Q: I have scale insects on my maple tree leaves. They look like cottony cushion scale but I have never heard of it on maple. What do you think? How can I control it? My trees are 30 feet tall.
A: I am so glad you brought a sample of the insect into the office so we could look at it under the stereoscope together. The scale is called maple cotton scale, Pulvinaria innumerabilis whereas cottony cushion scale is Icerya purchasi, which I am sure clears that up completely for you doesn’t it?
Maple cotton scale is found on several other common hardwood trees such as ash, elm and boxelder. If scale populations are heavy enough the tree may show twig and limb dieback as the insect spends the winter on the twigs once the leaves drop off. In extreme cases, it is possible to lose the tree. Usually, sooty mold indicates the presence of the insects but weather conditions may control the presence of mold in the air and therefore on the tree. High concentrations of honeydew may drop on cars, lawn furniture or outdoor barbeque grills, which could also be a nuisance.
Since the tree is so large, it is impossible to apply horticulture oil directly to the leaves and stem of the tree. I suggest you use a systemic pesticide which contains imidacloprid. This should be applied to the root area totally under the canopy of the tree. The tree takes the chemical up through the vascular system and distributes it to the leaves. The insect pierces into the leaf and takes up the chemical into their digestive system causing it to die. You may need only one application of the chemical as it lasts for 6-9 months. Follow the directions on the pesticide label. Do no apply more product than the label suggests. I have heard people complain the product does not work when they spray it directly onto the insect. This product must be taken up through the root area of the plant and the insect must ingest via its piercing/sucking mouth parts. Direct application to the insect is useless. Remember: “The Label is the Law”. Avoid applying a chemical that contains both insecticide and fungicide unless you know the plant has both problems.
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