Mites Like It Hot
Mites damage plants by piercing plant tissue and sucking out liquids. Damaged areas appear as yellowish white spots (stippling) from destroyed chlorophyll in the leaf surface. As populations increase, the whole leaf will eventually yellow. Heavily infested plants will also have webbing present. Crop losses may occur when 30 percent of the leaf surface is damaged.
Plant inspection is the only reliable method to assess the presence of mites. Mites like it dry and warm. They are often found near vents, doors and heaters in greenhouses. A good technique is to tap the leaves over a sheet of white paper, dislodging mites and making them easier to identify. Using a good hand lens is essential to viewing mites in egg, nymph and adult stages.
Biocontrol with natural enemies can be very effective on mites. However, they are rarely effective on cyclamen or eriophyid mites. Probably the best way to manage these mites is to remove and destroy infested plants as soon as they are detected.
Neoseiulus californicus, predatory mite, is effective both preventatively and to clean up hot spots of spider mites. Phytoseilus persimilis, predatory mite, is also effective on a curative basis. Neoseilus is supplied in tubes of 1,000 to 2,000 adults mixed in vermiculite or corn grits. To increase effectiveness:
- Concentrate predator introductions at spider mite hot spots.
- Gently roll the tube to mix the predatory mites equally in the carrier before application.
- Place predators directly onto infested plants.
- Store in refrigerator at 55oF for up to five days.
For more details on biocontrols, see the Greenhouse IPM with an Emphasis on Biocontrols handbook. For additional commercial recommendations see the Production Recommendations for your state or expanded article here.
References: Thomas, C. and Rajotte, E. 2005. Greenhouse IPM with an Emphasis on Biocontrols. Pennsylvania Integrated Pest Management Program.