Scale insects on pine
Amy Jordan, Special to the Gazette
Thursday, May 14, 2009
Plant problems are often apparent on plants before we actually notice them, and by then it is usually too late to intervene. This is why it is important to get out in the yard and look closely at what is happening. By doing this, you not only are able to enjoy the positive attributes of your plants, but you are also able to catch problems before its too late.
If you have pine trees, there are many problems you may have noticed on them. With close inspection, you may see white flecks or brown bumps on the needles and stems. These strange growths are actually protective coverings of insects called scale.
In Kansas, pine needle scale overwinter as maturing/matured females. The soft-bodied female scale is protected beneath the white scale covering. Eggs develop in late winter and early spring. As they are deposited, the female’s body shrinks, making room for them beneath the scale cover. Once eggs mature, crawlers hatch. They move out to settle on pine needles and begin feeding, completing development in three stages. The white waxy protective cover is produced from glands on the bodies of third instar individuals.
Pine needle scales produce two generations a year in Kansas with crawler activities roughly occurring in mid-May and early June and again in mid to late July. While inspecting samples brought in to my office this week, I saw that crawlers are present now.
Heavy infestations of pine needle scale may weaken and kill branches and have been reported to kill entire trees. Many sources recommend applying nerve insecticides as crawlers emerge from beneath the protective cover. This requires close monitoring to determine proper timing. While this can be done, horticultural oils offer a less tedious alternative. Horticultural oils are active against all scale life stages. Although suffocation is the primary mode-of-action for oil treatments, oils also penetrate cellular membranes causing disruptions that lead to cellular death. There are noticeable signs that oils are actively working. Within a week after applying, the normal healthy “white” appearance
of pine needle scale covering changes. The oil alters the makeup of the waxy scale cover making it transparent so eggs and remnants of females are visible. Flipping the scale cover, eggs are dark and are clumped together. The female scale is also darkened. (Healthy eggs would appear bright pink and loose.) Horticultural oils provide no residual control once they have dried. Because scales are small and needle clusters thick, misting will not provide satisfactory control. An adequate amount of spray must be applied to thoroughly cover foliage and ensure direct contact with intended targets.
Pine tortoise scale feeds on many types of pine trees, including Scots, Austrian, and red. Immature females, which are round, brown, and wrinkled in appearance, overwinter on twigs. Eggs are laid underneath the body of adult females. Eggs may hatch into young crawlers from May through June, depending on temperature. Crawlers eventually establish in suitable locations and initiate the feeding process.
Crawlers may spread to other plants via wind currents or by birds. Females are capable of producing up to 500 crawlers. Males, similar to most scale species, develop into winged individuals, which fly and mate with females. The males cannot feed and eventually die. There is usually one generation per year.
Pine tortoise scale feeding causes yellowing of needles, stunted needle growth, and under
extensive populations may even result in pine death. In general, young pine trees are more susceptible to pine tortoise scale than mature trees, and foliage closer to the ground tends to support higher populations of pine tortoise scale than foliage higher in the tree canopy. In addition, pine tortoise scales producer large quantities of honeydew, which serves as a growing medium for black sooty mold fungi. Under heavy infestations, entire trees may appear black.
Insecticides that may be useful for control of pine tortoise scale include acephate (Orthene), imidacloprid (Merit), insecticidal soap, and horticultural (=summer) oil. These insecticides need to be applied when crawlers are active in order to achieve maximum control of pine tortoise scale and alleviate problems next year.
F Amy Jordan is a horticulturist with K-State Research and Extension in Lyon County.