Chapter 17 Integrated pest management.
After studying this chapter, the student should be able to
* Understand the importance of an integrated pest management program
* Discuss the components of an IPM program
* Describe monitoring techniques
* Discuss biological control
* Understand how to develop an IPM program
The controversy surrounding pesticides is well known. Improper pesticide use can be hazardous to both the applicator and the environment. Turfgrasses can be injured by applying too much, or the wrong, pesticide. Some of the chemicals kill earthworms, natural enemies of turf pests, and other beneficial organisms.
Pesticides may also be very expensive because of the cost of the materials and the labor and time required to apply them. Insurance premiums can be quite high for businesses using pesticides.
The public perception of pesticides continues to be largely negative. Increasingly, golfers, homeowners, and other people who use turf are expressing concerns about pesticide applications. Moreover, pesticide regulations are making it more difficult and costly to apply pesticides.
The turfgrass manager needs to reduce the use of toxic pesticides whenever possible. To accomplish this goal, an integrated pest management program should be developed.
What Is Integrated Pest Management?
Integrated pest management, abbreviated as IPM, is a program that integrates many different techniques to avoid or reduce a pest population or minimize its impact. Cultural, biological, and chemical controls are used. An important part of an IPM program is looking for pests. A scout determines which pests are present and monitors their population.
In the past, pesticides were applied in anticipation of a problem or when a few pests were seen. In an IPM program treatment is not considered necessary until the pest population is high enough to cause unacceptable damage.
IPM is an approach that uses multiple tools to suppress pests rather than simply resorting to traditional pesticides every time a problem occurs. By carefully monitoring pest populations the turf manager can determine whether control is necessary and if past control efforts were successful.
An effective IPM program requires the turf manager to be knowledgeable about turfgrass culture, turf pests, and all of the possible control measures (Figure 17-1). Extensive knowledge of turfgrass culture is critical because the first step in the prevention of pest problems is to maintain healthy plants. IPM is a much more sophisticated approach than the control programs of the past, where chemical sprays were the automatic response to the sighting of a single insect or weed. Education is an integral part of an IPM program.
An IPM program should be cost effective and site specific. Conditions vary greatly from one turf site to another, so the program must be developed with local conditions in mind (Figure 17-2).
Figure 17-1 Types of information a turfgrass manager needs to know about an insect pest in a monitoring program. A. IDENTIFICATION OF THE PEST AND THE INJURY IT CAUSES TO TURF 1. What does the insect look like? 2. On what types of sites and on which turfgrasses does the injury occur? 3. What part of the plant is attacked? 4. What does the injury look like? 5. At what time of year is the turf injured by the pest? B. LIFE CYCLE 1. Which is the injurious stage (instar 1, 2, 3, etc., adult)? 2. At what time of the year does the injurious stage occur? 3. Does this stage live in the soil, thatch, or on the surface? 4. Which stage is easiest to control? 5. When does this controllable stage occur? 6. What environmental conditions (rain, drought, heat, etc.) favor the insect and which ones result in a population decline? C. MONITORING 1. Which monitoring techniques works best for this insect--checking a square foot of soil, flotation in a can, pheromone trap, irritating drench to make pest come to the surface, etc. 2. How many insects per square foot can the turf tolerate without showing injury? 3. How much damage is acceptable to the customer, golfer, owner, etc.? 4. Are there other stresses present that will cause the turf to be less tolerant of the insect injury? 5. Will the grass recuperate quickly from the injury?
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IPM does not mean that pesticides are never used. Situations arise when there are no other effective alternatives. However, the pesticide selected should be the one that is least toxic to the applicator and the environment. It is applied in a safe manner at the correct rate when the pest is in a controllable stage.
Components of an IPM Program
The first step when developing an IPM program is to set objectives or establish goals. In most cases the primary objective is to reduce pesticide use. An equally important objective is to improve the turf so that it is more tolerant of pest injury and better able to recover from pest problems.
The turf manager needs to discuss the proposed program with all of the involved parties. The golf course superintendent confers with the green committee, and the lawn care company representative talks to customers. Everyone who will be affected by the program should have input.
