Insect and Disease Management Guide for Woody Plants in North Dakota

F-1192 (Revised)
SEPTEMBER 2005

North Dakota State University
Fargo, North Dakota 58105

For more information on this and other topics, see: www.ag.ndsu.edu 

Table of Contents

How to Use This Guide

This guide provides diagnostic aid and management practices for very common, frequently noticed and particularly problematic insects, mites and diseases of trees and shrubs in North Dakota. Many other pests and diseases are present on woody plants in North Dakota and tree and shrub owners may encounter them. The pesticide use information in this guide is not intended for food-bearing trees and shrubs.

The first steps in maintaining healthy woody plants are to identify the species of tree or shrub and know what is considered "normal" for that species. If the growth or form of a particular tree or shrub is not normal, then correctly diagnosing the cause is critical to proper management. Often, management means providing conditions that do not favor development of the problem, whether its origin is an insect, disease or environmental. When tree and shrub owners know the identity of the host, they can use the "Host Index" (pages 10 and 11) to identify its common pests quickly. The pests are described in more detail and with management information on the page numbers listed in parentheses in the "Host Index." See the "Disease Control Products" list and "Insect/Mite Control Products" table at the end of this guide for common pesticide products.

Many of the serious insect and disease problems in North Dakota are often associated with stressed trees and shrubs. The text refers to the discussion "Maintaining Healthy Trees and Shrubs" (page 3) for some of these pests.

Prevent Problems by Maintaining Healthy Trees and Shrubs

Some pests, such as many of the wood-boring insects and canker-causing fungi, are opportunistic, becoming serious problems on trees and shrubs that are under considerable stress. Inadequate moisture, extremes in temperature, unfavorable soils, herbicide injury, mechanical injury and tree age are stress factors often associated with trees in the northern Great Plains. These factors and others, such as defoliating insects and diseases, often will predispose trees to opportunistic insects and diseases. This section deals primarily with trees in landscape settings, but the principles also apply to trees in conservation and natural settings.

Maintaining Healthy Trees and Shrubs

By learning which trees are in their landscapes, tree owners can become aware of the moisture, light, nutrient and other environmental needs of their trees. They can address these requirements to attain the healthiest trees possible. Conscientious tree owners already practice many measures to improve tree health to sustain vigorous, healthy-looking trees. Occasionally, these measures need some minor adjustments to address particular pests that threaten specific trees. Since many insect pests and diseases attack only certain tree species, tree owners who know their trees can become aware of the pests that pose a threat. Providing prime environmental conditions reduces the likelihood that opportunistic insects and diseases will kill trees.

Reducing Stress in Newly Planted Trees and Shrubs

Trees and shrubs are very susceptible to opportunistic insects and diseases when they are recovering from the planting/transplanting process and becoming acclimated to new locations. In broadleaf trees, symptoms of planting/transplanting stress may include leaf wilting or rolling and browning of leaf margins, while conifers may show an overall gray-green discoloration of foliage and tip dieback of needles. All trees with transplant stress show reduced growth and may have sprouts (adventitious shoots) developing from the trunk and off the sides of large limbs. To reduce the susceptibility to such stress, select the right tree for a given location, use the appropriate planting technique, mulch, water, don't fertilize, and provide protection from physical injury and sunscald.

Select the Right Tree

Selecting trees and shrubs for planting in a particular site should include considerations of hardiness, moisture requirements, insect and disease resistance, mature size and freedom from insects and diseases at the time of purchase. Plants generally should be labeled for U.S. Department of Agriculture hardiness zone 4 in southern North Dakota and for zone 3 in northern North Dakota. Plants labeled for warmer (higher numbered) zones may develop dieback of branch tips if they survive the winter or may grow well for several years only to die in a year that exceeds their hardiness limits. Placing trees and shrubs where other environmental requirements, such as soil conditions, moisture, light and space, are proper will improve establishment and long-term resistance to opportunistic insects and diseases. Some plants have been selected specifically for resistance to important insects and diseases and should be used if a particular pest problem is known for the area. Trees and shrubs should not be purchased when they have poor form or are infested with insects or diseased while in the nursery. If a homeowner desires a particular tree species, select the right location for that species. If a particular site needs trees, select species that thrive under the conditions at the site (e.g., willow and dogwood in wet areas, Russian-olive and caragana in alkaline areas or linden and arborvitae in shaded areas).

Planting Technique

Do not let tree roots dry out before, during or after the planting process. The planting hole can greatly affect the health of a newly planted/transplanted tree. Plant a tree so that the root crown is no more than 1 inch below the soil surface after settling. Holes should be dug at least two to three times wider than the root ball to provide for free growth of the roots. The sides of the hole should not be left glazed after digging. Roughen them to allow adequate movement of water and air to the roots and growth of roots out into surrounding soil. Before placing a tree or shrub in a hole, direct circling roots away from the root ball. If the circling roots are too large to redirect, cut them off with a sharp blade to prevent girdling of the plant years later. Many people feel that securing trees to stakes whenever they are planted always is necessary. This type of support is necessary usually only when a tree is tall, slow to recover, heavily foliaged or planted in a sandy site or playground. Most small trees and shrubs do not require staking and will develop strong trunks faster if allowed to move freely with the wind.

