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Chapter 14 Weeds.

OBJECTIVES

After studying this chapter, the student should be able to

* Explain why a correct turfgrass maintenance program results in less weed competition

* List some of the more important weed species

* Identify the different types of herbicides

* Discuss the methods of controlling annual grasses, perennial grassy weeds, and broadleaf weeds

Introduction

Any plant that is growing where it is not wanted can be called a weed. Coarse-leafed tall fescue is desirable in roadside areas, but is considered a weed on a better quality lawn (Figure 14-1). Creeping bentgrass can be a serious problem on a lawn, but is the perfect choice for a golf course green. Many plants such as dandelions and crabgrass are described as weeds regardless of the type of turf in which they are growing.

Broadleaf weeds are very noticeable in a turf area because their appearance is much different from that of grasses. Their broader leaves ruin the uniform appearance that is expected of a quality turf (Figure 14-2). These weeds have a particularly disruptive aesthetic effect if they produce flowers and seedheads (Figure 14-3). Certain grass species are considered weeds because they destroy the uniformity of the turf. Their leaf texture may be coarser than that of the desirable turfgrasses. They may grow in unattractive clumps, have poor color, form unsightly seed stalks, or have a different growth habit (Figure 14-4). Annual grasses such as crabgrass and goosegrass and the annual subspecies of Poa annua die each year, leaving dead areas in the turf (Figure 14-5).

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Weeds also cause problems by competing with turfgrass for sunlight, nutrients, and moisture. Weeds can spread rapidly in a turf by means of seeds, rhizomes, stolons, and various underground storage organs such as bulbs and tubers (Figure 14-6). For example, the appearance of a few broadleaf plantain plants in a turf may not be considered a serious problem, but each plant can produce thousands of seeds (Figure 14-7). If bare spots are present in the turf, some of these seeds will successfully germinate and in a short time numerous plantains may appear.

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Weed control implies chemical control to many people. However, the best weed control strategy is to prevent weed populations from appearing in the turf at all. This can be accomplished by intelligent establishment and maintenance. Weeds become a problem when turfgrasses either lose or do not achieve the proper density (Figure 14-8). Weeds gain a foothold and flourish on bare areas not covered by turfgrass. If the grasses are adaptable to the site and the maintenance operations are performed correctly, the turf should be thick enough to choke out most weed problems.

The presence of a sizable weed population indicates that the turf is too open or thin and that the management program needs improvement. Practices such as fertilization, irrigation, mowing, and disease and insect control should be reevaluated. Weaknesses in the program should be identified and corrected. It may be necessary to reseed or overseed with turfgrass species and cultivars that are better adapted to the site. Properly maintained, well-adapted turfgrasses are able to outcompete weeds. Weed problems are normally minimal when turf density is high.

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By identifying the weed species that predominate, the turf manager can sometimes discover why the weeds outcompete the desirable grasses. For example, the presence of annual bluegrass, pearlwort, moss, sedges, rushes, or alligatorweed as the major weed problem suggests that the site is too wet. Cutting back irrigation or improving drainage may reduce the weed population. Goosegrass, birdsfoot trefoil, prostrate spurge, black medic, or yellow woodsorrel populations indicate droughty conditions. Increased irrigation will make turfgrasses more aggressive. When weeds such as clovers, common speedwell, birdsfoot trefoil, or hawkweed are predominant, low fertility is often the problem. Applying more nitrogen will cause the desirable grasses to be more competitive.

Large populations of shallow-rooted weeds may be the result of significant soil compaction. Annual bluegrass, broadleaf plantain, prostrate spurge, knotweed, goosegrass, and corn speedwell are examples of weeds that do well on compacted soils. Core cultivation will help the turfgrasses by allowing deeper rooting. Mowing too close leads to an invasion of low-growing weeds such as annual bluegrass, chickweeds, some of the speedwells, and moss, which are better adapted to low mowing heights than most of the turfgrasses. Raising the cutting height will strengthen the desirable grasses and encourage their spread. Taller weeds such as burdock, teasel, and bull thistle can be partially controlled by lowering the cutting height. It is important not to lower the height so much that the turfgrass is weakened.

Types of Weeds

The characteristics of turfgrass weed species vary tremendously, but all have the ability to persist even though the grass is cut regularly. Generally, they survive mowing because of a low growth habit. Weed species are either broadleaf (dicotyledon) or grassy type (monocotyledon). They can be further divided into annuals, biennials, and perennials.

Annuals complete their life cycles in one year or less. Summer annuals, such as crabgrass, germinate in the spring and die in the fall with the onset of colder temperatures. The seeds they produce during the growing season remain in the soil over the winter and germinate the following spring when soil temperatures increase. Winter annuals, such as common chickweed and annual bluegrass, germinate in late summer or early fall, overwinter in a dormant state, and continue to grow the following spring. Death occurs during the summer after seed is produced.

