Lawn Care Tips
Improving Dallisgrass Control with Well-Timed Herbicide Applications By Matt Elmore, Ph.D., Assistant Professor and Extension Turfgrass Specialist, Mississippi State University
D
allisgrass (Paspalum dilatatum Poir.) is a warm-season perennial grass native to South America that was introduced to the United States in the late 1800s. Currently, it is one of the most problematic turfgrass weeds in the Southeast. Tolerance to close mowing allows it to proliferate in most managed turf areas, including golf course fairways. Dallisgrass can be identified by its bunch-type growth habit, coarse texture and rapid vertical growth compared to desirable turfgrasses (Photo 1). Other identifying features include a membranous ligule and prominent midrib (Photo 2), which can help distinguish it from other bunch-type grassy weeds such as crabgrass (Digitaria spp.). Dallisgrass produces seedheads from as early as late May through October, which further aid in identification (Photo 3). Unlike most bunchtype grasses, dallisgrass produces short rhizomes that serve to increase the diameter of the plant and store carbohydrates (Photo 4). These reserve carbohydrates make controlling dallisgrass extremely difficult, even with systemic herbicide applications. Controlling dallisgrass with herbicides requires multiple herbicide applications over several seasons. 8 • Mississippi Turfgrass • summer 2016
Selective control in warm-season turfgrass
Regardless of the herbicide you select for control, application timing is very important. Research consistently demonstrates that applications made in early to late fall while dallisgrass is still actively growing, but before winter dormancy, provide better control than those made during late spring or summer. Regardless of the herbicide combination, several sequential applications are usually required for complete control. Larger plants will generally require more applications for control. Currently, programs of at least three sequential applications are recommended. Applications in the fall should begin not prior to September and when the average 24-hour air temperatures fall below 72°F for at least three consecutive days. In a typical year, this might occur around mid- to late September in Mississippi. The average 24-hour air temperature can be determined by averaging the high and low air temperature for a particular day. The second application should be made four to six weeks after the first application when dallisgrass regrowth is observed. A third application in the spring when
dallisgrass regrowth is observed (usually in mid- to late April) improves control compared to two fall applications (Photo 5). Most herbicides claim only dallisgrass suppression on the label. This means these products have significant activity against dallisgrass but not enough to provide commercially acceptable control. These products will be effective if multiple applications are made at the proper time.
MSMA
As of this writing, MSMA cannot be used on residential, commercial or athletic field properties. It may be used twice annually on highway rightsof-way, twice per crop in sod production and as a spot treatment on golf courses (spots less than 100 ft2 and less than 25% of the golf course). These restrictions are expected to remain in place until at least 2019. For more information on these EPA restrictions, see http://www2.epa.gov/ ingredients-used-pesticide-products/ monosodium-methanearsonate-msmaorganic-arsenical. Two fall and one spring application of MSMA at 2 lbs./A applied at timings described above generally provide