COTTONY MAPLE SCALE is an insect pest of maples, especially silver maples and locust trees primarily, but also will infest several other species. The pest is very common in the tri-city area of Michigan at this time. Although the insect does not usually cause much damage to the tree, it is truly a pest to the humans who live below because of the copious honey-dew excretions of the insect. The honey-dew falls onto surfaces below and sooty mold proliferates in the sticky sweet substance.
Treatment of the scale is difficult, especially on large trees. Sprays are often ineffective and can worsen the condition if done in May and June, because beneficial predatory insects are killed while the adult scales are largely resistant to treatment by sprays. The white egg sacs burst open in July as the eggs hatch and the immature scales crawl out to the leaves. Sprays coating the underside of the leaves at this time can be effective, but thorough coverage is difficult.
Systemic insecticides applied by trunk or soil injection have shown some good success, but the response may be delayed and the treatments are more costly than sprays. One good thing about systemic treatment is that it does not kill the beneficial predatory insects (twice-stabbed ladybugs and tiny parasitic wasps).
LECANIUM SCALE is another "soft scale" insect which is very prevalent in the tri-city area at this time. This scale is very prevalent on ash trees, sugar maples and oaks, but can infest many species of deciduous trees.
Like the cottony maple scale and other soft scales, the lecanium scales excrete large amounts of honey-dew with its attendant nuisance factor. However, these scales also cause significant lower branch dieback and can be seriously stressful to the tree. We see many ashes and sugar maples in Midland with severe lower branch dieback caused by this scale insect.
This scale's life cycle is slightly different that the cottony maple scale, with the eggs hatching slightly sooner in June or early July. Systemic insecticides have been shown to be effective against this insect if used with the right timing, and these treatments do not kill the beneficial insects.
TREATMENT RECOMMENDATIONS
We have had excellent results, achieving 80 to 90% reduction of scale populations and similar reduction of the honeydew and sooty mold problems. Our treatment of choice is trunk injection of imidacloprid, sometimes supplemented by trunk injection of acephate at the same time. The acephate gives quick, but short term kill and the imidacloprid lasts for two to three seasons. We also suggest that homeowners drench the soil each spring with Bayer tree and shrub care to "boost" the imidacloprid level in the tree. The tree may never need another injection. The cost for trunk injection is usually around $10 per trunk diameter inch for trees up to 24" and $12 per trunk inch for larger trees. The rate may be reduced if several trees are treated in one yard or neighborhood.
EXPECTATIONS FOR RESULTS
The injected chemical takes 4 to 6 weeks to spread throughout the canopy of the tree. In addition, it does not necessarily go into 100% of the branches, so some branches may still have scale.
In most single stem trees, we see 80 to 90 % reduction of scale populations and honeydew production for two to three years. In multiple stem trees, it can be difficult to get more than 60 to 70 % canopy coverage and scale control.
If we inject in the spring, we sometimes see some control in June, but often not until July and August when the new generation hatches, begins feeding and are killed.
In addition, late injections in September or October may not give much control the next spring, but should give good control beginning with the new generation hatch the next summer.
The ideal time for injection is May, June, or July so that the chemical is at its peak in July, August and early September when the crawlers are actively feeding.
If control is not achieved by the August after injection, then we will give additional injections at no charge.