One of the crucial decisions to be made is how much damage will be acceptable. Generally, if there is zero tolerance for injury, such as on a putting green, the amount of pesticide used is higher than in a rough or on a lawn, where some injury can be tolerated. The tolerance level is also called an aesthetic threshold, or sometimes a client threshold. How much damage will the customer, club membership, or owner accept?
The aesthetic threshold in turn sets the action threshold. The action threshold is the point at which the manager must take some kind of action to avoid surpassing the tolerance level. For example, the manager may treat when he or she finds ten first instar grubs per square foot (0.09 [m.sup.2]) because he or she knows this number will result in unacceptable injury when the grubs get bigger and feed more. Turfgrass thresholds are hard to set because they are a subjective, aesthetic decision. The degree of injury that is tolerable varies significantly between people and also depends on the type of turf area (Figure 17-3).
IPM programs have the best chance of success when there is general agreement that pesticide use reduction is a desirable goal. At the beginning of the program mistakes may be made, and more injury than people are used to may occur. Alternative controls can also be more expensive than traditional pesticides. Consequently, the turf manager needs the support and understanding of all the parties affected by the program.
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In some cases IPM programs are mandated by government agencies, school boards, or other organizations. It seems inevitable that eventually everyone who uses pesticides will be required to develop an IPM program.
The turf manager must constantly monitor pest populations. This is hardly new, as agricultural workers have always been instructed to look for pests. But in an IPM program this monitoring is performed in a more methodical, thorough way. Generally, the person who is monitoring does so regularly. Golf courses are scouted at least once a week, and greens are checked daily for disease.
The pattern is important. When monitoring an area, the object is to look at enough turf to be able to make an accurate appraisal of pest populations. However, to keep the program cost effective the scout cannot take the time to check every square foot. Consequently, patterns are selected that allow the scout to visually inspect the area in a thorough but time-efficient manner (Figure 17-4).
The scout needs to carry a hand lens, knife, hand trowel or soil sampler, plastic vials or bags to hold specimens collected, a notebook for keeping records, pest identification books if necessary, and anything else that is helpful. He or she has to be well trained in pest identification and monitoring techniques. The success of the IPM program depends on his or her conscientiousness and skills.
An important part of monitoring is recordkeeping. The scout must note any pest populations or problems of significance. Different types of forms have been developed to record this information (Figure 17-5). Besides inspecting for insects, diseases, and weeds, the scout also notes other types of problems such as a leaking sprinkler head, compaction, or a dry spot.
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It is usually the turf manager's job to evaluate the information and make a decision about the necessity for action. The scout's report allows the manager to continually know what is happening on the golf course, athletic field, or lawn. The manager has to judge whether the pest population is or will become large enough to cause unacceptable damage or aesthetics.
The advantages of scouting are obvious. By having a regular report on turf and pest conditions, there should be no unpleasant surprises such as a sudden loss of grass. The manager can intervene before serious problems occur. Unnecessary pesticide applications can also be avoided. A further benefit is the opportunity to improve the maintenance programs because cultural problems are noted as well as pest concerns.
To be most effective, monitoring should occur at least once a week. This is a problem for lawn care companies because generally lawn care specialists visit their clients' properties only once a month, unless they are also mowing the turf, and the properties need to be scouted more frequently than this. Thus, an IPM program requires more visits, which will increase the cost of lawn care for the customer. Many people respond positively because they want a safer, more environmentally sound lawn care program. Other customers do not like the greater expense, especially when they see the scout walking around apparently doing nothing. Communication is very important. The customer must understand that even though the lawn care company employee is not spraying, she is performing a valuable service.
The information collected by the scout can be reported in many different ways. An example of a form used on a golf course is shown in Figure 17-6. Insects are normally counted per square foot. Weeds can be counted, or the percentage of the turf area they cover can be estimated. Damage from insects, nematodes, or diseases can be reported as low, moderate, or high, or they can be quantified more exactly on a scale of 1 to 5 or 1 to 10 or as a percentage of the total area. After a pesticide application the scouting report can be used to evaluate the effectiveness of the material.
