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May 9, 2003

Christmas Tree Scouting Report -
Number 7

Welcome to the Christmas Tree Scouting Report for the week ending May 9, 2003. To receive a FAX of this week's message, please call (814) 865-1636. To report pest activity at your location or request email report, please call 717 772-5229. 

This week's wet weather has been ideal for the spread of Rhabdocline needlecast, the most important disease of Douglas fir in Pennsylvania. In Columbia, Lebanon, Northumberland, Schuylkill and York counties this week, infected areas on the undersides of needles were split open, exposing the orange surface of the fungal spores. Most growers have already applied their first spray of fungicide to their Douglas fir trees. The second spray should follow one week after the first and the third spray two weeks after the second. An additional 4th spray may be need three weeks after the third spray if wet weather continues. Fungicides for Rhabdocline needlecast protect expanding needles before they are exposed to the fungus; if only one or two chemical applications are applied, the later expanding needles will not be protected and will be susceptible to infection.

European pine sawfly larvae were observed in Lebanon County this week on Scotch pine. They have been active in most of the state for several weeks. This insect is not a fly, as the name may lead one to believe, but is in the order Hymenoptera, with the bees and wasps. The larvae are dull gray with light green and black stripes running longitudinally and the head capsule is shiny black. In fall, females insert overwintering eggs into pine needles. Eggs hatch in late April or early May and feed only on old needles. The larvae feed in colonies and, when young, they can only digest the outer edges of older needles. This feeding causes the needles to appear straw-like and twisted. As the larvae grow, they are able to eat the entire needle and often defoliate one or more branches. Larvae found in Lebanon County this week were ½" in length and eating whole needles. Since this insect does not eat new needles it rarely kills trees. It can, however, severely decrease growth rate and take away from the aesthetics of a tree. If colonies are few and scattered, knocking the larvae from the tree and crushing them is recommended. If more sever, use a currently registered insecticide preferably against young larvae.

Elongate hemlock scale crawlers are beginning to emerge on true firs in York County this week. In Columbia and Schuylkill Counties no crawlers were observed. This scale is found only on the undersides of needles. The narrow females are 1-3 mm long, light-to-medium brown, with a transparent covering. Males are smaller, narrower and powdery white. This insect over winters in several stages, causing crawler emergence to occur throughout the season. Because of the constant crawler emergence, sprays should be repeated throughout the summer at intervals recommended on the label of the product selected. Sprays should begin when crawler are first noticed and continued through September.

White pine weevil adults are still beginning found on terminals in Columbia and York Counties this week. When terminals were examined, eggs and larvae were found. Soon these infested leaders will begin to yellow, appear stunted, and curl into the shape of a shepherd's crook. At this point the best control would be to cut out infested terminals and removing them from the field before the new adults emerge.

We continue to monitor Douglas fir needle midge traps at sites in Lehigh and Northumberland counties. To date, no adults have emerged. Controls for this newly detected pest must be directed against adults when they emerge from their overwintering sites under trees.

Balsam twig aphids are now in the new growth of true firs and soon the growth will be twisted due to their feeding. Spraying once damage becomes apparent will not reduce damage or control the aphid population. It will, however, reduce numbers of beneficial predatory insects such as lacewings, syrphid flies and ladybird beetles. For growers with balsam twig aphid problems, your next opportunity to control this pest is next spring. In the meantime, let the naturally occurring predators do their best.

Cooley spruce gall adelgids were found this week in the new growth of Douglas fir in Columbia County. As the needles expand, the area where the adelgids are feeding will yellow and bend or kink. Control for this insect is not possible until this fall.

Pine bark adelgids were noticed on the newly expanding candles on white pine this week in Columbia and York Counties. This insect is not usually a serious pest in Christmas trees but has been known to require control in young plantings of white pine.

Spruce spider mites should now be hatched from their overwintering eggs at most sites statewide. This marks the best time to apply one of the newer chitin-inhibiting miticides and get the most effect from the single application permitted by the label.