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May 31, 2002

Christmas Tree scouting Report

Welcome to the Christmas Tree Scouting Report for the week ending May 31. The next report will be available after 4 PM on Friday June 7. 

By now all growers know just how severe the frost damage was to their trees the week of May 20. Frost killed new growth is quite evident at many sites in the Commonwealth. In addition to Douglas fir, which seems to be the most likely to suffer this damage, reports of Norway and Colorado spruce and several species of true fir, including concolor, have been received. At some sites, it was the younger trees that were especially hard hit. Last weeks questions regarding whether or not to continue rhabdocline applications can easily be answered when the fields are evaluated for frost damage. In addition, fruiting bodies from more southern sites are starting to darken, marking the end of the sporulation period for rhabdocline. Before applying any additional fungicide sprays, each grower needs to examine the trees at their site. If the opened fruiting bodies are dark brown to black, viable spores are not present and the need for fungicide protection has passed for 2002.

Cryptomeria scale, an armored scale pest of true firs, has started to deposit eggs in Berks, Dauphin, and York counties. But farther north, in Schuylkill County, no eggs are present. This scale has been troublesome for growers, particularly in the southeastern counties, for many years. There are apparently two generations of this scale, with the first generation crawler emergence usually recorded in mid-June. Egg deposition usually starts in late May, so we appear to be right on schedule. Growers may not know they have this scale insect until the population is well established. By that time, needles are showing bright yellow spots on the upper surface, marking the sites where scale insects are feeding on the undersurface of the needles. Lower branches are usually the first to show damage and also support the heaviest populations. Multiple applications of registered insecticides are effective in controlling this persistent pest but thorough coverage and timing are essential.

In Northumberland County, most pine needle scale crawlers have settled and started to feed on needles of eastern white pine. The settled crawlers are still slightly susceptible to insecticides but it is the red crawler that is most easy to control. With most of the scales producing their protective coverings, control is greatly decreased. Growers will have to wait for the emergence of the second generation crawlers in July if they wish to gain control of this pest.

Pine tortoise scale has not started to deposit eggs on Scotch pine in Dauphin, Northumberland or Perry county farms visited this week. This soft scale is a common and serious pest of Scotch pine in Pennsylvania. Infested trees are often covered with sooty mold growing on honeydew produced by the mature scale insects. The honeydew is also attractive to ants and some stinging insects, which may become a problem during shearing operations.

White pine weevils continue to be found on terminals of white pine, spruce and Douglas fir. In Perry County, very few eggs are unhatched but, in Schuylkill County, some eggs are still present. Larvae at all sites are maturing and continue to feed under the bark, causing the new growth to discolor and droop. Mechanical control is available to growers wishing to prune out and destroy damage tops. All pruning should go down to good wood and the infested leaders destroyed.

We are finding a different spider mite at several locations. The mite, unofficially known as the Admes mite, was first detected in Centre County about four year ago. At the original site, it was causing browning of needles of Norway and white spruce. It was also found in Lebanon County the following year. Recent samples collected from Colorado spruce in Northumberland and Schuylkill counties indicate the mite is fairly widespread. Although the Northumberland site had a very high population, no significant damage was apparent. This spider mite has short hairs on its body, unlike spruce spider mite, which has long dorsal hairs. Admes mite is larger and generally dark with red legs. The mites can be seen with the naked eye on the needles and have a curious habit of molting in groups on the needles. This leaves behind lines of cast skins, which appear white.

The more familiar spruce spider mite is building high populations on true firs at sites visited in Dauphin and Schuylkill counties. Excessive silk production is evident and chlorosis of needles is present. In addition to the spider mites, eriophyid mites are still causing damage to spruce in Adams County.

Balsam twig aphids are nearing the end of their annual life cycle and we expect to find overwintering eggs present on the new growth within the next two to three weeks. Winged adults should be present now. This is the stage that migrates to uninfested trees to establish new populations for the following year. These adults may be unfamiliar to many growers, since they only occur during this generation. Control of these stages is still not practical since the damage has already been done for the year. Growers should plan on control for next spring, before budbreak, if they wish to prevent balsam twig aphid to firs, including concolor.

Cooley adelgids are producing eggs on new growth of Douglas fir in Northumberland and York counties. These eggs are deposited by females under masses of white waxy filaments that resembling a minute cotton balls. Another pest producing white waxy coverings over eggs are the pine bark adelgids on the new growth of eastern white pine. Although unsightly, these adelgids generally do not cause significant damage on these hosts and control is not necessary. On spruce, the galls formed by the adelgids are much more serious and easily degrade or kill branches. Galls are very apparent at the present time. If only a few galls are present, hand removing and destroying can be very effective. But, this is generally not practical for large plantings, so fall applications of a registered insecticide are recommended.

Overwintering eggs of bagworm eggs are hatching in Schuylkill County. Although generally a pest of juniper and arborvitae, bagworm can quickly defoliate mature spruce trees and are often found on Douglas fir and pine. The easiest time to control the larvae is when they are young. Bacillus thuringiensis, otherwise known as Bt, is very effective on young larvae.

The next report will be available after 4 PM on June 7.