Section CHAPTER 1 INTRODUCTION TO DISEASE AND ENVIRONMENTAL DAMAGE

Transcription

1 Section CHAPTER 1 INTRODUCTION TO DISEASE AND ENVIRONMENTAL DAMAGE A tree disease may be defined as any injurious condition often expressed by the abnormal growth or development of various parts of a tree caused by an agent other than animal pests or fire. Disorders that lead to tree death, reduce tree growth, lower quality, or predispose trees to attack by other agents are included in this definition. There are two broad categories of tree diseases infectious and noninfectious. Infectious diseases are caused by living agents, mostly fungi, that spread from infected trees to contaminate others. Noninfectious diseases, often termed physiological diseases, are caused by nonliving agents. They do not spread from one tree to another. Several factors influence the severity of damage that diseases can inflict. Some tree species enjoy remarkable resistance to specific diseases. Some diseases may, in turn, be particularly virulent during certain phases of their development. More often, however, the environment and other site-related circumstances may decrease (or increase) the resistance of attacked trees. They may also enhance (or limit) the growth and infection capacity of the causal disease. As a result, diseases may vary in importance between tree species within one region of the province or in the same tree species in different regions. Diseases usually do not seriously threaten the existence of plantations, but they may cause severe losses if trees lack vigour, if the weather has been excessively moist and cool, or if there are other environmental abnormalities. As with insects and mites, Christmas tree disease problems can be foreseen early in their development provided plantations are visited frequently enough. With diseases, however, cultural and mechanical control strategies usually take precedence over chemical treatments, which very often cannot be efficiently or economically applied in plantations. All references to figures in this section are for colour photographs, which are found in the colour plate index. Contributed by: T. R. Renault Canadian Forest Service Atlantic Forestry Centre P.O. Box 4000, Fredericton New Brunswick, E3B 5P7 and D. B. Marks Canadian Forest Service

2 Section CHAPTER 2 FIR AND SPRUCE NEEDLECASTS, FIR AND SPRUCE NEEDLE RUSTS, YELLOW WITCHES BROOM, SHOESTRING ROOT ROT FIR and SPRUCE NEEDLECASTS Hosts: Balsam fir and spruce species. Importance: Usually most severe on small trees or on lower branches of larger trees. Occasionally, individual trees are severely attacked. Damage: Infected needles turn brown. Needlecast damage can be confused with winter drying, but with needlecast damage, the discoloured needles usually occur mixed with healthy ones on the same twig. Seasonal History: Spores (microscopic seedlike bodies) are released in early summer and infect new needles, which turn red the next summer. In the second or third summer, black lines (Figure 33) or dots form on these needles producing a new supply of spores. Infected needles usually drop after black lines have produced spores on three-year-old growth. Look For: Trees with an uneven distribution of twigs that have brown needles mixed in with green, healthy ones (Figure 34). Control: Remove severely infected trees from the plantation. Keep weed cover low. Underpruning. FIR and SPRUCE NEEDLE RUSTS Hosts: Balsam fir and spruce species. Importance: Usually most severe on small trees or on lower branches of large trees. Tree grade is lowered if 30 per cent or more of the foliage is affected. May reduce growth, but rarely kills trees. Damage: Severely infected trees appear yellowish in July and early August. In late autumn, infected needles may drop, leaving thin or bare twigs. Rust is confined to new foliage on balsam fir and to new and occasionally old foliage on spruce. Seasonal History: Needle rusts must spend a period each year on a deciduous plant or shrub before they can reinfect trees. From mid-june to early August, small orange blisters on individual needles release spores (microscopic seedlike bodies) that are carried to the alternate host. Infected needles are yellow from late June to early autumn (Figure 36). Small yellow dots or clusters are formed on leaves of the alternate host, followed by tiny hairlike structures that mature and release spores. These spores infect needles of balsam fir and spruce the next spring. On blueberry, a balsam fir rust causes small witches brooms that produce spores for one or more years. Infection is very dependent on spring weather.

