Greenhouse Insect and Mite Pest Management
Insect and Mite Pests Commonly Found in Greenhouses
Mealybugs
Mealybugs are small, sluggish insects, about 1/8-inch long (See Figure 27.7). Mealybugs are covered with a white, waxy powder with threadlike projections around their perimeter. This waxy powder serves as protection from chemical pesticide applications. Clusters of mealybugs look like a cottony mass. Mealybugs are serious greenhouse pests because the crawlers spread rapidly and exist under bud scales and within leaf axils. Mealybugs feed on a wide range of host plants. Foliage plants in greenhouses and interior plantscapes are very susceptible to mealybugs. Vegetables such as tomato, cucumber, and eggplant can serve as hosts for mealybugs as well. The most significant mealybug species attacking greenhouse crops are the citrus mealybug (Planococcus citri) and the longtailed mealybug (Pseudococcus longispinus).
Life Cycle
Some species lay eggs; others give birth to live young. Citrus mealybugs produce eggs in cottony structures called ovisacs. Eggs hatch into nymphs called crawlers in about 10 days. The crawlers move around the plant to find a suitable feeding site and then begin to feed on plant sap.
Types of Damage
Mealybugs have piercing, sucking mouthparts. Their feeding causes stunting of plants, and leaves tum yellow and appear distorted. Mealybugs, like aphids, excrete honeydew that serves a substrate for black sooty mold development, affecting the cosmetic value of the plant.
Monitoring
Early detection is very important for effective control. Greenhouse workers should be trained to recognize these pests and the early symptoms of damage. Ants climbing on the plant can indicate a problem with scales.
Cultural Strategies to Manage Mealybugs
Heavily infested plants should be discarded. Clean pots thoroughly and inspect used pots and edges of trays for egg masses and/or crawlers.
Biological Management Strategies
There are numerous parasitic wasps that attack the citrus mealybug and several predatory beetles. The parasitic wasp, Leptomastix dactylopii, is efficient in controlling citrus mealybugs but is not effective for other mealybug species. With heavy infestations, this parasite works well in conjunction with the mealybug destroyer (Cryptolaemus montrouzieri). Adult female wasps search the leaves for larger stages of mealybugs.
Biorational Management Strategies
Microbials. Beauveria bassiana is a fungus that secretes enzymes, which dissolve the insect's cuticle. After it enters the insect's body, the fungus produces a toxin that weakens the insect's immune system. Thorough coverage is needed so the fungal spores contact the insect. Repeated applications may be needed.
Insecticidal Oils and Soaps. Insecticidal oils and soaps can sometimes be effective, killing more life stages of these pests than many contact insecticides, but they provide no residual control. Again, thorough coverage is critical.
Chemical Management Strategies
If contact insecticides are used, they should be applied during the crawler stage of mealybugs. Repeated applications are therefore necessary to contact the susceptible stages as they are produced. Spray intervals will depend on the residual effectiveness of the insecticide used, which may vary from 0 to 3 weeks. The inclusion of a spreader-sticker can improve coverage, penetration, and residual activity, although the risk of phytotoxicity may be increased
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