Weed control in spring-seeded hard and tall fescues

With appropriate herbicide use, tall fescue, but not hard fescue, can be established in spring with seed.

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Peter H. Dernoeden, Ph.D. Steven J. McDonald, M.S.
 May 2013 Research: Weed control

Hard fescue naturalized areas are growing in popularity because they require fewer pesticide and management inputs, they create an aesthetic “wild” appearance and they reduce the carbon footprint.
Photo by Peter Dernoeden

Hard fescue (Festuca brevipilia) is grown in naturalized areas on golf courses and other low-maintenance sites in transition and northern regions of the United States. Naturalized areas are intended to receive only minimal mowing and few inputs of fertilizer, water and pesticides. The keys to hard fescue survival are to avoid mowing during hot and dry weather in the summer and to control weeds, especially when stands are immature.

Tall fescue (Festuca arundinacea) has supplanted the use of Kentucky bluegrass (Poa pratensis) for use in green surrounds and roughs in the transition zone and other regions. Tall fescue is preferred over Kentucky bluegrass because tall fescue establishes more rapidly and requires fewer irrigation, fertilizer and pest management inputs.

The optimal time to establish cool-season grasses from seed is late summer and early autumn. Spring seedings are fraught with problems including heavy weed competition, environmental stresses and disease pressures. Regardless, spring seeding sometimes becomes necessary, and weed control is a major requirement for having any chance of success.

Pre-emergence herbicides for cool-season grass seedbeds

Before Tenacity (mesotrione, Syngenta) became available, the only pre-emergence herbicide used in cool-season grass seedbeds was Tupersan (siduron, PBI-Gordon). It is well documented that Tupersan effectively controls crabgrass (Digitaria species) in seedbeds. We are aware of only one study in which the ability of Tenacity and Tupersan to control weeds in a spring seedbed have been compared. In a springseeded stand of tall fescue, Tenacity was found to be more effective in promoting establishment than Tupersan because Tupersan did not control broadleaf weeds (1). In that study, Tenacity and Tupersan controlled crabgrass, but Tenacity also controlled broadleaf plantain (Plantago major), henbit (Lamium amplexicaule) and yellow woodsorrel (Oxalis stricta).

May 2013 Research: Weeds

Tall fescue has supplanted the use of Kentucky bluegrass for use in green surrounds and roughs in many regions.
Photo by Steven McDonald

Hard fescue germinates rapidly, but it takes many weeks of suitable temperatures and moisture for it to tiller and develop into a turf. Most fall hard fescue seedings do not evolve into a turf until the following May or June. Tall fescue also germinates quickly, but is more aggressive than hard fescue and generally establishes more rapidly.

In view of the importance of minimizing weeds in spring seedings, research is needed to determine whether Tenacity and Tupersan can improve our ability to establish hard fescue in the presence of different weed species. According to their labels, Tenacity and Tupersan can damage some species of fine-leaf fescue, but we are unaware of any studies involving the use of either herbicide in spring-seeded hard fescue.

The objectives of this study were to determine safe and effective use rates of Tenacity for use on hard fescue during spring establishment; to document weed competition effects on hard fescue and tall fescue establishment as influenced by the herbicides evaluated; and to expand information on the spectrum of weed control activity of Tenacity in seedbeds.

May 2013 Research: Weed table 1


Study sites and establishment

The hard fescue study was conducted at the University of Maryland turfgrass research facility in College Park, Md., in 2009 and 2010. The tall fescue study was conducted in 2010 at the Maryland site and on a renovated lawn in Spring City, Pa.

2009: Hard fescue, Maryland

The study site was treated with Roundup (glyphosate, Monsanto) in fall 2008, tilled in spring, and seeded (5 pounds seed/1,000 square feet) with Aurora Gold hard fescue on April 9, 2009. Starter fertilizer (18-24-12) was applied at a rate of 1 pound nitrogen/1,000 square feet at seeding, but no additional fertilizer was applied thereafter.

Tenacity was applied once before the emergence of the hard fescue and weeds (that is, preemergence) on April 13 and again (that is, postemergence or sequentially) on May 19, 2009, at the rates shown in Tables 1-3. Dismiss (sulfentrazone, FMC Corp.), Drive (quinclorac, BASF), and Drive + Dismiss were applied once post-emergence on June 10, 2009. Drive was included in the study because of the heavy and unexpected development of large populations of smooth crabgrass (Digitaria ischaemum). Dismiss was applied to control an equally heavy invasion of yellow nutsedge (Cyperus esculentus).

The site was not routinely irrigated because frequent and heavy rainfall occurred in May and June, but was irrigated thereafter to avoid drought stress, which only was an issue in July. Rainwater frequently inundated the study area in the spring, which negatively affected hard fescue development. The site was not mowed until June and thereafter was mowed about once a month and only during moist periods to a height of 3.5 inches (8.8 centimeters).

2010: Hard fescue and tall fescue, Maryland

The study site was an undisturbed area treated with Roundup on April 5 and then disk-seeded on April 6, 2010. Coyote II tall fescue and Chariot hard fescue were seeded in closely juxtaposed monostands with 6 pounds seed/1,000 square feet.

