One of the more difficult insects for Christmas tree growers to control is the pine tortoise scale (Toumeyella parvicornis), a North American native. This scale is often found on Scotch, Austrian, Jack and red pines, and several species of southern pines. Eastern white pine is not generally attacked. In North Carolina, the pine tortoise scale can be particularly severe on Virginia pine, which is a major Christmas tree species in the eastern part of the State. The insect usually does not cause mortality, although it is possible. Its major impact is through the reduction of growth and the secretion of "honeydew," which accelerates development of an unsightly black fungus. This fungus discolors trees making them less attractive and often unmarketable.
The natural range of the pine tortoise scale is from the Dakotas eastward to the Atlantic Ocean and south to Florida. Depending on the location and weather, from one to four generations per year can occur. In North Carolina, two to three generations may be anticipated. Due to the lapse of time for emergence of crawlers from a single generation and the overlapping of generations, several stages of development may be observed at the same time.
Scales over-winter on trees as immature females, which are brown, generally circular in shape and about 1⁄4 inch long. In the spring, the females mature and produce eggs. This sequence occurs in March to April in North Carolina, later in the more northern parts of the scale's range. As the eggs hatch, juvenile "crawlers" develop beneath the female and emerge (April to May in North Carolina). Crawlers move away from the parent, settle on a twig, and begin forming a white crystalline substance on their bodies. Shortly thereafter, males emerge from a pupal stage and fertilize the immobile, immature females. Males have no functional mouthparts and soon die, leaving only females. As the females continue to feed, they begin secreting honeydew, which, in turn, hastens the development of the sooty mold fungi.
In states containing the more northern and western portions of the pine tortoise scale range, one generation per year is observed. However, two generations per year is often observed in North Carolina; the first generation of new females usually reaches maturity in late June to early July, and the cycle is repeated.
Field scouting for the pine tortoise scale is important for successful control. Only by recognizing and monitoring the pest in its various life stages can proper measures be taken.
Control of adult pine tortoise scales by insecticide sprays is difficult due to the relatively hard covering on the mature insect. Thus, insecticide sprays should generally be applied only when crawlers are present. As many crawlers may settle under young, developing needles or under the bodies of the previous generation's females, a thorough, high pressure spray application is required. The best time for control of crawlers is during the first generation. In the spring, crawler emergence is more uniform, and good control early in the year will prevent later population build-ups.
Only insecticides labeled for scales should be applied, and it is often a good idea to vary the chemical used. Experience indicates that repeated use of a single insecticide may reduce the number of beneficial insects, thus resulting in a greater scale problem. Applications of broad-spectrum insecticides may also harm beneficial insects.
Insecticidal soaps and horticultural oils may be used in late fall or early spring to treat overwintering females. These compounds will usually not harm beneficial insects. Again, good coverage is essential if scales are to be controlled. Care should be taken to avoid rates, spray timings, or application methods that might result in damage to the trees.
Often, infestations are localized in a small portion of the field. Trees known to have scales should be tagged and then treated when crawlers are observed. Control in this manner may prevent the need to treat an entire field. It is also worth remembering that honeydew is often a sign of scale infestation, but treatment should not be delayed until honeydew is noticed.
Control of ants in Christmas tree fields will also help reduce scale populations. Ants are attracted to the honeydew and may actually protect the scales by killing the scales' natural enemies.
For further information on this or other Christmas tree pests, please contact your local N.C. Cooperative Extension center.
Publication date: April 24, 2014
Revised: Jan. 10, 2019
Recommendations for the use of agricultural chemicals are included in this publication as a convenience to the reader. The use of brand names and any mention or listing of commercial products or services in this publication does not imply endorsement by NC State University or N.C. A&T State University nor discrimination against similar products or services not mentioned. Individuals who use agricultural chemicals are responsible for ensuring that the intended use complies with current regulations and conforms to the product label. Be sure to obtain current information about usage regulations and examine a current product label before applying any chemical. For assistance, contact your local N.C. Cooperative Extension county center.
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