May 17, 2006

Christmas Tree Scouting Report Number 10 - May 17, 2006
Weekly newsletter compiled by Sandy Gardosik, PA Department of Agriculture.

I'm still seeing active spruce spider mite populations on Fraser fir in Adams, Berks, Dauphin, Lancaster, and Lebanon counties. The cool spring temperatures we are having tend to extend the life cycle of spruce spider mites allowing female mites to lay more eggs and since all active life stages feed, longer life may result in added feeding damage. Since the first several generations of spruce spider mites feed on the old growth and don't tend to move to the new growth untill it begins hardening off, mite controls need to reach the old growth. Most insecticides and miticides, unless otherwise stated on the label, require two sprays, 7 to 10 days apart for effective mite control.

Rhabdocline needle cast on Douglas fir is still showing signs of active fruiting bodies in Berks and Bucks counties. Growers in the more southern counties may be closing in on their third spray for the season. A fourth spray may be necessary three weeks following the third spray if the spring temperatures stay cool and damp or if Swiss needle cast is affecting your Douglas fir.

Eggs of the pine needle scale are hatching on Scotch pine in Lancaster County. Look for dark red crawlers on the needles near white, oyster-shaped female coverings. If populations are light, natural enemies such as lady beetles or lacewings may keep the population to a minimum. Sprays are most effective toward active crawlers with two applications 7 to 10 days apart. This scale has two generations in Pennsylvania with the second-generation crawlers emerging in mid-July.

Clusters of Cinera aphids were found on shoots and in the new candles of scotch and white pine in Lancaster County. These aphids over winter on trees as eggs, hatch in spring and can reproduce quickly. Aphids suck sap from shoots and needles excreting large amounts of waste or "honeydew". This honeydew attracts secondary pests, such as ants, and serves as a substrate for sooty mold development, causing branches to look black. If populations are detected, treat individual trees and protect natural enemies by using insecticidal soap, a good alternative to conventional insecticides.

A few crawlers of the elongate hemlock scale (EHS) were observed on Fraser fir in Schuylkill County. Look for tiny yellow crawlers on the underside of needles. Unlike other scale pests of conifers that have well defined "crawler emergence periods", EHS is difficult to control because crawlers are present throughout the growing season. Begin spraying once crawlers are observed with 4 applications of dimethoate 267 applied at 3-week intervals.

Cryptomeria scale is another pest that can build up quickly on true firs and create chlorotic spots on tops of needles and make trees unfit for sale. This scale is easier to control because of its well-defined crawler emergence period. No eggs were found under the adult female covering this week in Berks County. Begin scouting for eggs the last week in May, looking for tiny bright yellow, jelly bean shaped eggs with a hand-lens by pulling back the scale cover or tapping shoots over a white paper plate.

Damage from the Douglas fir needle midge was evident when new needles were observed in our spray trial plots in Bucks County. Needles appear kinked similar to damage produced at this time by Cooley spruce gall adelgids nymphs but the chlorotic spotting from Cooley feeding is more defined. When needles are examined from underneath the black nymphs can be seen on the surface of the needle. The Douglas fir needle midge is now inside the needle and you would need to cut into the needle to find the larva. Results from spray trails conducted in 2006, when chemicals were applied before midge emergence, and in 2005, when chemicals were applied at midge emergence will be shared at future meetings.

If you have any pest information to report please email Sandy Gardosik at or call (717) 772-0521 and give pest, host plant and county where observation was made and I will include this information in the next report.