Mulch

Mulch placed over the soil surface above the tree or shrub root system helps conserve moisture, moderate soil temperature, and control weeds around trees and shrubs. Tree and shrub owners may use either organic or inorganic mulch. Organic mulch may be composed of bark or wood chips, straw, partially decomposed leaves or other materials. These mulches decompose over time and should be replenished as needed. Organic mulch should be applied 3 to 4 inches deep, leaving a 4- to 6-inch mulch-free area around woody stems. Inorganic mulches include plastic, crushed rock, woven fabric and other materials. Crushed rock may impede trunk expansion. Solid plastic mulches may impede or prevent root development because they do not allow air or moisture to move into or out of the soil from above. Do not use mulch when the soil is poorly drained.

Water

Too much or too little water seriously stresses newly planted trees and shrubs. The site should be thoroughly watered immediately after planting. Thereafter, monitor the soil regularly to prevent drying out. If rainfall is inadequate, the soil around the plant's roots should be watered deeply approximately every 10 to 14 days. If you are not sure if the soil is drying, dig down 3 to 4 inches next to the plant. Moist soil at that depth verifies the tree doesn't need watering at that time, while wet soil may indicate over watering. In particularly light soils or dry areas, consider a drip irrigation system. Avoid water that is high in salts when watering trees.

Fertilizer

Do not fertilize trees during the season when they are planted. Woody plants rarely need nutrients beyond those naturally occurring in the soil to remain healthy. If trees or shrubs appear to need fertilizer, apply only the amount needed for optimum growth and health. Too much fertilizer can increase tree and shrub susceptibility to certain insects and diseases. Nitrogen fertilizers should not be applied from July 1 to Sept. 15, since such applications may result in growth that does not harden off adequately prior to winter.

Pruning

Tree limbs may be broken before or during planting, and improper pruning sometimes occurs prior to purchase. Broken limbs should be removed after the tree is planted with a cut made just outside of the branch collar (Figure 1).

Pruning to improve tree structure should be delayed until the tree has become established and no longer is showing symptoms of transplant stress. The adventitious shoots often associated with transplant stress usually do not contribute to tree structure and should be removed as soon as they develop. Asphalt-based wound treatments do not hinder pathogens' infection of the wound, and because they slow callus growth, they actually may favor infection. They also may be toxic to plant tissues.

Figure 1. Proper and improper pruning techniques.

Protecting Newly Planted Trees

Bark of young trees is very susceptible to natural and man-induced injuries. Injuries that lawn mowers and weed trimmers cause are common problems for landscape trees. Homeowners can place hardware cloth or tree guards around the base of trees to prevent bark injury that rodent feeding and lawn-care equipment cause. Tree wraps and white paint have been used to prevent injury from sunscald. Proper mulching decreases the need for weed cutting next to the trunk and reduces movement of potentially damaging machinery next to the tree.

Maintaining Established Trees and Shrubs

As with all living things, trees and shrubs become old and die. Established trees die at an unnecessarily early age when they are subjected to a stressful environment. Identifying and mitigating stress factors can add many years to a tree's life.

Water

Research has shown that many opportunistic insects and diseases cause more tree injury when trees lack adequate water; however, similar problems can develop when trees have too much water. Proper water amounts are especially important for building food reserves during early and midsummer and for building tissue moisture levels going into winter. Many tree roots are deeper in the soil than turf roots; therefore, trees should be watered for longer periods of time than turf alone. This allows the water to move through the turf and deeper into the soil. Generally, trees need to be watered less often than turf but require more water in a given area than turf during each watering. If the soil remains too wet, consider aerating the soil or improving subsurface drainage.

Avoid Tree Injury

Trees often are damaged by chemicals and lawn-care equipment, and during construction activities. Damage to roots from trenching, soil compaction, de-icing salts and herbicides may not become evident for several years after the incident occurred. To reduce injuries from herbicides, de-icing materials and other chemicals, carefully choose safe products and apply them cautiously. One herbicide that very commonly damages landscape trees is dicamba, which is an ingredient in several broadleaf control mixtures used in lawns; herbicides containing dicamba should not be applied over roots of trees. To avoid some physical injury to trees, notify construction and landscape maintenance people of tree-care priorities and use mulch to keep lawn mowers, weed whippers and other equipment a safe distance from the trees. Remove tree wraps and other materials that encircle limbs before they girdle branches and stems.

Remove Broken and Diseased Stems

Broken stems and branches should be removed from a tree as soon as possible (Figure 1). Pruning can remove some diseases, such as cytospora canker on spruce. Pruning to remove diseases should be done during dry periods and is best done during late winter after the hardest freeze, but before buds begin to swell in the spring. If the tree species is susceptible to diseases that can be transmitted on pruning tools (e.g., fire blight), and the disease-causing organism is present, the tools should be cleaned properly between each cut.

