Verdure: ‘Pre-haps’ you should think about that herbicide application?

Mississippi State researchers took a close look at how several commonly used pre-emergence herbicides specifically impact the roots of hybrid bermudagrass.


Pre-emergence herbicides generally have negative consequences on turfgrass rooting and growth from establishment. For hybrid bermudagrasses, which are sprigged or sodded, pre-emergence herbicides can affect rooting, but we don’t know how they affect that rooting — for example, items such as root architecture (the spatial arrangement of the roots) or the amount of carbohydrates within the roots.

So the folks at Mississippi State University decided to look at these rooting factors, studying the effects of commonly used pre-emergence herbicides on the root architecture and carbohydrate content of Latitude 36 hybrid bermudagrass.

In a repeated greenhouse study, Latitude 36 was plugged into the center of pots and maintained at a height of 1.5 inch (4 centimeters), with growth measured as the bermudagrass established. The following pre-emergence herbicides and rates (all rates shown in pounds a.i./acre; kilograms a.i./hectare are in parentheses) were sprayed, all as individual treatments to four replicate pots of bermudagrass: (1) untreated control; (2) prodiamine, 0.53 (0.59); (3) pendimethalin, 1.5 (1.68); (4) dithiopyr, 0.5 (0.56); (5) atrazine, 1 (1.12); (6) simazine, 2 (2.24); (7) atrazine + S-metolachlor, 1 + 0.77, (1.12 + 0.86); (8) oxadiazon, water-soluble powder, 2 (water-soluble powder, 2.24); (9) oxadiazon, granular, 2 (granular, 2.24); (10) flumioxazin, 0.26 (0.29); (11) S-metolachlor, 2.5 (2.80); and (12) indaziflam, 0.03 (0.03).

After all sprays were applied at 40 gallons/acre (374 liters/hectare), plants were allowed to dry for three hours, after which, 0.2 inch (5 millimeters) of irrigation was applied. Collected data were hybrid bermudagrass cover (weekly for 10 weeks), new root dry weight, length, surface area and diameter (at weeks 4, 6 and 10), and new root carbohydrate content (at 6 and 10 weeks).

Both runs of the experiment produced the same types of results (the experiment was conducted twice, from April to June 2016 and from July to September 2016). Only two pre-emergence products did not increase the time it took to achieve 50% bermudagrass cover: atrazine and the granular applied form of oxadiazon. Application of any other pre-emergence materials increased the time it took the bermudagrass to cover the pot (compared with the control), and coverage was especially slow when indaziflam or the liquid form of oxadiazon was applied (those treatments never got the bermudagrass to 50% cover). Note that indaziflam is not labeled for use during sprigged establishment but was included as a treated control. In other words, if no treatment effect was observed, then something went awry during the experiment. And liquid oxadiazon may be safened considerably if turf is irrigated immediately after application.

At six weeks after application, applying any of the pre-emergence materials reduced total new root growth (as determined via dry weight). The same results were observed at 10 weeks in the first run of the experiment. In the second run, however, application of flumioxazin increased the dry weight of the roots.

Root length was also often negatively affected by the application of pre-emergence materials. Only the application of simazine or the granular form of oxadiazon did not reduce root length (at four weeks). Application of S-metolachlor or indaziflam had the most long-term effects, with reduced root length for the entire 10 weeks of the study.

What about the root carbohydrates? Typically measured to help understand physiological stresses on a turfgrass plant, carbohydrates can affect green-up, growth and sprigging success. In this study, however, no differences were detected in the total amounts of nonstructural carbohydrates as a factor of these herbicide applications.

At the rates applied, the pre-emergence herbicides indaziflam, dithiopyr and S-metolachlor were not safe on newly established Latitude 36 hybrid bermudagrass. Applying other pre-emergence materials was less damaging, with the bermudagrass roots able to recover from the applications by 10 weeks after treatment. And finally, remember these results are experimental, and rates and materials may not always follow the labels.

Source: Begitschke, E.G., J.D. McCurdy, T. Tseng, T.C. Barickman, B.R. Stewart, C.M. Baldwin, M.P. Richard and M. Tomaso-Peterson. 2018. Preemergence herbicide effects on hybrid bermudagrass root architecture and establishment. HortScience 53:567-572.

Editor’s note: Read all of Beth Guertal’s recent Verdure columns.

Beth Guertal, Ph.D., is a professor in the Department of Crop, Soil and Environmental Sciences at Auburn University in Auburn, Ala., and the 2019 president of the Crop Science Society of America. She is a 21-year member of GCSAA.