Only four herbicides are registered for smooth crabgrass or goosegrass control on creeping bentgrass golf putting greens. None of the four herbicides control weedy grasses for the entire season or control weeds postemergence when applied once at labeled rates. Three of the product labels prohibit repeated use or application during stressful summer conditions. We hypothesized frequently applying herbicides at low doses could provide season-long control of summer grasses while minimizing turf injury. Seven field experiments were conducted on creeping bentgrass putting greens to evaluate various herbicides applied monthly, biweekly, or weekly for postemergence and residual control of goosegrass and smooth crabgrass as well as creeping bentgrass putting green tolerance. Metamifop applied twice monthly at 200 g ai ha−1, topramezone applied eight times weekly at 1.5 g ae ha−1, and siduron applied weekly at 5.6 kg ai ha−1 or four times biweekly at 11 kg ha−1 did not injure creeping bentgrass greater than 10% and maintained creeping bentgrass quality and cover equivalent to nontreated turf. Weekly or biweekly programs of fenoxaprop or quinclorac caused unacceptable injury and quality decline. Metamifop applied monthly and either fenoxaprop program controlled both smooth crabgrass and goosegrass by 97% to 99% throughout the growing season. Programs containing either quinclorac or siduron controlled smooth crabgrass by 99% to 100% but did not control goosegrass greater than 39%. All topramezone programs controlled smooth crabgrass by 69% to 77% and goosegrass by 93% to 98%. In additional studies, siduron applied five times biweekly did not injure creeping bentgrass on putting greens and controlled smooth crabgrass by more than 90% at seasonal, cumulative rates between 17 and 65 kg ai ha−1. This method of frequent, low-dose herbicide treatment to control smooth crabgrass and goosegrass on golf putting greens is novel and currently could be legally implemented with siduron.

Bermudagrass growing in a creeping bentgrass green is a severe problem where both grasses are grown. An experiment was conducted to determine the effects of multiple flurprimidol-herbicide applications on tolerance of bentgrass and on suppression of three bermudagrass cultivars in bentgrass. Application of 1.4 kg ai ha–1 flurprimidol on April 15 and 0.8 kg ha–1 repeated on June 1 injured creeping bentgrass 44% in 1988 and 22% in 1989. Bermudagrass was suppressed from the two flurprimidol applications until mid-June in 1988. Growth in 1989 was not influenced by number of applications since bermudagrass was suppressed only until late May. Application of 0.8 + 54 kg ai ha–1 flurprimidol plus siduron on April 15 and 0.4 + 27 kg ha–1 on June 1 injured creeping bentgrass 23 to 28% and suppressed bermudagrass until mid-July in 1988 and mid-June in 1989. Application of 0.8 + 1.7 kg ha–1 flurprimidol plus ethofumesate on April 15 and 0.4 + 0.8 kg ha–1 on June 1 injured creeping bentgrass 25 to 28% and effectively suppressed bermudagrass until late August in 1988 and late June in 1989. Application of 0.8 + 54 kg ha–1 flurprimidol plus siduron or 0.8 + 1.7 kg ha–1 flurprimidol plus ethofumesate applied in June or June and July to plots treated in April did not improve bermudagrass suppression. In most instances there was an inverse relationship between bermudagrass suppression and number of bermudagrass stolons. There were interactions between flurprimidol-herbicide treatments on bermudagrass cultivars on number of stolons but not on suppression.

Dithiopyr was applied to ‘Penneagle’ creeping bentgrass seedlings 2, 4, and 8 wk after emergence (WAE) in separate studies in the summers of 1992 and 1993 to determine seedling tolerance. Dithiopyr emulsifiable concentrate (IEC) was applied at 0.14, 0.28, 0.42, and 0.56 kg ai/ha, and granular (G) dithiopyr (0.1G) was applied at 0.14, 0.21, 0.28, and 0.42 kg/ha. Dithiopyr applied 2 WAE caused unacceptable injury regardless of rate or formulation. Injury was characterized by stunting of plants, leaf tip die-back, yellowing of older leaves, and a visible decline in quality. Injury increased with increasing rate. In 1992, the EC and G formulation of dithiopyr caused similar responses, whereas in the summer of 1993, the EC caused greater turf injury. Dithiopyr applied 4 WAE caused less injury than when applied 2 WAE, and injury was acceptable. Dithiopyr applied 8 WAE only slightly injured creeping bentgrass at the high rate for both formulations in both years.

Preemergence applications of herbicides were evaluated for their effect on establishment of zoysiagrass (Zoysia japonica Steud.) with competition from either smooth crabgrass [Digitaria ischaemum (Schreb.) Muhl. # DIGIS] or goosegrass [Eleusine indica (L.) Gaertn. # ELEIN]. When ‘Meyer’ and ‘Belair’ zoysiagrass plugs were grown in sand and treated in the greenhouse, none of the herbicides reduced root weight or length. When plugs were grown in a Sassafrass sandy loam, bensulide {O,O-bis(1-methylethyl)-S-[2-[(phenylsulfonyl)amino] ethyl] phosphorodithioate} and simazine (6-chloro-N,N′-diethyl-1,3,5-triazine-2,4-diamine) reduced root weight, and simazine reduced root length of Belair, but not Meyer. In smooth crabgrass-infested field plots, more stolons were produced from Meyer plugs treated with simazine, oxadiazon {3-[2,4-dichloro-5-(1-methylethoxy)phenyl]-5-(1,1-dimethylethyl)-1,3,4-oxadiazol-2-(3H)-one}, and siduron [N-(2-methylcyclohexyl)-N′-phenylurea] than plugs treated with bensulide, metribuzin [4-amino-6-(1,1-dimethylethyl)-3-(methylthio)-1,2,4-triazin-5(4H)-one], or the untreated control. At the end of two growing seasons, metribuzin-treated plots had significantly less zoysiagrass than other plots. Oxadiazon, DCPA (dimethyl tetrachloroterephthalate), and siduron enhanced the field establishment rate where Meyer zoysiagrass was competing with high populations of smooth crabgrass.

