May 25, 2001
Christmas Tree Scouting Report
Welcome to the Christmas Tree Scouting Report for the week ending May 25. The next report will be available after 4 PM on Friday June 1. To receive a FAX of this week’s message, please call (814) 865-1636. If you would like to report pest activity at your location, please call 717 772-5229.
Pest activity has slowed down since the spring rush and some growers are finding pests they overlooked earlier this spring. Balsam twig aphid is feeding on the new growth of true firs and curled and distorted needles are starting to appear. During the past week, scouts in Northumberland County found the aphids feeding within the tender new cones. In Berks County damage is already present on new growth. Natural enemies are the grower’s only ally at this time of year. Chemical controls may kill some of the aphids but the damage will remain and those aphids that escape control will be depositing overwintering eggs in the next several weeks. If you are considering harvesting a block of Balsam, Fraser or Canaan fir next year, you should evaluate your balsam twig aphid damage this year. The most important time to keep these sucking insects under control is during the year of harvest. Observations now can allow you to plan ahead for next spring
Galls of eastern spruce gall adelgids are appearing on branches of Norway spruce in Lebanon County. These small galls look like swollen areas at the base of current year’s shoots. As the galls mature, they will constrict the flow of nutrients to the branch, causing the entire branch to die. Unlike the Cooley gall adelgids, that only damages branch tips, Eastern spruce gall adelgids can quickly disfigure the entire tree and cause major branch mortality. Growers with damage should consider controls applied in fall, between single application at that time of year can eliminate this pest from Norway spruce.
On Douglas fir, evidence of Cooley adelgids feeding includes chlorotic spots and needle kinking and bending. This damage is largely aesthetic but may, in severe cases, reduce tree vigor. Cooley adelgids, on both Douglas fir and Colorado spruce can also be controlled in the fall.
Scotch pine growers who have had a history of pine needle midge damage to leaders should be planning controls for the next week or two. A single application of a registered insecticide can reduce needle loss on terminals.Pine needle midge is a small fly that lays eggs in the needles when they are starting to separate from the candle and sheath. When the eggs hatch, the yellow larvae feed at the base of the needles, inside the needle sheath, causing the needles to bend and drop from the tree.In some areas this is referred to as the pine-needle bending midge because of the characteristic damage. Light infestations are not serious but heavy damage and loss of all needles from the leader will result in leader death.
European pine sawfly larvae have finished feeding and are dropping from the branches of Scotch pine to pupate in the soil. Adults of these wasp relatives will emerge in late summer or early fall. After mating, the females will use their saw-like ovipositor to deposit series of single eggs along the needle. The eggs will remain inside the needles through the winter. The European pine sawfly is a pest of two and three-needle pines.
Introduced pine sawfly is usually associated with eastern white pine. This sawfly overwinters as a pupa in the soil or on the branches of the host tree. Adults have emerged and we should soon start to see the colorful yellow and black larvae on the needles. These larvae feed singly as they mature and cause considerably less damage than the European pine sawfly.
Rhabdocline needlecast is starting to wind down in the Harrisburg area. Most Douglas fir growers have already applied their third spray to prevent infection on the new growth. As the infected last year needles complete their spore release, the undersides of the needles turn from light tan to dark brown to black. When most of the fruiting bodies are dark brown or black, sprays can be discontinued. In cool, wet springs, a fourth spray is often needed. To decide if you need another application of fungicide, examine the fruiting bodies at your location.
Cryptomeria scale females are maturing and will be starting to deposit eggs in the next several weeks. This week, samples collected had females with immature eggs inside their bodies. Observations in the last four years indicate there are two generations of this armored scale. Although it is a relatively new pest of true firs, it can become very damaging if undiagnosed. Bright yellow spots on the upper side of the needle are diagnostic for this scale. To verify the identification turn the branch over and look for a crust of scale insects. When rubbed, the bright yellow scale insects should be seen.
Another scale pest of true firs is the elongate hemlock scale. In some areas, this scale is becoming serious and growers are having a difficult time getting the scale insect under control. This scale may produce symptoms similar to cryptomeria scale. It also feeds on the underside of needles and populations of a mixture of both scales are not uncommon. Elongate hemlock scale can be separated from cryptomeria scale by the white strings of wax produced by the male scales. Coverings of male cryptomeria scales look like their female counterparts.
In Columbia County, settled crawlers of pine needle scale were present on Austrian pine. In most areas, the window of control for this armored scale pest of pines has closed. A second generation will appear in July, providing another opportunity for control.
Damage from white pine weevil is becoming evident. Terminals containing larvae are usually browned and wilting on both eastern white pine and Douglas fir. On spruce, the damage is not as apparent but a trained eye can detect the wilting terminal. Mechanical control or pruning out infested terminals should be done at this time of year. Remove the terminals from the field and be sure to prune down to good, solid wood.
The next report will be available after 4 PM on June 1.