3 Section FIR AND SPRUCE NEEDLECASTS, FIR AND SPRUCE NEEDLE RUSTS, YELLOW WITCHES BROOM, SHOESTRING ROOT ROT Look For: Yellow needles on current growth. Rows of white or orange spore-filled blisters erupting from needles (Figure 35). Control: Removal of alternate hosts near the trees reduces the intensity of new infections. For balsam fir, remove fireweed, ferns, and blueberry. For spruces, remove Labrador tea. Trees with heavy needle loss should be retained for another year as the new foliage may not become infected. YELLOW WITCHES BROOM Hosts: Balsam fir. Importance: Trees may be culled if brooms become large. Damage: A rust fungus causes abnormal shoot growth to form a conspicuous witches broom. Spindleshaped swellings may develop on infected branches and stems at the base of brooms. Needles drop from the brooms before each winter. Seasonal History: Spores (microscopic seedlike bodies) develop during the summer in two rows of orange-yellow blisters on the yellow, dwarfed needles of each broom. Infected needles drop each year but the disease continues to live in the woody tissue of brooms. New shoots growing from brooms and their needles become infected as soon as they begin growth each year. Spores released from diseased needles must infect and develop on another plant, chickweed, before the fungus can reinfect trees. When the rust matures on its alternate host, a new batch of spores is released. If they are carried to their coniferous host, new brooms may develop. Look For: Bushy branch formation without needles in winter. Short, curved yellowish needles during growth season (Figure 38). Proliferation of buds or shoots on certain branches or the stem (Figure 37). Control: Remove all rust brooms by pruning in early spring when they are small and before trees reach marketable size. Brooms attached to secondary branches can usually be removed without serious foliage loss. However, the brooms often require the removal of main branches to which they are attached. Brooms can be reduced significantly by removing the alternate host as much as possible inside the plantation. Herbicide: Glyphosate (Roundup). SHOESTRING ROOT ROT Hosts: All conifers and hardwoods. Importance: Infected trees die.

4 Section FIR AND SPRUCE NEEDLECASTS, FIR AND SPRUCE NEEDLE RUSTS, YELLOW WITCHES BROOM, SHOESTRING ROOT ROT Damage: The fungus lives in stumps and the roots of dead trees and infects living trees through the roots. It attacks trees of low vigour that have been weakened by insect attack, stand thinning, storm damage, and so on. The bark and wood of infected roots and root collars are rotted, and trees die when girdled by the fungus. Needles of conifers usually turn light yellow, and eventually red-brown. Pitch flows may occur at the base and root collar of infected conifers. Seasonal History: A layer of white fanlike growth with dark brown to black shoestrings can be found beneath the bark at ground level throughout the year. In early autumn, and occasionally during wet summer periods, light brown mushrooms often grow near the base of dead or dying trees and near old hardwood stumps. These produce and release spores (microscopic seedlike bodies), which may infect dead trees or stumps. Look For: Uniform yellowing, then reddening of crown (Figure 39). Pitch flow on bark at the root collar. Whitish fans of fungus under the root collar bark (Figure 40). Control: Avoid planting on former hardwood sites. Otherwise, remove and destroy as many stumps and large roots as possible before planting. Plant species that are suited to the site. Maintain conditions for vigorous growth, especially by not planting too deeply and spreading roots in the planting hole.

5 Section CHAPTER 3 RED FLAG OF BALSAM FIR, LOPHODERMIUM NEEDLECAST, RHABDOCLINE NEEDLECAST, SWISS NEEDLECAST RED FLAG OF BALSAM FIR Host: Balsam fir. Importance: Usually only a few branches on each tree are affected, but the presence in mid-crown may lower the value of the tree or cause it to be culled. May be caused by fungi, sawyer beetle feeding, or hail damage. Damage: Outer portions of branches and twigs become red and die. When a fungus is the cause, a constriction or sunken area is usually visible at the junction of living and dead portions of the branches. Hail wounds or lesions usually occur on the upper side of branches and twigs and on the side of the tree facing the storm. Broken branches are often evident on the ground. Wounds may be entry points for diseases that can kill twigs and small branches. Feeding by adult sawyer beetles on the bark of twigs and small branches usually several centimetres back from the tip causes scars on twigs and red flag. Seasonal History: After branches or twigs are girdled, outer portions become red brown. This condition is visible from early summer until the next spring, when red needles may fall leaving affected portions bare. If fungi are the cause, thin black structures that produce spores (microscopic seedlike bodies) may be found during late spring and summer near the junction of living and dead tissue. Severe hail storms usually occur during spring and summer and damage is noticeable soon after. As the season progresses, the outer ends of severely wounded branches wilt and die. Adult sawyer beetles emerge from infested logs or trees between mid-june and mid-july and feed. Then they fly to newly cut logs, dying or fallen trees and tree tops, where they mate and lay eggs. These hatch in about 10 days and the young larvae excavate galleries between the wood and bark. In early fall, they bore into the wood where they overwinter. They continue feeding during the second season, hibernate again, and pupate the next spring, after which the adults emerge. Look For: Discoloured outer branch (Figure 41) or twig portions. Lesions, scars, or constrictions at the border between green and brown needles. Occasional broken branch tips under trees. Control: Prune affected twigs or branches back to a point where the inner bark is green. Normal shearing will often provide this result. Remove dead or windthrown trees and tree tops from woods surrounding Christmas tree plantations, to prevent a build up of populations of sawyer beetles.

