April 27, 2001
Christmas Tree Scouting Report
Welcome to the Christmas Tree Scouting Report for the week ending April 27. The next report will be available after 4 PM on Friday May 4. To receive a FAX of this week’s message, please call (814) 865-1636. To report pest activity at your location, please call 717 772-5229.
Rhabdocline needlecast seems to be on everyone’s mind this week. Not only do the infected trees look like they are dying, but the time for control is eminent. The appearance of the needles is useful in telling whether the problem is rhabdocline, Swiss needlecast, or a root problem. Rhabdocline is the only one with distinctly edged red-brown splotches. Both of the others cause a more gradual chlorosis of needles, starting from the tip backward. Fruiting bodies of rhabdocline are found on the undersides of infected needles.They may appear as puffy areas and will gradually swell until the surface of the needle splits open. You can speed up the process by putting an infected sprig into a glass of water. When exposed to moisture, mature rhabdocline fruiting bodies will split open, revealing thousands of minute tan spores. This is the infectious stage and your cue to get ready to spray. The only method of preventing infection to new growth is to cover the elongating needles with a protective fungicidal spray.
For the best results in preventing Rhabdocline infection, thorough coverage and accurate timing are required. Watching for budbreak in your own field is essential. When 10% of the trees in a block have buds breaking, it is time for the first application. The second spray should be applied in another 7 days with a third spray in another 14 days. For growers serious about preventing late-winter reddening of Douglas fir needles, and the subsequent needle drop associated with this disease, a commitment to complete the series of sprays is required. Skipping the second or third spray will assure that you will have the plenty of reddish brown trees at this time next year.
Spruce spider mites are hatching at most locations in the Harrisburg area. Heavy populations may even have some webbing showing as the mites vie for good feeding areas. Immature mites produce silk in order to escape to new locations with less feeding pressure. The silk is also their means of dispersal throughout a block of trees. Growers wishing to control these pests should be making an application of approved miticides. Miticides that interfere with chitin production are best applied at this time of year to provide long term control.
White pine weevils continue to feed and lay eggs on terminals of conifers. A grower in northeastern Pennsylvania reports capturing four weevils in detection traps at 11 Growing degree-days. Now is the time for control of the adults, before the females deposit large numbers of eggs. In our scouting, eggs were present but no larvae have been found.
Pine bark adelgids eggs are hatching and predators are being attracted to infected shoots, where they will feed on the crawler stage of this bark-feeding insect. Multicolored Asian ladybeetle are common on infected trees and this week, a syrphid fly larva was observed feeding on unhatched eggs in Perry County.
White pine and Scotch pine growers should identify areas infested with pine needle scale before new growth begins and crawler emergence is at hand. These white armored scale insects are easy to spot on the green needles. But, when new growth starts, finding the scales back on last year’s growth will be a challenge. To have good control of the crawler stage, monitoring should be considered. In the past, crawlers have emerged when common lilac is in full, or just past full, bloom. Blossom heads already started to appear on these phenological indicator plants this week.
Your spring opportunity to control Cooley adelgids and Eastern spruce gall adelgids on Douglas fir, Colorado spruce and Norway spruce has passed. The stem mothers are starting to deposit eggs and with Norway budbreak starting in Schuylkill County, control would not be effective.
European pine sawfly eggs have hatched in Lebanon County but the first instar larvae have not started feeding. Finding these young larvae and removing their clusters is an excellent method of non-chemical control.
The next report will be available after 4 PM on May 4.