Mealybug & Scale Control
Of the approximately 15 species found in ornamentals in greenhouses, the most common species are citrus mealybug (Planococcus citri) and long-tailed mealybug (Pseudococcus longispinus). Their host range is extensive and includes most foliage plants grown in plantscapes, and they have even been found on vegetable crops such as cucumber. Citrus mealybug prefers soft-stemmed plants, but can also be a problem on woody plants. Other species that may occur are obscure, citrophilus, grape, and ground mealybugs.
LIFE CYCLE: A complete life cycle takes from one month up to a year, depending on temperature. Females of most species lay eggs in a cottony white mass. These hatch into crawling nymphs that migrate over the plant in search of feeding sites. The female nymphs develop through 3 growth stages. Long-tailed mealybugs give birth to live young and do not produce this cottony material. Male mealybugs develop wings and resemble fluffy gnats or wasps, flying to fertilize females.
CONTROL: Before releasing biological controls, prune out and destroy infested foliage, and hose plants with a strong stream of water to reduce mealybug numbers. Ant control may be necessary when implementing beneficial insects, as ants are attracted to the honeydew produced by mealybugs, and they may disrupt the oviposition of beneficials. Sound Horticulture offers Cryptolaemus montrouzieri (see Cryptolaemus) as well as the mealybug parasitoids Anagyrus pseudococci and Aphytis melinus (see Aphytis) as biological control of mealybug. Stratiolaelaps scimitus ‘Womersley’ can be used to control root mealybug (see Stratiolaelaps). Green and brown lacewings are also effective in controlling mealybug (see Green Lacewings). Check the progress of biological controls by inspecting the new growth for signs that mealybugs are disappearing.
SCALES suck plant sap, attacking both old and new growth. Their feeding causes distortions, stunting, and yellowing of foliage. They also produce large amounts of honeydew, which supports the growth of unsightly sooty molds on leaves. There are two types of scale: soft scale (Coccidae) and armored scale (Diaspididae). Black scale, hemispherical scale, brown scale and nigra scale are common soft scales that attack a variety of foliage plants. California red scale and purple scale are examples of armored scales. It is important to correctly identify the scale species because some biological controls are specific to a particular species or group of scales.
LIFE CYCLE: Scales have 3-6 generations per year indoors. Each female lays up to 2,000 eggs, sheltered under her outer shell. The eggs hatch after several days into minute crawlers, which migrate over the plants looking for feeding sites. Females die once they have laid their eggs. Female scales look like circular or oval bumps (2-4 mm, 1/10th inch) on stems and the under surface of leaves. Adult males are winged and rarely seen. Scales develop fastest in warm, humid conditions, especially in the shade.
CONTROL: Close examination with a hand lens is necessary to detect scales. They often go unnoticed until the honeydew they produce is conspicuous, or until plant growth is stunted or distorted. Before releasing biological controls, prune out and destroy severely infested branches, treat infested plants with insecticidal soap sprays to reduce scale numbers (this is most effective on the crawler stage of scales), and mist plants with water to remove excessive honeydew. Scale outbreaks often occur in early January or February, which means that biological controls should be released in the summer or by late November. Sound Horticulture offers Cryptolaemus montrouzieri (see Cryptolaemus) as well as the parasitoids Anagyrus pseudococci and Aphytis melinus (see Aphytis) as biological control of scale. Green and brown lacewings are also effective in controlling scale (see Green Lacewings).