Cultural Control
Cultural control refers to changing the physical environment of the plant, its condi• tion, or the behavior of the pest. Cultural control measures disrupt the normal rela• tionship between pest and host in order to prevent or suppress an infestation. Cultural controls make the pest less likely to survive, grow, or reproduce. Maintain an environ• ment that is best for the grass species and variety under cultivation. At the same time, avoid providing ideal growth conditions for pests as much as possible.
First and foremost, variety selection and proper establishment are basic cultural control measures. Other common cultural practices employed in turf include thatch management and proper mowing, watering, and fertilization regimes. Aerating soil and cultivation practices that improve water infiltration (spiking, vertical mowing, or coring) can help.
Mechanical (Physical) Control
Mechanical controls involve the use of some mechanical device to control pests. Use of traps, screens, nets, or other barriers to prevent pests from entering an area are also examples of mechanical control. So is use of sticky yellow monitoring cards for flying insects. However, these are not practical for use in turf.
Sanitation
Sanitation involves general cleanliness. This is a way to reduce the levels of pathogens and other pests in the turfgrass environment. Using pest-free seed, sprigs, or sod is a sanitation strategy. Careful disposal of diseased clippings is another.
Tools must be clean to prevent spreading pathogens and/or weed seed. Remove ac• cumulations of soil, plant sap, or other debris from all equipment-mechanized equipment and hand tools. Routinely disinfect turf management equipment. In addition, avoid spreading disease by foot traffic.
Chemical Control
Pesticides are chemicals designed to kill disease-causing organisms, insects, weeds, and other pests. However, they can also harm humans or nontarget organisms in some situations. For that reason, it is extremely important to use them properly. In addition, it is very important that turfgrass managers keep up-to-date. New products come “on line,” and others are taken off the market. In some cases, use patterns change. New application methods are constantly being developed. Pesticide applicator recertification programs and professional organization meetings provide continuing education and updates for turfgrass managers.
When using pesticides, placement, timing, and application methods are critical. To be effective, they must be applied correctly and at the proper time and rate. In many cases, pesticides need to be used at a certain stage in a pest’s life cycle. Applying them too early or too late is a waste of time and money. Poorly timed applications may pose a threat to the treated turfgrass as well as to other organisms and the environment. In addition, pesticides must contact the target pest directly or be placed where they will be eaten or absorbed. For example, spot treatment with herbicides is an effective way to control isolated weeds. However, broadcast herbicide applications must be uniform or results will be streaked and spotty.
Fungicides are pesticides used to manage plant pathogens. A contact fungicide affects only the portions of a plant covered by the spray. A penetrant fungicide is active at the site of placement but also enters the underlying tissue in amounts that are toxic to an invading fungus. Some penetrant fungicides are not transported within the plant. These localized penetrants remain at or near the site of placement. Other penetrants are translocated (moved) in the plant’s water• conducting tissue (xylem) and move upward (only). Finally, systemic penetrants are distributed uniformly throughout the plant. They move in both the xylem and the phloem.
Herbicides are pesticides used to kill or alter the growth and development of undesirable plants (weeds). Some control a wide range of plants, while others only affect certain types.
A nonselective herbicide affects or kills most or all types of plants. A selective herbicide controls some plants but does not affect all species. Different herbicides have different placement and timing requirements. A contact herbicide affects only the portions of a plant covered by the spray. A systemic herbicide translocates (moves) throughout a plant. A postemergence herbicide is applied to existing weed plants. Postemergence herbicides are applied after weed seeds germinate. A preemergence herbicide is applied to soil before weed germination. Preemergence herbicides affect and control germinating seeds.
Insecticides control insect pests. A nonselective insecticide affects or kills many kinds of insects. A selective insecticide controls some types of insects but does not affect all species. A contact insecticide must touch an insect to have an effect. A stomach poison insecticide may be applied to a leaf or other plant tissue a pest insect will consume. Stomach poison insecticides affect insects when they consume them. A systemic insecticide may be applied to soil. Systemic insecticides will be absorbed by growing plants and kill insects that feed on them.
As a rule, pest control programs that rely only on pesticides are severely limited. This is true for a number of reasons. In some cases, there are few or no legal, effective pesticides registered for a particular use. In other cases, labels restrict use in sensitive areas (ex. near waterways). Even when a pesticide is registered for a site and species or variety of turf, its use may not be appropriate or advisable in all locations and situations.In some cases, customers or the public object to the use of chemical controls. Increasing pest resistance is another issue.
However, a sound, effective IPM plan often includes chemical controls. When se• lecting a pesticide, always follow these steps.
- Identify the source of the problem. Be sure a pest caused it. Be sure a pesticide can solve the problem.
- READ THE LABEL. Be sure you can use the product for the problem at hand, and in the manner you plan to use it. Consider efficacy, timing, site, equipment available, etc. Be sure the product will not leave an offensive odor or residue.
- Be sure the product has a low potential for producing phytotoxic effects.
