Entomological Society of America | 4/22/2019 | Via ScienceDaily
A simple change in the choice of grass varieties for many lawns in the United States could be a key tool for fending off fall armyworm infestations, according to new research.
St. Augustinegrass (Stenotaphrum secundatum) is the most common turfgrass species in the southeastern United States, and it is typically planted with a single cultivar across an entire lawn. But multiple cultivated varieties, or cultivars, of St. Augustinegrass are commercially available, and landscape entomologists at the University of Florida and the U.S. Department of Agriculture recently sought to find out which, if any, of those cultivars offered natural resistance to the fall armyworm (Spodoptera frugiperda), a caterpillar that commonly damages lawns.
Their tests found that none of the six common St. Augustinegrass cultivars rose above the rest in resisting fall armyworm infestation. But, when the cultivars were planted together in mixtures of two or four cultivars, it was a different story. The fall armyworm clearly preferred the single-cultivar plantings.
“We were most surprised by how clear the effect of cultivar diversity was on fall armyworm host selection and feeding,” says Ethan Doherty, biological scientist at the University of Florida’s Indian River Research & Education Center and lead author on the study. “The insects had a consistent preference for the cultivar monoculture plantings, and we saw that the effect of cultivar diversity became increasingly more pronounced as diversity increased from two to four cultivars. We didn’t expect such a clear result.”
Doherty conducted the research as part of his master’s degree studies with advisor Adam Dale, Ph.D., assistant professor of turfgrass and ornamental entomology at UF, and Robert Meagher, Ph.D., research entomologist at the USDA-Agricultural Research Service’s Center for Medical, Agricultural, and Veterinary Entomology. Their report is published today in the journal Environmental Entomology.
To test the fall armyworms’ preference among single and multiple St. Augustinegrass cultivars, the researchers conducted a variety of tests. They fed groups of the caterpillars, or larvae, diets of single cultivars to compare the susceptibility of each cultivar to the insects. Then they fed the larvae mixed diets of grass clippings, one cultivar at a time but changing the cultivar every two days.
In another test, they placed the larvae in enclosed plantings of one, two, or four cultivars, allowing them to choose among the cultivars in the plantings. In these tests, the larvae were measured for qualities such as weight, development rate, and survival rate.In a pair of host-selection tests, the team built larger enclosures that each contained three different planting zones — one with a single cultivar, one with two, and one with four. Then they placed fall armyworm larvae or adults in the center of the enclosures and, for larvae, recorded the number that chose each option at various intervals over a period of three days and, for adults, recorded the number of egg masses laid in each planting after three days.
Find more information on the study.