Bermudagrass vs. Armyworm | Yorick alert!

Bermudagrass vs. Armyworm |  Yorick alert!

Photo: Fall armyworm feeding on bermudagrass clippings.
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Credit: Gurjeet Singh

TIFTON, GA: A study conducted at the University of Georgia sought to determine the level of host plant resistance that could be ensured by several promising experimental bermudagrass genotypes against potential damage by fall armyworm.
Researchers Gurjit Singh, Shimat Joseph, and Brian Schwartz evaluated 14 different new bermudagrass species to determine their comparative levels of host resistance in the laboratory, and published their findings in the article “Screening Newly Developed Bermudagrasses for Host Plant Resistance to Fall Armyworm (Lepidoptera: Noctuidae )” in Hortscience.
Fall armyworm (Spodoptera frugiperda) is particularly devastating to warm-season turfgrass species, including Bermuda grass, a widespread grass grass often used on golf courses, sports fields and ornamental landscapes across the country and around the world. Infestations with Spodoptera frugiperda are often sporadic; However, when this happens, the damage can be severe.
“Research on genetic resistance to FAW in bermudagrass has been ongoing for more than half a century at Tifton,” Schwartz notes. “It will certainly take a focused, collaborative effort for many more years if we are to make an impact for turf managers in the future.”
In Georgia alone, the turfgrass industry is worth $7.8 billion. From July to late November, landscape maintenance companies and homeowners often use environmentally unsound pesticides to protect residential and public lawns in urban and suburban areas. Golf courses and turf farms typically use an abundance of insecticides such as bifenthrin to maintain large swaths of turf to protect against fall armyworm.
Resistance of host plants against Spodoptera frugiperda can be a valuable tool to reduce or prevent the use of these insecticides.

“The Bermudagrass Fall Armyworm is an interesting system to work on but requires careful handling of the first and second instar larvae during feeding and taking necessary measurements for larval survival and development,” Singh adds. “More attention was paid to avoiding larval death due to manual handling, which ultimately helped.” To get a better picture of the results.”
The early larval stages of fall armyworm usually go undetected because they remain hidden within the grass canopy during the day until the larvae reach the fourth or fifth instar. Young larvae feed on grass blades, while late instar larvae feed on stems and grass blades. Severely affected grass appears brown because most of the grass blades have been consumed. Compared to young instars, late instar larvae are more tolerant to insecticides.
Turf breeding programs have always focused on improving aesthetic characteristics and tolerance to abiotic factors, such as drought and foot traffic. Because insecticide resistance and off-target effects of insecticide applications pose serious concerns for the turfgrass industry, alternative control options have recently been emphasized.
Because there are no known Spodoptera frugiperda-resistant bermudagrass varieties available in the turf industry, researchers tested 14 promising experimental bermudagrass genotypes for resistance to fall armyworm damage and compared their performance to that of the emerging standard bermudagrass “TifTuf.” . These experimental genotypes are considered “elite” because of their superior turf quality, drought tolerance, shade tolerance, rapid growth, and resistance to foot traffic during multiple years of field testing.
For the study, all turfgrass genotypes were maintained in a greenhouse at the University of Georgia, Griffin Campus. The bermudagrass cultivar 'TifTuf' was used as a control for susceptibility, and bermudagrass 'Zeon' was used as a control for its resistance to fall armyworm.
The experiment was conducted by adding armyworm treatments to each isolated Bermudagrass variety. Larval survival and development were recorded at 2-day intervals. To document larval development, larval length from head to abdominal tip, head capsule width, and larval weight were recorded.
To determine the performance of bermudagrass relative to controls, survival, development, and overall susceptibility indices were developed. A standard has been developed to compare the performance of Bermuda grass with the commercial standard “TifTuf”. Fulfillment of the criterion is “high” if the genotype proves to be more resistant than the commercial standard, “comparable” if it proves similar, and “low” if it fails by comparison.
Researchers identified a few new Bermuda grasses that were similar to the industry standard “TifTuf” in terms of susceptibility to armyworm infestation. Some genotypes were less susceptible to neonates, while other bermudagrasses showed reduced growth rates, which may expose larvae to extreme weather and predation. The results also demonstrated that resistance or susceptibility screening can be achieved by evaluating pupal parameters, which will be particularly useful when breeders are screening armyworm resistance or susceptibility using several genotypes simultaneously.
Although this study identifies a few promising experimental genotypes, further studies are warranted to understand the consistency of their performance under field conditions because host plant resistance remains a desirable goal in managing fall armyworms in turfgrass.
“Turf producers, golf course superintendents, and homeowners have spent a significant amount of money managing fall armyworm,” notes Joseph. “Toward developing fall armyworm-resistant bermudagrass, this study is an important first step,” he continues.

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The full article is available on ASHS Hortscience Electronic journal website: https://doi.org/10.21273/HORTSCI15293-20. Or you can contact Brian Schwartz of the University of Georgia at tifturf@uga.edu or call him at (229) 386-3272.
Founded in 1903, the American Society of Horticultural Science (ASHS) is the largest organization dedicated to advancing all aspects of horticultural research, education and application. More information at Ashs.org.


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