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Pests of indoor plants. December 26, 2002.
Probably the most common pests of indoor plants are Fungus gnats (Sciarids), also referred to by some as flower flies. These small (less than 5mm) black gnats have one pair of dark wings. The adult flies occur around potted plants and landscapes wherever there is moist dark decaying vegetation. Their larvae feed upon fungi and the decaying vegetation. Therefore, rich organic soils, such as with peat moss, will be most attractive to them. Although the adults are a nuisance, the larvae feed upon tender roots of newly started cuttings and spread disease. These seldom seen slender, glassy larvae are the real pests.
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| fungus gnat adult, ~2x | fungus gnat larva, ~2x |
(Insect photos from IPMimages.org http://www.ipmimages.org/)
If infestations become bothersome, the adults can be controlled by gently vacuuming the plants. Another method is to purchase yellow “sticky traps.” These not only kill gnats, but also act to monitor populations.
A bacterial product, “Gnatrol,” can control fungus gnat larvae. However, there are some reports of Gnatrol being inhibited by organic matter like peat moss. Another alternative is to use beneficial nematodes http://www.biologicco.com/products/L&G scanmask.htm to kill gnat larvae. Control is generally long lasting, months when the nematodes are properly applied.
Next most common pests of indoor plants are probably whiteflies. These chalky white, 2-3mm insects suck plant juices. They often rest on the under sides of plant leaves, but fly up in a cloud when disturbed. Their larvae also occur under leaves. The larvae move very little, if at all, and appear as minute protuberances, scale- like. Whitefly larvae secrete sticky “honeydew” which encourages mildew, sooty leaves, and other problems.
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| whiteflies, adults, ~2x | whitefly, larvae,~2x |
(insect photos from IPMimages.org http://www.ipmimages.org/)
Gentle vacuuming and yellow “sticky traps” as above are helps for the adults.
Praying mantises are generally unavailable during winter months to use as whitefly predators. The best biological control commercially available is Encarsia Formosa, a minute wasp both parasitizes and preys upon whiteflies. Figure on five Encarsia per plant. http://www.ipmlabs.com/ If using Encarsia, stop vacuuming, chemicals, and remove sticky traps. Look for the blackened larvae as a sign that the Encarsia are working.
Text copyright by Albert Pye, Ph.D., BioLogic Company http://www.biologicco.com/
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