Biennials, such as wild carrot, burdock, and bull thistle, live for two years (Figure 14-9). Perennial weeds, like most turfgrasses, live for longer than two years. Simple perennials reproduce by seed. Common examples are dandelions, plantains, and chicory. Creeping perennials reproduce by seed, but can also spread by means of rhizomes, stolons, and underground storage organs such as bulblets. Examples of creeping perennials are quackgrass, nutsedge, and white clover.

[FIGURE 14-9 OMITTED]

Selecting the proper herbicide and application time for controlling a weed species is determined by the life cycle of the weed and whether it is a broadleaf or grassy type. Generally weeds fall into three control groups--annual grasses, perennial grasses, and broadleaf weeds. This classification is important to the turf manager because each group is controlled differently (Figure 14-10).

Herbicides

Herbicides are chemicals that control weeds. They can be selective, killing one type of plant but not injuring another. 2,4-D is a widely used herbicide that controls a number of broadleaf weed species but will not adversely affect mature turfgrass if applied properly. Nonselective herbicides, also called total vegetation killers, control both broadleaf and grass plants.

Some herbicides are applied to the soil before the time when the weeds are expected to appear in the turf. These preemergence herbicides form a toxic chemical barrier near the soil surface and destroy seedlings before they emerge. This type of herbicide is primarily used to control annual grasses. Mature, established grasses are not killed by preemergence herbicides because their roots are beneath the chemical barrier. Postemergence herbicides are applied after the weeds have appeared above the soil surface. This type is used primarily against broadleaf weeds and perennial grasses.

The vast majority of herbicides used by the turf manager are systemic. They enter the weed through its roots or leaves and are translocated throughout the plant by the vascular tissue. Eventually the systemic herbicide kills all parts of the plant. A few herbicides occasionally used by turf specialists are the nonsystemic or contact type. They kill only the parts of the plant to which they are applied. The turf manager must be aware of the characteristics of herbicides (Figure 14-11).

Soil sterilants are nonselective chemicals that retain their toxicity for long periods. The sterilant kills any sprouting seeds or plant parts that begin to grow in the soil where it is located. Sterilants are used in parking lots, on paths, under fences, and other areas where any vegetation is undesirable.

Fumigants can be applied to the soil to control weeds, seeds, nematodes, disease-causing microorganisms, and insects. However, because of pesticide regulations and expense they are generally used only on specialty turf areas such as golf greens.
   All chemicals suggested for use in the following discussions should
   be applied in accordance with the directions given by the
   manufacturer on the container label. Any deviation from the label
   instructions is a violation of the law. The turf manager should
   check the current status of a pesticide being considered to be
   certain that its use has not been restricted by federal, state, or
   local regulatory agencies. Some pesticides registered by the
   Environmental Protection Agency are not registered for use in all
   states.


The turf manager must also be sure that the herbicide is not toxic to the desirable turfgrasses. Metsulfuron, for example, is safe to use on bermudagrass, centipedegrass, zoysiagrass, and St. Augustinegrass, but kills bahiagrass (Table 14-1). Varietal differences can occur. Meyer zoysiagrass is tolerant to MSMA, but the cultivar Emerald is sensitive to it. Closely mowed turfgrass is often more susceptible to herbicide injury. Stress can reduce tolerance. Cool season grasses are more sensitive to herbicides during the hottest, driest parts of the summer; warm season species are more sensitive during spring greenup or droughty periods.

When warm season grasses are dormant in the winter, they can be safely treated with some herbicides that would cause severe damage if applied when the grasses were actively growing. In some southern states diquat is used for winter annual weed control in dormant bermudagrass. The pesticide would injure actively growing bermudagrass.

Essential information about the use of a herbicide is found on the product label. Any questions that remain after reading the label should be referred to the Cooperative Extension Service or to the product manufacturer. Most companies have toll-free 800 numbers.

It is important to consider the efficacy of a herbicide. How well will it work against the weed species prevalent in the turf area? The site should be surveyed to determine which weed species are present and which are most common. Obviously, the herbicide or herbicides selected must be able to successfully control the weed population growing on the site. Herbicides do not work equally well against all weed species. Bensulide is very effective against crabgrass, but its control of another annual grass, goosegrass, is relatively poor.

When selecting a herbicide, turf managers should also try to use the material that is least toxic and most unlikely to cause environmental problems. For larger areas, cost is a factor.

Controlling Annual Grasses

Annual grasses such as crabgrass, goosegrass, foxtail, barnyardgrass, annual bluegrass, fall panicum, and field sandbur are often controlled with preemergence herbicides. Commonly used preemergence chemicals include benefin, bensulide, dithiopyr, metolachlor, oxadiazon, pendimethalin, prodiamine, and siduron. Most applications occur in the spring and are aimed at summer annuals such as crabgrass and goosegrass.

