Dormant oil sprays for scales

Dormant oil sprays for scales

  • Updated

Dormant oil sprays are applied to plants during mid to late winter to control overwintering some insects, like scales.

Some plants infested by scale insects include lilac, dogwood, Euonymus, apple, pear, other fruit trees, crabapple, oak, ash, and maple.

The dormant season is a good time to check these plants for scales. With no leaves on plants, these tiny insects are easier to see on branches and small twigs.

Close inspection is needed as these insects are adept at camouflaging themselves. To the inexperienced eye, they can appear to be a natural part of bark on individual stems.

If scales are found, options for control include pruning and destroying infested branches; applying a dormant oil to suffocate the insect; or waiting until eggs hatch and applying an insecticidal soap, summer oil, or an insecticide labeled for use on the plant to be sprayed.

Depending on the type of scale, these insects can be oval or circular shaped and bronze, tan, brown or white in color. Some resemble small shells, others look like raised brown buds, and some even resemble plastic foam.

Scales usually overwinter in the egg stage beneath a waxy covering; hence the name scale. When eggs hatch, the almost microscopic crawlers move out or upwards to a new location on a branch. They attach themselves, grow their own waxy covering for protection, and feed on sap from beneath the scale.

If populations are allowed to build up, a heavy scale infestation can weaken plants, kill branches, reduce fruiting, and eventually kill entire plants.

Dormant oils may be the most effective option. Because scales are small enough to miss during an inspection, it would be easy to overlook removing an infested branch when pruning.

And it can be difficult to detect when scales hatch. Insecticidal soaps and most insecticides need to be applied when young scales are in the crawler stage. This is a very short period of time and the optimum time for a spray application could be missed.

If a dormant oil spray is used, read and follow label directions closely. Dormant oils need to be applied before plants break bud or tender plant tissue will be damaged. Thorough coverage of branches and twigs is needed for good control.

Dormant oils also need to be applied when temperatures are above 40 degrees Fahrenheit; and applied early enough in the day to dry before freezing. If the oil freezes before it dries, plants can be injured.

Kelly Feehan is a community environment educator for Nebraska Extension-Platte County.



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