Cultural and Chemical Control of Ground Ivy (Glechoma hederacea)

Ground ivy is a common broadleaf weed that disrupts turf uniformity and is diffi cult to control. The objective of this fi eld research was to evaluate cultural and chemical control of ground ivy. Increasing annual nitrogen fertilizer applications from 0 to 196 and 293 kg·ha–1 reduced ground ivy cover by 24% and 32%, respectively. At 26 weeks after treatment, 1.1 kg·ha–1 isoxaben applied in May limited ground ivy spread by 34% compared to the control. Triclopyr, 2,4-D, or fl uroxypyr applied at the highest-labeled rate in October provided superior ground ivy control by the following May. Combining an annual fertility program of 196 kg·ha–1 nitrogen and an application of 1.1 kg·ha–1 isoxaben with or after an application of 2,4-D, fl uroxypyr, or triclopyr in the fall can maximize ground ivy control. Chemical names used: N-[3-(1-ethyl-1-methylpropyl)-5isoxazolyl]-2,6-dimethoxybenzamide (isoxaben); [(3,5,6-trichloro-2-pyridinyl)oxy]acetic acid (triclopyr); (2,4-dichlorophenoxy)acetic acid (2,4-D); [(4-amino-3,5-dichloro-6-fl uoropyridyl)oxy]acetic acid (fl uroxypyr). Ground ivy (Glechoma hederacea L.) is a creeping perennial weed in turf in the cooler climates of northeastern and midwestern United States (Mitich, 1994). During summer and fall, populations rapidly increase in size through vegetative propagation of new ramets along stolons. Eventually the turf site is populated with patches of ground ivy, resulting in a nonuniform turf stand. Once established, controlling ground ivy is challenging for the lawn care industry. In a survey of lawn care operators (LCOs) in Indiana, 49% of respondents reported poor or fair control of ground ivy and 40% reported nonuniform control (Table 1). Additionally, 86% indicated repeated herbicide applications were necessary for successful ground ivy control, further suggesting chemical control of ground ivy is challenging. Time, money, and effort spent on controlling ground ivy is considerable since 31% of the LCO customers had ground ivy on their property. However, there has been little research focusing on ground ivy control using herbicides common to LCOs (Hatterman-Valenti et al., 1996). Furthermore, of those reports that evaluated herbicides commonly used by LCOs (Czarnota et al., 2001; Olson and Hall, 1988; Vrabel, 1987), application was done in had not been fertilized during the experiments or during the previous 2 years. The soil was a Chalmers silt loam (fi ne silty mixed mesic Typic Haplaquoll) with a 7.0 pH, 0.133 meq·g CEC, 4.7% organic matter, 219 kg·ha P, and 510 kg·ha K. Plots were irrigated as needed to prevent drought stress and mowed three times per week at 6.4 cm with clippings returned. All herbicide treatments were applied in 374 L·ha water with a CO 2 -pressurized backpack sprayer using a three-nozzle (TeeJet XR8002VS, Spraying Systems Co., Wheaton, Ill.) boom at 207 kPa. Nitrogen fertility study. Fertilizer treatments were applied to plots containing uniform stands of ground ivy beginning on 15 May 2000 and 14 May 2001. Average initial ground ivy cover was 32% in 2000 and 45% in 2001. Treatments were a three by three factorial with three annual nitrogen rates (98, 196, or 293 kg·ha) and three application schedules (heavy spring, heavy fall, or equal spring, summer, and fall), and an untreated control was included for comparison. Fertilizer and scheduled rates are given in Table 2. Fertilizer application dates were 15 May ±1, 25 July ±2, 18 Sept. ±2, 17 Oct. ±2, 15 Nov. ±2, 23 Mar. ±2, and 23 Apr. ±1. On each application date, total nitrogen was applied as 50% (by N content) urea (46N–0P–0K) (Shaw’s, Knox, Ind.) and 50% sulfur-coated urea (32N–0P–0K) (Shaw’s, Knox, Ind.). The experiment was a randomized complete block design with three replications. While percent ground ivy cover was visually estimated every 4 weeks for 1 year during each experiment, only data collected 12 months after initial treatment (MAIT) for each experiment are presented. Preemergence herbicide study. Three 10.2cm-diameter × 8-cm-deep plugs of ground ivy were transplanted into plots on 14 May 1999 and 10 May 2000. One week later, the following preemergence herbicides were applied at the highest-labeled rate or at one-half the highest-label rate for kentucky bluegrass (Vencill, 2002): prodiamine (2,4-dinitroN,N-dipropyl-6-(trifl uoromethyl)-1,3-benzenediamine) (Syngenta, Wilmington, Del.) at 1.7 or 0.9 kg·ha, dithiopyr (S,S-dimethyl 2-(difluoromethyl)-4-(2-methylpropyl)-6(trifl uoromethyl)-3,5-pyridinedicarbothioate) (Dow Agro Sciences, Indianapolis) at 0.6 or 0.3 kg·ha, isoxaben (Dow AgroSciences, Indianapolis) at 1.1 or 0.6 kg·ha, or pendimethalin (N-(1-ethylpropyl)-3,4-dimethyl2,6-dinitrobenzenamine) (BASF, Research Triangle Park, N.C.) at 3.3 or 1.7 kg·ha. Percent ground ivy cover was rated visually at 6, 12, and 26 weeks after treatment (WAT). Treatments were a 2 × 4 factorial with two rates and four herbicides, and an untreated control was included for comparison. The experiment was a randomized complete block design with three replications. Postemergence herbicide study. Ten postemergence herbicide combinations were sprayed at the highest-labeled rate or at one-half the highest-labeled rate for kentucky bluegrass on plots containing dense, uniform stands of ground ivy on 30 Oct. 1999 and 15 Oct. 2000 (Table 3) (Vencill, 2002). Average initial spring rather than fall when broadleaf weed control is often performed (Kohler, 2002). Ground ivy stolons creep beneath the turf canopy when colonizing new areas (Birch and Hutchings, 1994; Hutchings and Price, 1999). Extensive rooting from these stolons makes mechanical control diffi cult. Nitrogen application (Dernoeden et al., 1993; Lowe et al., 2000), irrigation (Gaussoin and Branham, 1989; Jiang et al., 1998), and mowing (Brede, 1992; Dernoeden et al., 1993) have been studied to limit encroachment of weeds other than ground ivy, but there are no reports of cultural control of ground ivy. Both preemergence (Turgeon, 1996) and postemergence (Monaco et al., 2002; Sterling and Hall, 1997) herbicides have been used successfully for decades to control grassy or other broadleaf weeds, but ground ivy control is challenging and inconsistent (Hatterman-Valenti et al., 1996). The objectives of this research were to evaluate nitrogen fertility programming, preemergence herbicides, and postemergence herbicides for ground ivy control. Materials and Methods Conditions common to experiments. All experiments were conducted for 1 year at the W.H. Daniel Turfgrass Research Center in West Lafayette, Ind. Experiments were repeated the following year on different but adjacent sites. Field plots (1.5 × 1.5 m) were located in full sun in a low-maintenance stand of kentucky bluegrass (Poa pratensis L. ‘America’) that HORTSCIENCE 39(5):1148–1152. 2004. Received for publication1 Apr. 2003. Accepted for publication 9 Sept. 2003. Graduate research assistant. Director of research. Associate professor; to whom reprint requests should be addressed; e-mail [email protected].