Damage

All scale insects have sucking mouthparts and feed on sap from the tree. Armored scale, like pine needle scale, burst plant cells and feed on the contents. Scale can remove large quantities of sap, stressing the host tree. Plants can usually tolerate small populations of scale. The extensive feeding by a larger population often leads to yellowing of leaves and dieback of twigs. Over time, an untreated population of scale may lead to the decline of the plant. Armored scale inject their waste back into the plant’s tissues, so no honeydew is produced.

Pine needle scale adults are concentrated on the host plant’s needles, where they feed on the sap, turning the needles yellow and brown. The scales feed on needle tissues which contain the green pigment chlorophyll. This pigment is essential for photosynthesis (production of plant food). The area around a feeding scale changes color, and when there is heavy infestation these spots of discoloration coalesce to cause entire branches or the entire tree to turn yellow or brown. Besides discoloration, severely infested trees experience needle loss, shorter needles, slowed tree growth, and may experience dieback or death.

Life Cycle

Pine needle scale has two generations each year. This species overwinters as eggs under the protective armor secreted by the female.

In May and June, they hatch into crawlers. Immature crawlers appear as purple or red-brown dots on needles and branches as they migrate around their host. Crawlers move around the host plant for several days and some may be transferred by wind to other plants where they can establish a new infestation. The crawlers settle on a needle, use their probing mouth parts to feed on the internal fluids of the needle, and eventually create their protective white coating.

Once the females establish themselves on a needle, they remain immobile there for the remainder of their lives. Adult females have a white elongated protective shell that is about one-third inch long with a yellow point at one end. Underneath the shell, their orange bodies are only one-eighth inch long and lack wings. The scales mature to adults by early July, after six to eight weeks of feeding. Males emerge with wings and fly to mate with females. Females lay about 40 red eggs underneath their white armor shell, then die.

The eggs start hatching after about four weeks, usually in mid-July, and the second generation of the year begins. This second-generation hatch spans about a month due to varied rates of scale development resulting from environmental conditions. The crawlers migrate, settle, feed, secrete their armor, then mature to adults and lay eggs at the end of the summer before they die and the eggs overwinter. In places where temperatures are warm well into the fall, scales may begin a third generation, but very few of these individuals survive through the winter. Timing of each stage of the pine needle scale life cycle can vary slightly depending on location and the year’s temperature patterns.

Management

Cultural Management

The best method for managing pine needle scale is prevention, minimizing any stressors so potential hosts are healthy and can stay strong through light infestations.

In the case of light infestations, infested branches should be removed as soon as they are identified to avoid spread to the rest of the plant. If feasible, heavily infested branches should be removed and destroyed. Branch and whole-plant removal should be done while the scales are immobile, since the mobile crawlers are more easily spread.

Biological Management

Pine needle scale has several natural enemies that are important for effective control. Scale outbreaks can occur following mosquito prevention spray, as the treatments can also eliminate beneficial insects.

Natural predators are effective in helping control minor infestations, but should not be solely depended on to fight heavy infestations.

Lady beetles and parasitic wasps leave their marks as small holes chewed through the white protective armor of scales. Lady beetles prey on scales while parasitic wasps lay their eggs inside scale bodies.

Populations of these beneficial insects can be maintained by avoiding excessive broad-spectrum chemical insecticides. Such applications may kill all insects except pine needle scale, creating prime conditions for spread and population explosions.

Chemical Management

Always monitor host plants to determine if chemical management is warranted. If an infestation is mild, it may be more beneficial to prune and allow natural enemies to do their work.

Horticultural oils and insecticidal soaps directed at crawlers can be effective against pine needle scale, while having a low impact on beneficial insects. Other insecticides can be used, but are likely to be harmful or deadly to a wide range of non-target species.

Due to their greater consequences, insecticides should be applied at a specific time to ensure peak effectiveness on the target pest. A scale’s protective armor is resistant to contact insecticides, but crawlers are highly susceptible, lacking any protection, so insecticides should be sprayed promptly after eggs hatch and crawlers are present.

It may be necessary to spray several times as second-generation crawlers hatch over a longer period of time. The insecticide label will give specifics as to timing.

Some, but not all, systemic insecticides are another management option. Systemics are taken up by the plant and distributed throughout the plant’s tissue to target feeding scales. Always read chemical labels carefully to ensure proper application technique and timing.

The pesticide information presented in this publication is current with federal and state regulations. The user is responsible for determining that the intended use is consistent with the label of the product being used. Use pesticides safely and wisely; read and follow label directions. The information given here is for educational purposes only. Reference to commercial products or trade names is made with the understanding that no discrimination is intended and no endorsement made by The Morton Arboretum.

For more information, contact The Morton Arboretum Plant Clinic at 630-719-2424 or plantclinic@mortonarb.org.