CRABGRASS CONTROL IN COOL-SEASON TURF WITH THE WET BLADE SYSTEM

Figure 5. Large crabgrass control 4 WAT by quinclorac, fenoxaprop, and MSMA applied as a foliar spray or with the wet blade system (WBS).

A * indicates significant difference between herbicide application methods at P = 0.05. Herbicide means within an application method shown with the same letter are not significantly different at P = 0.05.

Figure 3. Large crabgrass control 1 WAT by quinclorac, fenoxaprop, and MSMA applied as a foliar spray or with the wet blade system (WBS).

Figure 2. A blade of grass after being mowed with the wet blade system. Blue dye was added to the herbicide solution.

Figure 1. Wet blade delivery system, a modified conventional mower with a mechanism to deliver herbicide onto the underside of the blade.

Figure 4. Large crabgrass control 2 WAT by quinclorac, fenoxaprop, and MSMA applied a foliar spray or with the wet blade system (WBS).

Figure 6. Kentucky bluegrass injury 4 WAT by quinclorac, fenoxaprop, and MSMA applied as a foliar spray or with the wet blade system (WBS).

CRABGRASS CONTROL IN COOL-SEASON TURF

WITH THE WET BLADE SYSTEM

W.L. Barker, J.B. Beam, and S. D. Askew; Department of Plant Pathology, Physiology, and Weed Science, Virginia Polytechnic Institute & State University, Blacksburg, VA 24061

INTRODUCTION

The Wet Bladeâ system (WBS) applies herbicide while mowing thus eliminating the need for a separate application (Figure 1). Cut leaf surfaces absorb chemicals more readily since cuticle and other barriers to chemical movement have been removed (Figure 2). “It allows for the selective application of various fluids such as pesticides,

HYPOTHESIS

When using systemic herbicides both WBS and foliar-spray spray application should control emerged large crabgrass (Digitaria sanguinalis (L.) Scop.) equivalently.

OBJECTIVES

The goal of this study is to compare WBS to foliar spray applications of quinclorac, fenoxaprop, and MSMA for postemergence large crabgrass control and Kentucky bluegrass (Poa pratensis L.) tolerance.

MATERIALS AND METHODS

The study was initiated at Blacksburg, VA on August 20, 2002 in established ‘Midnight’ Kentucky bluegrass turf infested with large crabgrass. Mowing height was maintained at 1.25 inches and fall fertilizer was excluded from the test site to promote heavy crabgrass infestation. Unfortunately, drought conditions were prominent and crabgrass was at the seedhead stage when treatments were initiated. The study was

growth regulators, biorationals, fertilizers, etc. to vegetation by causing a minute amount of chemical to be immediately absorbed into the vascular system of a plant at the moment the plant is cut by a rotary or other cutting blade” (Skroch et al. 1998). Cut dogfennel [Eupatorium capillifolium (Lam.) Small] absorb 70-80% of applied herbicide immediately and 90% within 60 minutes after treatment (Wahlers et al. 1997). Furthermore, herbicide was

within 12 hours after treatment translocated to dogfennel roots (Wahlers et al. 1997). “The WBS is a non-spray, enclosed system that provides precise pesticide application thereby reducing the quantity of chemical needed and eliminating worker exposure and drift” (Skroch et al.

1998) (Figure 1). Applying chemical only to cut plants reduces the likelihood of herbicide movement compared to foliar-spray application (Figure2). Recent concerns over pesticides detected in soil and water sources (Gallagher et al. 1996) have made off-site chemical movement a public forum. Although potential benefits abound, limitations to the WBS should be considered. Since chemicals are only

RESULTS AND DISCUSSION

Skroch et al. (1998) evaluated the WBS for use on rights-of-way to control several woody plant species and also in turf where it controlled dandelion (Taraxacum officinale Weber) and white clover (Trifolium repens L.). Environmental conditions were unfavorable in Blacksburg, VA in late August and influenced data taken from this study.

