Bermudagrass roadblocks

The author is an extension forage specialist with the University of Georgia who is based in Tifton.

Bermudagrass is one of the primary perennial forages produced in the Southeast, covering approximately 3 million acres in Georgia alone. Although bermudagrass is used for livestock around the world, intensive management in hayfields and pastures is largely exclusive to the United States. Much of the scientific breeding of bermudagrass has historically occurred in Tifton, Ga., and the surrounding region.

There have been extensive improvements to bermudagrass genetics since the 1930s, including higher production, leaf spot resistance, and better digestibility. Overall, newer hybrid cultivars are recognized for their superior yield and nutritive value compared to common ecotypes and older hybrids.

Despite these improvements, though, there are many challenges that continue to impact the future of bermudagrass. The following are challenges with regard to emerging research and possible solutions to ensure bermudagrass production continues to prosper in the Southeast.

Stem maggots, slow growth

The bermudagrass stem maggot (BSM) has severely damaged stands since it was discovered in the Southeast in 2010. Larval feeding extending outward from the terminal node of the plant can kill the top two to three leaves on the stem, stopping growth of the damaged tillers and potentially reducing the number of tillers on the plant. Damage is most severe in late July to September when the region observes its warmest temperatures of the year.

Strategically timed pyrethroid applications can minimize adult BSM populations; however, a long-term solution would require the development and release of BSM-tolerant bermudagrass genotypes. Previous research has shown that varieties like Tifton 85 and Coastcross II have up to 50% less BSM damage than finer-textured varieties.

Modern breeding efforts are focusing on the selection of more BSM-tolerant genotypes, but renovating fields to establish an improved bermudagrass cultivar can be expensive and time consuming. With that said, it is hypothesized that despite the renovation costs, new cultivars will be more cost-effective over time because of lower chemical and application costs associated with the BSM.

In addition to BSM, a rising number of bermudagrass producers note challenges with green up following winter dormancy. This may be attributed to plant disease, unbalanced soil fertility, and encroaching weeds. It is likely that these factors are interacting over time to cause compounding challenges and leading to stand decline.

The number of reports has steadily increased since 2020, which was an above-average rainfall year for much of the Southeast. Excess rain delayed harvests throughout the season and wet conditions increased the presence of the pathogen that causes leaf spot. Extensive damage occurred in many fields when the pathogen attacked the stolons and rhizomes, causing fields to brown and begin thinning out. Certain cultivars, such as Alicia, were more prone to disease than others.

As fertilizer prices continued to climb in 2021 and 2022, many producers removed one or more nutrients from their annual fertilizer plan and applied only nitrogen to bermudagrass pastures or hayfields. While nitrogen fertilization is important for improving forage yields, potassium is critical for disease resistance, root development, cold stress, and overall plant health.

Potassium-stressed bermudagrass is vulnerable to early yield decline because of the thinning canopy cover. Thinning may be exacerbated by unseasonably warm winters followed by late freezes. Therefore, fall applications of potassium are crucial for successful overwintering of the stands.

When poor stand persistence is coupled with BSM damage, it is not surprising that many producers are seeing invasive weed species move into their bermudagrass pastures and hayfields. The most prevalent species are perennial grass weeds like smutgrass, vaseygrass, knotroot foxtail, and herbicide-resistant annual ryegrass.

There are no affordable and effective options for postemergent control of these perennial grass weeds in established bermudagrass within a single season. Current research shows multiple herbicide applications may be required for each of these weeds across multiple seasons. Herbicide-resistant annual ryegrass is also spreading in the region and is difficult to control with postemergent herbicides alone. Previously, pre-emergent options have been ineffective, but new products like indaziflam are showing promise.

The impact of slow bermudagrass green up on forage yield has not been directly addressed. Even so, factors including a timely harvest, sufficient stubble height, balanced fertilization, near-neutral soil pH, and insect and weed control are critical to protecting the longevity and production of a bermudagrass stand.

Sprigs and cold tolerance

Perhaps one of the most limiting factors affecting the expansion of improved bermudagrass, especially newly released varieties, is the deficit of sprigs and lack of trained personnel to plant them. Most sprigging involves planting vegetative propagules that contain tillers, rhizomes, stolons, and root portions; however, some cultivars may be established via stem cuttings or tops.

Dissemination of public releases of vegetatively propagated forages is mainly done through cooperative extension services and direct connections with stakeholders. However, breeding stock is extremely limited, and stakeholders may only receive limited planting material to start a small nursery on their own operation.

The viability of the vegetative planting material is the most important factor in establishment success of bermudagrass, and research is underway to address these concerns. Establishing new bermudagrass cultivars from tops will eliminate the need for specialized harvesting equipment as tops can be harvested with common machinery. This enhances establishment opportunities for producers, which will aid in dissemination of the new cultivars. Furthermore, it will benefit availability since harvesting tops does not disrupt the rhizomes or soil, so the nursery plants need less time to regrow before the next harvest event.

Climatologists have documented notable changes in temperature and precipitation patterns in the Southeast that have contributed to an expansion of warm-season species in its Northern region. In the transition zones between warm-season and cool-season perennial grass-dominated regions of North America, warm-season grasses can maintain productivity at higher temperatures while cool-season grasses put on minimal vegetative growth during summer.

For this reason, warm-season grasses could replace a portion of the grasslands in areas at greater than 35° latitude. Unfortunately, some bermudagrass pedigrees are less tolerant of cold temperatures and may not survive Northern environments. Ongoing research is identifying germplasm that meets the needs of farmers transitioning to warm-season production systems.

Despite the many challenges facing bermudagrass production in the Southeast, area researchers are working to ensure its persistence, productivity, and availability for the future. Development of improved cultivars and refined management is crucial to the continued success of bermudagrass in this region and beyond. These improvements are possible with the continued collaboration among bermudagrass breeding programs and forage agronomists. For more information, visit bit.ly/HFG-CIB.