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May 25, 2005

Christmas Tree Scouting Report -
Number 8

Welcome to the Christmas Tree Scouting Report for the week ending May 11, 2005. The next report will be available after 5 PM on Wednesday, May 18. To receive a FAX of this week’s message, please call (814) 865-1636. If you have pest activity to report, or would like to receive this report by e-mail, please leave a message at 717 772-0521 or e-mail sgardosik@state.pa.us and your name will be added to the distribution list.

Early symptoms from the Douglas fir needle midge are apparent in the new growth of Douglas fir at our study site in Bucks County. Infested needles appear bent or kinked, with the kinked point being lighter in color than the rest of the needle. When the undersides of kinked needles are examined with a hand-lens, tiny depressions can be found where the larvae entered the needles. As the larvae feed and grow within the needle this area will swell and occasionally discolor from yellow to purple and then to brown by fall. Damage to new Douglas-fir needles by Cooley adelgid may also superficially resemble Douglas-fir needle midge damage at this time, but with Cooley damage you will find either the black nymph or the protective white cottony material on the undersides of damaged areas of needles.

Needles infected with Rhabdocline needle cast were actively sporulating on Douglas-fir in Adams, Dauphin, Franklin, Lancaster and York counties this week. Some growers have applied their third spray by now – you should plan a third spray two weeks after your second application. Growers can do a quick test to determine if a fourth spray will be needed two weeks after the third by taking an infected twig and placing it in a container of warm water for about 10 minutes then checking for swollen orange areas on undersides of needles.

Bagworms are beginning to hatch on Colorado blue spruce in Dauphin and Lancaster counties. Look for miniature bags about 3mm long on the needles near the old bags. After the eggs hatch inside the overwintering bags, the larvae spin a silk thread, exit from the bottom tip of bag, and either spin down to lower branches or get blown by the wind to surrounding areas. Because most eggs have yet to hatch it is best to wait until the majority of larvae are out and actively feeding before applying controls, (but before larvae become large). Bacillus thuringiensis or “Bt” is a good biological insecticide for controlling lepidopteran pests when their caterpillars are young and actively feeding.

There are high populations of balsam twig aphid nymphs on the new growth of Canaan and/or Fraser fir in Adams, Carbon, Franklin and York counties this week. To prevent damage to new growth, controls are best applied before bud break.

No eggs were found underneath the coverings of adult female cryptomeria scales in Dauphin, Franklin or Lancaster counties. I expect to see eggs within the next week and subsequent egg hatch about two weeks later. You should plan to spray about mid- June (stay tuned!).

Elongate hemlock scale crawlers were more numerous this week on grand fir and Fraser fir in Adams County. Growers in the more southern counties may want to begin a spray program of three to four sprays about four weeks apart, weather permitting. A few crawlers were found on Fraser fir in Carbon County this week at Dr. Paul Heller’s spray trial site. Paul predicts he will begin his spray trials in the next 7 to 10 days.

It seems this spring’s alternating cool- warm-cool temperatures have made it difficult to control spruce spider mites. Some growers had to respray to achieve satisfactory control. This year, the early spring rains that normally help wash mites from the trees was lacking.

Diplodia shoot blight was found affecting the new growth of Scotch pine in Lancaster County. This is a very common disease of Austrian, Red, and Scotch pine. This fungal disease is active all season (except in very dry conditions) so spray controls are not practical. The most effective control measure is to remove infected shoots and burn them.

The next report will be out on Wednesday June 1 st after 5:00pm.