Chapter 26 Plant injuries: identification and care.
Upon completion of this chapter, you should be able to
* describe the common causes of injuries to landscape plants
* distinguish between those that are caused by insects and diseases and those caused by other things
* explain the ways that insects and diseases are spread
* describe the most common symptoms of plant injury
* classify weeds in several different ways and explain how they injure landscape plantings
* apply the principles of control to plant pests
* explain the different formulations of chemical pesticides
* describe integrated pest management
Plant Injuries and Their Causes
Anything that impairs the healthy growth and maturation of a plant may be regarded as an injurious agent. Some injurious agents cannot be transmitted from plant to plant. Others can be transmitted and are regarded as either infectious or infestious. An infected plant has the injurious agent active within it. An infested plant has the injurious agent active on its surface. Some causes of plant injury are members of the plant or animal kingdom and are biological in character. Others are environmental or circumstantial and nonbiological in nature.
When an injurious agent is biological and either infectious or infestious, it also is parasitic. A parasite is an organism that cannot manufacture its own food. So yes, humans are parasites, as are rodents, deer, rabbits, and other animals that can cause injury to plants, but they are not involved with plants at the cellular level. Therefore, in a discussion of plant parasites the term is usually applied to insects, bacteria, fungi, viruses, and nematodes. Every one of these parasites has its own branch of science devoted to its study. This chapter can only touch on the high points of what is known about them and how they affect the growth and development of landscape plants. In the same way, our consideration of weeds will focus narrowly on how they affect landscapes, not on their biology. Table 26-1 illustrates the various categorizations of the injurious agents of landscapes.
Different Forms at Different Times
Just as plants change their appearance at different seasons and at different stages of their lives, insects and the agents of plant disease do, too. Most people understand that butterflies were once caterpillars, and some may know that the grub worms found in their lawns will later become the June bugs that buzz around their porch lights. Insects are among nature's most extraordinary animals, changing their appearances and forms dramatically as they grow. That change is known as metamorphosis. Depending upon the species of insect, it may have as many as four different stages of development. Not all stages during the life cycle of an insect are injurious to plants. For effective control of insect damage, a landscaper must know
* the insects likely to affect particular plant species
* the stage(s) of the insects' lives that do damage to the plants
* how to recognize the presence of insects
* how to match a type of injury with a specific insect
The bacteria, fungi, viruses, and nematodes that cause plant diseases are collectively termed pathogens. Many pathogens, especially fungi, also have different stages in their development. While neither as visually dramatic nor as readily visible to the eye, the changes during the life cycles of pathogens determine when and how they do the most damage to plants. Because they are so small, their presence can go unnoticed until the plants begin to show signs of injury. For effective control of disease damage, a landscaper must know:
* the pathogens to which the landscape's plants are most susceptible
* the environmental conditions most suitable for pathogen development
* the potential sources of pathogens in the landscape
* how to recognize the presence of pathogens and the onset of disease
* how to diagnose a specific disease
Weeds injure landscape plantings both visually and culturally. They mar the attractive and tidy appearance of the design. Most significantly, they compete with the desirable plants for water, nutrients, and even sunlight. While weeds do not have the complex multiple life stages of insects and pathogens, they do have times during their growth from seed to maturity when they are more easily controlled, and a landscaper must know those times of vulnerability.
Most of the damage caused by larger animals is a result of their feeding and not related to their stage of growth. It may be more predictable at certain seasons of the year when other food sources are limited, such as the winter months. It may also occur in late evening or in remote areas where there is less likelihood of the animals being frightened away by people.
How Insects and Diseases Are Spread
It is not necessary to understand every biological nuance of insects, pathogens, and weeds to understand how they enter the landscape and how they move from plant to plant and area to area. In most cases, they get assistance. Often, it is the landscape personnel and/or the clients and their guests who provide that assistance.
Plant pests can be brought into a landscape setting on the plants that are purchased from a nursery or other supplier whose production hygiene was faulty. This is especially probable when plants for the landscape are collected from the wild, accepted from friends, or obtained from any source that does not guarantee its stock to be pest-free. They can also be carried in by the wind or bodies of water that pass through the landscape site. Animals such as dogs and cats make nice vehicles for pests, as do the cars, trucks, bicycles, and equipment of people who live, visit, or work at the property. Weeds can be introduced by the means described and are also frequently contained in soil additives, mulch, or seed.
