May 18, 2001
Christmas Tree Scouting Report
Welcome to the Christmas Tree Scouting Report for the week ending May 18. The next report will be available after 4 PM on Friday May 25. To receive a FAX of this week's message, please call (814) 86-1636. if you would like to report pest activity at your location, please call 717-772-5229.
Two important scale pests of pine are active at this time. A quick review of scale biology will help growers develop control plans for any scale pest of conifers. For any scale, the easiest stage to control is the crawler stage. The winged males and the crawlers are the only stages that can move about. They are also the only stages that lack a waxy covering, or teste, that protects the fragile scale insect from desiccation, drowning, and most importantly, exposure to insecticides. Male scales do not feed - their only purpose is fertilization of sessile females. But, the crawler must begin to feed within 24 hours or starve. The scale insect will spend the remainder of its life at the feeding site selected by the crawler since the legs, and ability to crawl are lost in the next molt. In exchange for the loss of mobility, the scale insect gains the protective covering. If it were not for the scale covering, control would be very easy at any time of year. But, since that is not the case, growers must be alert for the presence of the crawlers if they wish to have good control. In addition, because scale insect eggs do not all hatch at the same time, control requires a minimum of two applications of insecticide labeled for scale control. The applications should be made 7 days apart to control scales as they emerge but before they initiate their waxy coverings.
During the last week to 10 days, crawlers of pine needle scale and striped pine scale have been observed on Scotch pine in the Harrisburg area. The crawlers of pine needle scale are brick red until they settle to feed. At that time they turn yellow-orange. Control is difficult once crawlers are settled. This armored scale will eventually produce white waxy coverings and feed on needles. There are two generations of pine needle scale in Pennsylvania each year.
The second scale of pine is a soft scale, the striped pine scale. For many years, this scale was called the pine tortoise scale. But several years ago, taxonomists agreed that there were actually two closely related species. In Pennsylvania, the predominant soft scale on pine is striped pine scale; pine tortoise scale is present but in much lower numbers. The control and biology of both species is the same. Crawlers are tan and resemble sawdust as they move over the bark. They are very mobile and easily move from tree to tree. Infested trees should note be removed during crawler emergence period and mowing should be discouraged. Both of these practices can spread this bark-feeding scale. Striped pine scale produces copious amounts of honeydew, which is attractive to ants, bees, and wasps. This honeydew also supports growth of sooty mold and heavily infested trees appear to be black. Both species of soft scale have a single generation each year.
Parasites and predators of both scale insects can help keep populations in check. The striped pine scale is frequently food for a lady beetle larva that resembles a mealybug. The larva is coated with white waxy material and often found inside the scale. Unsuspecting growers have attempted to control these larvae only to find out they are the good guys.
Balsam twig aphids have moved into the new growth of Canaan and concolor firs in Adams. Fraser fir, being a little slower to break bud, have stem mothers and their offspring feeding on the unopened buds. It is evident these aphids are feeding by the amount of honeydew being found on the buds. As stated last week, chemical control at this time is not practical.
In York County, pine spittlebugs are evident on many eastern white and Scotch pines. These insects generally do not cause appreciable damage. however, there has been evidence presented to indicate that their feeding site is the inroad for many diseases, including diplodia tip blight or Sphaeropsis. Control for spittlebugs can only be applied when the adults emerge.
We are starting to see fewer adults but more damage from white pine weevil. Terminals examined this week contain mostly larvae with very few eggs. In Perry County, terminals of infested trees are dwarfed and beginning to droop. In Cumberland County, candles of eastern white pine are entirely hollow due to larval feeding. If you are able to spot this early damage, you can effectively control white pine weevil in the field by pruning out the damaged tissue. As a general rule, all leaders removed should be destroyed in order to prevent the pest from completing its development.
Bagworms are still in the egg stage and efforts to chemically control these defoliators should be delayed until egg hatch in mid-June. Handpicking bags can be useful if completed before egg hatch.
European pine sawfly larvae are about 3/4" long and consuming entire needles. This is the most damaging time for these gray-green larvae. Hand removal is the most effective method when larvae reach this size.
We continue to receive reports of Gypsy moth larvae feeding in conifer plantations. In Northumberland County, young larvae seeking food are damaging candles of eastern white pine. In Perry County, larvae are consuming needles on new growth of spruce. According to reports from Department of Conservation and Natural Resources Forest Pest Management, the mild winter and dry spring have contributed to significant numbers of larvae and damage potential is high in some areas.
Large, brown aphids are active on pines and spruce at some locations. These aphids are in the genus Cinara and are the insects mistaken by homeowners as tick. They are highly attractive to ants because of the honeydew they produce. Cinara aphids do not usually cause significant damage.
The next report will be available after 4 PM on May 25.