Fertilization

Soil fertility seldom is a problem for established trees in North Dakota landscape plantings; however, there are exceptions. Trees and shrubs should be fertilized if they show symptoms of nutrient deficiency or produce inadequate growth after they are established. Soil or leaf tissue analyses may be useful in determining deficient nutrients. Certain nutrients may not be available to plants even though they are present in the soil. Yellowing (chlorosis) of leaves due to low iron availability is the most commonly diagnosed micronutrient deficiency of North Dakota trees. Too much fertilizer also can cause problems. Excess nitrogen fertilization has been proven to increase damage that certain insects and diseases cause on woody plants.

Monitor for Insects and Diseases

Insect and disease problems can cause stress that leads to increases in those or other pest problems. Finding and managing an insect or disease problem before it causes serious damage may increase the likelihood of plant survival and continued aesthetic performance. The Host Index can be helpful in identifying an unknown problem.

Rejuvenating Shrubs

To rejuvenate many decadent deciduous shrubs, cut them back 4 to 5 inches above the ground and allow new shoots to grow. This generally does not work for conifers and may result in more insect or disease problems in some deciduous shrub species (e.g., honeysuckle aphid on honeysuckle). Some flowering species require several years of growth to restore a full complement of flowers.

Removal of Declining/Hazardous Trees

No one gains by having sick or ugly plants in the landscape. As with all living things, trees have a given life expectancy and that expectancy is shorter in the northern Great Plains than other areas. Declining trees may serve as reservoirs for various insect and disease problems. Large, old trees can become hazardous, threatening lives or property as they decline and decay. If tree owners can't mitigate the hazard, they should remove those trees. Also consider removing the tree if it no longer provides desired functions, such as beauty, shade or wind protection and cannot be restored to provide these functions.

General Insect and Disease Management

Tree and shrub owners have many factors to consider when dealing with insect pests and diseases of woody plants. The most important factor is that woody plants have many defenses against insect pests and diseases, and usually are successful in defending themselves when they are attacked. Further, no species of woody plants are without problems; many insect pests and diseases are easier to manage than other problems. Sometimes, insects and fungi are secondary; that is, they are present only on plants that other problems have damaged. Some problems may be the result of insect or pathogen activity, but no sign of those organisms still may be visible by the time someone notices the damage. Also, not all insects or microorganisms associated with trees and shrubs cause problems; some are beneficial and even may be required for the plants to grow normally. Thus, do not place too great an emphasis on insects and pathogens as the cause of woody plant problems. Deal with them on a similar level as other woody plant problems; spraying or removing plants often are ill-advised first choices that are not appropriate.

Insects and pathogens coexist with woody plants in their natural habitat. The amount of damage that pests cause can vary substantially. Conversely, the amount of damage an individual tree or plant can sustain and remain healthy also is highly variable. On the whole, the natural system is balanced so usually neither the woody plants nor the insects and pathogens are exterminated. However, in a given situation, some woody plants may be damaged seriously or even killed. Also, when a change occurs in the natural system, such as when plants, insects or microbes enter new areas, the natural system may find a new balance. The changes may be subtle or imperceptible, or they may be catastrophic.

The relative health of woody plants and how well they provide their expected benefits can be manipulated to some extent. In the case of a plant health issue, evaluate what functions are expected of the plants, how the problem affects those functions, and whether management of the problem can retain or restore the expected function. The role, biology and effect of insects or diseases that may be involved should be included in evaluations. Correct diagnosis of the problem is critical to proper treatment. Careful observation of how a problem developed, the pattern of occurrence of the problem, and the association of harmful factors with that development and occurrence can be very useful in diagnosing the cause of woody plant problems.

Limited information can be provided in this space; many more potential insect and disease problems exist than are included here. Many other resources contain additional information. Finally, professionals are available to help in diagnosis, evaluation and management of woody plant pest problems. These include NDSU Extension Service county agents, North Dakota Forest Service foresters, USDA Natural Resources Conservation Service district conservationists and foresters, local arborists, nurseries, consultants, city foresters, the NDSU Diagnostic Laboratory, and NDSU Extension and research staff. Tree and shrub owners may need one or more of these sources of help to get the information to deal with the problem. However, consulting with local professionals first is best. Plant owners generally can obtain a satisfactory diagnosis and management plan with a little effort. However, because so many potential pest problems exist, and they may be intertwined into a mass of other problems, satisfactory diagnosis or management of some situations sometimes can be very difficult or not possible.

Disease Management

Disease Diagnosis and Management

As stated in the General Insect and Disease Management section, woody plant health problems have many causes, most of which cannot be covered in this publication. This section deals primarily with biotic diseases, those that plant pathogens cause. Some general guidelines can be applied to disease management even when a specific diagnosis of the problem is not made. In this general section, these are discussed by the type of disease involved, i.e., foliage diseases, canker diseases and stem decays.