Once on the site, the pests can be spread from plant to plant and from one area to another by natural means such as the wind and splattering rain. They can also be carried by people's hands or garden tools that become contaminated during their use on an infected or infested plant. Some insects can also crawl and/or fly, so their movement through a planting, once infested, is easy. Because insects and pathogens reproduce often and in large numbers, it takes very little of either when transferred to become a sizable presence in short order.
The Symptoms of Injury
When we look at a plant and determine that something is wrong, we are witnessing the plant's response to some type of irritant. The responses of plants to insects and pathogenic irritants are termed symptoms. Some symptoms are common to numerous insects and diseases; other symptoms are almost unique to certain pests. The symptoms of an insect or pathogen's activity in or on a plant may change as its life cycle advances or as the severity of the plant's response increases. The sum of all the symptoms expressed by a host plant from the time it is initially infected until it either recovers or dies is known as the symptom complex.
Infection of a plant by pests is not a static condition. The symptoms expressed early in the infection may be quite different from those expressed later. For any one pest, however, the symptom complex is usually specific. To diagnose a disease or insect problem correctly requires recognizing the specific changes each major pathogen or insect can create in a host.
Symptoms may be influenced by an assortment of factors including the species of the host plant, the environment, the quantity of infectious material (inoculum) present, the insect population, and the stage of development of the insect or pathogen. Furthermore, symptoms can result from other causes such as a damaging environment, improperly applied chemicals, animal injury, and mechanical damage. For this reason, it is often necessary to isolate and identify the specific agent of plant injury or to consider other possible sources of irritation before the cause of plant symptoms can be established.
While specific symptoms cover a wide range often separated only by subtleties, collectively they can be grouped into major categories that permit description and comparison, Figure 26-1.
Plants may wilt from lack of water. If such a symptom is environmental in its cause, the plant will recover when water is applied. If pathogens attack the plant's vascular system, which permits it to move water up its stem, or if insects destroy the plant's root system, the wilting will be permanent. When fungi invade the tender stem tissue of a young seedling, the disease damping-off develops, the seedling wilts and drops over to die.
[FIGURE 26-1 OMITTED]
Color changes may be widespread through most of the plant or localized as spots, rings, and lesions. When a plant does not receive enough light to enable it to make food efficiently through the process of photosynthesis, it is in a state known as etiolation. If adequate light is provided in time, the plant will return to full health. When a plant turns yellow, but does not lack light, the symptom is termed chlorosis. Chlorosis is probably the most common of all color changes. It can be caused by insects, pathogens, or environmental problems.
Rotting results from a destruction of cells within the host plant, causing a release of the cellular fluids. It may be accompanied by a strong, often foul odor. Rots may be dry or soft and occur in the roots, leaves, stems, buds, or fruits of the host plants. They are usually the result of plant diseases or freezing.
Death of Tissue
When plant tissue dries out and dies, it usually turns brown or black and is said to be necrotic. The dead tissue, or necrosis, may be located on leaves as spots, or centered in young buds. It may also be extensive, encompassing entire branches as in blights. Insects, pathogens, or environmental factors can cause necrosis. It ranks with chlorosis as a highly common symptom. It is often the final symptom in the symptom complex.
All or part of a plant can be reduced in size as a result of insects, nematodes, and other pathogens, especially viruses. Dwarfing may result from the reduction of water uptake at a time when new tissue is expanding. Insects or nematodes (microscopic worms) in the root system of a plant may create such dwarfing. The symptom is caused by either a reduction in the size of cells produced by the host plant or by a reduction in the number of cells that it produces.
Increase in Size
Plant parts may become malformed in response to insect or pathogen irritants. As cells increase in size or in number, symptoms are expressed as galls, witches brooms, swollen roots, abnormal shoot growth, scabs, and fasciations.
Insects may bore into plant trunks, chew their way within leaves, or burrow up and down the stems. Borers and leaf miners commonly create such injuries in plants.
Leaves riddled with holes are symptomatic of both insect and pathogenic causes. Insects usually cause holes by feeding on the leaf tissue. When caused by pathogenic activity, the holes are usually preceded by necrotic lesions and spots that represent dead cells. As the tissue dies in these localized areas, the necrotic spots drop out, creating the holes.