6 Section RED FLAG OF BALSAM FIR, LOPHODERMIUM NEEDLECAST, RHABDOCLINE NEEDLECAST, SWISS NEEDLECAST LOPHODERMIUM NEEDLECAST Hosts: Most species of pine, Scots and red pine being most susceptible. Importance: Kills seedlings. Brown needles make Christmas trees unsightly and unsaleable. Damage: Can cause excessive defoliation of early needles. Heavy needle loss also weakens trees, reduces their growth, and makes them more prone to other pests. Damage on larger trees is usually restricted to the low branches located in moister layers of air. Seasonal History: The fungus releases spores during rainy weather from August to October. These land on healthy needles and infect them. Yellow and brown spots appear and eventually the needles dry up and fall. The fungus overwinters on these fallen needles. Another kind of spore is formed and released to again infect foliage from mid-summer to early fall. Look For: Severe drop of older needles, giving branch tips a tufted appearance. Brown needles in older foliage, often mixed in with green needles. Irregular greenish brown spots and bands on older needles in late summer and fall. Brown needles with structures like coffee grains, some slit open, associated with narrow black bars and transverse black lines. Control: Reduce air humidity at ground level by mechanical or chemical weeding. In addition, remove unnecessary low branches to ease air flow. Long-needled Scots pines are more resistant than shortneedled varieties and should be given preference. Chemical control of the disease calls for three sprays of a fungicide during the periods of spore dispersal, from early August to October. RHABDOCLINE NEEDLECAST Host: Douglas fir. Importance: A major needle disease of Douglas fir wherever it is grown. Severe infections lasting two or three years can ruin or greatly reduce a plantation s capacity to produce suitable Christmas trees. May cause mortality in young, dense plantations when associated with Swiss needlecast. Damage: Severe infections cause unsightly discoloration. Much crown thinning also results from the complete shedding of all but the current year s needles. Seasonal History: The fungus overwinters on living infected current year s needles. Spores are produced in late winter and released from May to July during moist weather, infecting new developing needles. Although needles become infected early in the growing season, discoloration is only detectable in the fall or winter.

7 Section RED FLAG OF BALSAM FIR, LOPHODERMIUM NEEDLECAST, RHABDOCLINE NEEDLECAST, SWISS NEEDLECAST Look For: Severe drop of noncurrent foliage during the summer. Yellowish needle spots or bands in the fall, changing to a reddish brown colour in late fall or winter (Figure 42). Velvety, light brown reproductive structures located in brown needles or lesions. Control: Plant only the kind of Douglas fir that have shown the most resistance to the fungus (such as Rocky Mountain variety). Remove infected trees to prevent or reduce disease buildup. Chemical treatments starting at bud burst and repeated at roughly weekly intervals until the buds are fully opened have given good results but are laborious and expensive. SWISS NEEDLECAST Host: Douglas fir Importance: Primary damage consists of premature needle shedding, resulting in thin-foliage Christmas trees that are unfit for sale. Especially damaging to Douglas fir planted off-site. Can cause mortality in young, dense plantations when associated with Rhabdocline needlecast. Damage: Causes shedding of older needles. Severely infected trees are often left with only the current season s foliage in November and December. Gives the crown an unattractive, skeletal appearance. Seasonal History: Infects needles on developing shoots in May during wet weather, at the time of bud burst. Shedding occurs two or three years after infection. Look For: Severe drop of older needles, particularly on lower branches, giving branch tips a tufted appearance. Yellow noncurrent needles in the spring, turning brown in the summer. Sooty needle undersurface, resulting from irregular rows of abundant black, dotlike reproductive structures. (Tip browning of the needles also helps distinguish this disease from Rhabdocline needlecast). Control: The best control is to plant healthy nursery stock. Also choose a variety of Douglas fir with known resistance to needlecast fungi (such as Rocky Mountain variety). Avoid planting on wet, poorly ventilated sites. Use caution in planting and shearing, as close spacing and dense shearing create highly favourable conditions for infection by restricting air circulation and keeping the foliage wet for long periods. Excellent protection has been obtained with a single spray treatment made 4-5 weeks after bud break, when shoots are 1/4-2 inches (1-5 cm) long.