Tenacity and Tupersan were applied initially on April 12 before the emergence of any seedlings, and sequential or post-emergence applications were made on May 12, 2010, at the rates noted in the data tables. Milorganite (6-3-0) was applied at 1 pound nitrogen/1,000 square feet on June 3, 2010.

The site was irrigated as needed to maintain a moist surface until seedlings emerged. Thereafter, the study areas were irrigated as needed to promote growth and prevent drought stress. The sites were not mowed until mid-June. Thereafter, the tall fescue area was mowed every two weeks to a height of 3 inches (7.6 centimeters). The hard fescue was mowed at 3.5 inches about once monthly in the summer and only when soil was moist.

2010: Tall fescue, Pennsylvania

The tall fescue study was also conducted in Spring City, Pa., where the study site was treated with Roundup early in the spring of 2010, tilled and seeded with 6 pounds seed/1,000 square feet with Coyote II tall fescue on April 30, 2010. Starter fertilizer (19-25-5) was applied at a rate of 1 pound nitrogen/1,000 square feet two weeks following seeding. The site received irrigation as needed to promote development and prevent drought stress. Treatments were applied as previously described on April 30 and on May 25, 2010. The turf was mowed every two weeks to a height of 3 inches.

May 2013 Research: Weed table 2


Treatments, 2009 and 2010

Soil was a silt loam with a pH of 5.6 and 1.6% organic matter in Maryland and 6.5 pH and 3.2% organic matter in Pennsylvania. The 5-foot (1.5 meters) × 5-foot plots were arranged in a randomized complete block with four replications.

All herbicides were applied in 50 gallons of water per acre using a CO2-pressurized (35 psi) backpack sprayer equipped with an 8004E flatfan nozzle. Post-emergence applications of Tenacity were tank-mixed with 0.25% (volume/volume) Activator 90 non-ionic surfactant. Drive treatments were tank-mixed with 1% (volume/ volume) methylated seed oil. Dismiss and Tupersan were not tank-mixed with adjuvants. The highest label use rate of Tenacity in a single application is 0.25 pound ai/acre, but the 0.5 pound ai/acre rate was evaluated to simulate and assess potential turf injury due to overlap.

Weed and turfgrass cover were assessed visually on a linear 0% to 100% scale, where 0 = no weeds or turf and 100 = entire plot area covered with weeds or turf. The major weeds in Maryland were smooth crabgrass, yellow foxtail (Setaria glauca), common Lespedeza (Lespedeza striata), common ragweed (Ambrosia artemisiifolia), field paspalum (Paspalum laeve), yellow nutsedge and relatively minor levels of yellow woodsorrel, broadleaf plantain and an unknown Coreopsis species. Yellow foxtail, ragweed and coreopsis plants in each plot were also counted on one date. Smooth crabgrass, ragweed and poke weed (Phytolacca species) were the primary weeds in Pennsylvania. Tall fescue cover data for Maryland and Pennsylvania were combined by statistically analyzing sites as blocks.

May 2013 Research: Weed table 3


Results and conclusions

Hard fescue, 2009 Weed cover.

In June 2009, the research area was frequently inundated by rainwater, and a variety of weeds rapidly invaded the site, making it impractical to assess individual weed species and hard fescue cover throughout June and July. A composite weed rating was obtained on June 8 and 24, 2009 (Table 1). Tenacity at all rates applied before the emergence of hard fescue seedlings and again post-emergence was effective in controlling smooth crabgrass, Lespedeza, yellow nutsedge and ragweed. Sequentially treated Tenacity plots were re-invaded in late summer by some yellow nutsedge, but not very much crabgrass or Lespedeza. Only yellow foxtail was problematic in sequentially treated Tenacity plots in 2009.

Hard fescue cover. In some areas the standing water from excessive rains killed hard fescue plants. The June 24 hard fescue cover rating indicated that many hard fescue seedlings had not survived the wet conditions and/or weed competition (Table 2). By Sept. 21, highest cover was observed in sequentially treated Tenacity plots (20%-35%), which was statistically similar to plots treated with Drive + Dismiss (13%). Field notes suggested that the high rates of Tenacity and Dismiss may have been injurious to the hard fescue seedlings, but the low levels of hard fescue were due mostly to weed competition and/or poor survival of seedlings. Regardless of treatment, hard fescue failed to produce a satisfactory turf by the end of the summer.

The study site was monitored in spring 2010. Over winter and into June 2010, hard fescue cover ratings increased greatly in plots treated with Tenacity, Drive, and Dismiss + Drive. By spring 2010, these plots had good hard fescue cover levels (Table 2). Sequentially treated Tenacity plots had suffered little crabgrass re-invasion.

