Biology and status of herbicide resistant goosegrass and its control options in Alabama

Introduction

Goosegrass (Eleusine indica), also known as silver crabgrass, white crabgrass, bullgrass or wiregrass, is a problematic annual grassy weed present across the agroclimatic regions in the U.S., particularly in the southeastern and mid-south (Holm et al.). It is ranked among the top five most troublesome weeds globally, causing 25-90% (Ma et al.; Lourens et al.) yield loss in both annual and perennial crops, as well as specialty crop and non-crop areas in the U.S. Goosegrass is a widely adapted weed believed to have originated in South or East Asia (Holm et al.), and currently reported as a serious weed in 46 different crops across 60 countries (Holm et al.). It is a difficult to control weed in turfgrass and rice and in the past decades, goosegrass has become one of the most troublesome weeds in the southeastern U.S. peanut, cotton, and soybean fields. This species is known for its high growth rate and rapid adaptability to new areas and production practices, making it a persistent problem for farmers. The management of goosegrass is further complicated by its ability to develop resistance to commonly used herbicides and its identification resemblance with few grassy weeds such as crabgrass. This article aims to provide an overview of the identification keys and the current status of herbicide-resistant goosegrass in Alabama and discuss potential control options.

Biology and Life Cycle

The unique biology of goosegrass contributes to its success as a weed. Goosegrass germinate in the spring and grow rapidly throughout the summer, mature in late summer, and produce seeds in autumn. The seeds are dormant when freshly matured, and germination is promoted by factors such as fluctuating temperatures, light, nitrate, chilling, scarification, and aging. Goosegrass can flower as soon as 30 days after germination under favorable conditions. The plants begin to sprout when soil temperature exceeds 65°F and can grow as short as 4 inches to as tall as 3 feet in height. Favorable traits like a wide emergence window throughout the crop growing season, deep root system, rapid tiller development and adaptability to various conditions allow this plant to thrive in different environments. Its high fecundity - producing up to 140,000 seeds/plant (Chin; Chauhan and Johnson) with longer persistence - some seeds surviving for 9-10 years in the soil (Schwerzel and Thomas), combined with multiple dispersal methods, makes it a highly aggressive and serious weed worldwide. Additionally, goosegrass serves as a secondary host for diseases, nematodes, and viruses affecting crops like peanut, corn, sugarcane, and rice. The species forms dense and pure stands, smothering out the low-growing crops like peanut, leading to poor crop stand and reduced yield (up to 25% in groundnut, 50% in cotton, and 90% in rice) (Ma et al.; Lourens et al.). Although it is a self-pollinating species, reported possibility of cross-pollination and wide diversity in the adaptive/weedy traits make the species more robust, promotes herbicide resistance proliferation in the cotton and peanut fields in Alabama and neighboring states (Fig. 1).

Figure 1.Goosegrass in cotton and peanut fields in Alabama (Credit: David Russell)

Identification

Goosegrass is identifiable by several unique characteristics. It has medium to dark green leaf blades that are ¼ to ½ inch wide and 2 to 10 inches long, with a prominent midvein and sparse hairs at the base (Fig. 2a). The plant features a short, jagged ligule that is divided in the center, and lacks auricles. The stems of goosegrass grow outward from a single growing point in a rosette pattern (Fig. 2b), typically lying flat against the soil surface. As the plant matures, the stems take on a silver or white appearance (Fig. 2b), earning it the nickname “silver crabgrass”. The seedheads consist of 2 to 7 spikes that radiate from a central stem, with each spike having two rows of spikelets arranged on either side, resembling a zipper (Fig. 2b).

Figure 2.Goosegrass plant and seedhead (Credit: Akashdeep Singh)

The seeds are 1 to 2 millimeters in length, elliptical, and with pointed or rounded tips. Key identifiers for goosegrass include the membranous and jagged ligule, absence of auricles, long sparse hairs at the base of the leaf blade, flattened white or silver stem bases, and the distinctive zipper-like arrangement of spikelets on individual spikes radiating from a central flower stem.

Herbicide Resistance in Goosegrass

Intensive herbicide use on goosegrass has led to the evolution of herbicide resistance in this species. The first-ever case of goosegrass herbicide resistance to dinitroaniline herbicides was first identified in a cotton field in South Carolina in 1984 (Mudge et al.). Over time, goosegrass has shown resistance to seven herbicide modes of action in agricultural fields (Heap) including Acetyl-CoA-carboxylase inhibitors (Leach et al.; Osuna et al.), the acetolactate synthase (ALS)-inhibitors (Valverde et al.), microtubule inhibitors (Zeng and Baird), glyphosate (Lee and Ngim), bipyrilidium (Buker et al.), PPO inhibitors (McElroy et al.). Moreover, goosegrass was the first species to have two target-site mechanisms in the same population that additionally confirs resistannce to glyphosate (Nunes et al.).