At the end of the year the information collected is included in an annual report which will help the manager anticipate and prepare for future problems (Figure 17-7).
Though visual examination is the most common monitoring technique, other tools can be used. A weather station is helpful because it can measure air and soil temperature, leaf wetness, relative humidity, soil moisture, and rainfall. Some of the weather instruments have the ability to use this information to predict the likelihood of a disease problem. They will alert the manager if the weather conditions are appropriate for several diseases, and state if a fungicide spray is recommended.
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Weather stations also record the accumulation of growing degree days (GDD), which is valuable in predicting the appearance of various stages in an insect's life cycle. Temperature has a major effect on insects' activities and the progression of the life cycle. Most insects are relatively inactive around 50[degrees]F (10[degrees]C), so 50[degrees]F or a temperature close to it is normally used as the base temperature. Averaging the daily maximum and minimum temperatures and subtracting the base temperature from this number calculates the degree-day accumulation. For example, if the daily high is 90[degrees]F, the daily low is 60[degrees]F, and the base is 50[degrees]F, 25 degree days will be accumulated. (90[degrees] + 60[degrees] 150[degrees]/2 = 75[degrees] average - 50[degrees] 25 = degree days.)
Degree day information can be obtained from the Cooperative Extension Service if the turf manager does not have access to a weather station. Degree-day data are very helpful because they tell the scout when to be on the lookout for various insect pests and which stage to expect. For example, using a March 1 starting date, the first activity of bluegrass billbug adults in the spring occurs between 280 and 350 degree days (base = 50[degrees]F).
This calculation is much more accurate than calendar date because the dates will change from year to year because of differences in temperature that season. There is also interest in correlating degree days with weed and disease appearance.
Degree-day information can be confusing because base thresholds other than 50[degrees]F may be used, and in warmer areas the accumulation starting date may be January 1 (Figure 17-8). February 1, March 15, and April 1 also are used, so it is important to know the specifics for each GDD prediction. For example, in Virginia, the peak flight and egg-laying period of the adult sod webworm emergence occurs at 380-488 degree days, but this is based on a start date of January 1.
Sometimes pest activity is correlated to the flowering of certain plants. Scouting for the annual bluegrass weevil on a golf course begins at forsythia full bloom, when the adults leave their overwintering sites and move toward the fairways (Figure 17-9). This correlation between insect activity and plant flowering is called phenology.
Pathologists are attempting to develop immunoassays for plant diseases. The test kits have a disease detector with antibodies that are specific for a pathogen. If the grass sample contains the pathogen, the antibodies bind to the pathogen and a color change occurs. The darker the color, the greater the amount of pathogen that is present. These kits not only identify the disease, but can also predict the potential severity of the disease by indicating the size of the pathogen population in infected plants. The kits should be valuable tools in the future.
Pheromone traps can be used to monitor moth species whose larvae feed on turfgrass. The pheromone is a chemical attractant that lures the moths into a simple trap from which they cannot escape.
Cultural Techniques Affecting Pest Management
Cultural techniques have a major impact on pest problems. Turfgrass that is established and maintained correctly will be less affected by pests and will recuperate quicker if injured. For example, healthy, vigorous grass produces a dense turf that resists weed invasion. When the turf is sparse and bare spots are present, weeds can gain a foothold and flourish. Poor management practices such as inadequate fertilization and cutting the grass too short are common reasons for a thin turf. Improving the maintenance program should increase the competiveness of the grass and result in a denser, less weedy turf and reduced herbicide use (Figure 17-10).
Correctly performing mowing, fertilization, irrigation, and other cultural practices is an essential part of an IPM program. Proper establishment is also critical, including the selection of species and cultivars that are well adapted to the site and exhibit resistance to diseases common in the area. Because of endophytes it is also possible to select some turfgrasses that resist surface-feeding insects. New insect- and disease-resistant varieties can be slit-seeded into older, pest-prone turfgrass stands.