The toxic chemical barrier formed at the soil surface by the preemergent herbicides usually lasts six to twelve weeks, depending on which chemical is used. Eventually microorganisms break down the herbicide.

Proper timing of an application is important. These materials must be put down before seed germination (Figure 14-12).With the exception of dithiopyr, they have little effect if applied after weed emergence. However, if the chemical is put down too early, it may lose its effectiveness before the peak germinating period ends. In colder areas, there is minimal microbial activity in the winter and early spring, so the preemergent herbicides can be applied in the late fall.

Preemergence herbicides are normally applied a few weeks before seed germination. In some areas a traditional method for crabgrass control is to time the application with the full bloom of forsythia. Another method is to apply the herbicide after the soil temperature at a 2-inch (5.1-centimeter) depth has been 55[degrees]F (13[degrees]C) for three or four consecutive days. Some turf managers wait until the mean air temperature is in the 55[degrees] to 60[degrees]F (13[degrees]-15.5[degrees]C) range for two weeks. Goosegrass germinates a few weeks after crabgrass.

Liquid and granular formulations are equally effective. In southern states two or three applications per growing season are usually necessary. If good control is achieved one year, it is often possible to skip a year before retreating with a preemergence herbicide.

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Postemergent control is also possible. Fenoxaprop is effective against summer annual grasses in cool season turf and zoysiagrass. It works best when weeds are in an early growth stage. Dithiopyr will kill annual grass plants that have not yet tillered. It can be used in most warm season and cool season turf and also acts as a preemergent.

The organic arsenicals, MSMA and DSMA, are labeled for use against emerged annual grasses. Two or more applications are required for adequate control, and they can be phytotoxic to desirable grasses. Cool season species are especially susceptible to injury.

Postemergence applications of metribuzin alone or in combination with MSMA provide good control of goosegrass in bermudagrass turf. Diclofopmethyl is used for the same purpose. Asulam is applied for postemergence control of goosegrass and crabgrass in St. Augustinegrass turf. Sethoxydim controls annual grasses in centipedegrass.

It is very important to check the label carefully before applying herbicides. Tolerances to herbicides can vary significantly between turfgrass species.

Preemergent applications for winter annual grasses occur in late summer or early fall.

Annual Bluegrass Control

Annual bluegrass (Poa annua) is a winter annual that can be very difficult to control. Because of its prolific seeding ability it is so competitive that large populations of annual bluegrass can be common on higher-maintenance turf sites (Figure 14-13). Complete control of annual bluegrass with preemergence herbicides is not possible.

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As explained in Chapter 4, both annual and perennial types of annual bluegrass exist. The annual subspecies is prevalent in warm season areas and produces seed in the spring which germinates in the late summer. Application of a preemergent such as bensulide or prodiamine before germination provides some control.

In bermudagrass, pronamide can be used for preemergent and postemergent annual bluegrass control. Atrazine, diquat, or glyphosate can be applied to dormant bermudagrass in the winter to kill annual bluegrass plants.

Annual bluegrass control is more difficult in cool season turf. The perennial biotype usually predominates, and its seed germinates throughout the season. Poa annua is dormant in the winter when the desirable cool season species are dormant, so it is not possible to kill the weed with a nonselective herbicide such as glyphosate, as in the South.

The annual bluegrass problem is greatest on golf courses. Preemergent herbicide applications of a material such as pendimethalin in the fall can help. However, successful control requires both chemical and cultural programs. Flurprimidol, paclobutrazol, and trinexapac-ethyl are growth regulators that suppress Poa annua by reducing its growth and competitive ability. The desirable grasses continue to grow and spread. The conversion can be speeded up even more by overseeding with turfgrass seed.

Ethofumesate provides very good control of annual bluegrass when applied as a postemergent. It is labeled for use in perennial ryegrass, creeping bentgrass, and Kentucky bluegrass turf. Because it kills Poa annua, dead spots will result when the chemical is applied to turf areas that have large patches of the weed. For this reason ethofumesate gives the best results when the turf is less than 20 percent annual bluegrass. Overseeding helps to fill in the areas where Poa annua has died.

Some golf course superintendents, when confronted with large fairway areas composed primarily of annual bluegrass, will spray with the nonselective herbicide glyphosate and kill everything. The fairway will then be reseeded. However, annual bluegrass will almost certainly dominate again in the near future if proper cultural techniques are not implemented.

