tt-101 BY DON MEEHAN

CONTROL OF LECANIUM SCALE

This year seems to be the year for Lecanium scale. As is often the case, insect populations build up to noticeable levels, and this is when I get calls. This season seems to be Lecanium Scale's year. Scales are sucking insects which feed on a variety of plant hosts. These include fruit trees, dogwood, maple, roses, laurel hedges, and almost every other kind of broadleaf host. Some years even evergreens are not safe from these pests. HOW DO YOU KNOW IF YOU HAVE SCALE? There are several kinds of scale insects, but we will discuss only Lecanium scale, "Lecanium corni", since it is the most common species found outdoors here in western Washington. This insect is noticeable in the spring since that is the time of the year when the scale shells are at full size. They appear on twigs and branches as hemispheres about 1/8 to 1/4 inch in diameter. They are usually chestnut brown, but their color can vary from host plant to host plant. Those I have observed this spring have been brown with white markings. Others may be brown with black markings. It is common to have powdery purplish-white wax present on the scale. On first glance at shrubs and trees you may not notice this pest simply because the size and color are often similar to buds. once discovered, you can be sure you have found it by lifting the scale off the twig; they are generally loosely bound. If careful, and only during the early spring, you will notice the underside of the scale is full of very small whitish to yellowish eggs. A hand lens or other type of magnifying lens will help to see this feature better. LECANIUM SCALE LIFE CYCLE Eggs found at this time of the year will hatch into crawler stage in late May to mid June. The hatch will be dependent upon temperature and can stretch over several days. Once the hatch has occurred, the small crawlers will migrate to the undersides of the host plant's leaves and begin feeding. They will feed into August before they migrate back to twigs and small branches. There they will complete their life cycle by maturing out in the spring with fully developed shell. They then lay their eggs and the female dies underneath the shell. There is only one generation each year. WHEN DO YOU NEED TO WORRY ABOUT CONTROLLING THEM? Control should only be considered if you have a severe infestation. Like aphids, scale insects produce honeydew which can create a sticky mess on cars sitting beneath infested trees. In addition, the honeydew will drip onto lower leaves of the plant, leading to the growth of black sooty mold. As with any sucking pest, they rob the plant of some of its nutrients, hence decreasing the vigor of the plant. A few scale insects on the plant do not warrant any other control than that provided by Mother Nature. There is a long list of natural predators that attack Lecanium scale. The ladybird beetles and green lacewings do an excellent job of eliminating the crawler stage. By using broad spectrum insecticides when the problem has not reached the severe stage will do more harm than good since it will indiscriminately kill the many GOOD insects. Once a severe infestation is discovered, and hand removal is impractical, there are a number of insecticides which will work well. The first thing to keep in mind is that it does little good to spray when the eggs, resting under the scale shell, have not hatched. They will be protected by the shell. You must wait for hatch to complete and the crawlers to migrate to the undersides of the leaves. You will know this has happened by simply picking off one or two of the shells each week in early June to see if they are empty. Once they are empty, you can be assured the hatch has begun. Before spraying, wait a week or two to be sure all eggs have hatched. Then select your insecticide, based on the type of plants you have in your yard. If you have edible plants, select a material that is safe. This may be necessary if you suspect drift might get on edible plants.




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