Q: Pine needle scale is a big problem in our company’s service area. We currently apply foliar spray products to manage pine needle scale, but have challenges scheduling jobs due to weather related issues. Are there other options?
— Scott Diffenderfer, Good’s Treecare Inc., Harrisburg, Pa.
A: Thank you Scott for sending this month’s question.
Pine needle scale is a common pest problem on conifer species across the country. Pine needle scale can infest pine, spruce and fir species, and is especially damaging on Scot’s, Austrian and mugho pines. Severe infestations of pine needle scale can result in significant damage and require insecticide treatments.
Pine needle scale adult females are distinctly white, and easily identified on the needles of host species. Needles may also turn a yellowish color and eventually become brown. The females are protected by an armored shell and when squished will exude a reddish-orange “juicy” ooze. Crawlers (juveniles) have two generations per year and can be identified with a hand lens in May and again in July. Pine needle scales are relatively immobile; crawlers will only move short distances on needles to feed. However, winged males can fly short distances and crawlers can be blown by wind to spread to new trees. Areas such as windbreaks where conifers are densely planted can be prime locations for pine needle scale.
Numerous scale insects are key pests throughout much of the United States and represent some of the most common pests that arborists are challenged with managing. Scale species are generally categorized into one of two groups — soft or hard/armored. Pine needle scale is part of the armored group because of the hard waxy shell that protects the wingless female and her newly laid eggs. Armored scales are unique from soft scales in that they feed using a long piercing mouthpart and do not produce “honeydew” (scale excrement). On the other hand, soft scales do not have an armored protective cover, have shorter piercing mouthparts, and produce honeydew. To ensure control of a scale pest it is important to diagnose the species and determine if it is a soft or armored scale, as management strategies will vary depending on the type of scale.
There are numerous foliar spray products that can be used to successfully control scales including pine needle scale. Foliar sprays will not provide acceptable results on females that are protected by their armored shell. Timing foliar sprays to occur when crawlers are active is essential, which makes detection and monitoring for the crawler stage important. Foliar sprays are a great option when immediate knock down of crawlers is required; however, due to their shorter residual, multiple applications may be required. For example, foliar sprays to control severe outbreaks of pine needle scale should be applied to control each generation of crawlers in May and again in July. As alluded in your question, operational challenges with weather can also make it difficult to control armored scales with sprays.
For many years, arborists have treated many species of soft scales successfully with systemic soil or tree injection applications of imidacloprid. However, systemic applications of imidacloprid have typically not provided acceptable levels of control on pine needle and most other armored scale species. More recently, systemic products with the active ingredient dinotefuran have been developed that are effective against many common armored scale pests. Dinotefuran can easily be applied to the soil as a soil injection or soil drench and can also be applied to the lower portion of the trunk as a systemic basal bark spray. Dinotefuran soil applications are translocated up into the crown of the tree faster than imidacloprid soil treatments, but may still require 2 to 3 weeks to move up into larger trees. Systemic bark sprays can move rapidly into the leaves of trees within a few days to control certain scale pests. When compared to foliar sprays, systemic applications of dinotefuran can provide greater operational predictability and more flexible application timing due to the ingredient’s longer residual.
Shawn Bernick is director of research and technical support at Rainbow Treecare Scientific Advancements, Minnetonka, Minn. He will be answering one tree health care question in each issue of Arbor Age throughout 2010. To submit your question for consideration, please e-mail Arbor Age editor John Kmitta at firstname.lastname@example.org. Be sure to indicate that the question is for the tree health care Q&A, and include your name and contact information.