The label is the law! It provides specific directions on how to use a pesticide product. Never do anything the label prohibits. Always follow label directions to the letter. Pesticides may only be used on sites and plants listed on the label. Follow directions specifying use amounts (application rates and number of applications) exactly. Legal use of a pesticide does allow the following:
- Applying pesticides at a concentration or frequency less than that specified on the label.
- Applying a pesticide for a pest not listed on the label. However, the site or plant must be labeled, and all instructions (timing and application equipment) must be followed.
- Mixing with fertilizers and other pesticides unless specifically prohibited by the label.
Applying pesticides “off label” is illegal. Applying properly labeled pesticides at inef• fective times and using pesticides to prevent an anticipated problem may contribute to secondary pest problems and target pest resistance.
In general, there are two approaches to pesticide use. You can prevent a pest outbreak by making an application before the problem appears (preventive). Alterna• tively, you can “cure” a pest problem after the problem is noticed (reactive). Preventive tactics are often the best strategy for management of some diseases. Prevention is also a good tactic for controlling crabgrass and . certain annual weeds. However, before using a preventive measure, be certain that the conditions require this type of action. Where possible, use a reactive approach. If you use a reactive approach, act only when a pest is present and occurs in high enough numbers to warrant use of a pesticide. A “wait and see” reactive approach can, in many situa• tions, minimize pesticide use.
Phytotoxicity
Phytotoxicity is plant injury. Phyto• toxic effects may be caused by exposure to chemicals, including pesticides, fertilizers, or growth regulators. They may also result from accidental or careless exposure to cleaning solutions or other harsh chemicals. Air pollution and acid rain are phytotoxic. For pesticides and fertilizers, the following situa• tions may result in phytotoxicity:
- Using a material improperly (ex: wrong site. rate, or time of year).
- Applying a chemical during adverse environmental conditions.
- Offsite movement (for example, due to drift or runoff).
- Accumulation of persistent residues in the soil or on plant surfaces.
Symptoms of phytotoxicity include:
- death of rapidly growing tissues;
- stunting or delayed development;
- misshapen or distorted stems, leaves or fruits;
- russeting or bronzing of leaves, or fruit;
- dead spots or flecks on leaves, dead leaf tips or margins; and
- dead areas between leaf veins.
Dead spots of uniform color that go through the leaf may also be clues to phytotoxicity. In addition, evidence of plant damage without signs of plant pests may indicate that a chemical imbalance is the source of the problem. Another warning sign is injury occurring over a short period of time that does not spread from plant to plant. For pesticides, consult spray records. They may tell you if a pesticide harmful to the injured plant was used nearby.
Here is a short list of factors that influence phytotoxicity.
- Pesticide I Plant Growth Regulator (PGR) Active Ingredient Characteristics: Some plants are very sensitive to certainchemicals. Be sure that the product label lists the type of turfgrass and site you wish to treat. Use pesticides according to label directions to prevent overexposure.
- Formulation Characteristics: Dusts and wettable powders are generally less phytotoxic than emulsifiable concentrates (ECs). ECs can sometimes dissolve the protective coating on leaf surfaces.
- Additives: Some adjuvants such as spreaders, stickers, and wetting agents may cause plant injury.
- Concentrations: The use of chemical concentrations higher than label rates is likely to cause plant injury. Exceeding the label rate or the number and interval of applications is illegal. Applying a material more frequently than the label directs may result in a toxic buildup.
- Method of Application: If the label describes a specific method of application, use it. Be sure foliar applications are thorough and even. High pressure sprays may force chemicals into sensitive tissues.
- Growing Conditions: Temperatures during and after treatments should be moderate. Unless the label states otherwise, treat foliage when dry. Wet foliage at the time of application or prolonged wetness of foliage after spraying can result in injury.
- Plant Growth Stage: Seedlings and fast-growing, tender young tissues are often more sensitive to chemicals.
- Mixing Pesticides or Pesticides and Fertilizers: Some chemical mixtures are incompatible. In some cases, chemicals may react to form a new substance, which may be harmful to the plant you wish to protect. If product labels do not have tank-mix instructions, do a “jar test.” Mix a small amount of the chemicals in the same proportion you will apply them. Observe this mixture for visible signs of a chemical or physical change. If you do not see any danger signals, apply the mix to a test area and watch for signs of phytotoxicity. Use the tank mix only if there are no ill effects.
To avoid phytotoxicity:
- Be certain the pesticide or PGR label lists the turfgrass species and/or variety and the site you wish to treat.
- Measure and prepare the chemical carefully, following all label directions. Be sure you are using the proper concentration.
- Use the proper application technique.
- Do not apply chemicals to turfgrass under abiotic stress. Avoid treating in the heat of the day. Spray when conditions will favor drying of wetted plant surfaces.
- Manage the application to prevent off target movement. Protect nearby plants that may be sensitive.
- Do not apply a chemical more frequently than the label directs.
The Quiz at the end of Section contains material from the previous two Sections.