The perennial biotype of Poa annua is very competitive in wet areas. Improving drainage and avoiding overwatering is important. Core cultivation is helpful because annual bluegrass tolerates compaction better than the desirable turfgrasses. Reducing nitrogen fertilization and changing application times may also help. For example, a nitrogen application in early spring benefits the annual bluegrass because it starts to grow sooner than most desirable grasses in the spring.

Lightweight mowing has resulted in a significant decrease in Poa annua populations. The lighter mowers cause less compaction and wear on fairways. Picking up the clippings in the mower baskets is also important. This may be because seeds are removed or because the clippings supply nitrogen, which favors annual bluegrass. Some theories hold that the clippings promote disease or decomposition products that injure the turfgrasses. Whenever turf is weakened or killed there is a good chance that annual bluegrass will appear in the bare spot because in the soil there are as many as 20,000 of its seeds per square foot (0.09 m2).

There is interest in using a bacterium for annual bluegrass control. The organism, Xanthomonas campestris, causes a wilt disease that can be quite destructive. The grass is mowed immediately after application of the product. The fresh wounds allow the bacteria to get inside the plants.

Some golf course superintendents decide to coexist with their annual bluegrass. This is often because past control efforts have failed. Annual bluegrass performs most satisfactorily where temperature extremes do not occur. The grass is susceptible to winter injury. In the spring and summer annual bluegrass must be protected from the annual bluegrass weevil, the black turfgrass ataenius, and diseases such as anthracnose and summer patch.

Controlling Perennial Grasses

Perennial grassy weeds can cause serious problems because they are so similar to turfgrasses that it is difficult to develop selective herbicides that will control them and not kill the desirable grass. This is especially true in cool season turf. Some experimental chemicals look promising. Presently a nonselective herbicide such as glyphosate is commonly used to spot-treat the patches of grassy weeds. The chemical is normally applied with a hand sprayer. The turf manager must be careful not to spray glyphosate on the adjacent desirable turfgrass.

Glyphosate is inactivated in the soil because it is bound tightly to soil particles. Consequently, it has no effect on seed. The areas that contained perennial grassy weeds can be reseeded shortly after a glyphosate application. A waiting period of seven days is necessary to ensure that the chemical has been translocated to the roots of the weeds. One selective material, chlorsulfuron, will control tall fescue in Kentucky bluegrass, fine fescue, bahiagrass, and bermudagrass lawns. However, it is usually spot-applied because it can discolor and suppress the growth of desirable grasses.

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In warm season turf there are some opportunities to selectively control perennial grassy weeds. For example, ethofumesate will suppress common bermudagrass in St. Augustinegrass turf, and sethoxydim can be used to remove bahiagrass from centipedegrass. Fenoxaprop will suppress bermudagrass growing in zoysiagrass turf, and repeat applications of MSMA will help to control bahiagrass that is infesting bermudagrass. Glyphosate can also be used to spot-treat undesirable perennial grasses.

Nutsedge, or nutgrass as it is sometimes called, is a sedge and not a true grass (Figure 14-14). However, it is a perennial monocot and is normally grouped with perennial grasses in discussions of weed control. Organic arsenicals were used for years to eradicate nutsedge, but they were not totally effective and could be phytotoxic to the turf. Bentazon, halosulfuron, sulfosulfuran, metolachlor, and trifloxysulfuron offer better control of yellow nutsedge with minimal phytotoxicity problems. Imazaquin is used for purple nutsedge control in warm season turf, with the exception of bahiagrass.

Controlling Broadleaf Weeds

The majority of herbicide applications are aimed at broadleaf weeds. Fortunately, most broadleaf weeds are relatively easy to control in turf because they are dicots and can be killed with herbicides that do not injure the turfgrass. One of the reasons broadleaf weed killers are selective is that dicots have their major meristematic area exposed at the top of the plant, while the crown of grasses is located at the base of the plant and is more protected from herbicides.

Selective herbicides such as 2,4-D, mecoprop, dichlorprop, dicamba, triclopyr, and clopyralid are commonly used to control broadleaf weeds. They are applied directly to the leaves.

A combination of at least two broadleaf herbicides is best. Using only one is less effective because some weeds growing in the turf may not be affected by the chemical (Table 14-2). For example, mecoprop alone controls only about 25 percent of the broadleaf weed species common in turf, but when mixed with 2,4-D it controls 65 percent. A mixture ensures better broad-spectrum weed control.

Broadleaf weed killers must be used carefully because they can injure nearby trees, shrubs, flowers, fruits, and vegetables if they come into contact with these plants. Drift is a common problem. The turf manager should spray these chemicals only when there is little or no wind (Figure 14-15). Amine formulations of 2,4-D, though less effective than ester formulations, are also less volatile and less likely to cause injury to adjacent broadleaf plants. Dicamba may leach through the soil, so it should not be applied above the root zone of trees and shrubs unless the rate is sufficiently low. It should not be used at all on turf areas that are directly above the roots of very sensitive ornamental plants.

