Map and monitor pests for premium control
Scouting your site for insect and weed problems may--at first--seem more time-consuming than simply spraying the whole area. But in the long run, it is a boon to ensuring effective control and the judicious use of chemicals.
Like most pest problems, you can anticipate the presence of weeds in turfgrasses. After all, for the most part, weeds are opportunistic plants. If you give them an opportunity to invade or infest an area, they will seize the opening.
Many weed problems in turfgrasses are associated with management problems. For instance, too much shade, compacted soils, poor fertility practices, low soil pH, improper mowing height and poor drainage area few of the situations leading to weed problems. However, from a practical standpoint, few situations exist that represent a "perfect" environment for turf growth. As a result, turfgrass-weed management will continue to challenge you. In addition, certain weed species have such a competitive advantage over the turf that they will continue to be problems regardless of the management practices you employ.
Scouting and mapping weeds The underlying assumption of weed scouting is that if you have a particular weed problem in a certain area, it will be there in equal or greater numbers in the future, particularly if you take no corrective measures to eliminate it. Weed seed can remain viable in the soil for many years. But, keep in mind that, in the case of perennial weeds, growth from seed is not necessary for recurrence. This is because underground vegetative structures allow these weeds to continue to be problems.
Therefore, scouting for weed problems and mapping areas can be beneficial and is an integral part of integrated pest management (IPM) practices. Scouting and developing weed maps can assist you in alleviating the underlying causes of the weed problem as well as targeting herbicide applications to weed-infested areas.
Weed scouting and mapping requires you to be able to properly identify the weed species present. You also need some basic knowledge of weed biology and weed life cycles. For instance, you must be able to determine whether the weed is a winter annual, summer annual, biennial or perennial--and if the weed is perennial, does it grow through the summer and go dormant in the winter, or does the weed grow through the cool months and go dormant in the summer? A detailed weed map with this information can be a valuable tool for you. Aside from helping alleviate the underlying cause of the weed problem, it allows you to target a pre-emergence application to certain areas. Or, in the case of post-emergence-herbicide treatments, it allows you to properly time applications so you can achieve optimum control and use the minimum rate. For example, annual weeds are more susceptible to herbicides when they are in the seedling stage. Many times, however, when weeds are in this stage, you can't see them under the turfgrass canopy. If they continue to grow, by the time they become readily visible in the turf canopy, they are more difficult to control. So it's important to know where they are even before they become visible.
Performing scouting/mapping When should weed scouting and mapping occur? In most areas of the United States, you should scout and develop weed maps twice a year. Perform mapping for summer annuals (such as crabgrass, goosegrass and foxtails) and perennials that grow during the warm months (such as nutsedges and Virginia buttonweed) in the latter part of the summer or early fall but before frost. This is the time of year when weeds that grow through the summer months are most abundant and readily visible. For winter annuals (henbit, chickweed, speedwells, etc.) and perennials that grow through the winter, you should map in the spring, when these weeds are the most abundant and visible.
Once you've developed your maps, you then must wait until the weed species is once again in its seedling stage before you can decide whether to apply a post-emergence herbicide. As stated previously, the seedling stage is when annual weeds such as crabgrass, goosegrass and henbit are the most susceptible to post-emergence herbicide applications. Summer annuals will be in the seedling stage in spring/early summer, whereas winter annual weeds will be in the seedling stage in the fall/early winter. Of course, the calendar date varies depending on your area of the country.
Weeds ID other problems, too When developing weed maps, it is helpful to indicate specific information about the site to help determine why a particular weed problem may exist at that location. For instance, does the site have too much shade? Is the soil compacted? Does it have drainage problems, or do certain areas tend to be wet? Is the mowing height correct? Is it sandy or does it tend to suffer from a lack of moisture? All of these conditions tend to favor certain weed species, and if these conditions continue to exist, certain weeds will invade in the future if they are not there already. In addition, correcting these problems can help alleviate certain weed problems. In fact, for many situations with tough-to-control weeds, control with herbicides can be so inadequate that repeated applications over several years still doesn't solve the weed problem.
In addition, certain turf-management problems can lead to the invasion of specific weed species. For instance, compacted soils typically lead to the invasion of goosegrass and prostrate knotweed. Therefore, the presence of either species should alert you to check for compaction. These two weeds (particularly goosegrass) are especially common on athletic fields. Look for goosegrass on areas of the field where traffic is the most intense. In these situations, you can continue to fight goosegrass with herbicides. But if you alleviate the compaction problem, along with developing a well-designed herbicide program, you'll provide much better control.
Annual bluegrass is another species that thrives in compacted soils. This weed also prefers wet soils and flourishes in areas where high nitrogen fertility has been practiced. Therefore, investigate potential drainage problems as well as give a close look to your fertility program.
At the opposite end of the spectrum, various clover species--such as white clover, large and small hop clover, black medic and broomsedge--can thrive in areas of low fertility. And close mowing enhances problems with crabgrass and annual bluegrass.
