Sunday 27 July 2008

Tipping the Scales

Photo: K Ashton, Lecanium scale

Your plants are having the life sucked out of them, literally!

Trees and shrubs are little more than sugar factories and there is no shortage of freeloaders that want a part of this sweet treasure.

In this case the culprit isn't some vegan vampire it may be a scale, a simple insect with a big appetite.

Scales are small insects that have evolved a protective waxy coating that protects them from the elements and predators. This waxy coating, or scale, is the source of the insects name and its secret weapon. The scale often resembles a twig, bud or the bark of its host, making it difficult to identify and confusing it's predators.

The insect spends most of its life immobile, sitting under its armor, quietly sipping sap with its mouth, firmly attached to it's host. As it grows it sheds its skin which becomes part of its protective coating. At a certain point in the year it lays eggs that develop into crawlers. These small exposed crawlers are so small that they escape predators can even blow on the wind to new host plants. Once they find a suitably delicious host they insert their mouth piece into the plumbing of the host and start their high carb diet. Some of the sap goes through the scale and drips onto the foliage or branches of the plant and leaves a stick black mess. There is still lots of energy in this mess and it is attacked by a sooty colored mold.

This black sticky film on the leaves of a plant, your patio furniture, or the paint on your car is often the first sign of a scale problem.

Scales come in two categories depending on the thickness of their waxy coating. Thickly covered scales, often looking like oyster shells under the microscope, are called armored scales. Less robustly covered scales are referred to as unarmored or soft scales. Typically the soft scales are covered in a waxy or fluffy protective coating that is thinner that their armored kin. Scales tend to be very host specific each one favoring a particular species or group of plants over all others.

Two common scales in the landscape are an armored scale on spruce and a soft scale on arborvitae. Pine needle scale, Chionaspis pinifoliae is an armored scale that prefers conifers to dine on. Spruce, pine, hemlock, yew and hemlock are all affected by this scale. This scale looks like tiny grains of white rice stuck to the trees needles.Predators will keep low levels of these in check but occasionally, in our landscapes they will reach numbers that require control. There are a number of products that can be used to control these but they all are best applied when the crawlers are active. This occurs in late June to mid July. It will take several years to get adequate control.

Arborvitae, cedars, are afflicted by a soft scale called Lecanium scale, Lecanium corni. This scale has evolved to look like a small shiny bud on the stem of the tree.

Lecanium scale's crawler stage is in mid July and applications timed to hit them while they are vulnerable are most successful. If your car is covered in sticky black sugar or if find something that looks unusual on your trees contact your Arborist. They will be able to tell if that lump on the branch is a scale and recommend a plan to thwart it's sweet tooth.

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