8 Section CHAPTER 4 SCHLERODERRIS CANKER, GLOBOSE GALL RUST, SIROCOCCUS SHOOT BLIGHT, PINE NEEDLE RUST SCHLERODERRIS CANKER Hosts: All pines and occasionally spruce. Importance: The European strain of the fungus can kill trees of all sizes and is considered extremely hazardous to red and Scots pine plantations. The North American strain causes limited lower branch mortality and only kills very small trees. It is the only strain found in Nova Scotia, but appears to have died out in the Province since Damage: Causes dieback of buds and small branches and leaves bare branch tips.when it reaches the stem the fungus may girdle the tree. Seasonal History: Infection of current foliage occurs throughout season during moist periods. Fungus kills the end branch portion and its terminal buds. Needles turn brown following spring and drop by fall. Spores form on dead twigs and infect the current shoot to complete the life cycle. Look For: Symptoms mainly on seedlings and the lower branches of trees. Brown or bare branch tips on older foliage in midsummer. Bud dieback in spring, associated on the same branch tip with yelloworange discoloration progressing from the base of the needles toward their tip (Figure 43). Control: Avoid planting trees in fields with poor air drainage or in areas of frequent frost. Use only disease free stock. Examine newly established plantations for early detection of dead or dying seedlings, and submit suspect seedlings for laboratory tests. Prune lower limbs and exercise good grass control to obtain adequate air circulation beneath crowns. Avoid shearing in wet weather. Periodically inspect plantations to locate and burn infected trees. Remove infected trees surrounding the plantation. Chemical treatment is too expensive for plantation use, but is feasible for nurseries. Spray Products: Chlorothalonil (Daconil, Bravo) GLOBOSE GALL RUST Hosts: Scots and jack pine. Importance: Causes moderate to severe branch mortality and may kill small scattered trees. Seedlings are girdled and killed quickly. Damage: Causes main stem and branch dieback, distorted and stunted growth. Seasonal History: Infection occurs on developing shoots in the spring. Small, scarcely detectable swellings develop at infection sites the following year. These galls enlarge each year and may become inches (25 30 cm) in diameter. Yellowish spores produced on galls two to four years old are released in May and June. Galls continue to produce spores each year until they completely surround and girdle the host branch or stem. Unlike other rust fungi in Christmas tree plantations, globose gall rust completes development on its pine host without alternating to another plant.

9 Section SCHLERODERRIS CANKER, GLOBOSE GALL RUST, SIROCOCCUS SHOOT BLIGHT, PINE NEEDLE RUST Look For: Unhealthy appearance of seedlings and individual tree branches. Entire crown at times also showing similar off-coloration. Branches and occasionally stems with varying size swellings, often covered with powder like, bright orange yellow spores (Figure 44). Control: Inspect planting stock for swellings caused by rust infection. Remove galls from trees in existing plantations, preferably before they start producing spores and infecting other trees. Maintain vigorous growth. SIROCOCCUS SHOOT BLIGHT Hosts: Pine, spruce, and hemlock. Importance: A relatively recent pest in the Maritimes. However, the serious deterioration it has caused to pine stands in Nova Scotia and its extensive infection of red pine plantations make this disease one of the major plantation problems in the Province. Damage: Fungus causes shoot dieback. A heavy attack leads to branch mortality and can kill trees of any size. Trees that survive often become misshapen. Seasonal History: The fungus overwinters in dead shoots. Spores, produced in May and June, are released during wet weather and rain-splashed to current shoots. Shoot deformity, needle drooping, and death progress rapidly from July to September. Look For: Dieback of current year shoots from July to October. Needle reddening associated with curled shoots and drooping fully elongated needles earlier in the year (Figure 45). Tiny pitch droplets on current shoots. Control: Avoid planting on humid, shady sites and on steep north and west slopes. Do not use coniferous foliage as a winter cover for seedlings, and also avoid their prolonged or unnecessary cover with shades. Pruning low-lying branches and maintaining good grass control help aerate and reduce stagnant humidity conditions that favour infection. To date, chemical control has only been developed for nursery situations. PINE NEEDLE RUST Hosts: Scots, red, and jack pine. Importance: Can greatly reduce growth in infected plantations. Rarely kills, except possibly smaller trees already weakened by insects, mites, or foliage diseases on current year growth. Damage: All needles, except those of the current season, may be badly damaged during severe outbreaks. Trees acquire a distinctive yellowish or whitish cast. Infected needles turn brown, die, and drop off.