Determining the Cause
Hundreds of combinations and variations of symptoms can result from the many possible causal agents, reactions of individual host plants, and unpredictable modifications caused by the environment. If the quick and accurate diagnosis of what is troubling a particular host plant in the landscape sounds difficult, be assured it is!
Some diseases, such as powdery mildew, are common to many plants, and once you become familiar with it, you will recognize it every time you see it. Some insects, like the aphids, attack many different plants, so they soon become familiar to landscape professionals responsible for keeping a property healthy. It isn't necessary to recognize and have a complete knowledge of every insect and plant disease in nature, because most landscapes within a geographic region will be affected by a limited number of pests that recur year after year. So it becomes important to learn to recognize them and learn how to protect the landscape against them. Still, early in the symptom complex it can be difficult to determine whether the problem you are seeing is caused by an insect, some type of pathogen, or some cultural or environmental problem.
Look for Signs
Insects leave tell-tale signs of their presence, and so do many pathogens and other parasites. There may be the actual insect there. That can make diagnosis fairly easy. However, some insects look like part of the plant they are infesting. Scale insects are an example: some are easily mistaken for bumps on the bark, and others resemble white lint and appear harmless. Aphids often have soft green bodies and cluster around the young tissue at the end of a twig where they can go unnoticed until the damage caused by their feeding begins to show.
At times, other evidence of insects will be the landscaper's only clue to their presence. There may be egg masses on the underside of leaves or in the junction where leaves meet the branches. Some insects will leave slimy trails or traces of webs as a sign of their activity. It can also be baffling to observe plants that have been chewed on, yet find no insect presence. That usually is evidence of nocturnal insects or slugs that feed at night and hide by day. Usually turning over nearby rocks or logs will reveal the pests.
Pathogens are usually more difficult to recognize because they are so much smaller. Often only a single cell in size, the signs of their presence are different from those of the insects or larger parasites. Bacteria and viruses are completely invisible to the naked eye. Only after the host plant begins to display symptoms of infection is their presence apparent and their identification possible. Fungi are larger and more complex, although still often microscopic. Some can be seen growing on the surface of leaves and other plant parts. An example is, again, the mildews. What the eye sees as the white powdery material on the leaves is actually the vegetative body of the fungus. Other fungi can be seen when they begin to reproduce and send their fruiting structures to the surface of the plant where they become visible to the eye. The bright orange spots of rust diseases are actually fruiting structures of the fungus that is growing inside the host plant. A simple magnifying glass will reveal the fungus, its fruiting structure, and its seed-like contents (spores) that enable it to spread.
Cultural and environmental injuries do not display the same types of clues to their cause, but there is evidence nonetheless. When the soil in which the plants are growing becomes deficient in one of the nutrients needed for healthy growth, symptoms of that deficiency will begin to show. Necrosis and chlorosis or other color change are among the most common symptoms of nutrient deficiency, but others may be displayed as well. Landscapers should be sufficiently knowledgeable of the soils in their region to anticipate the likely nutrient needs of the plants they install and maintain on a recurring basis. An overall knowledge of the symptoms of nutrient deficiency is also important and is certain to be a part of the educational background of well-trained landscape professionals.
Nutrient deficiencies may appear as patterned symptoms, such as yellowing between the veins of the leaves. They may also appear as localized symptoms, perhaps affecting only the tips of the plant or only the lower, mature leaves. At other times, the symptoms will be widespread with all parts of the plant showing the color change or growth reduction.
Injuries that result from improper culture, such as mowing too short, over-fertilizing, or not providing the proper amount of moisture, are recognizable by the time of their occurrence--they will become apparent shortly after the cultural malpractice has happened.
Environmental injury is often the easiest to diagnose, as when the damage is found only on the side of the plant that is most exposed to strong winter wind or hot summer sun. If the only plants injured are those closest to a walk or roadway that is heavily salted during the winter, then determining the cause of the problem is not difficult. Other types of environmental injury are not as immediately apparent. The symptoms of polluted air will appear slowly and may be evident only on certain plants. Temperature extremes, such as frost or sunburn, may be long gone before the symptoms of their damage are manifested, leaving the late-arriving landscaper to wonder about the cause.
