Mealybugs are typically a problem on long-term crops such as orchids, foliage plants that are often found in retail greenhouses, conservatories, and interiorscapes. Common species include the citrus mealybug (Planococcus citri), longtailed mealybug (Pseudococcus longispinus), and obscure mealybug (Pseudococcus viburni). Other mealybugs that have been introduced into the USA, which may be present in greenhouses, include the pink hibiscus mealybug (Maconellicoccus hirsutus), maderia mealybug (Phenacoccus madeirensi), and the Mexican mealybug (Phenacoccus gossypii).
Longtail mealybug. Photo from David Cappaert, Michigan State University, Bugwood.org Mealybugs usually enter a greenhouse on already infested plant material. Now is a good time to inspect any tropical plants that you are thinking of overwintering in your greenhouses. Look on leaf undersides, petiole and leaf junctions, and near the base of plants. Mealybugs can also be found on the inside of container lips and in the drainage holes of containers. On standard plants, they may hide under the tape on the garden stakes. Mealybugs can live for 2 to 3 weeks without hosts. Power washing the greenhouse between crops is helpful to remove mealybugs hiding in cracks and crevices. Young, immature mealybugs prefer to move to tip growth to feed, so inspect stock plants before taking cuttings. Susceptible plants, should be monitored closely and include coleus, rosemary, sage, Swedish ivy, artemesia, Ipomoea, and gardenia.
Chemical control is difficult because the mealybug’s waxy covering reduces its contact with spray materials. Crawlers, with the least wax, are most susceptible to chemical treatments. The systemic insecticide, Safari, is very water soluble and effective against mealybugs as a drench treatment. Recent research has also shown that Celero, Aria & Talus or Talus also work well. Repeated applications may be needed as eggs hatch throughout the growing season.
Stanton Gill, University of Maryland reports that growers of edible herb crops may apply insecticidal soap (containing fatty acid and alcohol) to dissolve some of the waxy coating, then follow-up with an application of horticultural oil a day later.
Biological Control of Mealybug
To choose the best natural enemy, it is important to have the mealybug identified to species. For example, the commercially available parasitoid, Leptomastix dactylopii only attacks the citrus mealybug. In general, predators are less efficacious against mealybugs than parasitoids. The mealybug destroyer, (Cryptolaemus montrouzieri) feeds on citrus and longtailed mealybugs as adults and larvae. .The wax-covered larvae resemble mealybugs, except they are twice as large and feed on mealybug eggs, crawlers, and honeydew. Adults and young larvae prefer to feed on mealybug eggs, however older larvae will attack any stage. The mealybug destroyer is also most effective during spring through fall; less so during winter.
Reprinted from a posting by Leanne Pundt, University of Connecticut and Tina Smith, University of Massachusetts on October 9, 2008 on the New England Greenhouse Update website http://www.negreenhouseupdate.info/greenhouse_update/index.php
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