April 19, 2002
Christmas Tree Scouting Report
Welcome to the Christmas Tree Scouting Report for the week ending April 19. The next report will be available after 4 PM on Friday April 26.
This week, several new pests are active and some trees are breaking bud! Rhabdocline is on the mind of many Douglas fir growers and rightly so. With buds breaking on <10% of the trees at a York County site on April 18, the Rhabdocline treatment period is starting. At the same time, fruiting bodies, but not the buds, were starting to open in Adams County. In Carbon, Columbia and Cumberland counties, buds are just starting to swell. Control of rhabdocline needlecast depends on fungicide applications to protect new growth from spores originating in fruiting bodies on last year's needles. Application of a registered fungicide should be made when 10% of the trees at the location have started to break bud. Each grower must evaluate budbreak at their own site since temperature variations will cause variations in budbreak.
Spruce spider mites are hatching statewide. In Carbon and Columbia counties earlier this week, the percent hatch was only 10%; in Northampton County about 50% of the eggs had hatched. By the end of the week, observations in Adams, Centre, Cumberland, Schuylkill and York counties showed that some overwintering eggs still remain. Although temperatures soared to record breaking highs this week, and growing degree-day accumulations more than doubled in many areas, high temperatures can also limit pest development. Insects generally have an upper development threshold that may prevent some pests from developing as rapidly as one would think. This also helps to explain the cool season vs. warm season mite categories that are often referred to when discussing mite biology. Growers wishing to apply a miticide that acts only on active stages should wait until hatch is complete before spraying.
Eriophyid rust mites on spruce and fir are cool season mites and populations that are extremely high this week can be expected to crash if temperatures do not moderate next week. In Carbon and Columbia counties, spruce rust mites are causing damage as they feed on last year's needles. These mites are very small and a handlens is required to detect them on the needles.
Cooley adelgids on Douglas fir have deposited eggs in Adams, Carbon, Centre, and Columbia counties. On Colorado spruce in Carbon, Centre and Westmoreland counties, the Cooley spruce gall adelgids stem mothers are covered with white fluffy wax but no eggs were found. Eastern spruce gall adelgids on white spruce in Columbia County have eggs in the cottony masses but buds are not opening. However, buds are starting to open on Norway spruce in Adams County, were eastern spruce gall adelgids also have produced eggs. Adelgid egg hatch is normally synchronized closely with budbreak, a feature of their life cycle that allows them to feed on the tender new growth, causing galls on spruces and chlorotic spots on Douglas fir. By next week we expect to see nymphs in the new growth at some locations. Spring control of Cooley and eastern spruce gall adelgids is no longer feasible.
Balsam twig aphid hatch is complete at most sites, especially in warmer locations. Nymphs and/or stem mothers were observed in Adams, Carbon, Columbia, and York counties. The stem mothers will give live birth to the next generation of nymphs, which will move to opening buds. As these 2nd generation nymphs feed on the tender needles, significant damage can occur. For growers wishing to limit damage, controls should be applied after hatch is complete but before budbreak. Budbreak of balsam fir was reported from Adams, Indiana, and York counties this week and in York County, cones are starting to appear on Fraser firs. These tender vegetative cones are alternate feeding sites for balsam twig aphids. When the aphids move into the cones, their disappearance can give growers a false sense of security. In addition, the cone structure will protect the aphids from chemical control measures. If you are in doubt about your aphid population, don't forget to check the cones.
White pine weevils were observed in large numbers feeding on terminals of Serbian spruce in northern Lycoming County and in Carbon, Columbia, and Susquehanna counties on eastern white pine. In Perry County, the number of eggs is increasing but hatch has not started. Any grower intending to control this pest with sprays should be finishing a first application of a registered insecticide this week. It is only necessary to spray the terminal of the tree to achieve control but in a spring such as this, a second application will probably be needed in several weeks.
Pine spittlebugs have hatched and small masses of spittle are present on Scotch and white pines in Centre, Perry, and York counties. These sucking insects will spend all their immature stages inside masses of frothy waste material on the host, making them impervious to sprays. However, when the adults emerge later in the season, sprays can be very effective in reducing populations.
European pine sawfly larvae have hatched in Allegheny and Westmoreland counties. Scotch pine growers should be on the lookout for clusters of ¼ inch gray-green larvae with shiny black heads. These sawfly larvae can cause significant defoliation as the feed on old needles. Hand removal or spot sprays are easy methods of control used by many growers.
Pine bark adelgids eggs are starting to hatch in Columbia County on eastern white pine. At his location, the nymphs were occupying feeding holes of white pine weevil, as well as feeding at the base of needles on elongating candles. Lady beetles and syrphid flies are often associated with this sucking insect and can generally keep it under control.
The first lilac blooms are starting to appear in the Harrisburg area, reminding us that pine needle scale crawlers will be emerging within the next several weeks. This event usually occurs when lilacs are in full to late bloom but it may be difficult to find crawlers behind the elongating candles at that time. To make observation of crawler emergence easier, growers can tag one or two infested trees and check these trees regularly for emergence of the vulnerable red crawlers. This will increase spray efficacy and go a long way in getting this scale insect under control.
We continue to find a few elongate hemlock scale crawlers at our study sites in Columbia and Schuylkill counties. In Adams County, several heavily infested trees were also observed to have limited crawler activity. At all sites, eggs were the predominant stages, but all stages were represented.
Your next report will be available after 4 PM on April 26.