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May 4, 2001

Christmas Tree Scouting Report

Welcome to the Christmas Tree Scouting Report for the week ending May 4. Your next scouting report will be available after 4 pm on Monday May 14. To report pest activity at your location please call 717 772-5229.

Growers should be starting to spray their Douglas fir for Rhabdocline needlecast. Growers as far north as Snyder County are seeing budbreak and fruiting bodies are cracking open on the undersides of needles. Rain and morning dew will allow these fruiting bodies to open and gradually release thousands of spores. Many growers in the Harrisburg area have already made the first application while northernmost growers will have a week or more to prepare.The only method of controlling this serious disease of Douglas fir is to prevent infection of new needles as they appear in spring. The first application of fungicide should be made when 10 % of the trees in the block have started to break bud. The second application should be made one week later and the third in another two weeks. Growers often question the application of fungicide before rain. Several hours of dry time before the precipitation will be sufficient to protect the new growth at a time when spore release will be occurring.

Spruce spider mites are very active and causing damage on firs as far north as Columbia County. Applications of miticides are advised if you intend to sell the trees this year. Many newer miticides have label restrictions on the number of application per year. Check the label of your material before making applications.

Balsam twig aphids are starting to move to the unopened buds. These are the “stem mothers” that will produce the damaging stages of this true fir pest. In Columbia County, the nymphs are active on old needles but farther south, in Lebanon County, nymphs and stem mothers are on buds of Fraser fir. At a known infestation in Dauphin County, the aphids had disappeared. But, when the newly emerging cones were examined, balsam twig aphids were inside the cones, feeding on the tender new growth. Next week is probably the last week for application of controls since budbreak is expected soon.

White pine weevil eggs have hatched in Perry and Snyder counties and the small larvae are beginning to feed in the inner bark. Insecticide application can still be made to kill the adults continuing to feed and deposit eggs. But, some damage can be expected to the terminals of infested trees. Early pruning of wilting terminals can eliminate the pest in early summer.

Cooley adelgid eggs have hatched on Douglas fir in York County. The active nymphs can be found on the newly emerging needles, where their feeding is causing chlorotic spots and distortion of the growth. It is too late to be effective with insecticides after the stem mothers deposit eggs under the white cottony masses. In all but the most northern locations, that event occurred within the last week or two.

Growers who failed to spray fresh stumps to control Pales weevil are experiencing feeding damage to valuable trees. In addition to eastern white pine, Pales weevil will also cause damage to Douglas fir and true firs. On Douglas, flagging of lateral branches may occur but on true firs, the damage is usually limited to the terminal. Growers may even mistake the feeding for hail damage. At this time of year, spraying stumps is not practical since the weevils have already deposited eggs and larvae are present. The only choice for a grower is the costly application of pesticide to the entire tree. This may prevent additional weevil feeding damage but will not be sufficient to protect the trees until harvest.Fall feeding from newly emerging adults will occur before the weevils settle to over winter. Foliar applications are more practical in the fall but cannot replace the stump treatments in early spring.

With lilac bloom starting in the Harrisburg area, growers should be monitoring pine needle scale for crawler emergence. The paprika like crawlers are difficult to see after new growth starts.To help you with monitoring for hatch, you can tag an infected tree and return to that tree for observations on a regular basis.

Pine bark adelgid crawlers are emerging in Adams County. They are moving onto the elongating candles to settle and feed on the bark. Severe infestations can result in yellowing or dwarfing of trees but in most cases these adelgids cause only aesthetic injury with the appearance of white waxy material on new growth.

Our next report will be available after 4 PM on Monday, May 14.