10 Section SCHLERODERRIS CANKER, GLOBOSE GALL RUST, SIROCOCCUS SHOOT BLIGHT, PINE NEEDLE RUST Seasonal History: Rust fungi cannot spread directly from one pine to another, but must first pass from pine needles to leaves of the common goldenrod or aster and then back to pine needles. The fungus overwinters in infected needles. Spores develop in these in May and June, are wind-dispersed, and infect goldenrod or aster leaves. Spores are produced on these plants and carried to pine, where they start the disease again in the needles. Look For: Orange droplets on needles surrounded by a yellowish area in early spring. Orange blisters and short, yellowish or whitish columns erupting from similar discoloured areas later in the season (Figure 46). Control: Severe cases of rust are almost always associated with prolonged periods of wet weather. Avoid establishing a plantation on a wet or humid site. Before planting, get rid of as much goldenrod or aster as possible by mowing or herbiciding. Try also to eliminate most of the alternate hosts in existing plantations and within at least 1000 feet (300 m) of them. In addition, prevent the development of tall, grassy vegetation that will greatly increase moisture and the likelihood of needle infection in August and September.

11 Section CHAPTER 5 SNOW BLIGHT OF CONIFERS, SPRING FROST, WINTER DRYING SNOW BLIGHT OF CONIFERS Hosts: Balsam fir, and pine and spruce species. Importance: Usually not serious on Christmas trees Damage: The fungus attacks needles under snow or foliage near a tree s stem that has been laden with snow for long periods in late winter and early spring. Affected needles turn brown and hang from the twigs. Seasonal History: In the fall, spores (microscopic seedlike bodies) are released from tiny black structures on previously browned needles. These spores are carried by the wind and spread the disease to other trees. Once the disease is established, it spreads from diseased needles to healthy ones under the protection of snow cover especially on milder winter days. Look For: Foliage browning, usually associated with a white cobweb like fungal growth on branches covered with snow for long periods (Figure 47). Control: On Christmas trees, the disease is usually not serious enough to warrant control measures. SPRING FROST Hosts: Balsam fir and spruce species. Pine species less often. Importance: Tree grade is lowered by red foliage or bare shoots. Severe damage for several successive years may cause crooked or forked tops. Damage: Greatest damage results after new growth has been produced in the spring. New shoots droop, die, and turn red. Severely affected trees appear reddish. Seasonal History: Reddened foliage remains on the tree until late autumn and may not drop until spring. Look For: High incidence of dead new shoots as soon as shoots start to elongate in May and until about the end of the first week in June (Figure 48). Dead current foliage throughout the growing season. Control: Remove red shoots when shearing. Harvest at an early age trees growing in frost pockets, and replace them with less susceptible species. Select late flushing trees during thinning operations.

12 Section SNOW BLIGHT OF CONIFERS, SPRING FROST, WINTER DRYING WINTER DRYING Hosts: All conifers. Importance: Tree grade may be lowered by severe needle browning followed by defoliation. Severe injury for several successive years may cause some tree mortality. Damage: Needles turn brown and drop. If buds are killed, new twig production is delayed or may not occur. Occasionally young twigs or seedlings die. Seasonal History: This condition may be caused during midwinter or early spring if cold weather is followed by higher temperatures with drying winds. Water is lost from needles and cannot be replaced because the soil and tree trunk may still be frozen. Look For: One side or the entire tree with reddish brown foliage in late winter and early spring (Figure 49). Older foliage brown, or twigs and branches bare. New shoots developing normally in May and June. Level of injury fairly uniform throughout plantation, invariably above snow line. Control: Remove bare and reddened twigs when shearing. Avoid planting susceptible species, particularly short-needled Scots pine varieties in wind exposed areas.