INSECT AND DISEASE PROBLEMS

    Insects and diseases can threaten tree health. As soon as you notice
    any abnormality in your tree’s appearance, you should begin a
    careful examination of the problem. By identifying the specific
    symptoms of damage and understanding their causes, you may be
    able to diagnose the problem and select an appropriate treatment.
    Stress 

    Basic elements that influence plant health include sufficient water and light,
    and a proper balance of nutrients. Too much or too little of any of these
    environmental conditions may cause plant stress.
    Environmental stress weakens plants and makes them more susceptible to
    insect and disease attack.
    Trees deal with environmental stresses, such as shading and competition
    for water and nutrients in their native environment, by adjusting their growth
    and development patterns to reflect the availability of the resources.
    Although trees are adapted to living in stressful conditions in nature, many
    times the stresses they experience in the landscape are more than they
    can handle and may make them more susceptible to insects and diseases.
    Diagnosis
    Correct diagnosis of plant health problems requires a careful examination of
    the situation.
    1 Accurately identify the plant. Because many insects and diseases are
    plant-specific, this information can quickly limit the number of suspected
    diseases and disorders.
    2 Look for a pattern of abnormality. It may be helpful to compare the
    affected plant with other plants on the site, especially those of the same
    species. Differences in color or growth may present clues as to the source
    of the problem. Nonuniform damage patterns may indicate insects or
    diseases. Uniform damage over a large area (perhaps several plant species)
    usually indicates disorders caused by such factors as physical injury, poor
    drainage, or weather.
    3 Carefully examine the landscape. The history of the property and
    adjacent land may reveal many problems. The number of species affected
    may also help distinguish between infectious pathogens that are more
    plant-specific as compared to chemical or environmental factors that affect
    many different species. Most living pathogens take a relatively long time to
    spread throughout an area, so if a large percentage of plants becomes
    diseased virtually overnight, a pathogen is probably not involved.
    4 Examine the roots. Note their color: brown or black roots may signal
    problems. Brown roots often indicate dry soil conditions or the presence of
    toxic chemicals. Black roots usually reflect overly wet soil or the presence
    of root-rotting organisms.
    5 Check the trunk and branches. Examine the trunk thoroughly for
    wounds because they provide entrances for pathogens and wood-rotting
    organisms. Wounds can be caused by weather, fire, lawn mowers, and
    rodents, as well as a variety of other environmental and mechanical factors.
    Large defects may indicate a potentially hazardous tree.
     6 Note the position and appearance of affected leaves. Dead leaves
    at the top of the tree are usually the result of environmental or mechanical
    root stress. Twisted or curled leaves may indicate viral infection, insect
    feeding, or exposure to herbicides. The size and color of the foliage may
    tell a great deal about the plant’s condition. Make note of these and any
    other abnormalities.
    Diseases
    Three things are required for a disease to develop:
    • the presence of a pathogen (the disease-causing agent)
    • plant susceptibility to that particular pathogen
    • an environment suitable for disease development
    Plants vary in susceptibility to pathogens. Many disease-prevention
    programs focus on the use of pathogen-resistant plant varieties. Even if the
    pathogen is present and a susceptible plant host is available, the proper
    environmental conditions must be present over the correct period of time for
    the pathogen to infect the plant.
    Diseases can be classified into two broad categories: those caused by
    infectious or living agents (diseases) and those caused by noninfectious or
    nonliving agents (disorders).
    Examples of infectious agents include fungi, viruses, and bacteria.
    Noninfectious diseases, which account for 70 to 90 percent of all plant
    problems in urban areas, can be caused by such factors as nutrient
    deficiencies, temperature extremes, vandalism, pollutants, and fluctuations
    in moisture. Noninfectious disorders often produce symptoms similar to
    those caused by infectious diseases; therefore, it is essential to distinguish
    between the two in order to give proper treatment.
    Insects
    Some insects can cause injury and damage to trees and shrubs. By
    defoliating trees or sucking their sap, insects can retard plant growth. By
    boring into the trunk and branches, they interfere with sap flow and weaken
    the tree structure. Insects may alsocarry some plant diseases. In many
    cases, however, the insect problem is secondary to problems brought on by
    a stress disorder or pathogen.
    It is important to remember that most insects are beneficial rather than
    destructive. They help with pollination or act as predators of more harmful
    species. Therefore, killing all insects without regard to their kind and
    function can actually be detrimental to tree health.
    Insects may be divided into three categories according to their method of
    feeding: chewing, sucking, or boring. Insects from each group have
    characteristic patterns of damage that will help you determine the culprit
    and the proper treatment. Always consult a tree care expert if you have any
    doubt about the nature of the insect problem or the proper treatment
    Chewing insects eat plant tissue such as leaves, flowers, buds, and twigs.
    Indications of damage by these insects is often seen by uneven or broken
    margins on the leaves, skeletonization of the leaves, and leaf mining.
    Chewing insects can be beetle adults or larvae, moth larvae (caterpillars),
    and many other groups of insects. The damage they cause (leaf notching,
    leaf mining, leaf skeletonizing, etc.) will help in identifying the pest insect.
    Sucking insects insert their beak (proboscis) into the tissues of leaves,
    twigs, branches, flowers, or fruit and then feed on the plant’s juices. Some
    examples of sucking insects are aphids, mealy bugs, thrips, and
    leafhoppers. Damage caused by these pests is often indicated by
    discoloration, drooping, wilting, leaf spots (stippling), honeydew, or general
    lack of vigor in the affected plant.
    Boring insects spend time feeding somewhere beneath the bark of a tree
    as larvae. Some borers kill twigs and leaders when adults feed or when
    eggs hatch into larvae that bore into the stem and develop into adults.
    Other borers, known as bark beetles, mate at or near the bark surface, and
    adults lay eggs in tunnels beneath the bark.
    Treatment
    The treatment method used for a particular insect or disease problem will
    depend on the species involved, the extent of the problem, and a variety of
    other factors specific to the situation and local regulations. Always consult
    a professional if you have any doubt about the nature of the problem or
    proper treatment.