All woody plant species have some pathogens that cause diseases in each category. A search of references or the Internet usually will provide some information about particular diseases. However, some pathogens are rare and reports about them are difficult to find. New pathogens are being found. Pathogens are being moved at a seemingly increasing rate into new regions from nearby states and distant continents. Their behavior in North Dakota may be quite different from other areas because of differences in host genetics and environmental conditions. However, gathering enough information from the literature or by observation to gain a basic understanding of the problem and to develop some likely effective disease management options usually is possible.

Foliage diseases

Description/Biology: Foliage diseases primarily affect only the leaves. Fungi cause most biotic foliage diseases of woody plants in the northern Great Plains, but some bacteria and viruses also cause foliage diseases. In addition, insects, air pollutants, chemicals and environmental factors can cause symptoms that are similar to those that pathogens cause.

After infecting a leaf, a foliar pathogen grows to colonize part or all of it. Most pathogens eventually cause a portion of a leaf to die; the dead area is called a lesion. Fruiting structures of fungal pathogens, in which spores are produced, usually develop within the lesion. Some foliage diseases have multiple infection periods within a single growing season (e.g., apple scab, powdery mildews). Others have a specific season during which infection can occur each year, but infective spores are not produced from those infections until subsequent seasons (e.g., Rhizosphaera needlecast, leaf curls).

Fungal pathogens of foliage most often overwinter in diseased foliage, either on the ground or on leaves that remain attached to branches through the winter. Pathogens that cause foliage diseases, especially those that cause anthracnose, also may overwinter on other plant parts, such as in twig and branch cankers (e.g., ash and oak anthracnose, fire blight), in reproductive structures such as seeds and seed stems (e.g., ash anthracnose), and in bud scales (e.g., leaf curl). Those pathogens that grow from the leaf into a limited portion of branch (locally systemic) can overwinter in those branches (e.g., juneberry black leaf). Those that have life cycles of one year or more overwinter in foliage that may or may not show symptoms (e.g., Rhizosphaera needlecast, Lirula needle blight). Rust fungi that cause foliage diseases generally overwinter as the cold-hardy spore stage (teliospores) in dead leaves or branch infections of the same woody plant species or in another woody or nonwoody host of the pathogen. Some pathogens overwinter in multiple ways.

Foliage pathogens may reach the infection site through several means, the most common of which are passive dispersal by rain splash or wind blowing spores from fruiting bodies on infected plant parts (e.g., anthracnose fungi, leafcurl fungi, needlecast fungi, mildew fungi, rusts, fire blight bacteria). Other means include active dispersal by insects (e.g., fire blight, viruses) or by humans through mechanical means such as grafting (viruses) and pruning (fire blight).

Wet weather is conducive to the development of several foliage diseases due to exudation of spores from fruiting bodies, an increase in spore dispersal by rain splash or a requirement of free moisture on the leaf surface for spore germination and infection. Many fungi that require free moisture for infection need at least 12 hours for the process to be complete, and availability of free moisture beyond 12 hours tends to increase the number of infections that occur. In addition to direct effects on the pathogen, wet weather and ample soil moisture can result in increased foliage diseases if they cause increased shoot growth and more succulent leaves, which tend to be more susceptible to many foliage pathogens than slow-growing or mature leaves. The amount of infection can vary greatly from one growing season to another, depending on the amount of wet weather.

Damage/Symptoms: Foliage diseases can appear as distortions, mosaics, distinct spots, indistinct blotches, or general death of individual or masses of leaves. Rusts will cause distinct spots and fruiting bodies that are yellow to orange during the growing season. Symptoms vary by both host species and pathogen. Sometimes, leaves will die or fall following only one infection. At other times, the leaves may remain attached and living even after numerous infections. In general, the more spots or blotches the leaves have, the less food they will produce to supply the plants' food reserves.

On an initially healthy plant, defoliation greater than 25 percent to 50 percent generally is considered "substantial." Defoliation and subsequent refoliation draws down food reserves within the tree. When substantial, this results in shorter shoots and smaller leaves. Several years of such defoliation may draw down food reserves to the point where twigs and branches begin to die back. This dieback starts at the top on deciduous trees and also may result in formation of epicormic branches (also known as water sprouts). On conifers, dieback begins at the bottom of the tree. Conifers are more sensitive to defoliation than deciduous trees.

The patterns of symptom occurrence and development are keys to discerning if a foliar pathogen or some other agent damaged the leaves. Foliage infections tend to occur in a random pattern on leaves in a given area. If spots occur uniformly within the leaves or among leaves, then the cause is less likely to be a foliage pathogen. If all the leaves on individual twigs, branches, stems or entire trees develop similar symptoms at the same time or progressively down the plant, then the problem likely is not a foliar pathogen. A canker, insect activity, hail damage or lawn mower damage can affect individual twigs or branches, resulting in dead or damaged leaves. The further down the plant the damage occurs, the greater the proportion of the crown that is affected.