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Postemergence herbicides such as 2,4-D, dicamba, and mecoprop kill broadleaf weeds by entering the plant and disrupting its metabolic processes. The herbicide must remain on the foliage for several hours or even a full day to allow lethal quantities of the chemical to penetrate the leaves. Rain should not be expected for twenty-four hours after the application. The turf manager should wait a few days before mowing the turf. Dicamba enters plants through both roots and leaves.

Granular herbicides should be applied when the weed foliage is moist. These dry materials stick better if leaf surfaces are wet. More herbicide is absorbed by the weed if there is good adhesion. Granular broadleaf weed killers should be spread after a rain or irrigation, or early in the morning when the foliage is wet with dew.

If performed properly, spraying usually provides better control than granular applications. Best control with either occurs when application coincides with vigorous weed growth. When the broadleaf weeds are actively growing, the herbicides are more effective because of greater absorption and translocation (Figure 14-16). The materials work especially well if the weeds are young and succulent. However, the plants should not be so small that it is difficult to contact their leaf surfaces with the herbicide. The turf manager should not mow the site for a few days before application. Cutting the weeds reduces the size of their leaves and the likelihood that the herbicide will land on them.

Some weeds, such as ground ivy, are easier to kill in the fall after a hard frost. At that point, they are moving carbohydrates to the roots for winter storage, and the herbicide is transported to the roots with the carbohydrates. A perennial will recover if its roots are not killed. The weakening of the ground ivy by cold may also make it more susceptible to a herbicide (Figure 14-17).

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Seedling grasses are susceptible to injury from broadleaf weed killers. Application should be delayed until the new turf has been mowed two or three times. After an application has occurred the turf manager should wait at least three or four weeks before seeding.

Even mature grasses can be injured if the turf is suffering from heat or drought stress. Warm season turfgrasses are susceptible to injury if treated in the spring before they have fully recovered from the winter.

Other postemergent herbicides such as metribuzin, metsulfuron, pronamide, atrazine, and simazine are used in warm season turf. Tolerances to these materials vary greatly among warm season turfgrass species, so it is important to read the label thoroughly. St. Augustinegrass and centipedegrass are sensitive to the phenoxy herbicides 2,4-D, mecoprop, and dichlorprop.

Knotweed, lambsquarter, purslane, spurge, and yellow woodsorrel are common summer annual broadleaf weeds. Henbit and common chickweed are winter annual broadleaf weeds often found in turf. Preemergence herbicides applied to control annual grasses will also kill some annual broadleaf weeds as they germinate. Perennial broadleaf weeds also produce seeds, and they will be affected. Isoxaben is a preemergent herbicide that is used primarily for broadleaf weed control.

Rules for Applying Herbicides to Control Broadleaf Weeds

1. Broadleaf herbicides generally work best on young, succulent plants.

2. The weeds should be actively growing at the time of application. Best control occurs when the air temperature is 65[degrees] to 85[degrees]F (18[degrees]-29[degrees]C). At higher temperatures leaf stomata may be closed, reducing herbicide movement into the leaves. Herbicides may volatilize (change to a gas) and drift when temperatures are greater than 85[degrees]F. Phytotoxicity to grass is also more likely.

3. Soil moisture levels should be adequate to ensure active growth, good translocation of the herbicide, and satisfactory root uptake if the material is absorbed by the roots. Irrigate before the application if the soil is dry. Avoid applications during long, excessively dry periods. Weed control is poor at times of prolonged moisture stress, and herbicides can be damaging to turfgrass roots.

4. Do not mow the turf right before the application. This ensures that there is sufficient leaf tissue on the weed for the herbicide to contact.

5. Avoid drift. If it is windy, do not spray.

6. Use low volumes of water when spraying. One gallon of water per 1,000 ft2 is a common recommended application rate.

7. Weed leaf surfaces should be moist if a granular material is used. Keep traffic off the treated area for at least eight hours.

8. Rain or irrigation should not occur for at least eight hours and preferably twenty-four hours after the application.

9. Do not mow until two days after the application. Mowing immediately will result in a removal of the herbicide before it can start to work.

10. Wait at least two weeks before retreatment. Do not be impatient--it may take one to four weeks for the weeds to die.

11. Grass seedlings are sensitive to herbicides. It is best to delay applications until the newly planted area has been mowed two or three times. If an application is necessary sooner, in some instances it is possible to apply the regular broadleaf weed killers at half the normal rate.

12. Do not apply herbicides to newly installed sod until it is firmly rooted.

13. Do not seed a treated area until at least one month after application.

14. Do not use grass clippings on gardens or around shrubs until the third or fourth mowing after application of the herbicide. Clopyralid is very slow to break down and can cause injury even after clippings have been composted.

