Cutting edge: Celebration bermudagrass, herbicide resistance in poa annua

Work from the University of Florida/Ft. Lauderdale and Purdue University features in April's research rundown.


Celebration bermudagrass research

Combined effect of water quality and nitrogen sources on Celebration bermudagrass performance and nitrogen absorption

Decreasing availability of potable water for turfgrass irrigation, even in high-precipitation parts of the U.S., has led to the exploration of nonpotable water resources for golf irrigation. Reclaimed effluent water has been used as an alternative to potable water to irrigate golf courses. A study was conducted in a greenhouse during fall 2021 (November-December) and spring 2022 (April-May) at the University of Florida/Fort Lauderdale Research and Education Center to explore the interaction of water quality and nitrogen source on the performance and nitrogen assimilation of Celebration bermudagrass.

Nitrogen was applied at a rate of 1 pound nitrogen per 1,000 square feet (49 kilograms per hectare) at the beginning of the study using either water-soluble AMS (21% nitrogen, 0% phosphorous, 0% potassium) or a 65% controlled-release fertilizer (42-0-0) compared to a nonfertilized control. Turfgrass was watered twice per week with reclaimed effluent water (3.3 ppm nitrate-nitrogen) or potable water (0.01 ppm nitrate-nitrogen) at gravimetric water content. Turfgrass quality (scale 1-9) and Normalized Difference Vegetation Index (NDVI; scale 0.0-0.99) were assessed weekly.

Clipping samples were collected weekly and oven dried to determine dry weight and later analyzed for nitrogen content and total assimilated nitrogen (TAN). Turf watered with reclaimed effluent water had a higher nitrogen content and TAN. Fertilized grasses assimilated more nitrogen during spring compared to fall. A higher clipping yield (more biomass produced) during spring compared to fall resulted in no difference in leaves’ nitrogen content between seasons. Overall, reclaimed effluent water increased nitrogen content and had no detrimental effect on turfgrass quality nor NDVI. — I. Alejandra Sierra Augustinus (, Patrick McLoughlin, A. Fernanda Arévalo Alvarenga, Marco Schiavon, Ph.D., University of Florida, Fort Lauderdale

annual bluegrass test patches

Prevalence of ethofumesate-resistant annual bluegrass on U.S. golf courses

Annual bluegrass (Poa annua L.) is the most troublesome weed in turf. Herbicide options for annual bluegrass control on golf courses are limited, and repeated applications are often necessary. Annual bluegrass is a prolific seed producer, which allows for more rapid development of herbicide resistance. Ethofumesate-resistant annual bluegrass plants have already been documented in grass seed production in Oregon. Therefore, a dose-response experiment was initiated to determine the potential level of ethofumesate resistance in Poa annua L. on golf courses.

Seed from 28 populations was collected from golf courses in Alabama, California, Indiana and Oregon. Additionally, two populations, one with known resistance and one with known susceptibility, were identified in preliminary testing and used as controls in this experiment. Individual seedlings from each population were transplanted into separate conetainers, then grown in the greenhouse until they reached two to three tillers in size, immediately prior to herbicide application. Ten doses of ethofumesate were applied using a compressed air track spray chamber: 0, .01, .02, .06, .11, .17, .23, .34, .46 and .92 pounds active ingredient per 1,000 square feet (0, 0.56, 1.12, 2.8, 5.6, 8.4, 11.2, 16.8, 22.4 and 44.8 kilograms active ingredient per hectare), with .02 to .05 pounds per 1,000 square feet active ingredient (1.1 to 2.2 kilograms active ingredient per hectare) as the label application rates for perennial ryegrass.

Biomass of plants was collected 28 days after application. Populations with resistance-to-susceptible ratio from 1.01 to 5.33 were found on golf courses. The most resistant population was found in California with ED50 .26 pounds active ingredient per 1,000 square feet (12.74 kilograms active ingredient per hectare). The results show that annual bluegrass develops resistance to ethofumesate in managed turf and the need for practitioners to implement resistance-prevention measures. — Vera Vukovic ( and Aaron J. Patton, Ph.D., Purdue University, West Lafayette, Ind.

Darrell J. Pehr ( is GCM’s science editor.