Riviera Bermudagrass Response to Pre-seeding Applications of Sulfonylurea Herbicides

‘Riviera’ Bermudagrass Response to Pre-seeding Applications of Sulfonylurea Herbicides

John B. Willis, Research Associate, Daniel B. Ricker, Graduate Research Assistant, and Shawn D. Askew, Associate Professor, Department of Plant Pathology, Physiology, and Weed Science, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061-0331

Corresponding author: John B. Willis. jbwillis@vt.edu

Abstract

Recent advancements in cold tolerance of seeded bermudagrass cultivars have allowed seeding to repair thin areas following winter kill. Areas devoid of bermudagrass are often unnoticed until herbicides are applied to remove perennial ryegrass and winter weeds from golf course fairways and athletic fields. Trials were conducted in Blacksburg, VA, with flazasulfuron, foramsulfuron, metsulfuron, rimsulfuron, sulfosulfuron, and trifloxysulfuron-sodium at 35, 28, 42, 35, 34, and 29 g ai/ha, respectively, applied 1 and 3 weeks before seeding (WBS) ‘Riviera’ bermudagrass to evaluate turf tolerance. Safety of these products can be ranked as follows: foramsulfuron = metsulfuron > rimsulfuron = sulfosulfuron > trifloxysulfuron-sodium = flazasulfuron. Results indicate foramsulfuron and metsulfuron can be used anytime prior to seeding bermudagrass, while some injury will occur from rimsulfuron and sulfosulfuron applications prior to seeding. Bermudagrass should not be seeded within 3 weeks of flazasulfuron or trifloxysulfuron-sodium treatments.

Introduction

Seeded bermudagrass cultivars have been developed with texture, color, and quality that rival many vegetative cultivars commonly used in sports turf in the transition zone. Some seeded varieties have improved cold tolerance, potentially reducing occurrence of spring dead-spot (3,7,14,16). One advantage of using seeded cultivars is the ability to repair damaged turf or winter killed turf areas by seeding. Repairing extensively damaged turf with sprigs or sod from vegetative cultivars is much more expensive and time consuming than reseeding damaged areas (16).

Spring dead spot, cold temperatures, and wear may injure bermudagrass causing canopy disruption. This damage may not be observed until herbicides are used for weed control or to remove perennial ryegrass in spring. A similar situation occurs when perennial weeds are controlled with sulfonylurea herbicides revealing areas with no or thin bermudagrass cover. When faced with these situations, turf managers may desire to reseed bermudagrass into voided areas. Recent emphasis has been placed on safety and weed control during establishment of seeded bermudagrass cultivars in the transition zone (8,10,12,13,18). Several postemergent herbicides have been evaluated for safety on established bermudagrass (5,9,17). Carfentrazone (2) and quinclorac (1) are the only herbicides registered for use during bermudagrass seedling emergence and field trials have confirmed their safety for this use on ‘Riviera’ bermudagrass. Safety of sulfonylurea herbicides applied before seeding bermudagrass is not well documented. The objective of these studies were to evaluate flazasulfuron, foramsulfuron, metsulfuron, rimsulfuron, sulfosulfuron, and trifloxysulfuron-sodium applied three and one week before seeding ‘Riviera’ bermudagrass.

Evaluating Bermudagrass Response to Herbicides Applied Before Seeding

Three field experiments were conducted at the Virginia Tech Golf Course (VTGC) in Blacksburg, VA, in 2004 and 2005. The soil type was a Groseclose loam (clayey, mixed, mesic, Typic Hapludalfs) with 4.5% organic matter and pH 6.2 at all sites. Kentucky bluegrass fairways maintained at 1.9 cm were sprayed twice with glyphosate at 1.4 kg ai/ha, 4 and 2 weeks prior to seeding to control existing turf, weeds, and common bermudagrass. Plots were core aerated and vertical mowed in two directions before seeding ‘Riviera’ bermudagrass at 48.52 kg pure live seed per ha, seed was roller packed, but not mulched. Seeding dates were 7 June 2004, 20 May 2005, and 15 June 2005 for trials 1, 2, and 3, respectively, and trials will be referred to as such throughout the paper. Experiments were irrigated daily until 80% cover was reached in the control plots and as needed to maintain favorable growing conditions thereafter. Cutting height was maintained at 1.9 cm. Fertility included 48.8 kg of N per ha applied as 10-10-10 at seeding, and 24.4 kg of N per ha applied as 46-0-0 every other week until 80% cover was reached in the nontreated plots. For the remainder of the growing season, 24.4 kg of N per ha applied as 46-0-0 was applied at monthly intervals. This fertility regime is common for seeded bermudagrass establishment in Virginia.