Other patterns can help discern if a problem is due to foliage diseases. Because wet leaf surfaces generally result in increased infection, portions of the plants that stay wet longer often have more disease. This tends to be the lower portion, the shaded side, the wind-protected side or the watered side of the crown. Thus, if leaves on one side of the plants are affected, but that is not the side that is wetter, the cause may be something other than a foliage pathogen, e.g., scorch if on the sunny side, herbicides drifting from that side or winter injury of conifer needles in portions of the crown that were exposed to winter winds and direct sunlight.

Comments: Generally, three types of management are available — cultural, chemical and genetic. With cultural control, some aspect of growing the trees is managed to reduce the threat of serious infection. For example, planting, thinning or pruning the plants to allow more air movement around and through them tends to reduce the amount of infection by foliage pathogens by allowing leaves to dry off more quickly after rain, morning dew or unintended watering while irrigating the lawn. Watering should be done after morning dew has already evaporated but early enough so the sprinkler water evaporates before nightfall. Reducing the amount of inoculum (source of infection, usually spores) can reduce the amount of infection. Spacing woody plants far enough apart so the pathogen has more difficulty spreading from one plant to the next also can reduce disease development. The exact distance varies by pathogen. Planting other kinds of trees and shrubs between plants that are susceptible can serve as a barrier for rain-splashed and windblown spores spreading from one plant to the next. Mulching or tilling fallen, infected leaves can reduce the amount of inoculum that can return to the plant. When planting trees and shrubs where infections exist, plant different species that are not susceptible to the existing pathogens.

With chemical control, a pesticide is used to prevent infection by or eradicate the pathogen at some key part of its life cycle. Pesticides are registered for management of most foliage diseases, but determining what pesticides are registered and the proper application schedule, and even finding a source for a particular pesticide for unusual diseases, sometimes is difficult. The sources of expertise listed in the section "General Insect and Disease Management" often can help provide such information, and an Internet search may be helpful. Using a pesticide that is labeled for a particular disease with the proper application schedule is especially important. Use pesticides only for those disease-host combinations that are listed on their labels. Also, pesticides must be applied with correct timing; otherwise, they will not give optimum control.

Knowledge of how a particular disease has developed is important in helping decide if pesticide applications are appropriate. If a disease has caused substantial damage in the area, then a serious potential may exist for future damage. Because this is not always the case, simple identification of some pathogens does not mean that damage will occur. Much depends on weather patterns, so a disease that develops to a serious level in one season may not in another season. Therefore, wait to see if conditions are conducive for disease development before making pesticide applications.

With genetic control, plants that are resistant to a particular pathogen are used to prevent or reduce damage. In general, few of the woody plants available in North Dakota have been selected for disease resistance. However, some possibilities are available, e.g., poplar cultivars that are resistant to Melampsora leaf rust or spruce species that are more resistant to Rhizosphaera needlecast than others. Favor increased genetic diversity whenever possible. If too many plants of a single species are present in a given area, a disease can increase quickly to a serious level and damage a high proportion of that species. Alternating two or more species in ornamental or conservation plantings can reduce disease development substantially on any one of those species. Avoid planting alternate hosts of rust pathogens in the same vicinity. This primarily applies to cedar-apple rusts, which alternate between junipers (Juniperus spp.) and plants in the apple family (e.g., apples, crabapples, juneberry, hawthorn).

Cankers

Description/Biology: Cankers are dead areas on the outside of branches or stems. They can be superficial on the outside of the bark or extend into the wood. Most commonly, they are associated with death of the cambium and result in discoloration and collapse of the bark in the cankered area. The margin of the canker expands as the pathogen grows into live tissue. If the bark is thick, it may not collapse or discolor. In such cases, the canker may be visible only if the bark is removed or the area outside the canker grows, resulting in a sunken area. Some canker pathogens tend to cause infection and canker growth during certain seasons (e.g., spring, growing season, dormant season), while others expand during most of the year. Some are considered annual cankers that require a new infection each year to form a canker, while others are perennial, expanding periodically or continuously over multiple years.

Fungi and bacteria cause cankers. The pathogens may be host specific, that is, infect only certain woody plant species, or they may have a broad host range. The pathogens tend to be weak parasites and often can survive in dead bark as saprophytes (organisms that live in dead and decaying organic matter). Complicating the issue, canker pathogens may infect branches dying from other factors. They then may remain restricted to the dying area or expand beyond the dying area.

Pathogens that cause cankers generally overwinter in cankered tissues on branches and stems. Some also overwinter on fallen leaves and in bark of branches that died of other causes. They generally infect trees through wounds and cause greater damage to trees under stress. Some of these pathogens infect healthy bark and reside there as latent (inactive) infections; such infections allow the pathogen to colonize branches rapidly if they become stressed or begin dying. Branches and limbs die as the expansion of the cankers girdles them. For fungal canker pathogens, small fruiting bodies usually develop in or on the bark of cankered areas, from which spores may be dispersed to other branches to cause new infections. Fruiting bodies may develop in the same season as the initial infection or as long as several years later. Bacterial canker pathogens do not produce fruiting bodies. Bacterial cells ooze onto the infected bark surface, from where rain splash, wind, insects and other means disperse them. Dispersal may occur in the same season as infection, the following season or both.