1 WAT. Foliar-spray applications of quinclorac at 0.56 lb ai/A and fenoxaprop controlled crabgrass between 20 and 30% more than the same treatments applied by the WBS (Figure 3). Application methods controlled large crabgrass equivalently when using quinclorac at the high rate or MSMA. WBS treatments controlled crabgrass between 20 and 28%. Both rates of quinclorac controlled crabgrass more than 48% and better than MSMA and fenoxaprop.

2 WAT. All foliar-spray applications controlled large crabgrass at least 200% more than all comparable wet blade treatments (Figure 4). WBS applied quinclorac (both rates), MSMA, and fenoxaprop controlled crabgrass less than 25%. Foliar-spray applied fenoxaprop, MSMA, and quinclorac at 0.56 lb ai/A and 1.13 lb ai/A controlled crabgrass 60, 45, 45, and 48%, respectively.

4 WAT. Fenoxaprop controlled crabgrass significantly more with

applied to cut plant surfaces, contact-type herbicides will likely perform poorly in the WBS. In addition, there is little or no soil contact from herbicides applied via the WBS, thus limiting residual weed control. Finally, weeds must be cut in order to receive treatment so herbicides applied by WBS will not affect low growing plants.

FUTURE RESEARCH

More studies must be conducted including replicating this study under more favorable conditions. This study will be repeated following the 2003 crabgrass emergence period and other studies will evaluate the WBS on more weed species.

LITERATURE CITED

Gallagher, D.L. et al. 1996. Ground water discharge of agricultural pesticides and nutrients to estuarine surface water. Ground Water Pub. Co. 16:118-129

Skroch, W.A. et al. 1998. Efficacy and application with the Burch Wet Bladeâ system.

Proc. South. Weed Sci. Soc. 51:218.

Wahlers, R.L. et al. 1997. Physiological characteristics of a stem cut and blade delivery method of application. Weed Sci. 45:746-749.

CONCLUSION

Suboptimal environmental conditions slowed turf and weed growth and likely influenced herbicide efficacy. Results suggest herbicides applied via foliar spray may

conducted as a randomized complete block with treatments replicated three times in a split-plot design. The main plot had four levels consisting of quinclorac at 0.56 lb ai/A and 1.13 lb ai/A, fenoxaprop at 0.07 lb ai/A, and MSMA at 1.25 lb ai/A. Subplots were application method consisting of either foliar spray application or WBS. A nontreated control was included for comparison. Subplots receiving foliar spray were 6 by 6 feet and subplots receiving the WBS were 6 by 30 feet to allow for start

and stopping distance. Application volumes were 1 and 30 gal/A for WBS and foliar spray, respectively. Turfgrass and weed height was 2 inches at trial initiation and the WBS was set to mow at 1.5 inches high. Foliar spray subplots were not mowed. Weed control was visually estimated at 1, 2, and 4 weeks after treatment (WAT) as percentage crabgrass control compared to the nontreated check on a scale of 0 to 100 (100% being complete control). Later ratings were not taken due to frost damage to the test site. Data were subjected to analysis of variance with sums of squares partitioned to evaluate the split plot treatment design. Appropriate means were separated using Fishers protected LSD test at P £ 0.05.

foliar-spray application (85%) compared to WBS (35%). Foliar-spray applied quinclorac and MSMA controlled crabgrass less than 40%, which was not significantly different from the same chemicals applied with the WBS.

INJURY. Kentucky bluegrass turf was injured 13% by fenoxaprop and 10% by quinclorac at 1.13 lb ai/A 4 WAT (Figure 6). Foliar-spray applied quinclorac at 0.56 lb ai/A and MSMA as well as WBS applied fenoxaprop, quinclorac (both rates), and MSMA injured turf less than 3%.

produce visual symptoms of control faster than the WBS. Under drought conditions, fenoxaprop controls crabgrass better when applied as a foliar spray compared to the WBS. However, effects of WBS-applied fenoxaprop, quinclorac, and MSMA on long-term large crabgrass control are inconclusive due to inherent environmental conditions of this study.