It's time to talk about scales. Not bathroom or fish scales, but the ones lurking in your landscape. Lurking may be a stretch. Scale insects have no discernable head or legs, live under a waxy covering and suck plant juices. Despite their resemblance to helmets, their feeding can weaken and even kill trees and shrubs. The tricky part about scale is they often go unnoticed until they reach high populations. In addition there are several different scale species with different life cycles.

Scale start out as eggs. The eggs hatch into crawlers that move along stems or leaves. Scale are not going to win any insect races. After all you can't expect much speed when the most mobile stage of a scale's life is called a crawler.

Once the crawlers locate a place to settle, they use their piercing mouthparts to suck out plant juices. Feeding causes leaf yellowing, plant stunting, and possible death of stems or the entire plant.

Adult scale don't move for the most part and therefore just look like part of the plant. To find out if your plant really has scale, take out your trusty horticultural tool, your thumbnail, and scratch the suspect bump on the plant stem or leaf. If it pops off then it may be scale. If it doesn't easily pop off, then it may be a lenticel or some other normal part of the plant.

A common scale is oystershell scale. It looks like, you guessed it, tiny grey or brown oystershells. Oystershell scale can be found on many plants including ash, redbud, birch, dogwood, elm, hemlock, maple, poplar, privet, walnut, and willow. This scale can reach high populations to kill stems. Oystershell scale overwinters as eggs located beneath the female covering.

As with many insect problems, stressed plants are more susceptible to attack than healthy plants. Therefore keeping plants healthy with proper watering and fertilizing will help and may help the plant to tolerate low populations of scale. Prune out branches heavily infested with scale to quickly reduce the population.

Timing is very important with scale control if you have chosen to use an insecticide. Adult scale are difficult to control. They are most susceptible to insecticides in the young crawler stage.

Accurate identification of which scale is present is crucial. Once you know the scale then you can get a prediction as to when the young crawlers may be present.

One method of scouting for scale crawlers is to wrap a piece of black electrician's tape around a branch with the sticky side out during the time the crawlers are predicted to be present. Crawlers will get stuck on the tape as they try to crawl across it.

The Vanhoutte spirea (Spiraea x vanhouttei) shrub can be a good indicator as to when to scout for oystershell scale crawlers. Drive down any older neighborhood now and you will see these large shrubs with arching branches covered in white flowers.

Oystershell scale on plants such as dogwood and lilac should be sprayed now with an insecticide as Vanhoutte spirea is in full to late bloom. Crawlers on plants including ash, lilac, and maple are sprayed with an insecticide when Vanhoutte spirea has completed blooming.

There are several pesticides labeled for scale control such as carbaryl (Seven), acephate (Orthene), malathion, insecticidal soap and horticultural summer and dormant oil. Generally multiple sprays ten to twelve days apart are needed. Dormant season oil sprays are not effective for oystershell scale control so now is the time to control these insects. Scale control requires a certain amount of vigilance. Be sure to read and follow all pesticide label directions.

For photos of oystershell scale, please visit http://www.ipm.uiuc.edu/landturf/insects/oystershell_scale/