![]() |
Français | Contact Us | Help | Search | Canada Site | ||||
AAFC Online | Links | Newsroom | What's New | Site Index |
PFRA Online | Staff | Programs & Services | Offices |
Prairie Farm Rehabilitation Administration |
||||||||
![]() |
![]() |
![]() |
Control of Borers in planted trees in the Prairie ProvincesINTRODUCTIONWood borers are important pests of trees and occur in such major groups of insects as beetles, moths, and horntails. Some species make burrows in the bark and wood, which become filled with fine, compacted frass. Most of this type infest only over-mature or otherwise weakened trees, and no effective applied control is known for them. Other species, however, make burrows in the bark and wood, which they keep open; since they are capable of attacking healthy trees, many are important pests in forests and in farm and urban plantings.In the Prairie Provinces the ash borer Podosesia syringas fraxini (Lug.) and the carpenterworm Prionoxystus robiniae Peck, which have open burrows, are serious pests of several kinds of trees planted for shade, ornamental and windbreak purposes. Since they prefer trees with sunny exposures, open-growing plantings are more seriously affected than denser, shelterbelt plantings. For this reason, shade and ornamental trees in parks, on boulevards and on private and public properties are especially vulnerable. HOST TREES AND DAMAGEThe ash borer attacks green ash and mountain ash. A closely related form infests lilac. The carpenterworm, which also attacks green ash and mountain ash, occurs abundantly in poplars (including balsam poplar in natural stands) and readily infests American and Siberian elms. In other geographical regions oaks, black locust, maple, willow, cottonwood, boxelder and fruit trees are recorded hosts. The borers devour portions of the inner bark and the outer sapwood; this produces dead, sunken areas on the trunks and branches, and frequently results in dead "stagged" tops. The aesthetic values of shade and ornamental trees thus affected are lost or greatly reduced. The tunnels in the wood, made by the borers, weaken the trees structurally and increase the hazard of breakage from winds. The burrows also permit moisture and decay to enter and cause further deterioration. Up to 50% of the green ash trees in some urban centres in the prairie region have suffered damage of this nature in varying degrees. SIGNS OF BORER ATTACKTrees infested with the ash borer or the carpenterworm show the following symptoms:
BORER DEVELOPMENT AND DESCRIPTION OF STAGESThe ash borer and the carpenterworm have four developmental stages - adult, egg, larva, pupa. The adults of both species are typical moths but differ greatly in size and appearance. The larvae are true caterpillars and bear several pairs of feet on the abdominal region of the body. Ash borerThe adults are wasp-like moths with clear or translucent wings. The males and females are alike. Their bodies are slender, dark brown or almost black with yellowish bands on the abdomen. The wings are narrow with a spread of approximately 1 1/4 inches. The legs are long and orange coloured. At rest, the moths frequently hold the end of the abdomen in a raised position. The eggs of the ash borer are elliptical in shape, gray or black and very small - 30 placed end to end would span only one inch. Ash borer larvae are tiny, white caterpillars with dark heads when newly hatched. The full-grown caterpillars are creamy white, about one inch long, with reddish-brown heads. The pupae are about 3/4 inch long and reddish-brown with small backward-projecting spines. CarpenterwormThe adults of the carpenterworm, unlike those of the ash borer, are large moths; the females and males differ greatly in appearance. The female is grayish and stoutbodied with a wing-spread of three inches. The front wings are mottled gray and black; the hind wings are smoky. The overall coloration of the female blends remarkably with the colour of rough bark and makes her difficult to detect when at rest. The male is less Stout than the female with a shorter body and a wing-spread of two inches. The front wings are also mottled gray and black but the hind wings are yellowish-orange with black base, and margins. Carpenterworm eggs are oval-shaped, 1/16 inch long and light to dark brown in colour. The shell is hard with a netlike pattern of ridges. The newly-hatched caterpillars are dark brown, slightly hairy with a large black head. They quickly attain a length of 1/8 inch. The full-grown caterpillars are two to three inches long, pinkish-white with brown heads. The pupae are brown and 1 1/4 to 2 inches long. They are equipped with circular bands of backward-pointing dark spines. LIFE CYCLES AND HABITSAsh borerThe ash borer requires a minimum of two years in which to complete its life cycle. The moths begin to emerge from the host trees in late May and are present till late July in the prairie region. The earliest recorded date for Saskatchewan, obtained from field studies, is May 31; the latest is July 18. The eggs are laid in crevices in the rough bark on the trunks and branches, and in wounds in the bark. Injuries to trees from cultivation, pruning, hail, frost or snow attract infestation, and old burrow openings in the bark encourage re-infestation. All sizes of trees may become infested but smaller, younger trees appear to be the most susceptible. The parts of the tree most frequently attacked are the lower portions of the trunk to ground level and the area where the lower branches arise. The larval period of the ash borer extends from July of the year when the eggs are laid to early May of the third year following oviposition. Most of the caterpillars start their burrows in cracks and crevices in the bark. Bits of fine frass and webbing indicate where the entries occur. Some also enter old burrows. At the end of the first season, when activity is discontinued, some of the borers will have penetrated into the wood; others may still be in the bark. During the second season the caterpillars enlarge and lengthen their burrows greatly. In large trees they bore into the sapwood at a slight incline for one or more inches, then turn upwards and outwards to terminate the burrows at the end of the season in or near the bark, a short distance above the level of the burrow openings. In small trees and in branches of