A randomized complete block experimental design was used and treatments were replicated four times in each trial. Treatments included a factorial arrangement of six herbicides and two application timings. Herbicides included flazasulfuron (not registered), foramsulfuron (Revolver), metsulfuron (Manor), rimsulfuron (Tranxit), sulfosulfuron (Certainty), and trifloxysulfuron-sodium (Monument) at 35, 28, 42, 35, 34, and 29 g ai/ha, respectively. Herbicides were applied 1 and 3 weeks before seeding (WBS). Nontreated comparison treatments were included. All herbicide treatments were applied with a CO₂-pressurized backpack sprayer calibrated to deliver 281 liters/ha with XR8004 nozzles, and all herbicides except foramsulfuron included non-ionic surfactant at 0.25% v/v. Foramsulfuron is sold as a prepackaged mixture of the active ingredient and appropriate surfactant load.

Data collected in these trials included visual estimates of turfgrass injury and cover. Ratings were recorded as visually estimated percentage, 0% being no injury or control and 100% being death of all visible foliage. Stand counts and average number of leaves per plant were also evaluated by taking five subsamples per plot using a randomly selected 127-cm² area of interest. Variance was tested for homogeneity before ANOVA using SAS version 8.1 (SAS Institute Inc., Cary, NC). Nontreated control data was deleted in turfgrass injury data to stabilize variance, since nontreated plots were arbitrarily assigned a value of 0 for turfgrass injury. A combined ANOVA was conducted with partitioned sums of squares to evaluate location and treatment effects and to represent the factorial treatment arrangement. Location was considered random, and mean square of treatment effects was tested using mean square associated with the random variable (11). Appropriate means were separated using Fisher’s protected LSD at P = 0.05.

Bermudagrass Response to Pre-seeding Applications of Sulfonylurea Herbicides

ANOVA reveled that application timing main effect was not significant for any data collected for any trial. Herbicide main effect was significant for data from all trial locations and all evaluation timings except the final evaluation (Table 1 and 2). The trial by herbicide interactions were significant for bermudagrass injury 4 WAS (weeks after seeding) and bermudagrass cover 4 and 6 WAS (Table 1 and 2). This interaction could be attributed to different planting dates and thus variable growing conditions for each trial. The varying growing conditions caused slower bermudagrass growth and in general slower recovery from herbicide injury. Growing degree day (GDD) accumulation at base 18°C from seeding to 1 and 4 WAS were 9 and 96, 0 and 88, and 11 and 120, respectively, for trials 1, 2, and 3. Lower temperatures and thus GDD accumulation are typical for the earlier seeding dates, these differences may partially explain the trial interactions in the early season bermudagrass injury and cover data (Table 1 and 2). Horowitz (4) concluded that bermudagrass growth is limited below 18°C, and others have used this temperature as a base temperature for bermudagrass growth models (12,15). However, later in the growing season as temperatures increase there were no significant trial interactions for bermudagrass injury 6 WAS and cover 12 and 16 WAS. Interestingly, stand counts and leaf number did not have a significant trial interaction, indicating that each herbicide had equivalent effects on stand reduction and growth stage regardless of environmental conditions at each location (Table 1). Late season bermudagrass cover ratings did not have significant trial interaction because aggressive bermudagrass growth throughout the summer overcame the differences in injury and cover noted earlier in the season (Table 2).

Table 1. Pre-seeding applications of sulfonylurea herbicides to ‘Riviera’ bermudagrass effects on bermudagrass injury, stand counts (#), and leaf counts (#)^x. Herbicides were applied 1 and 3 weeks before seeding, but were pooled because application timing main effect was not significant.

Herbicide (g ai/ha^y)	Bermudagrass injury (%)				Stand #^x	Leaf #^x
	4 WAS^y			6 WAS	4 WAS
	Trial 1	Trial 2	Trial 3	6 WAS	4 WAS
Flazasulfuron (35)	26 a^z	56 ab	73 a	62 a	15 c	3.3 c
Foramsulfuron (28)	6 b	16 e	7 b	15 b	19 bc	4.6 a
Metsulfuron (42)	6 b	18 de	29 b	18 b	20 ab	4.5 a
Rimsulfuron (35)	9 b	43 bc	24 b	24 b	20 ab	4.3 ab
Sulfosulfuron (34)	3 b	33 cd	11 b	19 b	21 a	4.7 a
Trifloxysulfuron-sodium (29)	23 a	67 a	71 a	62 a	17 bc	3.5 bc
Nontreated	—	—	—	—	20 a	4.7 a
LSD^y	10.7	15.4	25.6	14.6	3.7	0.8

^x Stand # (count) is the count of bermudagrass seedlings per 127 cm2 and leaf # (count) is presented as average number of leaves per plant in the 127 cm2.