Broadleaf weed control in warm season species is performed anytime weeds are actively growing. For cool season turf, control occurs in the spring, late summer/early fall, or late fall. Fall applications are generally preferable to spring treatments. Fall broadleaf weed control works very well on cool season turf because the turfgrasses are more likely to fill in bare spots vacated by the weeds then and the weeds are transporting a large amount of food to the roots for winter storage. There is excellent movement of herbicides into the weeds' roots, which results in better weed control. Another advantage of a fall application is that any accidental injury to desirable broadleaf plants will be less important because most will soon drop their leaves or die anyway.

Proper timing is critical when broadleaf species that are difficult to kill with herbicides are present in the turf. Applications should occur at the specific time of year when the weed is most susceptible. When large weed populations or difficult-to-kill weeds are present, repeat applications may be necessary.

Grasses under stress can be injured by broadleaf weed killers they would normally tolerate. Excessively high application rates can result in injury to healthy grass. Proper application techniques are essential (see Appendices B and C). Herbicide residues can remain in a sprayer even after it has been carefully cleaned. Serious injury can occur if the same sprayer is used to apply other pesticides to plants that are sensitive to the herbicide.

SELF-EVALUATION

1. The presence of a large weed population indicates that changes should be made in the --.

2. -- annuals germinate in the late summer or early fall.

3. -- perennials reproduce by seed, rhizomes, stolons, and underground storage organs.

4. -- herbicides kill all types of plants.

5. Annual grasses are primarily controlled with -- herbicides.

6. Broadleaf herbicides in a granular form work best when the leaf surfaces of weeds are --.

7. Herbicides should be sprayed when there is little or no --.

8. Discuss the differences between the two subspecies of Poa annua.

9. The presence of which specific weeds indicates that the site is too wet?

10. Discuss the rules to follow for the proper application of a broadleaf herbicide.

11. What type of cultural techniques can result in lower annual grassy weed populations?
Table 14-1 Tolerance of Established Warm Season Turfgrasses to
Some Postemergence Herbicides *

HERBICIDE       BAHIAGRASS        BERMUDAGRASS      CARPETGRASS

Atrazine          NR                 NR               NR
Bentazon          T                  T                NR, T
2, 4-D            T                  T                t
Dicamba           T                  T                t
DSMA, MSMA        NR, S              T                NR, S
Fenoxaprop        NR, S              NR, S            NR
Imazaquin         NR, S              T                NR, t
Mecoprop          T                  T                t
Metribuzin        NR, t              T                NR, S
Sethoxydim        NR, S              NR, S            NR, t

HERBICIDE     CENTIPEDEGRASS   ST. AUGUSTINEGRASS   ZOYSIAGRASS

Atrazine          T                  T                 t
Bentazon          T                  T                 T
2, 4-D            t                  S                 T
Dicamba           t                  S                 T
DSMA, MSMA        NR, S              NR, S             t
Fenoxaprop        NR, S              NR, S             T
Imazaquin         T                  T                 T
Mecoprop          t                  t                 T
Metribuzin        NR, S              NR, S             NR, S
Sethoxydim        T                  NR, S             NR,t

* D = use when turf is dormant; NR = not registered for use on
this turfgrass species; S = sensitive, herbicide will injure
this turfgrass species; t = species shows intermediate tolerance
to this herbicide, injury may occur, especially at higher rates;
T = species tolerant to this herbicide at labeled rates. The
pesticide user must always check the product level for species
and cultivar tolerance information. Some cultivars may be less
tolerant than others. Closely mowed or stressed turf is often
more susceptible to injury.

Table 14-2 Advantages of Using a Herbicide Mixtures because of
Resistance of Certain Weed Species

                                 HERBICIDE
                                                        2,4-D +
                                                        MECOPROP +
WEED                   2,4-D     MECOPROP   DICAMBA      DICAMBA

Common chickweed        R *         I          S            S
Black medic              R          I          S            S
Purslane                 I          R          S            S
Red sorrel               I          R          S            S
Broadleaf plantain       S          I          R            S
Buckhorn plantain        S          I          R            S
Knotweed                 R          I          S            S
Spurweed                 I          S          I            S
White clover             I          S          S            S
Field pennycress         S          I          S            S

* R = resistant; S = susceptible; I = intermediate
susceptibility--applications may have to be repeated
for satisfactory control.

Figure 14-7
Approximate number of seeds produced by single
plants of certain weed species.

