|University of Kentucky Entomology|
by Lee Townsend, Extension Specialist
University of Kentucky College of Agriculture
Mealybugs and Fletcher scale can infest Taxus. While they are distinctly different in several ways, their biologies are similar, as is their management.
Mealybugs are scale-like insects that feed on plant sap and typically are covered with a grainy white secretion that gives them their name. The white covering and long filaments make this mealybug stand out at branch forks where it tends to settle. The sparse yellow foliage of heavily infested plants often is covered with the black growth of sooty mold fungus. These sap-feeding insects spend the winter as nymphs that become active again in the late May. Females produce from June in early summer.
Fletcher scale is a soft scale that infests Taxus and arborvitae. Females are light brown, globular, and about 0.2 inches in diameter. The small yellow crawlers move only a short distance from the female before settling to feed. There is one generation per year. Damage symptoms resemble those for Taxus mealybug.
Alternatives for crawler control
• Cultural control
Scales tend to thrive on stressed plants. Following a recommended fertility program and watering regime will promote plant health. However, over-fertilization favors scale buildup. If practical, improve plant sites to reduce stress and promote growth. Severely prune back heavily infested branches and protect new growth with insecticide applications.
• Insecticidal Sprays
Horticultural oils kill by suffocation or after penetrating over-wintering stages of the insect. Consequently, they may not be effective where several layers of scale coverings have accumulated.
Dormant oils are typically applied during February or March but may not be very effective against armored scales. Highly refined supreme, superior, or summer oils can be used on many trees and shrubs during the growing season. Read the product label for guidelines on plant sensitivity and temperature restriction before buying and using these products.
Insecticidal soaps are long chain fatty acids that kill susceptible insects through direct contact. Like horticultural oils, they require thorough coverage. Soaps leave no residue so repeated applications may be needed for some pests. These products may burn the foliage of sensitive plants, such as Japanese maple, so check the label for information about the plant species that you intend to treat.
A variety of natural and synthetic insecticides are labeled for use as sprays to control scale crawlers on landscape trees and shrubs. While the residual life of these products is generally longer than oils and soaps, timing, coverage, and precautions on damage to some plant species are very similar to those for oils and soaps.
• Systemic insecticides
Imidacloprid (Bayer Advanced Garden Tree & Shrub Insect Control Concentrate) is applied as a drench around the root zone of infested plants. This water soluble insecticide is taken up by the roots and transported throughout the plant where it is ingested by sap feeding insects. This provides a means of scale control without reliance on sprays. However, it may need to be applied several weeks before crawlers are active for best results.
The success or failure of control efforts may not be readily apparent but here are some things to check.
Scale insects can be attacked by a variety of lady beetles, predatory mites, and small parasitic wasps. Lady beetle adults and larvae can be seen but mites and parasitic wasps are very difficult to see. You can conserve natural enemies by using insecticidal soaps and oils which have limited impact on beneficial species in comparison to other control alternatives.
CAUTION! Pesticide recommendations in this publication are registered for use in Kentucky, USA ONLY! The use of some products may not be legal in your state or country. Please check with your local county agent or regulatory official before using any pesticide mentioned in this publication.
Of course, ALWAYS READ AND FOLLOW LABEL DIRECTIONS FOR SAFE USE OF ANY PESTICIDE!
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