It is not the purpose of this text to identify specific insects, diseases, nutrient deficiencies, or other causes of injuries to landscape plants (there are many excellent resources available to accomplish that). Rather, this chapter is intended to illustrate the need for proper and complete training for those who choose to practice as landscape professionals--the ability to recognize the cause of a plant ailment or to anticipate the potential for injury in advance can make the difference between a successful landscape and a disappointing one.
A weed may be defined as a plant having no positive economic value and/or growing where it is not desired. Unlike insects and pathogens, weeds do not rely on a host plant for food. Instead, weeds compete with other plants for the materials that both need to grow and thrive. In addition, weeds often serve as alternate hosts, providing sites for the over-wintering of insects or pathogenic inoculum. Some fungi need weed species in which to produce one or more spore forms as part of a complex life cycle.
Classification of Weeds
Although much larger than insects or pathogens, weeds share one attribute with them: a variety of life cycles. A landscaper who must control weeds needs to be able to identify the specific weed and understand its life cycle.
Annuals. These weeds complete their lives in one year. Summer annuals germinate in the spring, grow most actively during the summer months, produce their seeds in the autumn, and then die. Examples include crabgrass, foxtail, spurge, and prostrate knotweed. Winter annuals germinate in the fall and grow into small plants before going dormant and overwintering. They then resume growth in the spring and complete their lives during the early summer. Examples of such weeds are wild garlic, chickweed, and henbit.
Perennials. These weeds live for several years and may produce seeds numerous times during their extended lifespan. Examples include dandelion, quackgrass, clover, and nutsedge.
Weeds have evolved to survive. They are prolific seed producers, with some species capable of producing more than a million seeds per parent plant. As with nonweed plants, some weed seeds germinate quickly and easily, while others remain dormant in the soil for some time. Weed seeds are usually distributed throughout a garden's soil, so turning over the earth may bring to the surface seeds that have been buried and dormant for several years.
The Principles of Control
The control of insects, pathogens, and weeds in a landscape depends upon how successfully the landscaper applies the four basic principles of control.
Exclusion is the first principle of control. It includes all the measures designed to keep a pest from becoming established in an area. The measures vary depending on the type of pest. The most logical application of this principle in landscaping is the use of plant material produced by a nursery that certifies its stock to be disease- and insect-free. To be doubly safe, a member of the landscape staff who is knowledgeable of plant pests should carefully inspect all nursery stock when it is delivered and before it is installed at a project site. Any material displaying symptoms of infection or signs of infestation should be rejected and returned to the grower. Another way to apply the principle of exclusion is to avoid materials that are certain to be contaminated, such as cheap grass seed mixtures or nonsterile mulches, such as hay or nonfumigated straw. Telephone companies or arborists often turn their cut wood into chips and then offer the material to anyone who will take it as a means of disposal. Landscapers who then spread it as mulch run the risk of introducing pest contaminants into a landscape that was formerly pest-free.
Eradication is the principle that seeks to remove or eliminate pests that are already in, on, or near plants in infested areas. The measures of eradication attempt to reduce the quantity of pathogenic inoculum, insects and their eggs, or weeds and their seeds.
* Isolating and destroying individual infected plants is time-consuming and expensive, especially on large landscape sites, such as parks, cemeteries, and commercial properties. If done as part of another routine maintenance task, such as pruning, then it can be cost-effective. In smaller, residential landscapes with comparatively fewer plants, the eradication of infected plants is easier because they will be more quickly noticed.
* Hand-pulling and cultivation are effective in the control of some weeds, especially if they have not yet produced their seeds. The technique usually does not remove all of the root system however, so the weeds may return.
* Destruction of alternative hosts such as weeds can also aid pest control. The alternative hosts may allow completion of the life cycle of a fungus or harbor insects that will later invade the garden.
* Plant rotation and soil treatments are both methods of eradicating pests that persist in the soil. Many pathogens overwinter as dormant spores on plant litter in the soil. If the same plants are used in that location the next year, as is often the case with flower plantings, the pathogen will be waiting to strike again. By using flowers that are not susceptible to the previous year's disease, the landscape can avoid another year of injury.
Treating the soil with heat or chemicals before planting can give protection to flower plantings and can be especially effective in more controllable areas such as raised beds and potted flowers.
* Destroying host parts that display evidence of insect or disease damage can reduce the amount of inoculum available for dissemination to nearby hosts. This is the benefit received when diseased limbs are cut from a tree, permitting the healthy parts to remain.
