Trouble with goosegrass control

By |  July 25, 2019 0 Comments
Goosegrass (Photo: Jim Brosnan, Ph.D.)

Goosegrass (Eleusine indica) infesting cleanup passes on a creeping bentgrass (Agrostis stolonifera) putting green. (Photo: Jim Brosnan, Ph.D.)

Goosegrass (Eleusine indica) is a problematic annual grassy weed found on golf course turf across the United States in summer. This species germinates from seed each spring, with emergence typically occurring several weeks after superintendents begin to see summer annual weeds such as crabgrass (Digitaria spp.) and prostrate knotweed (Polygonum aviculare).

Often termed an indicator weed for its ability to thrive in compacted soils, goosegrass most commonly is found in highly trafficked areas on golf courses such as cart paths, entry/exit areas from teeing/greens complexes, collars and putting surfaces (Figure 1).

Preemergence herbicides are a principal means of controlling goosegrass. Herbicides including oxadiazon (e.g., Ronstar), indaziflam (e.g., Specticle Flo), prodiamine (e.g., Barricade), dithiopyr (e.g., Dimension) and pendimethalin (e.g., Pendulum AquaCap) are labeled for goosegrass control in warm-season and/or cool-season turfgrass. Superintendents also can find combination products containing these active ingredients in mixture with one another or other herbicides.

For example, superintendents use a mixture of bensulide plus oxadiazon (e.g., Anderson’s Crab/Goose Preventer) for goosegrass control on creeping bentgrass (Agrostis stolonifera) putting surfaces in the Southeast. Superintendents typically apply reemergence herbicides for goosegrass control in sequential application regimes; the first application is timed to combat crabgrass emergence, with the sequential application positioned to target goosegrass.

Seedling goosegrass (Eleusine indica) emerging in late spring. (Photo: Jim Brosnan, Ph.D.)

Seedling goosegrass (Eleusine indica) emerging in late spring. (Photo: Jim Brosnan, Ph.D.)

Superintendents electing to control goosegrass with postemergence herbicides have a small group of herbicides from which to choose. Warm-season turfgrass options include the acetolactate synthase (ALS) inhibitors (foramsulfuron [i.e., Revolver], thiencarbazone-methyl plus foramsulfuron plus halosulfuron [i.e., Tribute Total]), metribuzin (i.e., Sencor), MSMA, 2,4-D plus MCPP plus dicamba (i.e., SpeedZone), as well as spot applications of topramezone (i.e., Pylex). In cool-season turfgrass, superintendents can make broadcast applications of Pylex, as well as SpeedZone, and fenoxaprop (i.e., Acclaim Extra). None of these options are labeled for use on putting greens, and many can induce transient turfgrass injury even when applied under optimal conditions.

The problem

Many golf course superintendents have reported that goosegrass control has become more challenging in recent years. Reasons for this turn of events are not clear, but several factors likely are involved.

Species adaptations

Weed species adaptation has shifted over the past several years, with warm-season weed species infesting golf course turf in more northern geographies. For example, doveweed (Murdannia nudiflora), once confined to the Gulf Coast, has become a problematic turfgrass weed as far north as central Tennessee. Green kyllinga (Kyllinga brevifolia) and false-green kyllinga (Kyllinga gracillima) are now problematic throughout the mid-Atlantic, north-central and northeast regions of the United States, as well. Once confined to more southern regions of the United States, goosegrass has become a common problem in states as far north as New Jersey and Pennsylvania, challenging superintendents with a new weed-control hurdle.

Mature goosegrass (Eleusine indica) in late summer. (Photo: Jim Brosnan, Ph.D.)

Mature goosegrass (Eleusine indica) in late summer. (Photo: Jim Brosnan, Ph.D.)

Loss of active ingredients

In the southern United States, two herbicides available to superintendents for postemergence goosegrass control have become limited. Diclofop (e.g., Illoxan) was once an effective option for postemergence goosegrass control in bermudagrass (Cynodon spp.) but is no longer sold commercially. Additionally, MSMA has activity on goosegrass, but in most states it can be applied only as a spot treatment to limited acreage. Use of MSMA in Florida is prohibited as of this writing.

Resistant biotypes

Cases of goosegrass evolving resistance to pre- and/or postemergence herbicides have become more common in recent years. While conversations about herbicide resistance often center on annual bluegrass (Poa annua), goosegrass is by no means immune to the problem. There are confirmed instances of goosegrass evolving resistance to mitotic inhibiting herbicides such as prodiamine (e.g., Barricade) and pendimethalin (e.g., Pendulum AquaCap), as well as oxadiazon (e.g., Ronstar), an inhibitor of protoporphyrinogen oxidase. Additionally, goosegrass has evolved resistance to the postemergence herbicide metribuzin (e.g., Sencor), and there are reports of populations evolving resistance to foramsulfuron (e.g., Revolver) as well. The development of herbicide resistance further limits the number of herbicides available to control goosegrass on a golf course.

