Saturday, May 30, 2015 By: Ask A Master Gardener

Controlling Euonymus and Other Types of Scale

Master Gardener: Treat plants for scale insects before they can cause damage

Brian Jervis: Ask a Master Gardener

Saturday, May 30, 2015

Q: What can I do to control those white scale insects on my euonymus shrubs? Eva, Tulsa

A: Scales are unique insects, and there are many varieties. Euonymus scales, like most scale varieties, are pests to a particular plant species. These insects tend to occur repeatedly and can be devastating to certain euonymus plants.

Scales are difficult to treat. Control is best achieved using a combination of scale-resistant plants, preserving natural predators, and insecticides. There is no one best insecticide for control. The OSU fact sheet “Ornamental and Lawn Pest Control,” available online, lists OSU’s recommendations.

Euonymus plants most susceptible to scale are Japanese and Wintercreeper euonymus and their cultivars; euonymus alata (burning bush) is totally resistant to infestation. The insect can occasionally crossover and involve plant species such as camellias, hollies and ivies.

Scale insects are broadly divided into soft and hard varieties. The soft ones, which includes mealybugs often seen on houseplants, are more easily treated with pesticides than those with hard shells, such as the euonymus scale.

Control strategies depend on understanding the life-cycle of scales. Female scales and eggs overwinter under a brown shell that is fixed in place. In spring, eggs hatch into small nymphs, called crawlers, which move about the plant and eventually evolve into males or females. The white males are gnat-like and mobile; the females, on the other hand, turn brown and fix themselves permanently to the plant where they restart the cycle. Euonymus scales will have three to four batches of young in a growing season, a batch every six weeks or so.

Scales have several predators that are helpful in their control, and efforts should be made to preserve them. However, the predators are often overwhelmed and an insecticide may be indicated. Insecticides used are either organics or man-made chemicals. They work either by contact or systemically (absorbed into the plants’ sap). There are any number of approaches to take with these products.

OSU’s recommended insecticides are listed in the fact sheet mentioned above.

An environmentally friendly treatment is a “superior” grade of horticultural oil, such as the Sunspray Ultrafine brand, applied before bud break in spring. Because of multiple generations of scale, it should be used repeatedly three or four times at four- to six-week intervals during summer. Read the label carefully as some plants are intolerant of various oil preparations.

During the summer treatments, a standard insecticide labeled for scale may be mixed with the oil. Alternatively, a systemic insecticide containing dinotefuran, as found in some of the Green Light and Ortho products, can be applied as either a drench or granules to the root zone once a year, in addition to the oil.

Contact the OSU Master Gardeners at 918-746-3701 for further assistance in controlling euonymus scale.

Garden tips

Insect alert: Now is the time to be on the lookout for bagworms on juniper and arborvitae and lace bugs on sycamore, pyracantha and azaleas. Contact Tulsa Master
Gardeners for control suggestions.

Do not work soil if it is too wet. Tilling it while wet will cause damage to the structure that will take a long time to recover.

Thatch is a layer of dead and living stems, shoots and roots that pile up on top of the soil at the base of lawn grasses. If it is more than a half inch thick, it should be removed with either a core-aerator or power-rake. Now is the time to de-thatch Bermuda and zoysia grass. De-thatch fescue, if needed, in the fall.


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