Some wounds and stresses commonly associated with increased canker development are drought, hail wounds and herbicide injury. Other situations that can increase canker development include excess shading of lower branches, standing or excess water, lack of cold hardiness, defoliation, damage to the stem or root system, ice damage, pruning wounds and openings in the bark that insects cause. Once a tree becomes infected, it initiates defense mechanisms to try to stop canker development. The success of these mechanisms is increased in plants with higher vigor, so encouraging high plant vigor or removal of stressing factors helps the plant defend itself. One exception to this is for fire blight cankers (page 39). In general, the plant defenses reduce growth of the cankers, allow development of callus at the canker margin or stop canker growth where the infected branch joins a larger branch.

Damage/Symptoms: The canker symptoms that usually are noticed are individual branches with wilted, discolored or dead leaves or individual dead branches without leaves. On a branch with an active canker, expanding areas of discolored bark extend out from the point where the canker originated. If the canker pathogen is in the inner bark or wood, peeling back the bark may reveal discolored plant tissue. However, the cankered area of some (e.g., fire blight) may be difficult to see during some parts of the year. As infected tissues die, the discolored area often becomes sunken. Cankers also may develop from pathogen invasion of dead or weak branches, twigs and fruit spurs. Individual branches or entire trees may be killed. The canker may continue to grow down the branch onto larger branches until the tree's defenses or the canker's biological limits stop its expansion. Dead leaves often remain attached to branches that were girdled and died during the growing season. On larger branches and main stems, slow-growing perennial cankers (e.g., those that Nectria species cause) produce what are termed target cankers because of the concentric rings of dead wood in the canker after several years. Fruiting bodies of fungal canker pathogens may form on the surface of the bark (e.g., Tubercularia) and/or embedded in the bark (e.g. Botryodiplodia).

Twig or branch dieback that other factors cause, such as cold injury or stress, can be confused with cankers because they can result in death of the bark to a specific point bordered by a raised margin, similar to the injury caused by cankers.

Comments: Positive identification of most canker pathogens requires laboratory examination, but some can be identified based on signs and symptoms in the field. However, their presence does not always establish their role as pathogens; they may have invaded or fruited on the dead tissue after something else killed it.

Because stress increases the risk and severity of canker problems, help woody plants avoid or reduce stress to reduce occurrence and severity of cankers. Selecting woody plants that are adapted to site conditions can help assure vigorous growth. Some woody plant species tend to be prone to canker diseases. These generally include fast-growing or marginally hardy species such as aspen, cottonwood, poplars, willows, Siberian elm, Siberian pea shrub (caragana), American plum, cotoneaster, honeylocust, Colorado blue spruce and Russian-olive.

Once cankers develop, treatment options are limited. Fungicides generally have not been effective in managing cankers. The direct treatment of choice is proper removal of the cankers and destruction of the tissue that was removed. This usually involves pruning the branch below the canker. Some cankers, particularly those that bacteria cause, should be pruned well below the discolored or cankered area because the pathogen may be located far beyond where the canker is visible. If cankers occur on larger branches or the main stem, removal of the diseased branch or stem will cause great damage. In these cases, consider removing the plant. Excising cankers from a stem or branch sometimes is possible. To do so, use a sharp knife to cut through the bark to the wood. Generally make the cut at least 2 inches beyond the margin of the discolored bark associated with the canker. Then remove all the bark within the cut. The removed area should be diamond shaped, preferably with the sides of the diamond somewhat rounded, but with the top and bottom pointed.

Pruning tools should be disinfected between cuts to avoid spreading the canker pathogen. If in doubt about whether pruning tools are contaminated, disinfect them in denatured alcohol or a 10 percent bleach solution. Prune in early spring as the cambium becomes active, but before the leaf and flower buds open, to reduce the threat of new infection. Pruning at this time will allow rapid callus development on the wounded tissue while the inoculum potential of canker pathogens is relatively low.

Stem decay

Description/Biology: Fungi cause stem decay. Most decay fungi are relatively host specific, but some infect several host species. Stem decay has been observed in all major woody plant species in North Dakota and many minor ones. Aspen, boxelder, buffaloberry, bur oak, caragana, cottonwood, green ash, plum and willow are particularly subject to stem decay in North Dakota. Spores that are deposited on exposed wood may cause infections if the condition of the wood and environmental conditions are favorable (usually warm and wet). The wood initially may be exposed because of wounds or through branches that died from shading, cankers or other causes. Tree experts think other microbes must colonize and modify the wood before most decay fungi can colonize it. The process and times required for such modifications are not adequately described or understood. Once decay fungi infect the wood, reasonably healthy plants can form barrier layers in response to infection. The barrier layers "wall off" the column of wood that existed when the plant first was infected (except when canker-rot fungi are present) and prevent the fungus from growing outside of that column. Any wood that develops outside of the barrier will be sound. However, if the infected trees are wounded or severely stressed, the fungus can escape from the contained area to invade other wood tissue, and the formation of barriers starts over. A continual change of balance may occur between the pathogen and the host with regard to where decay occurs.

