Managing scale on your fruit trees requires a multifaceted approach
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Nanette Londeree
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Ever notice a pretty healthy-looking fruit tree in your garden that seems to have a trail of ants hiking up the trunk? On closer observation to see where those ants are going, you spy some branches and stems that appear kind of bumpy and glisten like someone sprayed them with sugar water. If so, you may have an infestation of scale.
These are strange little pests; their name refers to the shell-like waxy covering that conceals their rather delicate bodies. They are generally inconspicuous insects — their color, shape, texture and other features vary with the species. They lack an obvious head, don't resemble most other insects and are either completely stationary or slow moving.
This group of insects suck juices from a wide array of plants and then pump out the excess in the form of a sugary substance called honeydew. Ants love this sweet stuff and will guard the area infested with scale to protect the pests and keep them producing the tasty treat.
If that isn't bad enough, the honeydew, which can coat leaves giving them that shimmering appearance, is a great food source for yet another problem, sooty mold. This is a fungus that looks like someone rubbed fireplace soot on the leaves, hence the name. If you can control the scale, you can eliminate ants and the potential for sooty mold.
While aphids and whiteflies also produce honeydew that attract ants, the three types of insects look and behave differently and it's easy to tell them apart.
There are two main groups of scale insects — soft and armored. Soft scales have a more rounded and convex cover that may be thin, cottony, powdery or waxy and doesn't lift off. These are the varmints that produce copious amounts of honeydew. Armored scales are tiny and flat; their hard, shield-like cover is composed of shed skins and wax and it can be separated from the insect's body. They don't secrete sticky honeydew. You need to know which type of scale is afflicting your plant, soft or armored, as the potential treatment may be significantly different.
You may find scale insects on plant branches, stems, twigs, trunks, foliage or fruit. Leaves may appear curled, look wilted, turn yellow or drop prematurely. They may cause deformed blemishes or discolored halos on fruit, leaves or twigs. Heavy infestations may severely stress your valued tree, leaving it more susceptible to attack by other insects like borers, or infection by disease.
Managing scale usually requires a multifaceted approach because of the pest's protective cover. Begin with good growing conditions and proper cultural care, especially appropriate irrigation.
Scale's natural enemies — small parasitic wasps and predators like beetles, lacewings and some types of mites, may be able to contain low populations of the pest. Plant nectar or pollen-producing flowers to attract and support these natural enemies.
Move next to disrupting the scale's pest-tending ants by pruning infested branches and removing weeds that provide a bridge between buildings or ground. Add sticky substances, like Tanglefoot, around the trunk that ants can't cross. If needed, utilize ant baits that attract the ants to the bait and that they in turn, take back to their nests.
If you need to move to some type of spraying treatment, timing is everything with these pests. Treat at a time when crawlers — the immature form that have legs and walk away from the mother scale to find new feeding sites — are the most active. A thorough spray of horticultural oil, applied either during the dormant season or soon after scale crawlers are active in late winter to early summer, can provide good control. Spray when there is no predicted rain or fog for a full day. It is important to completely cover the infested plants — all above ground plant parts, for effective control.