Hard fescue, 2010

Hard fescue cover. In 2010, Tenacity applied sequentially to the seedbed had promoted establishment, but hard fescue cover generally was less than desirable throughout the rating period. On the final rating date, extremely poor hard fescue cover (1%-10%) was observed in plots treated with Tenacity at 0.5 pound ai/acre, Tupersan (both treatments) and the untreated control (data not shown). Poor hard fescue cover was caused by competition from yellow nutsedge in Tupersan- treated plots and from crabgrass in the control plots. The single application of Tenacity at two times the label use rate (that is, 0.5 pound ai/acre) provided inferior weed control compared to sequential applications, and it was phytotoxic. Relatively good hard fescue cover (57%-62%), however, was observed in plots treated sequentially with Tenacity (data not shown).

Weed cover. As observed in the 2009 hard fescue study, crabgrass, yellow nutsedge, Lespedeza and ragweed were effectively controlled by Tenacity applied sequentially, but Tenacity was weak to ineffective against yellow foxtail (Table 3). Tupersan had effectively controlled crabgrass and yellow foxtail, but was ineffective against Lespedeza, ragweed and yellow nutsedge. There were lower levels of yellow nutsedge in untreated compared to Tupersan-treated plots because of crabgrass competition. By July, existing low levels of Lespedeza and yellow foxtail plants began to increase in size and became competitive in Tenacity-treated plots.

Field paspalum was the most invasive weed in Tenacity-treated hard fescue by late summer. Tupersan was more effective than Tenacity in controlling field paspalum, but both herbicides reduced paspalum levels compared to the control (Table 3).

On most golf courses, these weeds would have been controlled post-emergence as soon as they had begun to dominate in order to promote density of the desired turfgrass species. This was not done in order to document the mid-summer progression of weed invasion and competition.

Tall fescue, 2010 Tall fescue establishment was assessed in Maryland and Pennsylvania in 2010. Crabgrass was the major problem in Pennsylvania, and it was most effectively controlled by Tenacity applied at 0.187 + 0.187 and 0.25 + 0.25 pound ai/acre and Tupersan applied at 12 pounds ai/acre (data not shown). By early August, numerous plots were dominated by weeds. The weed species and levels of control in Maryland were similar to those previously described for hard fescue (data not shown). Field paspalum was less invasive in the more competitive tall fescue. When data were averaged over the two sites, there were few differences among herbicide treatments except for Tupersan applied at 6 + 6 pounds ai/acre, which was generally less effective in promoting tall fescue establishment during the summer.

All herbicide-treated plots had more than 81% cover by September, and by October all herbicide- treated plots had equivalent cover ranging from 90% to 98% tall fescue (data not shown). Although crabgrass levels were reduced only by about 50% in some of the herbicide-treated plots in Pennsylvania, this was enough reduction in competition to allow for good tall fescue development at the end of the study. Similarly, the high level of yellow nutsedge in Tupersan-treated plots did not have a debilitating effect on tall fescue establishment, whereas the slower developing hard fescue was unable to compete with this weed.

In the final analysis, by October, there were no differences in tall fescue cover (90%-98%) in herbicide- treated plots (data not shown). However, untreated control plots had only 22% tall fescue cover. Hence, for purposes of tall fescue establishment in spring seedings, Tenacity at a rate as low as 0.125 + 0.125 pound ai/acre is adequate, but a rate of 0.187 + 0.187 should be considered if high levels of crabgrass are anticipated. The single 12 pounds ai/acre rate of Tupersan was shown to be both effective and logistically more economical to apply than sequential (that is, 6 + 6 pounds ai/ acre) applications of Tupersan.

Summary

Data confirm that it is extremely difficult to successfully establish hard fescue in the spring and that seeding this species should be avoided until fall. Tall fescue is more competitive than hard fescue with weeds in spring seedings.

Data also showed that tall fescue cannot compete with heavy weed pressure when seeded in the spring unless appropriate herbicides are used. Tenacity or Tupersan alone were not sufficient to promote complete tall fescue cover before the onset of summer. It is likely that a more liberal use of nitrogen and appropriate post-emergence herbicides would have resulted in more rapid tall fescue establishment. Further it should be noted that this study was conducted in a transition zone region and that results may vary in other areas of the U.S.

Tenacity controlled a diverse array of weed species including an annual grass (crabgrass), a perennial grass (partial control of field paspalum), broadleaf weeds (Lespedeza and ragweed) and yellow nutsedge. Most of the control was preemergent in nature, but the second application of Tenacity did have post-emergence activity. Unpublished field studies and observations have shown, however, that Tenacity has little pre-emergence activity on the above-mentioned weeds in mature turf. Similarly, Tupersan is only effective in controlling crabgrass and yellow foxtail in a seedbed and not in mature turf. This likely occurs because these herbicides can make contact with bare soil in a seedbed situation.

Acknowledgments

We thank Dr. Michael Agnew and Syngenta Crop Protection for their interest in and support of this research.

Literature cited

  1. Willis, J.B., J.B. Beam, W.L. Barker and S.D. Askew. 2006. Weed control options in spring-seeded tall fescue (Festuca arundinacea). Weed Technology 20(4):1040-1046.

Peter H. Dernoeden (pd@umd.edu) is a professor of turfgrass science at the University of Maryland, and Steven J. McDonald is president of Turfgrass Disease Solutions LLC.