Plan of action

What can superintendents do to combat the goosegrass issue? The answer to this question is not simple and will require diverse tactics.

Effect of volumetric soil moisture content (VMC) on goosegrass control 28 days after treatment with Tribute Total at 3.2 oz/A in a greenhouse with surfactant. (Photo: Jim Brosnan, Ph.D.)

Effect of volumetric soil moisture content (VMC) on goosegrass control 28 days after treatment with Tribute Total at 3.2 oz/A in a greenhouse with surfactant. (Photo: Jim Brosnan, Ph.D.)

1) Identify the root cause of the issue. It is important to remember that goosegrass is an indicator weed. The presence of goosegrass should be a signal that soil conditions need to be improved to support the growth of healthy turfgrass. Doing so will allow turf to be more competitive against goosegrass infestation. Research conducted at the University of Florida demonstrated that the lack of bermudagrass cover on trafficked tee complexes was more of a factor in goosegrass infestation than soil compaction. Take time to improve the growing environment, but also to identify the causes of its deterioration. Can course traffic patterns be altered? Does turf receive enough light to grow optimally? Far too often, the immediate action once goosegrass is present is to chemically remove plants with an herbicide. That process does not address the root cause of the issue, and goosegrass is then a continual problem.

2) Scouting for timely applications. As a rule, weeds are easier to control when they are smaller in size. This is certainly true in the case of goosegrass. Scouting problematic areas of the golf course for goosegrass plants can facilitate applying postemergence herbicides when plants are most vulnerable (Figure 2). It is difficult to control large, multitiller goosegrass (Figure 3) with a single herbicide application.

Recent research conducted at the University of Tennessee highlighted that soil moisture can affect the efficacy of many postemergence herbicides labeled for goosegrass control. For example, my team reported only 20-percent control of goosegrass when we applied Tribute Total to plants acclimated to soils of less than 12-percent moisture content, compared with 95-percent control when the application was made to goosegrass growing in soils with a moisture content of 12 percent to 20 percent (Figure 4). Although we still have more to learn about this response (follow-up research is being conducted in 2019), superintendents should avoid making applications to plants that have been acclimated to dry soils for extended periods in order to maximize product effectiveness.

While scouting can help maximize effectiveness of postemergence herbicides, timing is a critical component in maximizing effectiveness of preemergence herbicides as well. Rutgers University has conducted elegant research the last two seasons to better understand environmental factors that trigger goosegrass germination in soil. The researchers aim to use their findings to develop a model that superintendents can use to optimally time preemergence herbicide applications for goosegrass control.

Bleaching of bermudagrass (Cynodon spp.) following applications of topramezone to control herbicide-resistant goosegrass (Eleusine indica). (Photo: Jim Brosnan, Ph.D.)

Bleaching of bermudagrass (Cynodon spp.) following applications of topramezone to control herbicide-resistant goosegrass (Eleusine indica). (Photo: Jim Brosnan, Ph.D.)

3) Managing potential resistance. Continually applying the same treatment for goosegrass control ultimately will select for resistant biotypes on the golf course. Resistance creates many challenges for superintendents. It reduces the number of herbicide options available for goosegrass control and often increases the overall cost of management. For example, researchers confirmed the presence of dinitronaniline-resistant goosegrass in Georgia following continued use of prodiamine (e.g., Barricade) and showed that superintendents could use oxadiazon (e.g., Ronstar) and indaziflam (e.g., Specticle Flo) as alternative preemergence options. However, most superintendents would find the cost of these alternatives to be greater than prodiamine.

Additionally, resistance can force superintendents to use herbicides that may induce temporary injury to desirable turfgrasses. In Tennessee, my team documented the presence of dinitroaniline-resistant goosegrass on golf courses and reported that topramezone (e.g., Pylex) could be used as an option for postemergence removal. However, these applications injured bermudagrass in research plots 34 percent to 60 percent for two weeks after treatment, with recovery not occurring for over a month. When applying over large acreage, the results may be objectionable to many (Figure 5). Similar issues with transient turfgrass injury can accompany summer applications of MSMA and metribuzin (e.g., Sencor) for goosegrass control in warm-season turfgrass as well.

To that end, it’s critically important that golf course superintendents diversify herbicides applied for goosegrass control. Have you used the same preemergence option for several years in a row? Change to something new this season, even if only on select holes of the course. Have you applied the same postemergence herbicide for several seasons to remove escapes? Consider a new mode of action this season, or even treating with a mixture of different products. Data clearly show that rotating or mixing herbicidal modes of action will reduce selection pressure for resistant weeds in a diversity of agricultural settings, including turf.

Goosegrass control is a challenging endeavor that has become more complicated in recent years. Superintendents will need their entire agronomic skill set to manage populations of this summer annual weed.

Jim Brosnan, Ph.D., is a turfgrass weed scientist at the University of Tennessee. You may reach Jim at jbrosnan@utk.edu for more information.



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