One of the most serious weed problems in the Southern tier of states is sedges. As a general rule, warmer climates have more sedge problems. In the Southern part of the country, west to Arizona, New Mexico and California, as many as 10 sedge species can be problematic. These include purple and yellow nutsedge, globe sedge and the various species of kyllinga that are spreading rapidly in many areas of the country. All sedges--particularly the kyllinga species such as green kyllinga (Kyllinga brevifolia) and smooth green kyllinga (Kyllinga gracillima)--thrive in wet, poorly drained soils. Because these weeds are aggressive perennials, they can spread rapidly and be difficult to control. It is essentially impossible to completely eradicate these species from a site if the soil is poorly drained. Similarly, yellow and purple nutsedge may invade an area because it is poorly drained, but both of these weed species can survive and spread in areas that have good drainage, too. In these cases, poor drainage may cause the weed to become established and it then may spread to surrounding areas.
Scouting and weed mapping can be important tools in managing weeds. In fact, they are critical factors in implementing IPM approaches to turfgrass management. The use of weed maps allows you to make herbicide applications only in areas that need them. And by knowing where certain weeds are likely to occur, you can control them with post-emergence herbicides when they are most vulnerable, thereby getting maximum control with minimum rates. Weed maps also can assist you with identifying underlying problems that may cause your weed problem.
You also can use pre-emergence herbicides in an IPM program. However, using pre-emergents requires additional emphasis on detailed scouting and mapping. For instance, you only can use pre-emergents in turf where weeds are a problem. Many weed species can be found only in certain areas, and you may not need a pre-emergent over the entire area. Goosegrass is a weed that typically exists only in certain areas. Obviously, a detailed map indicating where the weed is a problem is necessary if you want to achieve acceptable control with pre-emergents.
Dr. Fred Yelverton is assistant professor and extension specialist at North Carolina State University (Raleigh, N.C.).
Soil-insect pests are among the most difficult and expensive turf pests to control. Pest mobility, few naturally occurring biological controls and little information about the specific soil-environment's effects on these insects' behavior all contribute to control difficulty.
Monitoring is a key step in effectively timing your application strategies and choosing products for controlling soil pests. Sometimes you may wonder if monitoring is cost-effective. Don't worry. It is. In fact, managers who monitor regularly--particularly those with limited budgets--often comment that they cannot afford not to monitor. Monitoring, or scouting, is a common-sense approach that involves looking at a landscape, or a part thereof, in an organized way on a regular basis and keeping records on what you see. Knowing where, when and how to monitor depends on the plants you grow, the potential pests and the priorities you or your client places on certain areas of the landscape.
Knowledge is key to monitoring A successful monitoring program depends on your being able to correctly identify pest insects and being knowledgeable about their life cycles. Usually, you'll monitor to determine the presence or absence of pests in an area or the presence of certain life stages that are most vulnerable to particular control strategies. For example, you'll have greater success controlling grubs with insecticides if you treat for them while they are young as opposed to when they are older.
Turf managers often monitor to determine the number of pests present at a particular time. Threshold numbers represent an estimate of how many of a particular pest are usually present before you notice damage. A word of caution: In landscape situations--particularly in turfgrasses--the type of turf species, your management practices (including irrigating, mowing and fertilizing), traffic on the turf and your or your client's expectations contribute to threshold numbers being very site-specific.
Monitoring should be an on-going process. Once you've observed vulnerable life stages, or seen that an area has exceeded threshold numbers, monitoring allows you to determine whether controls have worked effectively. So monitoring can be an effective evaluation tool.
Monitoring also allows you to determine where pests are located in relation to where they are not located--that is, to pinpoint the location of a pest population. After all, soil pests are not usually evenly distributed over an area. Therefore, product and labor costs make large treatments--the "shotgun" approach--unaffordable.
Mapping: The most important elements Mapping involves recording the location of soil-insect pests on landscape maps. Mapping is not a new concept for landscape managers. In the past, many landscape professionals constructed maps of each property they managed. They assigned each plant grouping or landscape area with a letter or number. They took notes about the property after each monitoring visit and referred to locations by their letter or number. Mapping insect pests involves the similar use of a landscape map and the recorded location of pest populations. This practice saves money because you don't have to treat the whole area--only the mapped areas where you've located pests.
Tawny mole crickets in the Southeast are the most expensive and difficult-to-control turf pests in that region. Areas that tawny mole crickets have tunneled through in the spring are also the areas in which tawny-mole-cricket females lay their eggs. Nymphs hatch during late spring and early summer. You should map infested turf in the spring when tunneling increases, then monitor those areas for first and peak hatching and treat them when young nymphs are present. It is not unusual for contract applicators to use maps constructed by turf managers to treat only infested areas rather than "wall-to-wall" treatments. Some golf-course superintendents have reported a 50-percent or more reduction in costs of mole-cricket control due to effective mapping and monitoring programs.
Other commonly mapped soil pests are grubs and imported fire ants. It's easy to map mole crickets and imported fire ants because of the visible signs of their presence on the turf surface. Over the last few years, Dr. Mike Villani (Cornell University, Geneva, N.Y.) developed a system for mapping grubs. He and his research team dug plugs with greens cup cutters and examined them for grubs. On a map, they recorded grub presence in a plug as a plus (+) and grub absence as a minus (-).
This process resulted in a profile of where grubs were located. Recently, because of the development of acoustic technology, researchers have listened to grubs in the soil. With this new technology, you can hear grub sounds and detect their presence without digging.
Monitoring is a must for effective--and cost-effective--control programs for soil-insect pests. Mapping is the next logical step following monitoring. Mapping refines control strategies and can make efforts even more cost-effective.
Dr. Patricia P. Cobb is professor/extension entomologist in the Department of Entomology at Auburn University (Auburn, Ala.).
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