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May 19, 2000

Christmas Tree Scouting Report

Welcome to the Christmas Tree Scouting Report for the week ending May 12. The next report will be available after 4 PM on Friday May 26.  To receive a FAX of this week’s message, please call (814) 865-1636. If you have pest activity at your location to report, or would like to receive email reports, please leave a message at 717 772-5229.

In Lebanon County, female cryptomeria scales have begun to deposit their eggs. Samples from Berks and Lancaster counties earlier in the week revealed the females had produced eggs but they had not yet been deposited. We expect to see crawler emergence within the next week or 10 days. This armored scale is a serious pest of Fraser and balsam fir and should not be treated lightly. Growers should be watching their own trees, particularly on south facing slopes. Crawlers emerge over a period of 1-2 weeks and this is the only opportunity for good control. A second generation of crytopmeria scale is also expected later this summer.

In York County, several second instar Gypsy moth larvae were found on Douglas fir in a plantation. These larvae may attempt to feed on conifer needles and significant damage can occur to spruce. However, Gypsy moth is not generally able to complete its entire life cycle on conifers.

In Schuylkill and York counties, numerous ladybeetle adults, as well as syrphid fly larvae, were feeding on the balsam twig aphids on true firs. Most people recognize the adult ladybeetles as “good guys” but their larvae and the syrphid fly maggots are usually not as easy to identify. The ladybeetles that commonly feed on balsam twig aphids are the introduced multicolored Asian ladybeetle. The larvae of this species are black with an orange saddle on their body. The spiny projections on the top of the larvae are usually noticeable when the larvae are almost mature. Syrphid fly larvae are typical of many fly larvae in that they do not have a distinct head capsule. They are pointed on both ends and do not have legs. The adult syrphids, or flower flies, may resemble small bees as they hover over the plants. But they can be distinguished by one pair of wings rather than the two pair possessed by bees. At this time of the year, these naturally occurring predators are the only feasible control for balsam twig aphid. Sprays may be effective in reducing the population but the damage will already have been done.

Spruce spider mite populations continue on spruce and fir at many locations. The best way to keep your trees damage free is to regularly monitor for these minute pests. Beating branches over a white paper will dislodge the tiny dark mites and give an effective measure of the population. Some references state that a population greater than 10 mites per branch should be controlled. Remember to use two applications of miticide, unless you are using one of the newer materials that should only be applied one time.

The elongating candles of eastern white pine are coated with the white waxy material covering adult pine bark adelgids. Females have deposited eggs under some of the white masses. These sucking insects may cause stunting and chlorosis but are generally not a serious problem.

Cooley adelgids on the new growth of Douglas fir in Lebanon, Schuylkill, and York counties have already deposited eggs for the next generation. Damage from these adelgids includes chlorotic spots and bending of needles. In severe cases, growth may be stunted. Spring control options have long expired and growers should wait for the fall window of opportunity for controlling this pest.

On Colorado spruce, newly formed galls caused by Cooley adelgids are present and on Norway spruce, eastern spruce galls have also started to form. As with the Cooley adelgid on Douglas fir, the next opportunity to control this pest will be in September.

In Lebanon County, European pine sawfly larvae have finished and have dropped to the ground to pupate. Adults will not emerge until fall, at which time the females will deposit eggs in needles of susceptible hosts.

Pine needle scale crawlers have started to settle on needles of Scotch pine in Lebanon and York counties. The settled crawlers are light tan and can be easily distinguished from the red crawler stage. Settled crawlers are not as susceptible to pesticides as they have started to produce a waxy protective covering. Since all eggs do not hatch at the same time, you must remember to make two applications of a registered insecticide, 7 – 10 days apart, if you want to control the first generation of this common scale insect.

White pine weevil damage is starting to appear at some locations. If the terminals and new growth of white pine, spruce, or Douglas fir appear to be wilting, you should suspect white pine weevil. To confirm the presence of the pest, peel back the bark from the terminal and look for the white, leg-less larvae in the brown galleries. Effective mechanical control can begin now, when the larvae are still small and damage is limited to the upper terminal. If terminals are cut out this early in the pest’s development, they can be left in the field.

Rhabdocline needlecast continues to sporulate at many sites. The only method of preventing infection is to keep applying a fungicide to the new growth. Spring rains will distribute the spores easily and a minimum of three applications of fungicide is needed to keep this disease of Douglas fir in check.

The next report will be available after 4 PM on May 26.