The cultural component is so important that some agriculturalists prefer the acronym ICM (integrated crop management) to IPM. Arborists have chosen the term plant health care to describe their management program because they believe that good cultural techniques are the most important part of any pest management strategy. Some turf professionals use the expression turfgrass management system (TMS) instead of integrated pest management for the same reason. TMS considers other potential environmental problems besides pesticides. Fertilizer pollution of groundwater and overuse of irrigation water are also addressed in this management program. BMP (Best Management Practices) is another acronym used and is the same as TMS. Perhaps IPM should stand for "intelligent plant management."
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Whatever terminology is used, it is impossible to reduce pesticide use without a strong cultural program.
A number of living organisms can be used to help suppress pest populations. These biological agents are generally nontoxic to higher animals and have few if any negative environmental effects. Biocontrol is very attractive for these reasons, and a tremendous amount of research is presently devoted to finding new and more effective organisms.
Paenibacillus (formerly Bacillus) popilliae, a bacterium, causes milky disease in Japanese beetle grubs. Another bacterium, Bacillus thuringiensis kurstaki, is sold commercially for caterpillar control. Other organisms being investigated include two fungi, Beauveria, which kills chinch bugs, and Metarhizium, which causes a fatal disease in white grubs. Xanthomonas campestris var. poannua, a bacterium, has been effective in controlling annual bluegrass in some studies.
Insect-attacking nematodes in the genera Steinernema and Heterorhabditis have shown promise against turfgrass insect pests. These beneficial nematodes enter the insect and release bacteria which quickly kill the pest (Figure 17-11). Because nematodes are aquatic animals that live in the soil water, they are very susceptible to desiccation. They must be applied to moist turf and soil and be thoroughly watered in. Insect control using nematodes is sometimes unsuccessful. This is usually because the nematodes were weak or dead before the application or were allowed to dry out when sprayed on the turf. Some of the species are not aggressive enough in searching for insect pests.
Despite these problems, nematodes have significant potential as control agents. Researchers will find more effective species, and companies will learn how to formulate them so they will remain viable during storage and shipment. Turf managers will eventually become accustomed to working with living pesticides.
Endophytes have already been discussed in some detail in Chapter 15. They are fungi that live in turfgrass plants but cause no detrimental effect. Instead, they actually give plant insect resistance because they give off chemicals that repel insect pests. They also make the plant more tolerant of drought, heat, and other stresses.
Endophytic fungi in turn receive their nutrition from plants, are protected inside the plant, and are disseminated in the plant's seed. Presently there are endophytic cultivars of perennial ryegrass, fine fescue, and tall fescue. Major efforts are under way to establish these beneficial fungi in other turfgrass species. Because endophyte levels are highest in the leaves they are effective in preventing injury by surface-feeding insects such as sod webworms, aphids, chinch bugs, and billbugs.
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Insect pests have many natural enemies such as ants, spiders, mites, ground beetles, rove beetles, wasps, and flies (Figure 17-12). Big-eyed bugs are predators of chinch bugs. A parasitic fly, Ormia depleta, whose larvae feed on mole crickets, has been used to help control this southern pest. Another parasite of mole crickets is a wasp, Larra bicolor. Both feed on nectar in the adult stage so planting certain flower species increases their survival rate. One of the positive results of reducing insecticide use is an increase in the beneficial insect population. Unfortunately, most insecticides kill both "good" and "bad" insects.
Certain microorganisms, such as species of the fungi Trichoderma and Gliocladium and the bacteria Pseudomonas and Enterobacter, suppress turfgrass pathogens. They are said to be "antagonistic" to pathogens. In some cases the antagonist feeds on the pathogen, but many give off chemicals that inhibit the pathogens or compete in other ways. The presence of these types of beneficial microorganisms results in lower populations of disease-causing fungi. Commercial products are available.
Adding compost or natural organic fertilizers to turf will build up antagonist populations because they serve as a food source for these organisms. In some cases the organic material already contains pathogen suppressive microorganisms. Some field studies have shown that the application of composts, compost tea, and organic fertilizers results in disease control comparable or superior to fungicides (Figure 17-13).