large ones the burrows penetrate to the centres and then rise for several inches before turning outward again, or they may pass through the trunk or branch to the bark on the opposite side. Masses of fresh moist frass ejected from the burrows are much in evidence in June and early July. During May of the third season boring is resumed until only a thin layer of bark or wood tissue remains to be penetrated. The caterpillars then pupate in the burrows behind this thin layer. Shortly before the moths are to appear, the pupae, with the aid of the backward-pointing spines on their hodies, wriggle forward, breaking the thin layer of bark or wood, and push themselves partly out of the burrows. The moths emerge and escape directly to the outside, leaving their pupal skins protruding from the burrow exits. CarpenterwormThe carpenterworm has a three-year or longer life cycle. The moths begin to emerge in early June from infested ash trees, and 10 to 14 days later from infested poplars, mountain ash and American and Siberian elm. The moths may be present till early August. The females are inactive and poor fliers because of their stout heavy bodies, whereas the males are strong fliers and very active. Mating and commencement of egg-laying takes place soon after the moths emerge, and each female may lay 300 eggs or more. The eggs are stuck firmly to the surface, usually in small groups, in cracks,crevices and wounds in the bark, or in or near old burrow openings.The attraction of wounded or previously infested trees for egg-laying along with the poor ability of the females to fly results in the development of "brood" trees from which numerous moths emerge year after year. More than 150 have been taken from the trunk of a green ash "brood" tree in a single season. Before ovipositing, the female probes the bark surface with the tip of her extended abdomen to locate suitable places for her eggs. The eggs incubate in 10 to 16 days and produce the small, dark, somewhat hairy caterpillars or larvae. The larval period extends from July of the year in which the eggs are laid to May of the following fourth or fifth year. The young caterpillars crawl about freely on the host trees soon after they are hatched and often cover long distances on the trunks before they begin to burrow. Small shelters, made of particles of frass and excrement held together by bits of webbing, are constructed by the young caterpillars to cover themselves and their burrow entrances. By August, frass ejected from the new burrows becomes noticeable. In the second and following seasons the burrows are greatly extended and enlarged, usually forming a maze of criss-cross tunnels in the wood of heavily-infested trees. During this period the caterpillars eject a great deal of coarse frass from the burrows which may cling ribbon-like on the outside of the trunk or accumulate like sawdust around the base of the trees. The caterpillars also return at intervals to the outer sapwood to feed. Often they emerge from the burrows to crawl about on the bark, and then re-enter the burrows. in May of the fourth or fifth year, depending on the length of time required for larval development, the caterpillars retreat to the upper parts of the burrows where, in specially prepared chambers, they transform into pupae. The period of pupal transtormation is relatively short, as the adults begin to appear in June. Before changing to the adult form, the pupae propel themselves downward by means of the backward-projecting spines on their bodies to the burrow openings so that the moths upon emerging from their pupal skins escape directly to the outside. CONTROLSeveral natural control factors affect the abundance of the ash borer and the carpenterworm in the Prairie Provinces. Woodpeckers dig out and feed on larvae in the wood. Moths are killed, newly-hatched caterpillars are eaten or lost before they can enter the trees and older caterpillars which emerge from the burrows and crawl about on the bark are destroyed. Parasites, disease, weather and the vigor of the host trees during the long period of caterpillar development also have controlling effects. These natural factors cause the fluctuations in borer abundance which occur in the absence of applied control. Despite the ameliorating effects of natural influences, applied control of the ash borer and the carpenterworm is usually desirable because of the importance of the trees they infest and the destructive capacities of the pests. The age, size and number of infested trees, the severity and extent of infestation, the value of the plantings and the availability of equipment and labour will determine the means used. The measures which may be employed involve prevention and applied control. A combination of both is usually desirable. PREVENTION
APPLIED CONTROLApplied control consists of physical means to destroy the pests and b) the application of chemical poisons. a) Physical Means
b)Application of Chemical PoisonsInformation on the use of chemicals for control of borers on trees is limited and fragmentary. Special procedures are required for worthwhile results. The measures currently recommended for control of the ash borer and the carpenterworm are:
In addition to using the right chemicals and equipment, both treatments must be applied thoroughly and at the right time for efficient results. To ensure that the best choice of treatment is made and the most up-to-date information on insecticide application is utilized, advice on the chemical control of borers in planted trees should be requested from one of the sources given below. When seeking advice on a borer problem indicate the species of trees affected, the appearance, location and extent of the visible injury and the number of trees involved with approximate ages and heights. This information is essential for correct identification of the borer problem and for determining the best control measures for it. Sources of InformationExtension EntomologistExtension Services Branch Manitoba Department of Agriculture 711 Norquay Byuilding Winnipeg, Manitoba Pest Control Specialist Plant Industry Division Saskatchewan Department of Agriculture Administrative Building Regina, Saskatchewan Entomology & Pesticides Section Crop Protection and Pest Control Branch Alberta Deprtament of Agriculture Agricultural Building Edmonton, Alberta |
|||||||
|