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May 23, 2003

Christmas Tree Scouting Report -
Number 9

Welcome to the Christmas Tree Scouting Report for the week ending May 23. The next report will be available after 4 PM on Friday May 30, 2003. To receive a FAX of this week's message, please call (814) 865-1636. To report pest activity at your location or request email report, please call 717 772-5229. For local Growing Degree Day information, please go to http://www.nass.usda.gov/pa/ and click on Crop Weather along the left margin.

Douglas fir growers should have applied two sprays for Rhabdocline needle cast by now. Growers in more southern counties should be planning a third spray in the next week. If this cool, wet weather continues into June, it may be necessary for growers to apply a forth spray three weeks following their third spray.

Last week pine needle scale eggs were beginning to hatch under the scale cover in Northumberland County. This week eggs were hatching in Adams County on Scotch pine, but were not yet out on the needles. In Dauphin and York counties no egg hatch was observed on Scotch or White Pine. In Westmoreland County, and in Pittsburgh, crawlers were moving out onto the needles. For best results, you should wait until crawlers are out on the needles to begin your first generation spray program.

Growers are starting to notice damage from balsam twig aphids feeding in the new growth of true firs. This damage appears as curling and stunting of new needles. The most efficient time to spray for this pest is before bud break. Once the new growth begins to appear the aphids are already there and feeding on the tender needles. Sprays applied now may reduce next year's pest population, but the aphids have already done the damage. Many different predators feed on balsam twig aphids and will provide some degree of free pest control at this time. You may have noticed lady beetles on damaged trees and if you look close you may even observe the larvae of the flower, or syrphid, flies. These pale green to yellow maggots look like slugs and each one can consume as many as 400 aphids during its development.

European sawfly larvae are ¾ inch in size in Lebanon County and consuming entire needles on Scotch pine. These larvae always feed in groups and are quite capable of stripping a tree of most of last year's needles. The fact that they only have a single generation each year and feed exclusively on the previous years growth reduces their importance as a pest. Hand removal is the most effective method when larvae reach this size. In the next week or so, the larvae will have completed their development and will drop to the ground to pupate. This process has already started in western counties and growers may find only defoliated branches where the groups of larvae were feeding.

Last week we discussed a spruce spider mite infestation found on large Douglas fir in Lehigh County. This week in York County this mite was found again on Douglas fir. The mites went unnoticed last year but were already producing webbing and were out feeding on the new growth. Remember, the spruce spider mite is not just a pest of spruce or true firs but all Christmas tree species. Infestations on pines and Douglas fir may not be common but do occur.

Last year a population of the Admes spider mite, a relatively uncommon pest of spruce in Pennsylvania, was found on Colorado spruce in Northumberland County. This is only the third report of this species in the state, following its initial discovery about 5 years ago. Admes spider mite can cause significant browning of needles of all spruces. The adults are much larger than spruce spider mite and tend to settle out on the needles in a "stretched-out" position. The mites are reddish with long legs and sort dorsal hairs. We are continuing to study this mite by following its life cycle throughout the growing season and will have more information when significant data has been collected.

This year we were also monitoring for the eastern pine shoot borer in Dauphin and Perry counties. This moth began to emerge in late April and peak counts were found in early May. We continue to find a few adults in the pheromone traps. Eastern white pine and Scotch pine are favored hosts of this native pest. However all pine, Douglas fir and white spruce are known hosts. The caterpillar of this small moth usually attacks new lateral side shoots and sometimes the terminal leader. Female moths begin laying eggs on the new shoots soon after emerging and young larvae bore into and feed in the center of elongating shoots. Once larvae are mature they chew an exit hole at the base of the shoot and drop to the ground to pupate and over winter. Look for yellowing and stunted shoots. On thinner shoots, wilting will be noticed. Damage is generally not severe unless trees are repeatedly attacked, in which case stunted, forked leaders and general loss of shape can occur. Some control is generally achieved by normal shearing of Christmas trees. Late shearing, however, may enhance population build-up by allowing larvae to complete their feeding and exit before the shoots are pruned. This pest does not cause widespread damage, and sprays are not generally recommended. Damage may mimic shoot feeding activity of adult introduced pine shoot beetles. However, the beetles feed later in the year and their galleries are not packed with frass and wood shavings. Galleries of eastern pine shoot borer are often packed with frass. In addition, the beetle creates perfectly round entrance and exit holes, while the exit hole of the moth larva is oval and irregular.