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Much more research is necessary in this area. Certain composts work better than others, and the age of the material is very important. There is also interest in finding ways to formulate antagonists and sell them individually as microbial fungicides.
Alternative chemicals are being developed. The neem tree, which is widely distributed in tropical and subtropical regions of the world, produces an oil in its seeds that has remarkable properties. It repels insects and acts as an antifeedant (prevents insects from feeding) and as an insect growth regulator. Insect growth regulators (IGRs) mimic hormones in the insect and disrupt some vital function. Most IGRs prevent insects from successfully changing into the adult stage.
Neem oil contains many insecticidal chemicals. Azadirachtin is the one presently being used in commercially available neem products. Neem oil extracts are so nontoxic that in some countries they are used in toothpaste. They also degrade quickly and do not appear to contribute to any chronic health problems.
Other IGR compounds are being investigated. Insects produce juvenile hormones to prevent them from becoming adults before they have attained the proper size. When they are ready to become adults, the hormone is no longer produced and the transition occurs. If an insect is treated with its own juvenile hormone at this time, it will die without reproducing. Researchers are also studying hormones that could disrupt mating and egg laying.
Halofenozide is a molt-accelerating compound that is very safe for the applicator and the environment. The chemical causes grubs to molt prematurely. Molting too soon results in death because the grubs have not stored enough energy to successfully complete this complex process.
Even when conventional, more toxic pesticides are the only choice, there is an IPM approach to their use. The least toxic chemical should be selected. It must be applied at the correct rate in a safe manner. If applied improperly, a control failure may occur, resulting in the need for another application.
The greatest problem applicators have is usually calibration. Many people who use pesticides apply too high a rate. Calibration is discussed in Appendices B and C.
The turf manager must understand all the characteristics of the pesticide selected. He or she must know enough about the life cycle of the pest to apply the material at the time when it will have the greatest effect.
The key to a successful IPM program is knowledge. The people involved in its implementation must understand how to grow healthy plants, the life cycle and characteristics of the pests they encounter, how to monitor correctly, and what alternatives are available when a pest problem requires action. It is obvious that the most knowledgeable turf managers will have the most successful IPM programs.
The turf manager can obtain this knowledge by taking college courses, attending educational meetings, reading turf books and trade magazines, and talking with other turf specialists. Even if the manager is skilled, the program may fail if her employees are not properly trained.
Putting It All Together--Three Examples
The following examples present a brief description of techniques associated with IPM programs.
Hairy Chinch Bugs in Lawns
Traditionally, hairy chinch bugs have been controlled by lawn care companies with "wall-to-wall" applications of insecticides. The response to any history of chinch bug injury in a town or neighborhood is often regular insecticide treatments of all lawns in the area every year. The size of the chinch bug population is ignored. IPM specialists seriously question the necessity and appropriateness of this approach.
Studies have shown that chinch bug numbers are largest on dry, sunny sites where there is a significant thatch layer and a large population of fine fescues. Chinch bug problems are much less likely on sites that are newly established, shaded, wet, have little thatch, and that are primarily tall fescue, Kentucky bluegrass, or endophytic fine fescues. It is obvious that every lawn in a town does not have the same potential for chinch bug problems. In fact, an individual lawn may have some areas that are prone to injury and others that are not (Figure 17-14).
A lawn care manager can accurately predict which lawns and parts of lawns are likely to have trouble. Even if a site is ideal for chinch bugs and has a history of injury, this does not mean that large pest populations are inevitable. Weather conditions have a great impact on the size of the population. Many of the adult chinch bugs die during the winter. This is especially true if there is no snow cover. Egg mortality can be quite high. During prolonged wet periods the disease caused by Beauveria bassiana can devastate chinch bug populations. Natural enemies such as big-eyed bugs may reduce the numbers significantly.
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The only way to know for certain whether a turf area will have problems is to sample it. The common method is to use a can or cylinder with both ends cut out. It is forced 1 to 2 inches (2.5 to 5.1 centimeters) deep into the soil and then filled with water to a level higher than the grass leaves. All chinch bugs in the turf will float up to the top in ten minutes. This should be repeated in several places where chinch bugs are likely to be found. The most accurate count occurs when it is hot and sunny and the foliage is dry prior to the water being poured in the cylinder.
