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April 14, 2000

Christmas Tree Scouting Report

Welcome to the Christmas Tree Scouting Report for the week ending April 14. The next report will be available after 4 PM on Friday April 21. 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.

The overwintering eggs of spruce spider mite have started to hatch. Last week we reported hatch in Adams County and this week the 6-legged larvae were found in Lancaster, Schuylkill and Snyder counties.  Spruce spider mite, a traditional pest of spruce, regularly causes serious damage to balsam, Canaan, and Fraser fir. Douglas fir is an occasional host. To prevent damage, growers should begin now to monitor populations on susceptible species by tapping branches over a white surface and counting the spider mites. At this time of year, most of the mites will be extremely small and may be either salmon or green in color. Regular monitoring can be used to determine when the population is increasing and when controls should be applied. Although many miticides require a second application 7-10 days after the first, some of the newer compounds only require a single spray. These newer materials may not be effective when populations are high and should be used before they build to damaging levels.

On Douglas fir in Berks, Lancaster, Schuylkill, and Snyder counties, many of the overwintering Cooley adelgids have matured into stem mothers. Grape-like clusters of eggs can be found under the white waxy threads covering the adelgids. On Colorado spruce in Snyder County, the stem mothers have produced the waxy threads but have not deposited eggs. At the same location, Eastern spruce gall adelgids on Norway spruce are also covered but no eggs were found. Before attempting to control these pests with spring applications, growers should verify that the adelgids have not already covered themselves with the white waxy threads, indicating it is too late for control.

Balsam twig aphids continue to hatch and mature on true firs. Nymphs were found on last year’s fraser fir needles in Berks and Schuylkill counties. To prevent the curling and distortion of needles associated with this pest, controls can be applied anytime between egg hatch and budbreak.

On white pine, pine bark adelgids have deposited eggs and hatch has started in Perry and Schuylkill counties. In Berks and Snyder counties, only eggs were present. A young ladybeetle larva was feeding among the hatched eggs at the Perry county site. The introduced multi-colored Asian ladybeetleis often seen feeding on these adelgids and may exert considerable control.

Now is the time to plan for control of the first generation pine needle scale. These elongate white scales are very distinct on pine needles at this time of year. But, after needle elongation starts, they will be more difficult to find. If you have a population of this scale pest and want to control it this spring, it is a good idea to mark several heavily infested trees and monitor them for crawler emergencel Bloom of common lilac has long been regarded as a phenological indicator for pine needle scale crawler emergence. For the last several years, however, we have not seen any crawlers until the lilac blossoms have started to fade.

White pine weevils have deposited eggs in the terminals of eastern white pine in Perry County but no larvae are present. Weevils can be found feeding on the leaders and the sap flow from their feeding wounds is apparent. In western Pennsylvania, weevils have started to feed but no eggs are present.

Pales weevil adults were active around Scotch pine stumps from trees harvested in 1999. These weevils have probably started laying eggs in these stumps but will continue to visit nearby blocks of conifers to feed on the bark of the healthy trees. The best way to prevent flagging of branches on the healthy trees is to control the weevils with stump drenches in early spring. Foliar applications to prevent flagging damage are not as effective and generally more costly.

Eriophyid mites continue to be active on Colorado spruce in Berks and Snyder counties. These minute, four-legged mites cause chlorosis of needles which may result in premature needle drop.

Douglas fir growers should begin planning for rhabdocline sprays to protect this year’s growth. At sites visited in the Harrisburg area, the fruiting bodies are starting to swell. When infected needles were placed in a glass of warm water, the fruiting bodies did not open, indicating they are not yet mature enough to release spores. We did notice some buds that are starting to swell in Snyder County. Each grower should monitor their own fields for bud break and plan you first application of fungicide when 10% of the trees in a block have started to break bud. Applications before that time will not be effective since the fungicide can only protect new growth, not kill the disease organism in old needles.

Look closely before identifying any strange gall-like structure starting to appear on Douglas-fir branches. In Berks and Lancaster counties, pink and brown, sharp-tipped cones are being produced. Cones are usually more abundant on trees under stress, and last years drought may result in increased cone growth this year.

The next report will be available after 4 PM on April 21.