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April 13, 2001

Christmas Tree Scouting Report

Welcome to the Christmas Tree Scouting Report for the week ending April 13.

The next report will be available after 4 PM on Friday April 20. To receive a FAX of this week's message, please call (814) 865-1636. To report pest activity at your location, call 717- 772-5229.

Last week I reported Zimmerman pine moth activity in western Pennsylvania but made an error on the timing of controls. Controls must be directed at the young larvae in early spring, not at adults, as reported. Zimmerman pine moth overwinters as a tiny caterpillar. In fall, newly hatched larvae may feed on the outer bark of their host, before creating a silken shelter in which they will spend the winter. This shelter is usually under a bark flap or in a crevice in the outer bark. As temperatures rise, larvae burrow into the inner bark to complete their development. Chemicals generally can not reach larvae in the inner bark so controls must be applied before the young larvae enters the inner bark, usually in early to mid-April.

This week's warm weather brought out most of the early season pests. White pine weevils are mating on terminals of eastern white pine in Schuylkill County, but no evidence of feeding was found. In Westmoreland County, Mike Masiuk reports finding mating adults and feeding on terminals but no eggs were found in the feeding niches. More than 60 weevils were caught in a white pine weevil detection trap in Perry County. This site has experienced extensive damage for years, without any attempt at control, making it ideal for trapping. Chemical controls for white pine weevil should be applied now to the top 1/3 of susceptible trees. In addition to eastern white pine, Douglas fir, all spruces and occasionally, even true firs can be infested with these terminal-killing weevils.

Balsam twig aphid eggs have started to hatch in Pennsylvania. They are feeding on the undersides of last year's needles of true firs. Jill Sidebottom, NC Fraser fir expert, reported 97% of the balsam twig aphid eggs had hatched at her monitoring site in western North Carolina. We expect to reach that level within the next week or two, depending on temperatures. At that time, growers wishing to control this pest can apply insecticides and prevent damage to new growth. Balsam twig aphid causes curling of needles and stunts growth. It is especially important to control this sucking insect in the year or two before sale.

Another pest that deserves attention early in the season is Cooley spruce adelgid. We have been observing nymphs on the undersides of Douglas fir needles and the waxy white threads they produce are more noticeable. If you want to control this pest, it must be done before they produce enough to be in the "cotton ball" stage. At this point, stem mothers are present and most likely producing eggs and controls will not be effective until October. Forsythia, blooming this week in Harrisburg, is not only a sign of spring, but also a reminder of when to spray for Cooley in the spring.

Mike Masiuk also reports hatch of European pine sawfly larvae in Westmoreland County. The larvae are only about 1/16 inch long and may be difficult to find. Look for their shiny black heads and the straw like remnants of needles. Young larvae are not capable of devouring the entire needle and the central portion is left behind, where it dries to a light tan. The European pine sawfly can be a serious pest of Scotch pine but is very easy to control without chemicals. The larvae feed in a group so removing the infested branch or shaking the larvae into a container to be destroyed is effective. Simply shaking the larvae onto the ground will not be effective since they will crawl back to the host.

Female pine bark adelgids are depositing eggs under their waxy, white covering. These adelgids are generally not serious pests unless the population is extremely high. In dense populations, yellowing of foliage, and general decline of the host may result.

In York County, the black jellybean-like eggs of Cinara aphids have hatched on pines. These aphids are generally not damaging unless the colonies are extremely large. Cinara species on spruce, however, can often be damaging to new growth later in the year.

Needlecast symptoms, especially Rhabdocline on Douglas fir, are easy to spot now, before new growth starts. It is also important to find the symptoms now because protective fungicides will need to be applied to protect the new growth and prevent infection from occurring.

The next report will be available after 4 PM on April 20.