Turf managers traditionally avoid seeding cool-season turfgrass in spring due to summer annual weed interference and poor growing conditions for cool-season grasses. Siduron is the most accepted herbicide for weed control in spring-seeded tall fescue, but it has low residual activity and does not control many weeds other than crabgrass. Isoxaflutole, mesotrione, and quinclorac were evaluated as alternatives to siduron. Single applications of these herbicides controlled crabgrass equivalent to or better than siduron. Sequential applications of isoxaflutole, mesotrione, or quinclorac effectively controlled smooth crabgrass without injuring tall fescue. Isoxaflutole and mesotrione controlled broadleaf plantain, henbit, and yellow woodsorrel; quinclorac marginally controlled henbit; and siduron did not control broadleaf weeds. Turfgrass cover 9 wk after seeding was dependent on environment and equivalent between treatments except at a location with predominately broadleaf weeds where siduron treatments resulted in less cover due to weed infestation. Sequential applications of isoxaflutole, mesotrione, and quinclorac provide an effective, safe option for chemical weed control during establishment of cool-season turfgrass.

Field trials were conducted in 2000 and 2001 in New Jersey to evaluate quinclorac and siduron for large crabgrass control in summer-seeded creeping bentgrass (‘L-93’). Bentgrass was surface seeded on June 30 and June 26 in 2000 and 2001, respectively. Treatments consisted of preemergence (PRE) applications of siduron at 3.4, 5.0, and 6.7 kg ai/ha and PRE and postemergence (POST) applications of quinclorac at 0.4, 0.6, 0.8, and 1.7 kg ai/ha. POST applications were timed to a crabgrass growth stage of three leaves to one tiller. All POST quinclorac applications included methylated seed oil at 1% (v/v). Percent crabgrass cover in untreated plots at 30 d after planting (DAP) averaged 10 and 50% in 2000 and 2001, respectively. All PRE treatments, with the exception of quinclorac applied at 0.4 kg/ha in 2001, reduced crabgrass cover by 80% or more at 30 DAP. Crabgrass control decreased in late August when siduron and quinclorac were applied at the lower rates in 2001. PRE quinclorac applications at the rate of 0.6 kg/ha or higher in 2000 or 1.7 kg/ha in 2001 caused significant thinning of the bentgrass stand at 30 DAP. All POST quinclorac treatments provided excellent crabgrass control in 2000, but the 0.8-kg/ha or higher rate was required to reduce crabgrass infestation levels by at least 80% in 2001. All POST quinclorac applications caused significant chlorosis to the creeping bentgrass in both years. However, significant thinning of the bentgrass stand was not evident, with the exception of 1.7 kg/ha, in 2001. These studies suggest that PRE applications of siduron should be used for the highest level of creeping bentgrass safety in summer restoration projects. The use of quinclorac should be limited to POST applications to control escaped crabgrass once the newly emerging creeping bentgrass has become well established.

Field experiments were conducted to evaluate the efficacy of herbicides and soil sterilants for the fairway conversion of ‘Tifway’ bermudagrass to ‘Zorro’ zoysiagrass. Treatments included glyphosate (4.48 kg ae ha−1), EPTC (7.84 kg ai ha−1), dazomet (338 kg ai ha−1), siduron (13.4 kg ai ha−1), glyphosate plus ETPC (4.48 + 7.84 kg ha−1), glyphosate plus dazomet (4.48 + 338 kg ha−1), EPTC plus siduron (7.84 + 13.4 kg ha−1), and dazomet plus siduron (338 + 13.4 kg ha−1). Glyphosate treatments were applied 5 wk prior to establishment (WPE), dazomet and EPTC treatments were applied 3 WPE, and siduron was applied at establishment. Dazomet and EPTC treatments were incorporated to a depth of 10 to 15 cm with a rotary tiller and rolled with a weighted roller to reduce losses from volatilization after application. Zorro zoysiagrass was established in June 2008 and 2009 using a mixture of rhizomes and stolons at a rate of 76 cm3 m−2. Results indicate that glyphosate + dazomet, glyphosate + EPTC, dazomet + siduron, and EPTC + siduron were equally effective at controlling Tifway bermudagrass. EPTC and dazomet controlled bermudagrass more effectively when used in combination with glyphosate or siduron. There were no significant differences in bermudagrass cover between the EPTC combinations with glyphosate or siduron and dazomet applied with glyphosate or siduron. Comparing EPTC- and dazomet-alone, EPTC yielded less bermudagrass cover (32%) than dazomet (71%). At present, research is limited on using EPTC for controlling perennial grasses in turfgrass systems. Data from these studies demonstrate the potential use of EPTC as a preplant soil herbicide to control hybrid bermudagrass during zoysiagrass renovation.