Calculating the area of the end of the cylinder allows the scout to determine how many chinch bugs there are per square foot. Rather than assuming that chinch bugs will be a problem, the scout has numbers that will tell him or her whether some type of action is necessary. The threshold is normally 20 to 30 per square foot (0.09 [m.sup.2]).
Monitoring has the greatest value when it is performed after the nymphs have entered the second or third instar. This occurs at 750-900 degree days (base = 7[degrees]C). Scouting should occur after the eggs of each generation have hatched. Sites prone to chinch bug injury are monitored several times, even if there are only one or two generations per season, because chinch bugs may move in from nearby areas.
No action is necessary if the populations are below the threshold. If the threshold is reached on certain parts of a lawn, those parts can be spot-treated. Even in warm, dry seasons, when chinch bug pressure is great, the turf manager knows that certain areas (wet, shaded, low thatch, etc.) will probably not require treatment.
If an insecticide must be used, the one that is least harmful to the applicator and the environment should be selected. Some entomologists recommend treating adults in the spring, when they first become active. This will minimize the effect on beneficial insects. A biological insecticide containing Beauveria is available. There is optimism that parasitic nematodes may eventually provide good control of chinch bugs.
Cultural practices can be helpful in reducing chinch bug populations. Thatch reduction and overseeding with endophytic varieties are common recommendations. Also recommended is increased irrigation, which lessens the moisture stress experienced by the grass. Frequent light irrigations to keep the surface moist will stimulate Beauveria and result in more diseased chinch bugs. One solution is to plant more trees and increase the amount of shade.
White Grubs on Golf Courses and Lawns
The white grubs discussed in this section are the larvae of the Japanese beetle, the European chafer, the northern and southern masked chafers, the Asiatic garden beetle, and the oriental beetle. They are more difficult to kill than chinch bugs and other surface-feeding insects because they are in the soil.
Grubs are most susceptible to control when they are in the first instar and still small, and when they are close to the surface feeding at the thatch/soil interface.
The date when eggs hatch and first instars appear varies from year to year because of weather differences. In one season eggs may hatch late because the soil is cool, and in another they may hatch early because of warm, moist conditions. If the soil remains very dry, eggs may desiccate and not hatch at all. If the soil is very wet, larvae and pupae may become diseased. As with chinch bugs, the key to a white grub IPM program is monitoring.
A scout must sample turf areas regularly until he or she discovers that the first instar grubs are near the surface. If the numbers exceed the threshold (usually 6-10 per square foot; Asiatic garden beetle = 20), treatment at this time has the greatest chance of success. Watering before or after the application will encourage the insects to feed near the surface. Irrigation will also help to wash liquid sprays off the foliage and into the soil.
On a golf course fairway the scout may take three or four samples across the fairway in rows 50 feet (15 meters) apart (Figure 17-15). The samples are pulled with a cup cutter, which has an area of 0.1 square foot. Multiplying the number of grubs found per plug by 10 converts to the number of grubs per square foot.
In many cases it is unnecessary to treat the entire fairway. Areas with grub populations at the threshold levels can be spot-treated. This type of monitoring often results in a 50 to 80 percent reduction in insecticide use. Some years environmental conditions are so unfavorable for white grub species that insecticides do not need to be used at all.
When insecticides are needed it is important to fully understand their characteristics. Repeat applications can be avoided if the turf manager selects the best material for the circumstances and applies it correctly. Many pyrethroids are registered for white grub control, but because they are insoluble, they do not penetrate the soil. Trichlorfon, however, is very soluble and will readily move down to the grubs.
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Imidacloprid is a very effective insecticide which lasts long enough in the soil that it can be applied early in the summer. The problem with this approach is that the turf manager does not know what the numbers will be per square foot in late summer when the eggs hatch. An application may be unnecessary.