Decay fungi may grow in wood for a few to many years before they cause substantial decay. As they grow and utilize nutrients in the wood, they break down cell walls so that the structure of the wood is weakened or destroyed. Such wood is referred to as decayed, punky or rotten. Once stem decay fungi have obtained an adequate food base from the decaying wood, they produce fruiting (spore-producing) structures to complete their life cycle. These structures grow on the outside of the wood or bark as mushrooms or conks (shelflike or rounded woody growths). Mushrooms produce spores in one season and then deteriorate, while conks may be annual or perennial. Perennial conks grow a new spore-producing layer each year. The wind disperses the spores to wounds or openings in the bark, thus continuing the cycle.

Damage/Symptoms: Branch and top dieback are common in trees with advanced decay, but determining whether the decay caused the dieback or whether stress allowed the decay to advance is difficult. The most obvious sign of decay in a woody plant is the fungal fruiting structure. Some decay fungi also cause cankers, or areas of dead bark adjacent to the decayed wood. Unless these signs or symptoms are present, determining if wood decay fungi infected a plant without examining the wood on the interior of the plant is not possible. When wood decays, it usually becomes soft and has a different texture, compared with sound wood. Depending on the fungus involved, the decay may occur in the heartwood (the central core of dead wood), sapwood (the outer wood) or both. Sapwood-decaying fungi usually are in the older, inner rings of sapwood rather than the most recent years' growth. Color of the decayed wood can range from white to yellow to dark brown. Trees that decay fungi have infected for a long time may be hollow. No single decay fungus uses all the wood components, so the hollows are most likely due to removal of decayed wood by carpenter ants, mammals or birds.

If a tree with mushrooms, conks or canker rot is in a location where it poses a hazard, have a professional arborist evaluate it to determine whether it remains structurally sound. If the tree has lost its structural strength, it should be removed. To estimate the amount of decay, take cores from the wood with an increment borer. Electrical devices are available to evaluate where decayed wood is present.

Comments: The best treatment against decay fungi is to maintain good tree vigor, minimizing wounds and other stresses, and allowing the trees to keep their own natural defenses at a maximum. Following proper pruning practices (page 6) is a critical part of this recommendation. Trees that develop from stump sprouts may get infected from the original stump if they become stressed or wounded while the old decay still is active.

Removal of trees with fruiting structures may be necessary to eliminate hazard risk. However, removal of a given tree with conks will not markedly reduce the chances for infection of nearby trees because spores from other infection sources can be dispersed over long distances.

Pesticide Safety

Modified from: "Pesticide Safety: A Guide for Gardeners and Homeowners"
NCR 590, June 1996

Julie Garden-Robinson,
Extension Specialist, Food and Nutrition

Greg Dahl, Pesticide Programs Specialist

Pesticides can be very effective tools in managing pest problems. If used improperly, they can cause serious damage to people, pets and the environment. Always use proper protective clothing and follow pesticide label instructions.

Read and Follow the Label Directions

As a pesticide applicator, you are legally responsible for reading, understanding and following the label directions. Pesticide labels usually will contain the following sections:

• Product name: Indicates type of pesticide or what types of pests it will control.
• Ingredient statement: Lists the amount of each active ingredient and the total amount of inert ingredients.
• Signal word: Indicates the toxicity of the product.
• Products labeled "DANGER POISON" and accompanied by a skull and crossbones symbol are highly toxic. Products labeled "DANGER" without the word "POISON" or the skull and crossbones symbol can cause severe skin injury or irreversible eye damage.
• Products labeled "WARNING" are moderately toxic or may cause moderate eye or skin irritation.
• Products labeled "CAUTION" are slightly toxic or may cause slight eye or skin irritation.
• Warning about potential hazards to humans, domestic animals and the environment. They
• also indicate special fire, explosion or chemical hazards and methods to avoid or minimize risks.
• Statement of practical treatment/ first aid information: Indicates antidote or first aid treatment to administer.
• KEEP OUT OF REACH OF CHILDREN: Pesticides always must be stored and kept out of reach of children.
• Directions for use: Warns that federal law requires the pesticide to be used according to label directions. Indicates location, amount, frequency, and method and timing of the application. The label also indicates when re-entering the treated area is safe. Do not exceed recommended limits.
• Other information on the label includes the
• name and address of the manufacturer, EPA registration and establishment numbers, and storage and disposal information.

