May 10, 2002
Christmas Tree Scouting Report
Welcome to the Christmas Tree Scouting Report for the week ending May 10. The next report will be available after 4 PM on Friday May 17.
This week, a limited number of pine needle scale crawlers are emerging in Lehigh County and at all sites scouted in the Harrisburg area this week. At most of the sites, however, the predominant stage is still the overwintering egg. This armored scale can infest any conifer but Scotch pine appears to be a preferred host, with extremely high populations not uncommon on this species. Since there are two generations of this scale insect each year, the potential for rapid build-up is much greater than striped pine scale, which only has a single generation each year. Control of pine needle scale depends on two applications of a registered insecticide, 7 to 10 days apart, when crawlers are active. Some control of the amber settled crawlers is possible but, for the most part, the active crawlers are the most vulnerable. Adequate coverage is important since this scale often settles between needle bases, where it may be protected from less thorough applications.
This week also saw the start of the sporulation period for pine-pine gall in Dauphin and Perry counties. This disease is specific to scotch pine and quite capable of causing branch mortality when the galls girdle the branches. Softball-sized galls are not unusual but the smaller, walnut-sized galls are most common. At the time of sporulation, the rounded enlargements on the branches and main trunk split open to reveal orange spores. The spores are easily discharged and can be carried by wind to infect healthy trees. Chemical control of pine-pine gall is not practical. Culling of infected trees is a good practice but not during the sporulation period. Dragging infected trees through the plantation will surely increase the infection next year.
A disease of Douglas fir that can be controlled chemically is the familiar rhabdocline needlecast. Many growers in the Capital area are working on their 2nd application of fungicide to protect the new growth. In Centre County, where budbreak has reached 50%, the first of three, or possibly four, applications should be completed. The timing of sprays is: first application when 10% of the trees have broken bud, 2nd application one week later, and a 3rd application after another two weeks have passed. In long, cool springs sporulation may occur over a longer period and a 4th application may be required.
European pine sawfly is causing defoliation of Scotch pine at sites in Dauphin and Northumberland counties. These larvae always feed in groups and are quite capable of stripping a tree of most of last year's needles. The fact that they only have a single generation each year reduces their significance as a pest.
Cooley adelgids are feeding on new growth of Douglas fir at most sites visited near Harrisburg. Close examination of the elongating needles will reveal chlorotic spots and kinks, as well as the adelgid nymphs. In Centre County, very few eggs have hatched but this event will be closely aligned to budbreak, when it does occur. Control is no longer practical this spring and growers must now wait until fall to attack this common pest. The same species of adelgid is also causing gall formation on new growth of Colorado spruce at some sites. On Norway and white spruce, the eastern spruce gall adelgids have already caused the trees to produce galls at the bases of the branches. When broken open, the nymphs can be seen feeding inside these succulent galls. Mechanical control is the only control for either gall on spruce until September, when chemical control is again possible.
Larvae of white pine weevils are starting to create galleries under the bark of eastern white pine in Perry and Snyder counties. Eggs are still present and adults are still feeding on the bark of terminals at most sites. In Snyder County, Norway spruce with sap droplets on the leader alerted to the presence of white pine weevils. Feeding adults and eggs were found under the bark at this site. Observing the weevils on spruce is much more difficult than on smooth barked species like white pine and Douglas fir. Because the weevils have been active since mid- to late March, growers may wish to make a second application of insecticide to the terminals of susceptible species to prevent egg-laying by females moving in from surrounding woodlots. White pine weevil is very common in the state and populations exist in wooded areas and landscapes, wherever susceptible hosts are found.
True fir growers are starting to report balsam twig aphids feeding in the new growth at many locations statewide. This generation of the gray-green aphid is the damaging generation. As the aphids feed on the new growth, the needles may be distorted or shortened, covered with honeydew, and the overall shoot growth stunted. Balsam twig aphid is relatively easy to control but action must be taken before budbreak, not after. No control is possible until next spring.
Eriophyid mites continue to cause damage to spruce at many locations. Extremely high populations may be resulting from the early egg hatch and cool spring. Infested trees usually are off-color, not chlorotic as with spruce spider mite. Close examination of the needles will reveal hundreds of tiny, wormlike mites. If the actual mites cannot be found, often evidence of their presence is visible. As the mites molt, they leave behind their exoskeleton, which is visible as a minute, white, string-like piece of debris on the needle. If the exoskeletons, but no active mites, are found check the new growth since some eriophyids were observed feeding on elongating needles this week.
Spruce spider mite populations continue to build and are causing significant damage at some sites. Excessive webbing on Colorado spruce was found in Snyder County. The population was very high and the needles appeared whitish, rather than the blue cast found on healthy trees. Fraser fir samples from northern Dauphin County showed significant damage in 2001 but very few mites could be found this year. Heavy rains can affect spider mites, and some of the precipitation we have enjoyed this spring may have literally washed the mites from the trees.
Admes spider mite, a relatively uncommon pest of spruce in Pennsylvania, was found on Colorado spruce in Northumberland County. This is only the third report of this species in the state, following its initial discovery about 5 years ago. Admes spider mite can cause significant browning of needles of all spruces. The adults are much larger than spruce spider mite and tend to settle out on the needles in a "stretched-out" position. The mites are reddish with long legs and short dorsal setae. Another mite with a similar appearance to Admes mite is the clover mite. Adult clover mites, sometimes referred to as the brown mite when found on aerial portions of plants, were evident on terminals of Fraser fir in Perry County. The mites are not on the needles but are moving about on the bark of terminals. Clover mite is not damaging to conifers but may cause concern if not properly identified.
Spittlebugs are everywhere, according to scouts from Centre County and Harrisburg. The nymphs are living in masses of their own excrement on branches of all pines, Douglas fir, and spruce. Occasionally, they are also found on true firs. Although they may appear disgusting, very little damage results directly from spittlebug feeding. However, their feeding sites may become pathways for plant pathogens.
We continue to see and receive reports of damage from Pales weevil. Flagging of lateral branches of pines, Douglas fir and true fir is not uncommon but growers may fail to recognize the cause. As adult weevils feed on healthy trees, they remove bark from branches, particularly near the nodes. Once the bark is gone the branch dies, or flags. Look for irregular patches where bark has been removed to diagnose Pales weevil damage.
The next report will be available after 4 PM on May 17.