May 24, 2002

Christmas Tree Scouting Report

Welcome to the Christmas Tree Scouting Report for the week ending May 24. The next report will be available after 4 PM on Friday May 31. 

Frost damage is the uppermost on most growers' minds this week, especially those with Douglas fir hit with one of killing frosts during the last seven days. Reports from Adams, Bedford, Centre, Mifflin and Lycoming counties indicate widespread damage to the tender new growth. In Adams County, the later opening buds seem to be the worst hit, while in more northern locations, all of the new growth was susceptible to damage. Within several days, you will be able to tell if the new growth was merely "stung" by the frost or completely killed. New growth that is "stung" will only have tips of needles on the upper side of branches killed, while growth that was severely frosted will turn pale pinkish green and quickly brown. At the present time, growers can only wait to assess the damage.

Douglas fir was not the only species damaged. Reports of Norway and Colorado spruce as well as concolor fir with frost damage were also received from Adams and Centre counties. A grower in Lycoming County reported frost damage to white pine, which was causing the candles to droop. This could mimic early white pine weevil damage, which is now starting to show up in Perry County. Candles on terminals damaged by feeding by white pine weevil larvae are changing from the normal light green to greenish-yellow or golden in color. At the study site in Perry County, shepherd's crooking of the new growth is not yet apparent.

With the frost damage, Douglas growers are asking about the need to continue rhabdocline applications. Is it still advisable to spray the fungicide if all the growth is dead? Several plant pathologists at PDA and Nancy Wenner at Penn State agreed that this must be a management decision for each grower. Factors to consider are the extent of the frost damage, age of tree, amount of rhabdocline infection currently in the field, number of new shoots that will reform and when they will appear, and finally, the number of viable rhabdocline spores still remaining to be discharged from the fruiting bodies.

Let's start with the last item. It is still early in the season and most fruiting bodies are just coming into peak spore release. This means that any new growth, including buds that reform and open, could still become infected. In general, the most severe frost damage is on the upper portion of the tree, with lower branches unharmed. Rhabdocline, in contrast, is usually heaviest on the lower branches. Also, frost damage may be less severe on one side of the tree, or on branches inside the canopy. How widespread was the frost damage? It is rare that an entire field has total frost kill. Pockets with severe damage will occur in every field, just as undamaged trees can also be found. The age of the tree will determine if you have several years to clear up the rhabdocline or you intended to sell the trees within the next 2 years. Some frost damage can be sheared from the trees but rhabdocline cannot. So it comes down to a matter of risk. Just how much are you willing to risk?

Some pests that are easier to make decisions about include spider mites and scale insects. This week we continue to see high populations of spruce spider mite in Centre County, with noticeable webbing on the needles. In York County, some pine needle scale crawlers are settled while others are still actively seeking a feeding site. Unhatched eggs remain at some Capital area sites while in State College, eggs have not started to hatch. Elongate hemlock scale crawlers continue to emerge and some settled crawlers are already present in Schuylkill County. Pine tortoise scale crawlers are emerging and already have started to settle on candles of Scotch pine at one Adams County site. At another nearby site, a soft scale on Scotch pine has not even started to deposit eggs. Could this be striped pine scale? Cryptomeria scale females are maturing but have not started to deposit eggs in Schuylkill County.

The next report will be available after 4 PM on May 31.