Halofenozide, the molt-accelerating compound, is very effective against some of the grub species and works best on the first instar. Some research performed on lawns has shown that the likelihood of European chafer grub problems can be predicted based on grass species present and the amount of shade (Figure 17-16). A lawn with little shade and predominately Kentucky bluegrass (risk category 9) has the greatest risk of European chafer injury.
The use of nematodes for white grub control is an alternative to traditional pesticides. Their performance is steadily improving with the release of more effective species and the development of improved formulations and application techniques.
Cultural practices that affect the size and vigor of the root system are important. Plants with a root system that is large and recuperative will be able to tolerate more root injury than plants with a root system that is small and unable to replace lost root tissue.
Proper fertilization, mowing, and irrigation will help to minimize the impact of white grub injury. Core cultivation is very important. Some turf managers apply biostimulants such as seaweed extracts to increase rooting.
The major effect of grub feeding is moisture stress due to root loss. Irrigating one or more times daily can help to compensate for the reduced root system. Frequent irrigation may keep turf alive and satisfactory for fairway use when the grub population far exceeds normal thresholds.
Pythium Blight on a Warm Season Athletic Field Overseeded With Perennial Ryegrass
On warm season zone athletic fields where cool weather occurs before the fall sports season is over, the grounds manager may choose to overseed with perennial ryegrass. The permanent grass such as bermudagrass will go dormant when colder temperatures occur. If the budget allows, overseeding with a cool season species will protect the permanent grass when it is not actively growing and provide a green color to the field. Perennial ryegrass is a popular overseeding choice because it comes up fast, wears well, and is very attractive.
Several weeks before the average first frost date the mowing height is decreased and the field is vertical-mowed in two directions. The perennial ryegrass seed is spread, worked in with a drag mat, and then topdressed. Winter overseeding techniques are discussed in more detail in Chapter 9.
Pythium blight is a disease that can be very destructive to perennial ryegrass. Caused by several Pythium species, severe outbreaks occur when the relative humidity is at least 90 percent for a continuous fourteen-hour period, and during that period the temperature reaches 86[degrees]F (30[degrees]C) or higher and is no cooler than 68[degrees]F (20[degrees]C). The disease first appears as small spots but these can enlarge rapidly if abundant moisture is present (Figure 17-17). The pathogen produces swimming spores (zoospores) that are very susceptible to desiccation. Cobwebby whitish mycelia is usually visible.
Pythium blight is a serious disease that can kill large areas of turf in a few days. Consequently, its appearance often results in the need for a fungicide application. However, steps can be taken to help avoid the disease. For example, overseeding too early in the fall when high temperatures are still a strong possibility will increase the likelihood of a disease outbreak. It is important to wait as long as possible before overseeding (Figure 17-18). Not using too much seed is also critical. If too many seedlings germinate the competition between them will be intense and individual plants will be weak. This results in an increased susceptibility.
Water management is the key to avoiding Pythium blight because the pathogen reproduces and spreads rapidly when the turf is wet. Avoiding overwatering is very important. During hot weather field managers may decide to irrigate frequently and heavily to keep the perennial ryegrass from becoming too dry. Excessive amounts of water can trigger a Pythium blight outbreak if the temperatures are high enough. Night watering should be avoided. Shortly after sunrise hoses can be tied between two turf vehicles and dragged across the field to knock dew and guttation off the leaves. The manager needs to try to minimize the extent and duration of leaf wetness.
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Adequate drainage significantly decreases the occurrence of Pythium blight. Ideally the field should be crowned enough to allow good surface drainage from the center to the edges of the field. Any low spots where water can accumulate should be filled in and leveled. If the field has good internal drainage than a crown may not be necessary. A sand or sandy soil should drain well. The installation of a subsurface drainage system is very desirable on any sports field.
Core aeration holes aid in water removal from soil surface when compaction is a problem. Aeration holes also allow deeper rooting so less irrigation may be required. If a thatch layer impedes water penetration or root growth, topdressing is suggested. Whenever possible, the grass should not be cut when it is wet. The mower can spread spores all over the field.