                                                            SEEDS
COMMON NAME                      SCIENTIFIC NAME          PER PLANT

Annual bluegrass                 Poa annua                  2,000
Barnyardgrass                    Echinochloa crusgalli      7,000
Common chickweed                 Stellaria media           15,000
Curly dock                       Rumex crispus             30,000
Dandelion                        Taraxacum officinale      12,000
Green foxtail                    Setaria viridis           34,000
Knotweed                         Polygonum aviculare        6,500
Broadleaf plantain               Plantago major            36,000
Veronica or purslane speedwell   Veronica peregrina         2,900

Figure 14-10
Examples of annual grasses, perennial grasses, and broadleaf
plants found as weeds in turfgrass.

ANNUAL                  PERENNIAL
GRASSES                 GRASSES

Annual bluegrass        Bentgrass
Barnyardgrass           Bermudagrass
Hairy crabgrass         Dallisgrass
Smooth crabgrass        Tall fescue
Green foxtail           Johnsongrass
Yellow foxtail          Kikuyugrass
Goosegrass              Knotgrass
Fall panicum            Nimblewill
Rescuegrass             Purple nutsedge *
Sandbur                 Yellow nutsedge *
Six-weeks fescue        Quackgrass
                        Smutgrass
                        Torpedograss
                        Velvetgrass

BROADLEAF WEEDS

Creeping beggarweed     Wild garlic           Pigweed
Field bindweed          Hawkweed              Pineappleweed
Bittercress             Healall               Broadleaf plantain
Burdock                 Henbit                Buckhorn plantain
Creeping buttercup      Ground ivy            Common purslane
Carpetweed              Knapweed              Shepherdspurse
Wild carrot             Knotweed              Red sorrel
Common chickweed        Lambsquarters         Speedwells (spp.
                                                Veronica)
Mouse-ear chickweed     Lespedeza             Prostrate spurge
Chicory                 Mallow                Spotted spurge
Cinquefoil              Black medic           Spurweed
Hop clover              Mugwort               Wild strawberry
White clover            Wild mustard          Thistles
Cranesbill              Wild onion            Prostrate vervain
English daisy           Birdseye pearlwort    Wild violet
Oxeye daisy             Field pennycress      Yellow woodsorrel
Dandelion               Pennywort             Common yarrow
Dichondra               Parsley piert         Yellow rocket
Curly dock

* Actually a sedge, not a true grass.

Figure 14-11
Characteristics of commonly used herbicides. Read the pesticide
label to obtain more complete information.

                                                TIME OF APPLICATION
                                                PR = PREEMERGENCE
COMMON NAME              TRADE NAME             PO = POSTEMERGENCE

Asulam                   Asulox                 PO
Atrazine                 Atrazine               PR, PO
Benefin                  Balan                  PR
Bensulide                Betasan,               PR
                           Bensumec,
                           Pre-San,
                           Weedgrass
                           Preventer
Bentazon                 Basagran,              PO
                           Lescogran
Bispyribac-sodium        Velocity               PO
Bromoxynil               Buctril                PO
Carfentrazone            Quicksilver            PO
Chlorsulfuron            TFC                    PO
Clethodim                Envoy                  PO
Clopyralid               Lontrel T&O            PO
Corn gluten              Dynaweed               PR
2,4-D                    Many                   PO
DCPA                     Dacthal                PR
Dicamba                  Banvel, Vanquish,      PO
                           K-O-G Weed Control
Diclofop                 Illoxan                PO
Diquat                   Reward                 PO
Dithiopyr                Dimension              PR, PO
Ethofumesate             Prograss               PR, PO
Fenoxaprop               Acclaim Extra          PO
Fluazifop-P-buty         Fusilade               PO
Fluroxypyr               Spotlight              PO
Foramsulfuron            Revolver               PO
Glufosinate-ammonium     Finale                 PO
Glyphosate               Roundup                PO
Halosulfuron             Manage                 PO
Imazaquin                Image                  PR, PO
Isoxaben                 Gallery                PR
MCPA                     MCPA                   PO
Mecoprop                 MCPP and               PO
                           several others
Metolachlor              Pennant                PR
Metribuzin               Sencor                 PO
Metsulfuron methyl       Manor, Blade           PO
Napropamide              Devrinol               PR
Organic arsenicals       Several                PO
  (DSMA, MSMA, etc.)
Oryzalin                 Surflan                PR
Oxadiazon                Ronstar                PR
Pelargonic acid          Scythe                 PO
Pendimethalin            PRE-M,                 PR
                           Weedgrass
                           Control, Pendulum
Prodiamine               Barricade              PR
Pronamide                Kerb                   PR, PO
Quinchlorac              Drive                  PO
Rimsulfuron              TranXit                PO
Sethoxydim               Vantage                PO
Siduron                  Tupersan               PR
Simazine                 Princep                PR, PO
Sulfosulfuron            Certainty              PR, PO
Triclopyr                Turflon                PO
Trifloxysulfuron         Monument               PO
  sodium
Xanthomonas              XPO                    PO
  campestris
Some Combinations
Benefin and              Team                   PR
  trifluralin
2,4-D and dichlorprop    Super Trimec           PO
  and dicamba
2,4-D and MCPP           Many                   PO
  and dicamba
2,4-D and triclopyr      Turflon II             PO
MCPA and MCPP            Triamine II            PO
  and dichlorprop
Oxadiazon and            Goosegrass/            PR
  bensulide                Crabgrass Control
Triclopyr and            Confront               PO
  clopyralid

