Get rid of scale insects

By Todd Vineyard | Published Wednesday, December 20, 2017

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One of the most common insects I find when making horticulture visits is the scale insect. One of the common scale insects that I find are the euonymus scale, a common insect that attacks many species of indoor and outdoor plants.

Many species of scale insects damage landscape plants, shrubs and trees. Scale insects insert their mouth parts into plant tissues and suck out the sap. When scale numbers are high, plant growth will be stunted, leaves will develop yellow blotches, branches will die and some or all of the leaves may fall off.

Although scale insects are common, they are probably the most misidentified of all insect groups. Scale insects are generally small (1/4 inch long or less) and often mimic various plant parts such as bark or buds. Other species appear as small, white, waxy blotches or small bits of cotton on leaves or stems. The one attribute of scale insects that leads to the misidentification is that they appear to be nonliving. Once the young crawlers settle on a plant, they generally don’t move and can be overlooked.

Depending on the species, scale insects can spend the winter as eggs, young or adults.

Because of their protective wax covering, most scale insects are very difficult to control with insecticides once they have settled. Scale insects are most vulnerable to spray formulations of contact insecticides during the crawler stage.

Many pesticides are available to consumers wanting to control scale. Pesticides work best on crawlers. For effective control, you may need to apply pesticides two to four times at 5-7 day intervals because most pesticides work for less than a week, but crawlers from a single generation can hatch over several weeks.

Regardless of the number of applications needed, you must cover the plant thoroughly with insecticide each time. Cover both sides of the leaves and all the twigs and branches.

Dormant oils should be applied before spring growth begins, when temperatures are above 45 degrees for 24-48 hours. Apply summer sprays when temperatures are below 90 degrees for 24-48 hours.

When scales are on plants that are actively growing, apply a systemic insecticide such as imidacloprid around the base of scale infested plants.

The following is a partial list of approved insecticides available for scale insect control: orthene, Azatin XL, Sevin, Di-Syston, Merit, Battle, horticultural oil, Olympic insecticidal soap and Distance. Read and follow instructions on the label. For a complete list of insecticides and information on scale insects come by the Extension office and ask for publication B-6097.

Todd Vineyard is a Wise County Extension agent.

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