^y Abbreviations: g ai/ha = grams active ingredient per hectare; WAS = weeks after seeding; LSD = least significant difference.

^z Means in the same column followed by the same letter are not significantly different according to Fisher’s protected LSD (P = 0.05).

Table 2. Pre-seeding applications of sulfonylurea herbicides influences ‘Riviera’ bermudagrass cover. Herbicides were applied 1 and 3 weeks before seeding, but were pooled because application timing main effect was not significant.

Herbicide (g ai/ha^x)	Bermudagrass cover (%)
	4 WAS^x			6 WAS			12 WAS	16 WAS
	Trial 1	Trial 2	Trial 3	Trial 1	Trial 2	Trial 3	12 WAS	16 WAS
Flazasulfuron (35)	19 b^y	14 de	7 d	73 cb	26 c	26 b	95 bc	99
Foramsulfuron (28)	36 a	38 a	34 a	88 a	70 ab	89 a	99 a	100
Metsulfuron (42)	38 a	37 ab	18 bc	95 a	74 a	77 a	100 a	100
Rimsulfuron (35)	34 a	21 cd	23 b	86 ab	52 b	87 a	100 a	100
Sulfosulfuron (34)	41 a	29 bc	26 ab	95 a	64 ab	79 a	98 ab	100
Trifloxysulfuron-sodium (29)	21 b	10 e	10 cd	70 c	29 c	36 b	93 c	99
Nontreated	34 a	38 a	31 a	87ab	83 a	88 a	100 a	100
LSD^x	8.8	9	9.3	14	19.3	15.2	4.6	NSD^x

^x Abreviations: g ai/ha = grams active ingredient per hectare; WAS = weeks after seeding; LSD = least significant difference; NSD = no significant difference.

^y Means in the same column followed by the same letter are not significantly different according to Fisher’s protected LSD (P = 0.05).

Pre-seeding applications of flazasulfuron and trifloxysulfuron-sodium severely injured seeded bermudagrass, significantly reducing cover, stand count, and leaf count compared to the nontreated plots. Rimsulfuron and sulfosulfuron injured bermudagrass at unacceptable levels (greater than 30%) only in trial 2. Rimsulfuron did reduce bermudagrass cover 4 WAS at trial 2, but long term establishment was not effected by either rimsulfuron or sulfosulfuron (Table 2). Pre-seeding applications of foramsulfuron and metsulfuron did not injury bermudagrass at levels of agronomic significance, nor did they reduce establishment of bermudagrass from seed (Fig. 1).

Fig. 1. Plot pictures highlighting effects of sulfonylurea herbicides applied pre-seeding on ‘Riviera’ bermudagrass establishment from seed. Pictures were taken 4 and 8 weeks after seeding (WAS).

These data suggest turf managers that use foramsulfuron and metsulfuron for weed control or overseed removal could safely seed to repair bermudagrass within 1 week of application. Seeding bermudagrass within 3 weeks of rimsulfuron or sulfosulfuron application could result in significant injury and delayed cover establishment, however long-term establishment will not be effected. Seeding bermudagrass within 3 weeks of trifloxysulfuron-sodium and flazasulfuron (Fig. 1) applications will result in high seedling mortality and limited establishment (Table 1 and 2). Others have found short seeding intervals following applications of sulfosulfuron in cool-season turf species (6), but warm-season reseeding intervals have not been published for any of these products.

Safety of these products applied before seeding can be ranked in the following order: foramsulfuron = metsulfuron > rimsulfuron = sulfosulfuron > trifloxysulfuron-sodium = flazasulfuron. Results from these trials indicate that foramsulfuron and metsulfuron can be used anytime prior to seeding bermudagrass. Bermudagrass may be seeded after rimsulfuron and sulfosulfuron only if some injury can be tolerated, otherwise the application to seeding interval should be greater than 3 weeks. Bermudagrass should not be seeded after flazasulfuron or trifloxysulfuron-sodium applications unless the interval is much greater than 3 weeks. ‘Riviera’ bermudagrass cover did reach acceptable levels of cover by 12 WAS in plots treated with flazasulfuron and trifloxysulfuron-sodium (Table 2), however this is not expectable in most turf management situations. Seeding bermudagrass after any herbicide application is risky, and should be avoided if possible for ideal establishment conditions. Practitioners should always consult product labels regarding proper seeding and treatment timing.

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