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June 16, 2000

Christmas Tree Scouting Report

Welcome to the Christmas Tree Scouting Report for the week ending June 16. The next report will be available after 4 PM on Friday June 23. 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.

Cryptomeria scale crawlers continue to emerge in Fraser fir plantings in Berks, Lancaster, Lebanon and York counties. Some crawlers have already settled and begun to cover themselves with a white waxy covering. These settled crawlers, or nymphs, have chosen the site at which the remainder of their life cycle will be spent. They will continue to feed and molt into mature nymphs and eventually adults at the same site on the needle. Since the only mobile forms are the crawlers and winged males, feeding damage is cumulative at the site and will result in pale spots on the upper surface of the needles.

Some cryptomeria scale eggs on these same trees are still unhatched. This is common and one of the reasons this pest is so difficult to control. In contrast to many pests that have a concise egg hatch, cryptomeria scale eggs hatch over a period of several weeks. Therefore, repeat applications of a pesticide must be made every 7 to 10 days until crawlers are no longer emerging.

White pine weevil larvae are feeding under the bark of eastern white pines, Douglas firs, and spruces and the death of leaders is easily detected. Control can be achieved at this time by pruning out the infected leader, down to good wood. Any material cut from the tree should be removed from the block since the larvae present are mature enough to complete their development in branches on the ground.

At many locations, Cooley adelgid nymphs are active on the new growth of Douglas fir. Growers may be tempted to spray for this pest at this time but should wait until fall to be effective with their pesticides. Sprays applied now would kill a segment of the population but many would escape. Also, most of the damage has already been done and adelgid feeding on needles at this time of year will not cause additional pale spots or kinks in the needles.

Larvae of introduced pine sawfly are feeding on eastern white pine in Lebanon County. These attractive yellow, white and black spotted larvae rarely cause significant damage since they do not feed gregariously. Individual larvae can be hand picked to avoid the need for sprays.

Pine needle midge damage was found on Scotch pine in York County this week. Yellow-orange larvae are still feeding at the base of the needles on the terminal. The characteristic damage – needles bent over at the base – is easy to spot on terminals and very light in this planting. Occasionally this midge causes defoliation of the entire leader.

Striped pine scale crawlers have settled on Scotch pine in York County. This soft scale pest of pines has a single generation each year. The scales that settle on the pine needles will be males, while the female scales settle on the bark.

Bagworms are still only about ¼ inch in length but are causing significant damage to spruce and fir in York County. Bt, the biological insecticide, is still effective at this time but before too long, a stronger chemical will be required to achieve control.

The same principle applies to Gypsy moth larvae that are causing damage to spruces in Snyder County. Frass is accumulating on branches of infested trees and the larvae are now over 1 inch in length. Biological insecticides are generally not effective at this stage and control will require a more potent chemical. This appears to be a bad year for Gypsy moth in areas north of Harrisburg, judging from the many calls received. Christmas tree growers who dig trees should be especially aware of this pest and the federal quarantine covering shipments to some states.

Both Cooley and eastern spruce galls remain green on spruces in many areas. Before too long, the adelgids inside the galls will mature and winged forms will emerge as the gall dries and opens. Before that time, mechanical control can be achieved by hand picking galls. If only a few trees are involved, this may be effective.

The first overwintering eggs of balsam twig aphid were found on Fraser fir in York County this week. Growers may notice the disappearance of the aphids and be lulled into a false sense of security. The aphid disappearance is normal and marks the end of their life cycle for this year. Until next spring, they will remain in the overwintering eggs on the stems.

Spruce spider mites continue to be active on firs and spruces at many locations. Several calls received this week indicate that mite damage has reached the level that most people notice something is wrong. Normally mite levels drop off due to warmer temperatures at this time of year. Although this is not the best time of year to be controlling these pests, controls can still be achieved with 2 applications of a registered miticide.

The next report will be available after 4 PM on June 23.