Herbicide Resistant Goosegrass in Alabama

Alabama growers, particularly those dealing with cotton and peanuts, are increasingly facing a potentially significant threat of herbicide-resistant weeds. In a recent study (McElroy et al., (2021) (Mcelroy et al.), paraquat resistance was detected in a population of goosegrass in a central Alabama vegetable field. Paraquat has been a cornerstone of weed control in vegetable production due to its effectiveness and broad-spectrum activity. However, the emergence of paraquat-resistant goosegrass populations threatens the sustainability of current weed management practices and necessitates the development of alternative strategies. Recently, goosegrass has survived through multiple herbicides, including acetochlor (PRE), glyphosate + dicamba (POST), glyphosate alone (POST), and clethodim alone (POST) in Alabama Peanut fields (Fig. 1).

Figure 3.Goosegrass accessions found resistant to labeled rates of herbicides tested.

Some goosegrass populations have shown more than 50-fold resistance to dithiopyr, prodiamine, pendimethalin, and oryzalin (Russell et al.). Also, it was confirmed that goosegrass plants collected from different parts of Alabama showed resistance to a few common herbicides including foramsulfuron and sulfentrazone (unpublished) (Fig. 3). In a preliminary study, goosegrass populations collected from the southeastern region of Alabama were shown to be potentially resistant to PPO herbicides (clethodim and fluazifop) as they have survived field rate application of these herbicides (Fig. 4).

Figure 4.Goosegrass populations collected from Dothan, AL after herbicide application (Credit: Esra Karaca)

The development of herbicide resistance in goosegrass is a growing concern in Alabama and other agricultural regions worldwide. With multiple herbicide options failing, developing effective management strategies for these resistant goosegrass populations is crucial to protecting crop yields and economic returns for Alabama farmers.

Control Options

Managing herbicide-resistant goosegrass requires a diversified approach that combines chemical and non-chemical control methods. To effectively manage goosegrass, similar to Palmer amaranth and other troublesome weeds, the aim should be preventative, thus, start with a clean field, free of goosegrass.

Cultural Management: For effective goosegrass control in container production, early physical removal is key. In field situations, ff left to grow, removal becomes challenging. Disking or tilling is effective, but mowing is not due to its prostrate growth habit. The use of cover crops has been shown to suppress the growth of goosegrass through allelopathic effects, which inhibit its germination and growth. Additionally, integrating cover crops into crop rotation systems can enhance soil health and reduce weed pressure by promoting biodiversity in the agroecosystem. The strategic use of crop residues can also influence the emergence and growth of goosegrass, as they can act as physical barriers to weed seed germination. By utilizing practices such as cover cropping, crop rotation, optimized tillage, and irrigation management, farmers can create an environment that is less conducive to goosegrass establishment and growth.

Mechanical Management: The centralized root system of goosegrass simplifies its mechanical removal compared to many other weeds. Small plants can be manually uprooted, but for plants that have grown to a diameter of 2-3 inches, a knife or gardening tool is beneficial. Tools such as the Weed Hound™ are effective in removing plants with a central taproot like goosegrass. If time permits and the area is not heavily infested, manual, or mechanical removal can be an effective strategy. Regular tillage can disrupt the life cycle of goosegrass by uprooting plants and preventing seed set, thereby reducing its population over time. However, the effectiveness of mechanical control can be influenced by the timing and frequency of tillage operations, as well as the specific growth stage of the goosegrass.

Chemical control: Preemergence herbicides can effectively control goosegrass. However, due to resistance issues, it’s crucial to rotate herbicides wisely. Despite the limited herbicide options for selective Goosegrass management, some can still offer effective control.

Conclusion

The emergence and increasing geographic distribution of herbicide-resistant goosegrass in Alabama is a pressing issue that requires immediate attention from researchers, extension agents, and growers. Developing effective and sustainable control strategies for this resilient weed is a complex task that requires a deep understanding of its biology, the dynamics of herbicide resistance, and the specific conditions of the production system. As our knowledge in these areas continues to grow, so will our ability to manage herbicide-resistant goosegrass effectively. Effective management of goosegrass requires an integrated approach that takes into account its biological characteristics and the specific conditions of the production system. In conclusion, to develop more nature-friendly and effective control methods in Alabama, resistance studies on goose grass are insufficient and more studies are needed. Including alternative solutions rather than just focusing on resistance detection will help open new horizons in the fight against goosegrass.

Take Home Message

• Goosegrass is an important problematic weed that has spread all over the world.

• Goosegrass is not only a problem in crop fields but also in lawn and turf systems.

• Goosegrass has developed resistance to several commonly used herbicides with different modes of action.

• New goosegrass control strategies are needed and integrated weed management solutions are critical.