* Removing infested refuse eliminates a site for the overwintering of pathogens or insects. Collecting grass clippings and raking fallen leaves applies this principle and can be accomplished as part of regular maintenance routines.
* Chemical sprays, dusts, and drenches are generally the most expensive methods of eradication. The products, collectively termed eradicants, strive to kill the pathogen before it can infect the host, kill the insect before it can do much damage or reproduce, or kill the weed before or shortly after it emerges.
Protection is the principle of control that sets up a barrier between the host plants and the pests to which they are susceptible. It is a shielding endeavor that can be accomplished either through manipulating the plants' growing environment or by applying chemicals.
* Manipulating the environment is an attempt to create conditions for growth that are more favorable to the host plant than to the pest. Most pathogens thrive in conditions of high humidity and moisture. Many diseases can be avoided by watering the landscape early in the day so that water can evaporate quickly from the foliage, rather than in the evening when leaves would stay wet all night. Also, by providing and maintaining nutrient, pH, and other cultural conditions that are more favorable to the host plant and less favorable to known pests, the landscaper can protect the plantings of the garden. A healthy, vigorously growing plant is one of the best defenses against pests.
* Chemical sprays and dusts can be applied to seeds, bulbs, foliage, and wounds of plants to place a barrier between the host and the insect or pathogens. In this case, it is essential that the chemical be applied before the pests arrive. It then kills them after they arrive.
Resistance is the fourth principle of control. It is an attempt to change a plant either physically or genetically so that it will suffer less from diseases and/or insects. Actual creation of the resistance is not something done by landscapers. It either occurs naturally where it is observed and then reproduced by plant breeders, or it is developed over time by plant geneticists and the resistant plants are eventually released for commercial and public use. However, it is the landscaper's selection of plant varieties known to be resistant to the pests of an area that makes application of this principle valid. Resistance is seldom total and may not last forever. All plants have some degree of susceptibility, and that susceptibility often increases with time. The loss or lessening of resistance to a pest does not necessarily mean that the host plant has changed. It may mean that the pest has altered in a way that allows it to infect the plant. Considering the reproductive potential of most pests and the rapidity of their life cycles, it is not surprising that resistance is often overcome by the natural mutation of insects and pathogens.
Pesticides are chemicals used to kill organisms that injure desirable host plants. If directed against insects, they are called insecticides; against fungi, they are called fungicides; against nematodes, nematicides, against bacteria, antibiotics or bactericides, and when directed against weeds, they are called herbicides. Pesticides are one of the weapons in a landscaper's arsenal of defenses against the pests of the landscape. Specific recommendations of what product to use against what pest can be obtained from a variety of sources. The chemical companies that develop and manufacture the products are certain to advertise them in trade magazines and through other media outlets. The final determination of what is recommended and safe for use in a particular state or region within a state is usually the responsibility of the scientists at the college of agriculture in each state. Landscapers should consult the list of approved chemical pesticide products for their state before purchasing and using a new product. That information is often available through the Cooperative Extension Service, which makes the latest research and publications of the colleges of agriculture available to the public, including industry practitioners such as landscape professionals.
Understanding chemical pesticides requires knowing what they are and what they are not. What they are is poisonous, not only to pests, but to animals and people as well. What they are not is medicinal. The belief that pesticides are medicines for ailing plants is misguided and implies a curative quality that is lacking. An infected plant can seldom be cured. Necrotic tissue cannot regain its life, holes chewed in leaves will not restore themselves, and galls will not diminish.
To be most effective, pesticides need to be on the plant before the pathogen or insect invader arrives so it dies promptly on its arrival. These pesticides can be regarded as protectants. If the pathogen is already on the plant host and about to infect or the insects are already feeding on the plant, then the pesticides must kill them immediately. Such pesticides are termed eradicants.
Herbicides also have varying forms of action. If the chemical kills all green plants, it is termed a nonselective herbicide. Those that kill some kinds of plants and not others are selective herbicides. These assorted products are also characterized by whether they kill on direct contact with the weeds or after the chemicals have been absorbed by the weeds, making the products systemic. Herbicides may kill the weed before they emerge from the soil (preemergence) or after they emerge from the soil (postemergence).
Whether the pesticide is a fungicide, nematicide, insecticide, or herbicide, it is usually available in several different formulations. The choice of formulation is based on:
* the size of the landscape property being treated
* the amount of active ingredient being applied
* other materials being applied along with the pesticide, such as other pesticides or fertilizers
* ease of application
Following is a summary of product formulations and their characteristics.
