopic, they are more easily detected on the white background and you can actually see them scurrying around with the naked eye. Once detected, spider mites can be easily controlled with either insecticidal soaps or horticultural oils used as per label instructions and not in the heat of the day as leaves could be burned.
Behind the scenes there are number of natural predators already present and working in your favor to suppress spider mites. These may include equally tiny protectors such as predatory mites, lady beetles, minute pirate bugs, predatory thrips and lacewing larvae. There are even reports that the ghost ant (a pest ant) is a predator of spider mites.
The two-spotted spider mite is common, but easily detected and conveniently managed with both cultural and least-toxic techniques. Don’t let spider mites get you down – knock them down first! For information on all types of common garden pests found in our area, please call our Master Gardener volunteers on the Plant Lifeline on Mondays, Wednesdays and Fridays from 1 to 4 pm at 764-4340 for gardening help and insight into their role as an Extension volunteer. Don’t forget to visit our other County Plant Clinics in the area. Please check this link for a complete list of site locations, dates and times – http://blogs.ifas.ufl.edu/charlotteco/files/2018/01/Plant-Clinics-Schedule.pdf .
Fasulo, T. R. & Denmark, H. A. (2016) Two spotted Spider Mite, Tetranychus urticae Koch (Arachnida: Acari: Tetranychidae). The University of Florida Extension Service, IFAS: