The nursery and landscape industry is facing many political, social, regulatory and environmental issues that dramatically impact the way business is conducted. For example: the Food Quality Protection Act of 1996 will change the way pesticides are regulated. Water quality issues affect all of Florida and U.S. agriculture. Pesticide use as it affects water quality is greatly impacted by regulatory issues. Moreover, the nursery industry is considered a 'minor use' crop by the pesticide industry and fewer pesticides for use on nursery crops remain labeled or will become labeled in the future.
Several myths concerning pesticide use are often stated incorrectly:
The purpose of pesticides is to control the target pest. Some have the potential to pollute ground water and may be hazardous to workers. They may also reduce the populations of natural enemies and other nontarget organisms. As a result of destruction of natural enemies, pest populations often resurge to higher levels. Moreover, secondary pests normally held in check by natural enemies that are removed by pesticides may also reach economic pest levels. With repeated pesticide use, through time the target pest or secondary pests may develop tolerance or resistance to the chemical. Therefore, use of chemical pesticides is costly and involves several tradeoffs. The newer, more specific pesticides are generally higher in purchase price and usually have shorter residual activity. Shorter residual activity may benefit natural enemies and decrease the risk of resistance development in the target and secondary pests. On the other hand, a shorter residual may require more frequent applications with higher energy expenditures. The true cost of chemical controls must include the purchase price per unit area of treatment and the overall efficacy including the period of residual activity plus or minus the social/environmental impact of the treatment.
Clearly, unilateral reliance on chemical controls for any type of pest is a thing of the past. Alternative approaches must be developed. Integrated pest management (IPM) is an alternative approach which seeks to minimize energy inputs of all types. With IPM all types of tactics and strategies including judicious chemical use are employed to suppress pests below economically important levels.
The theory from which IPM principles are derived is known as agroecology. Agroecology recognizes that the artificial environments that our crop culture and management practices impose is different in many respects from natural undisturbed ecosystems. However, the same natural laws and functional components operating in natural ecosystems, such as water, nutrient, mineral and energy cycles, also apply. From the theory we derive the methods of IPM: applied ecology. The tools from this methodology involve habitat manipulations. The goal of IPM is to suppress pests in an environmentally and socially acceptable manner, while sustaining the land and its people. The "bottom line" is that this must be achieved at a level which allows humans to making a living.
IPM is a change in philosophy from reliance on chemicals. IPM is a decision making process that is knowledge intensive. It is based on recognition of the economic threshold concept whereby the importance of pest damage or potential damage is measured against control costs. Most growers recognize that pest and beneficial or non-pest organisms are different. The precept of IPM is that all populations of pest species are not regarded as pests meriting controls until they reach a level where the value of the accrued damage or predicted damage is more than the cost of the required controls. Around this threshold revolve the IPM decision making methods and risks. It is difficult both psychologically and logistically to detect a population of a well known pest species, e.g. twospotted spider mite, and decide to ignore it. IPM requires a different attitude about risk and commitment to the process unlike unilateral chemical pesticide use.
IPM is both a philosophical and a practical approach to pest control. While there are certain principles applicable to all ecosystems, no two nurseries or landscapes are the same. We do not mean to imply that components of the entire ecosystem are not important to the population dynamics of pests. Areas surrounding crops are often critical in pest management as reservoirs for natural enemies and pests. However, every site and its history are different from micro to macro climate, plant composition, culture and management practices, etc. IPM will involve a prescription for each location and nursery block. Broad concepts provide only the framework to facilitate thinking and synthesis. In practice, IPM is local!
In practice, IPM relies on monitoring (scouting) for pests and their natural enemies, integrating the data with knowledge of the plant, weather, etc., and then making decisions as to the need and type of intervention. Regardless of the decision made, follow up sampling to ascertain the status of the pest population and to evaluate efficacy of the applied controls should be undertaken. As will be discussed, use of preventative tactics that manipulate the biological components such as host plant resistance, biological controls and proper culture and management practices, etc. are highly recommended.
There are also some myths about IPM:
Successful practice of IPM requires a great deal of knowledge. Practitioners must have a knowledge of horticulture and the culture and management of specific plant species. Similar knowledge of the biology and ecology of pests is also important. Knowledge of the advantages, disadvantages and uses of the various control methods available is critical. Sources for this knowledge include trade organizations, cooperative extension agents and state specialists, and private sources including consultants. Chemical industry representatives are also an important source. Develop a personal library of reference material. Because of the risk and knowledge required to successfully practice IPM, the practitioner's personal strengths and weaknesses must be dealt with effectively.
Changing to IPM can be difficult for the grower or landscaper because of the overwhelming quantity of information that is available and necessary to be successful. John Naisbitt said in Megatrends 2000: "The world is drowning in information, but thirsty for knowledge". The difference between information and knowledge is the difference between perception and understanding. The IPM practitioner must organize and synthesize information to meet local needs. There are several concepts or techniques that will help the IPM practitioner synthesize IPM information into practical knowledge without having to become a scientist.