                         TYPE OF WEED CONTROLLED
COMMON NAME              AND OTHER COMMENTS

Asulam                   Primarily used to control annual grasses in
                           St. Augustinegrass turf
Atrazine                 Annual grasses and broadleaf weeds in
                           St. Augustinegrass, centipedegrass, and
                           zoysiagrass
Benefin                  Annual grasses
Bensulide                Annual grasses
Bentazon                 Nutsedge
Bispyribac-sodium        Annual bluegrass, rough bluegrass, and some
                           broadleaf weeds in creeping bentgrass and
                           perennial ryegrass turf
Bromoxynil               Broadleaf weeds
Carfentrazone            Broadleaf weeds and silvery thread moss
Chlorsulfuron            Primarily used for tall fescue control
Clethodim                Annual and perennial grasses in
                           centipedegrass
Clopyralid               Broadleaf weeds
Corn gluten              Annual grasses
2,4-D                    Broadleaf weeds
DCPA                     Annual grasses; also postemergence for
                           speedwell (veronica)
Dicamba                  Broadleaf weeds
Diclofop                 Goosegrass control in bermudagrass
Diquat                   Annual weed control in dormant bermudagrass
Dithiopyr                Preemergent for annual grasses with some
                           postemergent activity if applied before
                           grass has tillered
Ethofumesate             Annual bluegrass, primarily as a postemergent
Fenoxaprop               Annual grasses
Fluazifop-P-buty         Primarily annual grasses in zoysiagrass
Fluroxypyr               Broadleaf weeds
Foramsulfuron            Annual and perennial grasses in
                           bermudagrass and zoysiagrass
Glufosinate-ammonium     Nonselective
Glyphosate               Nonselective, kills all types of plants
                           including perennial grasses
Halosulfuron             Nutsedge
Imazaquin                Some grasses, sedges, and broadleaf weeds
                           in warm season turf
Isoxaben                 Preemergence control of some broadleaf
                           weeds, limited control of annual grasses
MCPA                     Broadleaf weeds
Mecoprop                 Broadleaf weeds
Metolachlor              Some annual grasses and sedges in warm
                           season turf
Metribuzin               Annual grasses and broadleaf weeds in
                           bermudagrass
Metsulfuron methyl       Bahiagrass and some broadleaf weeds in
                           warm season turf
Napropamide              Annual grasses in warm season turf
Organic arsenicals       Annual grasses
  (DSMA, MSMA, etc.)
Oryzalin                 Annual grasses in warm season turf
Oxadiazon                Annual grasses
Pelargonic acid          Nonselective soap product
Pendimethalin            Annual grasses
Prodiamine               Annual grasses and annual broadleaf weeds
Pronamide                Primarily annual bluegrass in bermudagrass
Quinchlorac              Annual grasses and broadleaf weeds
Rimsulfuron              Broadleaf weeds in bermudagrass,
                           centipedegrass, and zoysiagrass
Sethoxydim               Annual and perennial grasses in
                           centipedegrass
Siduron                  Annual grasses in seedbeds
Simazine                 Annual grasses and broadleaf weeds in St.
                           Augustinegrass, centipedegrass,
                           zoysiagrass, and some bermudagrass
                           cultivars
Sulfosulfuron            Sedges and certain annual and perennial
                           grasses and broadleaf weeds in warm
                           season turf
Triclopyr                Broadleaf weeds
Trifloxysulfuron         Sedges and some annual and perennial grasses
  sodium                   and broadleaf weeds in bermudagrass and
                           zoysiagrass
Xanthomonas              Annual bluegrass
  campestris
Some Combinations
Benefin and              Annual grasses
  trifluralin
2,4-D and dichlorprop    Broadleaf weeds
  and dicamba
2,4-D and MCPP           Broadleaf weeds
  and dicamba
2,4-D and triclopyr      Broadleaf weeds
MCPA and MCPP            Broadleaf weeds
  and dichlorprop
Oxadiazon and            Annual grasses
  bensulide
Triclopyr and            Broadleaf weeds
  clopyralid
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Author:Emmons, Robert D.
Publication:Turfgrass Science and Management, 4th ed.
Date:Jan 1, 2008
Words:6055
Previous Article:Chapter 13 Pesticides.
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