June 8, 2001
Christmas Tree Scouting Report
Welcome to the Christmas Tree Scouting Report for the week ending June 11. The next report will be available after 4 PM on Friday June 18.
The armored scale pest Aspidiotus cryptomeriae, or cryptomeria scale, is depositing eggs at sites in Adams, Berks, and Lebanon counties. A Lehigh County grower also reports finding eggs at his farm. These eggs are the signal to prepare for control measures within the next week or two, when crawler emergence begins. Our observations during the last several years indicate that crawlers start to emerge somewhere around 600 GDD. The GDD readings at the Berks county site we are visiting are still under 500. However, several warm days can quickly boost the cumulative total over the 600 mark. Growers of true fir in the southeastern counties should be making observations on their trees and begin the series of sprays when the first crawlers are found. To look for crawlers, a 15X or higher handlens is usually needed. But, if you lack the handlens, you can tap the branch over a dark surface and observe the minute yellow crawlers moving across the surface.
The crawler stage is the most vulnerable to pesticides because it lacks the waxy covering of settled stages and the movement of the crawler increases the likelihood of coming in contact with the pesticide. As with all scale insects, the crawlers must settle to feed within the first 24 hours or risk starvation. They are still somewhat vulnerable for a short period of time, until the waxy coating is produced. But, the most opportune time for control is during crawler emergence.
Bagworms are starting to feed on needles of conifers in Lebanon County. The tiny caterpillars are building bags from a combination of silk and plant tissue. Some bags observed this week are only 1/16th inch long. Since bagworms effectively camouflage themselves with plant tissue, they are difficult to find on the host at this stage. But, now is the best time for controlling these defoliators. As mentioned last week, the biological insecticide Bacillus thuringinesis is very effective in controlling caterpillars, especially when they are young. Bt, a shortened name for this insecticide, is the active ingredient in several compounds and is readily available.
Striped pine scale continues to be a mystery this year. At locations in Adams and York county, crawler emergence has not started. Previously, we had reported on crawlers at some locations. This difference in emergence from location to location is one of the main reasons scale insects are so difficult to control. It is also justification for time spent scouting you own field.
Pines with frothy masses of sticky liquid are very noticeable as the pine spittlebug completes its development. The black and tan nymphs can be found inside the spittle mass, where they feed on the bark of new shoots. The spittle mass is created by the insect from waste materials and offers protection from parasites, predators, environment and, of course, pesticides. If your plantation has a serious spittlebug problem, you should wait until the adults have emerged from the masses to spray. To determine if the adults have emerged, squeeze several masses between your fingers to look for the nymphs. No nymphs usually means adults are emerging.
It is increasingly difficult to find balsam twig aphids on firs. This means the last generation adults are starting to deposit overwintering eggs. To find the eggs, look on new growth about 1 inch below the bud. Eggs are usually found at the base of a needle and are covered with white waxy rods. Newly deposited eggs are pale but they darken to almost black in a short time. It is sometimes easier to find eggs on shoots that are not heavily damaged as opposed to those with a lot of distortion.
Introduced pine sawfly larvae are feeding on needles of eastern white pine in Lebanon County. The small larvae are more difficult to identify than when mature but if you look at the side of the larva, you can observe the small yellow spots characteristic of this sawfly.
Spruce spider mite continues to have a successful spring. The cool nights and below normal rainfall have contributed to high populations in many areas. In addition to spruce, true firs, including concolor fir, are common hosts plants. Spider mite damage to Douglas fir and pine is much less common but not unheard of. Regular monitoring for active mites is the only way to prevent damage.
White pine weevil grubs are maturing but have not all started to pupate in the terminals of their host trees. There is still some time to prune out the infested terminals and use mechanical control to prevent another generation from completing development. Don’t forget – the terminals must be destroyed to prevent the weevils from completing development on the ground. And, be aggressive and cut down to good wood.
The next report will be available after 4 pm on Friday, June 15.