Influence of spring-applied preemergence herbicides on bermudagrass in nematode-infested soil

S. Bruce Martin ¹, J. Camberato¹, and L. Mudge²

¹Department of Plant Pathology and Physiology, and Faculty of Soils and Land Resources, Pee Dee Research and Education Center

²Rhone-Poulenc Ag Company, Chipco Division

Preemergence herbicides for crabgrass and goosegrass control are generally applied around early spring in coastal region golf courses. Some preemergence herbicides used, such as pendamethalin, have been shown to reduce plant root development as well as function as a herbicide. Other herbicides, such as oxadiazon, have not been shown to inhibit root development. In early April it has been observed that larvae of several plant parasitic nematodes begin actively feeding on bermudagrass roots that have resumed growth or have been initiated from rhizomes and stolons. The effects of herbicide inhibition and nematode feeding on rooting may be manifest throughout the season and be compounded in subsequent years. An objective of this research is to quantify the effects of preemergence herbicides and nematode populations turfgrass root development.

General Methodology

Experiments were conducted at three locations in 1995 (Sunset Country Club in Sumter, SC; Sandhills turf farm in Candor, NC; and two sites at Pineland Country Club in Nichols, SC). Herbicide treatments were applied by March 1 and were; no herbicide, pendamethalin (3.0 lb a.i./acre as Lesco Pre-M 60DG), and oxadiazon (4.0 lb a.i./acre as Ronstar G). Nematicide treatments were applied in the first two weeks of April and treatments were no nematicide or fenamiphos (10.0 lb a.i./acre as Nemacur 10G). The same experimental treatments had been applied to the plots at Candor and at one Pineland site (Pineland II) the previous year. Experiments at Sunset and the other Pineland site were applied for the first time in 1995. There were four replications of each treatment at Pineland and Sandhills and five replications at Sunset.

Eight soil cores 2 cm in diameter were extracted to a depth of 20 cm from each plot. Roots were extricated from the soil mass by hand washing. Cleaned roots were stained with methyl violet and length, width, and surface area determined by scanning procedures. The extent of root system necrosis was rated visually on a scale of one to ten with one indicating complete necrosis and ten indicating no necrosis.

Results and Discussion

Root length and surface area of bermudagrass were not affected by herbicide treatments (Table 1 and 2). Root measurements were made in early August, approximately five months after the application of herbicide treatments. Herbicide treatment effects may have occurred shortly after herbicide application, but not persisted until August.

Nematicide applications substantially increased bermudagrass root length and surface area at two of the four locations (Table 1 and 2). The effect of the nematicide on rooting was independent of the herbicide treatment.

Average root width was not affected by the herbicide or nematicide treatments (data not shown). Width was 0.36, 0.33, 0.35. and 0.39 mm for Sunset, Sandhills, Pineland I, and Pineland II, respectively.

Root necrosis was decreased by nematicide treatment at the Sandhills site, but not at the other sites (Table 3). Perhaps necrosis due to nematode feeding was evident only at the Sandhills site because rooting at this site was decreased more by nematodes than rooting at the other sites.

The reductions in rooting and increased necrosis found at Sunset and Sandhills sites likely reduce water and nutrient use efficiency, turf resistance to stress, and turf recovery from damage.