Plant diversity is much higher in nurseries and landscapes than in typical agricultural crops. Despite the diversity, most problems are confined to a few plants and pests. One technique to deal with the diversity present is the key plant/key pest concept. This is the recognition that certain problem plants and/or their problem pests exist. Use them as tools to focus resources and as indicators of the timing of other pest problems that they may herald. Monitor these plants more closely for the occurrence and early detection of chronic pests. Maintaining specific records of local areas will develop the necessary information on key plants and pests. The Orton system, COINCIDE, is based on the principle that bloom patterns or other plant phenological events can be used to determine and predict the occurrence of pests in the same local environment.
Another concept to help synthesize information for IPM decision making is the feeding behavior/role that pests display in the ecosystem. This was coined to provide growers a method to organize information about the role, behavior and biology of arthropod pests. Three categories of pests are recognized relative to their feeding habits in relation to host plants: specialists, generalists, and opportunists.
Specialists feed on one or a few host plant species. These arthropods are more closely linked chemically and behaviorally to their limited range of host plants. An example is the crapemyrtle aphid which feeds only on crape myrtle. Since these pests are often more closely tied to the physiology and biochemistry of the host plant, their seasonal abundance is often more predictable.
Generalists pests have a broader host range and the risk of an infestation spreading to other plant species is greater. Twospotted spider mites are generalists. While generalist pests may have a broad host range, they may do better on certain preferred host plants or under specific environmental or cultural and management practices.
Opportunists are pests which often act as saprophytes and attack weak and dying trees. They may have a narrow or broad host range but their presence often indicates that the plant is injured or stressed. Examples of opportunists are the boring insects such as the clearwing moths, family Sesiidae, the bark beetles, family Scolytidae, and the flatheaded wood borers, family Buprestidae. Some boring insects have long life cycles with extended emergence and oviposition periods not readily predictable. Others have short life cycles and mass attack trees, quickly killing them, making control difficult. Culture and management practices and site factors associated with plant vigor relate to borer susceptibility.
Another concept to facilitate IPM decision making relates to the status and dynamics of the pest population when it is detected. In agronomic crops often clear economic or action thresholds related to yields are established based on cumulative plant damage or pest numbers. For woody landscape plants, the premium is on appearance. Thus, aesthetic thresholds are often exceeded by the very presence of pests in many circumstances and tolerance for damage can be very low. For nursery plants, pest damage more directly translates into monetary loss. However, the actual value of pest damage is less clearcut since individual plants are of low value and through pruning or other techniques the damage may be ignored or the plant regrown. In landscapes, plants are not grown for profit so thresholds are less determinate. The economic threshold concept may not be the optimum approach.
Several pertinent questions lie at the core of this disparity between IPM in agronomic and nursery crops. What growers really are forced to decide is, in relation to the damage loss, whether controls should be applied immediately or can the decision be delayed or ignored. Obviously, the amount of damage present is important, but the first question asked by the grower is: What is the risk of more damage and spread of this infestation to surrounding plants and other areas?
The answer relates to the pest's population quality and dynamics. In other words, what is the population's future direction?
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Is it decreasing - meaning that the damage is done and numbers are declining; is it static - meaning that it is dormant or may increase or decrease; is it increasing - growing in number and damage, in which case, immediate controls are probably necessary?
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The ability to categorize infestations in this manner is not easy but it will direct thinking away from the presence (bad = control) / absence (good) approach. The population status approach uses all the information available in the process and can save money and time in the absence of a clear economic threshold. Furthermore, the aesthetic threshold, while low, varies with consumer perceptions which are variable and subject to change.
What criteria can be used to assess the status or dynamics of pest populations?
Decreasing populations: There is obvious damage present and the infestation may have been detected too late. Only a few pests are present which are mostly adults. The host plant may be preferred or non-preferred; more often populations remain at lower levels on non-preferred hosts. There may be a large number of natural enemies present that are controlling the pests. It may be the end of the season or your records on the site and its plants indicate this pest species is at the end of its normal infestation period. Decreasing pest populations are often controlled, which is a waste of resources, and due to the impact on natural enemies, often does more harm than good.
Static populations: Money can also be saved by not treating static pest populations. In this case the risk is greater due to the possibility of the population increasing and causing more damage. Such populations may have caused low to high damage, so the damage level may not be as helpful. The pests present may be in the pupal or other dormant stage, the host plant may be non-preferred and natural enemies may be observed regulating pest numbers. Prediction models based on weather or temperature or your records of the site and pest may indicate no need for treatment at this time. Delaying controls for static populations until the next scheduled sample date usually saves money. Doing nothing is often the best management decision but risk is involved!
Increasing populations: Pest populations that are increasing in number and damage should receive the most attention. During the growing season when prediction models or records indicate the highest risk for pests, more pest populations reach damaging levels. Knowing the biology of the pest will indicate the time of year to expect specific pests. In the southeast, many pests occur in fall and winter. Increasing populations usually have immature and adults present, with low to moderate damage to the plant. Natural enemies may be few or in low numbers because of the lag period between the start of pest infestations and detection of it by natural enemies. Pests do better on preferred host plants and this should be considered in the decision. Prior use of insecticides not selective of beneficial insects may also help induce increasing populations of pests. Record keeping and phenological models can be very useful to plan for and anticipate pest outbreaks.