Saturday May 26, 2007
I am treating some trees with some kind of bug or something I cannot identify. They are all over the limbs and around the leavestems, they are about as big as a grain of wheat, color is brown to black and they leave sticky residue on the leaves and on the ground. I don't belive that they are aphids but I do see aphids on some of the leaves. Please help me with the ID and the proper control. Jason
I believe you probably are dealing with a scale insect of some sort, and from the stickiness you are seeing it would be one of the "soft" scale species, rather than an armored scale. What you see is actually a wax covering the female scale creates over herself as she matures, and beneath this she then produces her mass of eggs, after which she dies. The eggs hatch to the tiny but mobile "crawler" stage, and these new insects move about and feed on the softer foliage with their sucking mouths. As the insects mature they finally settle down in one place, form that wax shell, and become sessile and unmoving for the rest of their lives as they continue to feed on the fluids of the plant. The male insects look like tiny wasps, and would not be recognized as scales.
Scales and aphids are related, in the Order Hemiptera and Suborder Sternorrhyncha, and both produce the sticky drops of honeydew that are excess fluids from the plant. The honeydew is rich in sugar, and is a big draw to ants and wasps that feed on it. It also drips all over things below the scales, such as cars or sidewalks, and makes a real mess out of those surfaces. There are a great many different kinds of scale insects, so exactly which one you are dealing with is hard to say. While a plant can tolerate small infestations, a large scale invasion will do some damage, since the scales are removing plant fluids and nutrients.
Control can be done a couple of ways, neither of which is guaranteed to get you complete control. During the winter you can apply dormant spray oils to the trunk and branches of the tree. The oil covers and smothers any insects or mites that are over-wintering on the sprayed surfaces and in the crevices of the bark, including eggs. With the tree fully leafed out this is not a good recommendation for actively growing trees. There are lighter "summer" oils, such as Saf-T-Side Spray Oil that could be applied to most trees with foliage, and could kill many of the scales and crawlers. About this time of year you also should expect the new crawlers to be on the trees, visible as tiny moving specks. This stage is exposed and susceptible to insecticides, such as the many pyrethroids labeled for T&O use. The wax covered stages are pretty much impervious to being contacted with water based sprays.
An application of Merit, in the winter, also could help control these things. It is applied to the soil, moves up through the roots and trunk, and settles in the foliage a few weeks later, but stays there through the season. This will be most effective against the earliest stages that feed on the green parts of the tree, but less effective on scales feeding on the stems. Right now I'd inspect carefully to see if crawlers are present, and if so treat with a product like Talstar or Tempo, using a spreader to enhance the penetration through any wax on the insect. Applications may need to be done several times around 2 weeks apart to get each new group of crawlers as they emerge, since the insecticide could dissipate quickly.
Mr. Pest Control
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