Solutions. The pesticide dissolves completely and uniformly into a carrier of water or oil. It does not precipitate out, so once dissolved the pesticide mix does not need to be agitated.
Emulsifiable Concentrates. Some pesticides are not water-soluble, but must be applied in a water carrier. A typical emulsifiable concentrate contains the pesticide, a suitable solvent, an emulsifier, and often a wetting agent, sticker, or antifoaming agent. The elements do not settle out, once mixed, so they only need periodic agitation to assure that the mixture stays uniform. The concentration of active ingredient is usually high in emulsifiable concentrates, making them dangerous to handle.
Wettable Powders. These pesticides are of limited solubility in water. They are combined with a filler material such as clay or talc as well as a wetting agent to permit their dispersal in a water carrier. They require continuous agitation to ensure uniform coverage. They are relatively low in cost and easily stored and handled but they are hazardous if inhaled or absorbed through the skin.
Granules and Pellets. Herbicides are often applied in this form. The pesticide is in the form of coarse, solid particles for easy application. The carrier may be sand, clay, ground corn cobs, fertilizer granules, or similar material. No dilution is required, since the percentage of active ingredient is lower than in other formulations, usually between 4 and 10 percent.
Fumigants. The pesticides are in the form of poisonous gases, and they are often highly toxic. They have limited use in landscaping except when applied to covered piles of soil for use in containerized plantings or similar specialized areas.
Flowable Suspensions. These are wettable powders, not soluble, that are suspended in a water-based carrier material. It is usually necessary to agitate the product during application to ensure a uniform coverage.
Dusts. These are fine powders containing the active ingredient in low concentrations and mixed with a high percentage of inert carrier material. Applied dry and directly to the plants, dusts leave a visible residue.
Water-Dispersible Granules. These are granular formulations that are applied in water. They have a low solubility in water, so continuous agitation is required during application to ensure even distribution.
Gels. A gelatinous form of the pesticide, gels are commonly used as the formulation inside containers that are to be returned for recycling. This formulation is often used in water-soluble, pre-measured packets.
Additional information about pesticide packaging, application, and use can be found in Chapter 30, Safety in the Landscape Industry.
Integrated Pest Management
A discussion of plant pest control cannot end with the final topic being pesticides because that would imply they are the final or ultimate choice of control measures. In recent years, it has been found to be more logical, more economical, and better for the environment to integrate a variety of techniques in the control of pests. Instead of waiting for a pest to appear and then treating it with a pesticide or anticipating that it will appear and applying a pesticide in advance, it is now considered wiser to monitor the host plants to determine if and when a pest appears and what can best minimize its impact. The technique is termed integrated pest management or IPM. It requires that the user/owner of the landscape be willing to accept some level of pest presence and not insist upon zero tolerance. The point at which the injury to the landscape's plantings or the number of pests present becomes unacceptable is termed the action threshold. The action threshold signals the need for control measures to be applied. It falls to the landscape management professional to know what represents the action threshold, to gain agreement and acceptance of that threshold by the client, and to know what control measures are appropriate.
Understanding how to manipulate the environment so that it favors the growth of the host plants more than that of the pests is vital. Knowing what potential pests are of concern in a particular landscape, their life cycles and appearance at different stages of their life cycle, and the times when they constitute the greatest threat to the host plants is also essential. Landscape monitors must also be able to recognize desirable or harmless insects or other agents. When the action threshold is near, the landscape monitor must advise the landscape manager of the proper control measures, be they cultural, biological, or chemical. Figure 26-2 illustrates the IPM Triangle, a graphic depiction of the relationship between host plant health, pest presence, and the environment within the landscape. The IPM Triangle also illustrates the level and diversity of educational preparation needed by anyone practicing landscape management today.
[FIGURE 26-2 OMITTED]
While the general public's acceptance and understanding of IPM are growing, there is still a need for customer education on the topic. Customers are reluctant to accept and pay for something they do not understand. A customer will understand receiving a bill for a landscape technician to spray the shrubs but may not understand being billed for someone to scout the property for pests and decide that no control measures are warranted. Still other customers may have to be convinced that a low level population of some insects on their garden plants is no threat to the landscape and can be kept at low levels with methods other than the blanket application of chemicals.