Though new grass needs fertilization to become established, high rates of water-soluble nitrogen predispose the plants to Pythium blight. Slow-release sources should be used. Some research indicates that natural organic fertilizers and composted materials help to suppress plant pathogens. Applying one of these materials may have a positive effect by stimulating the growth of populations of microorganisms that are antagonistic to Pythium. The biological fungicide TurfShield contains Trichoderma harzianum, a fungus that produces toxins that harm the pathogen.
Despite these Pythium avoidance techniques, warm humid weather may still result in the appearance of blight. Unless there is going to be a dramatic and immediate change in the weather, a fungicide application will be necessary. Pythium has exhibited resistance to some fungicides. Rotating between fungicides with different modes of action is probably the best way to avoid resistance problems. Proper field construction and good maintenance practices will result in less Pythium pressure and fewer fungicide applications. Reduced fungicide use decreases the likelihood of resistance occurring.
Integrated pest management is a relatively new concept in the turfgrass industry. Turf managers who have implemented IPM have experienced a reduction in the use of traditional pesticides. The future development and commercial release of insect growth regulators and biological control agents such as fungi, bacteria, insects, and nematodes will greatly strengthen IPM programs.
1. What is an action threshold?
2. How often are golf courses scouted?
3. How many degree days are accumulated when the daily maximum temperature is 87[degrees]F, the minimum daily temperature is 52[degrees]F, and the base temperature is 50[degrees]F?
4. What is a pheromone?
5. What is an endophyte?
6. Why do nematode applications sometimes fail to control pests?
7. What is an antagonist?
8. What is an IGR?
9. Which sites would be most likely to have high populations of hairy chinch bugs?
10. How can the turf manager help to compensate for the loss of roots due to white grub feeding?
11. Develop an IPM program for a turf insect pest that is common in your area.
12. Develop an IPM program for a turfgrass disease.
13. Discuss why some people prefer the terms integrated plant management or turfgrass management system rather than integrated pest management.
14. Pyrethroids do not work well for the control of soil insects because the insecticides are --.
15. The usual action threshold for white grub is -- per square foot.
Figure 17-7 Typical annual report form for an athletic field. YEAR--WEEDS LOCATIONS CONTROL METHOD crabgrass in bare spot rototilled, resodded by goals DISEASES LOCATIONS CONTROL METHOD leaf spot south end was irrigating too much--cut back on irrigation slit seeded in resistant varieties INSECTS LOCATIONS CONTROL METHOD none seen no control necessary CULTURAL LOCATIONS CORRECTION PROBLEMS overwatering all purchased moisture sensors for field not mowing frequently all talked to maintenance enough in summer supervisor--he's made fields the top mowing priority Figure 17-8 The growing-degree-day accumulation in North Carolina begins on January 1. This figure illustrates that degree-day accumulation can vary significantly within a state. (Courtesy of the North Carolina Cooperative Extension Service) AVERAGE GROWING-DEGREE-DAY ACCUMULATIONS FOR 15 MAY (AIR, BASE 50[degrees]F) FOR FIVE LOCATIONS IN NORTH CAROLINA.(25-YEAFROM NC COOPERATIVE EXTENSION SERVICE) GROWING DEGREE DAYS LOCATION (AIR, BASE 50[degrees]F) Wilmington 1,000 Fayetteville 800 Raleigh 650 Statesville 600 Asheville 500 Figure 17-16 Risk rating system for European chafer larvae on residential lawns. Lawns with risk category less than or equal to 4 need not be sampled and need not be treated. (Courtesy of Cornell University) PERCENT PERCENT OF LAWN RISK OF LAWN COMPRISED OF CATEGORY IN SHADE KENTUCKY BLUEGRASS 1 >60% <30% 2 >60% 30-60% 3 30-60% <30% 4 30-60% 30-60% 5 >60% >60% 6 30-60% 30-60% 7 <30% <30% 8 <30% 30-60% 9 <30% >60%
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|Author:||Emmons, Robert D.|
|Publication:||Turfgrass Science and Management, 4th ed.|
|Date:||Jan 1, 2008|
|Previous Article:||Chapter 16 Turfgrass diseases.|
|Next Article:||Chapter 18 Other turfgrass problems.|