Special Precautions when Using Pesticides

• Examine the area to be treated and the surrounding area. Are plants or animals present that the pesticide could harm? Don't spray if you cannot guarantee they will not be injured. You are responsible for any damage that could occur.
• Wear all protective clothing and equipment
• listed on the label, such as long-sleeved shirts, coveralls, chemical-resistant gloves, goggles, etc.
• Use pesticides only on plants designated on
• the label.
• Calibrate the sprayer or applicator to apply the correct amount. Appling more pesticide than
• the label states is illegal and unsafe.
• Use all chemicals in well-ventilated areas to avoid inhaling fumes. Work outdoors if possible. Use protective gloves and/or masks when label instructions recommend them.
• Be especially careful while working with the concentrated pesticide during mixing.
• Don't spray on a windy day, when the spray could drift on you or into a neighbor's yard.
• Do not eat, drink or smoke when using
• pesticides because traces of the chemicals may be transferred from hand to mouth.
• Wash hands thoroughly with soap and water after handling pesticides and before eating.
• Avoid wearing soft contact lenses when dealing with pesticides. Soft contact lenses may absorb vapors from the air and hold them against
• your eyes.
• Always avoid unnecessary exposure to pesticides. Be especially careful to keep children, pregnant women, sensitive individuals and pets away from areas where pesticides are being or have just been applied.
• An alternative is to hire a professional pesticide applicator. Be sure the applicator is certified and has good references.

Disposal of Pesticides

• Never put potentially hazardous waste, such as pesticides, directly in the garbage.
• Share remaining pesticides with someone who can use them as intended.
• Don't pour remaining chemicals down the drain.
• Triple rinse empty glass, plastic and metal pesticide containers by filling the containers
• one-quarter full of water, covering tightly and shaking. Apply the rinse water on the original targeted area. Wrap the container in newspaper and send to the landfill or dispose of as directed on the label.
• Do not reuse empty pesticide containers.
• Wrap aerosol containers in several layers of paper and place in a covered trash container.

Storage

• Store pesticides out of reach of children — in locked cabinets or in cabinets with childproof latches.
• Store pesticides only in their original containers with labels visible and intact.
• Mark the date on containers that are put into storage with a permanent marker and keep an up-to-date list of products and purchase dates near the storage area. Use oldest products first.
• Keep metal containers dry to prevent corrosion and possible leakage.
• Seal containers tightly after using.
• Store all pesticides away from food, feed, seed, fertilizer or water.

Dealing with Spills

• Don't leave the spill unattended. Send someone else for help.
• Keep people, especially children, and pets upwind and away from the spill.
• Protect yourself by wearing AT LEAST the protective clothing and equipment listed on the pesticide label.
• If indoors, ventilate the area with fans and open windows and doors.
• Try to confine the area of the spill. Use a nonflammable absorbent material, such as cat litter, to soak up the spill.
• Place the material in a noncorroding container, such as a plastic bucket with a tight-fitting lid.
• Seal the container and label it with product name, amount and absorbent material used.
• In some communities, the product will need to be safely stored until the community holds a household hazardous waste collection.
• Rinse the area several times with water and rags. Wash the area to remove traces of the product. Don't use household equipment to clean the spills, as this equipment will need to be discarded to avoid contamination of your household.

Safety Clothing and Equipment

Check the label under "Hazards to Humans and Domestic Animals" to see what special protection you need when applying a pesticide. Protective clothing may include a hat, goggles, mask, rubber gloves, rubber boots and/or a long-sleeved shirt and long pants. A respirator approved for pesticides may be needed for some pesticides that pose a risk from inhalation.

Clothing Cleanup

• Prerinse contaminated clothing.
• Keep clothing used during pesticide application separate from family laundry. Launder clothing using hot water and a heavy-duty detergent after each use.
• Clean washing machine after use by running it through a normal wash cycle without clothing.
• Line-dry clothing (see Extension publication
• HE-382, "Guidelines for Safely Laundering Pesticide-Contaminated Clothing," for further information).

Application Equipment and Cleanup

• The pesticide sprayer or applicator needs to be in good operating condition and properly calibrated to apply the correct amount of pesticide.
• Clean all equipment, including mixing tools, after each use. Triple rinse with clean water and allow to dry.
• If you used a sprayer, rinse it with a small amount of water and spray over an area that may be treated legally. Clean the sprayer with water or as directed on the label. Rinse well and spray on an area that can be treated legally.
• For information on calibration of pesticide sprayers or applicators, contact your county office of the NDSU Extension Service or your pesticide supplier.

First Aid

Always read the first aid information on the label before applying the pesticide to know what to do in case of accidental contact with the skin or eyes. When seeking medical help, always bring the pesticide label.

• Skin exposure: Drench the skin and clothing with water, then remove all contaminated clothing and wash skin thoroughly with soap and water. Wash hair and fingernails thoroughly, also.
• Eye contact: Rinse eyes immediately with a stream of clean water and continue rinsing for 15 minutes. Victim should blink as much as possible.
• Inhalation: Get to fresh air immediately. Begin artificial respiration if the victim isn't breathing. Seek medical help.
• Ingestion: Check the product label to see if it recommends inducing vomiting. Sometimes vomiting is dangerous. Seek medical help.

F-1192 (Revised)
SEPTEMBER 2005