Dormant oil sprays control specific insects

2013-02-14T08:19:00Z Dormant oil sprays control specific insectsBy Kelly Feehan Columbus Telegram
February 14, 2013 8:19 am  • 

Dormant oil sprays are applied to plants during mid to late winter to control specific insects, usually scales. Now is the time to inspect plants and prepare to apply dormant oils if scale insects are found.

The dormant season is a good time to inspect plants for scales. Without leaves on plants, these small insects are easier to see on branches and small twigs.

Scales are 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 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.

While feeding on plant sap, a heavy scale infestation can weaken plants, kill branches, reduce fruiting  and kill entire plants.

Some plants to inspect for scale insects are lilac, dogwood, Euonymus, apple, pear, other fruit trees, crabapple, oak, ash, maple, pine, spruce and yew. Scales are most common on these plants but can attack many others.

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

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 easily 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.

Here is a reminder of our next lawn and garden class that is open to the public. On Tuesday, Feb. 19, we will be covering drought effects and recovery care of lawns and trees. The class will be held from 6:30 to 9 p.m. at the Courthouse community room.

John Fech, extension educator, will teach about lawns, and Laurie Stepanek with the Nebraska Forest Service will teach about trees via distance learning. If you are interested in attending this or other garden and landscape classes, call (402) 563-4901 for a flyer or email

Kelly Feehan is an extension educator-horticulture with the University of Nebraska-Lincoln, Platte County Extension office. Reach her at (402) 563-4901or by email at

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