As public awareness and industry acceptance of IPM programs increase, it will become the expectation, not the exception, throughout the landscape industry. Once every employee can become a knowledgeable spokesperson for environmentally sound pest control, then the landscape profession and the nation will have taken a significant step toward safer and more natural techniques of pest control.
A. Fill in the blanks in the following table to measure your understanding of which plant irritants are infectious and which are infestious.
B. Define the following terms.
5. symptom complex
C. Indicate which principle of pest control is being applied when the following measures are taken.
1. A landscape contractor installs plants certified by the grower to be pest-free.
2. Plants are not watered after 2 P.M. to allow them to dry off before evening.
3. A landscape management company hauls away all debris from a planting bed before winter sets in.
4. A diseased street tree is cut down and hauled away before the disease spreads to other trees nearby.
5. The state association of landscapers funds research at their college of agriculture to speed development of a new resistant variety.
6. Healthy nursery plants are sprayed in the spring before the onset of the rainy season.
7. Tulip bulbs that were stored in a bag where diseased bulbs were found are dusted with a pesticide before being planted.
8. An IPM monitor finds a sign of insect pest presence on a single plant and quickly and completely destroys it, leaving the rest of the planting pest-free.
9. The soil to be used in hanging baskets of flowers is fumigated before planting.
10. The local utility company has offered free mulch, produced when it put the cut limbs from its pruning operations through a wood chipper. The landscape company declines the offer.
D. Indicate if the following statements are true or false.
1. Weeds are parasites.
2. Weeds may serve as hosts for insects or pathogens.
3. Weeds are visible problems only. They do not persist unseen in the soil.
4. All weeds are perennial.
5. Dormant weed seeds can persist in the soil for several years.
6. The action threshold signaling the need for control is a common standard that can be applied to all plants and landscape sites.
7. IPM monitoring requires the immediate recognition of when the action threshold for a plant is near.
8. Manipulation of the growing environment can eliminate the need for an IPM program.
9. Wettable powder formulations of pesticides are more easily dissolved in a water carrier than pesticides in solution form.
10. If applied early in the symptom complex, pesticides can cure an infected plant and erase all symptoms of the pest's presence.
1. Select a common insect or disease problem for your region of the country. Assume that you do not know a proper control for the problem. Check the following three sources for control recommendations: the local Cooperative Extension Service, a nearby locally owned garden center staff person, the products available at a local chain store such as Wal-Mart or Tru-Value Hardware. Also compare the recommended application rates, time of application, and frequency of application. How similar or dissimilar is the information? Which would you use as a professional and why?
2. Go in search of the signs of pests. Select several nearby plants that are displaying symptoms of injury. Then try to determine if the cause is an insect, a pathogen, another parasite, or something else in the environment. A magnifying glass may help. Look for actual insects, or egg masses or webs, spores or ooze. Perhaps the distribution of the symptoms will suggest that the injury is caused by a nutrient deficiency or an external environmental irritant.
3. Evaluate the impact of weeds on host plant growth. Seed two greenhouse flats with annual flowers. Use weed-free soil in one and untreated soil in the other. Monitor growth of the seedlings over time. If the weeds are permitted to grow unchecked in the one flat, what is the impact on the growth and development of the flower seedlings compared to those in the flat where weeds offer no competition?
Jack E. Ingels
State University of New York
College of Agriculture and Technology
Cobleskill, New York
Table 26-1 Injurious Agents Infectious Infestious Biological Agents of Injury Insects Occasionally Yes Mites No Yes Fungi Yes Occasionally Bacteria Yes No Viruses Yes No Nematodes Yes Yes Rodents, rabbits, deer No No Slugs and snails No Yes Weeds No No Parasitic plants Occasionally Yes Other Causes of Injury Snow, ice, wind, sun scald, hail No No Mowers and other mechanical tools No No Vandalism No No Nutrient deficiency No No Fertilizer burn No No Chemical injury No No Drought No No Poor drainage No No Incorrect light exposure No No
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|Title Annotation:||SECTION 3 Landscape Maintenance|
|Publication:||Landscaping Principles and Practices, 6th ed.|
|Date:||Jan 1, 2004|
|Previous Article:||Chapter 25 Maintaining landscape plants.|
|Next Article:||Chapter 27 Care of the lawn.|