J. Bryan Unruh

Factors affecting seed germination of tropical signalgrass (Urochloa subquadripara)

Abstract Tropical signalgrass is one of the dominant weeds in the Florida turfgrass industry and is potentially troublesome for the southeastern turfgrass industry. Tropical signalgrass is especially problematic for St. Augustinegrass sod producers because of lack of control options. The objectives of our research were to determine the effect of light, pH, temperature, water potential, and planting depth on tropical signalgrass germination and emergence. Tropical signalgrass germination does not require light and is optimum at pH 5 to 6, temperature 25 C, and water potentials greater than − 0.4 MPa. Tropical signalgrass shoots emerged from depths of 0 to 7 cm, with maximum germination when placed on the soil surface. Tropical signalgrass seedlings emerged in the field during the second week of March in Ft. Lonesome, FL. Weekly mean soil and ambient air temperatures at the time of emergence were 20 C. Tropical signalgrass emergence was first observed at 118 and 73 growing degree-days (GDD) (13 C base temperature), with a peak emergence period at 222 and 156 GDD for 2001 and 2002, respectively. Nomenclature:  Tropical signalgrass, Urochloa subquadripara (Trin.) R. D. Webster BRASU; St. Augustinegrass, Stenotaphrum secondatum (Wait.) Kuntz.

Fumigant Alternatives for Methyl Bromide Prior to Turfgrass Establishment1

Potassium azide (PA) (112 kg/ha), oxadiazon + 1,3-dichloropropene (1,3-D) (168 kg/ha + 140 L/ha), dazomet (392 kg/ha), dazomet + chloropicrin (392 + 168 kg/ha), dazomet + 1,3-D (392 kg/ha + 140 L/ha), iodomethane (IM) (336 kg/ha), metam-sodium (MS) (748 L/ha), MS + chloropicrin (748 L/ha + 168 kg/ha), and MS + 1,3-D (748 + 140 L/ha) were evaluated at Jay and Arcadia, FL, in 1998 and 1999 as alternatives to methyl bromide (MeBr) fumigation for the management of common turfgrass weeds. Potassium azide was as effective as MeBr in controlling ‘Coastal’ bermudagrass, yellow and purple nutsedges, alexandergrass, broadleaf signalgrass, tall and sharppod morningglories, and various winter annual broadleaf weeds, but it failed to provide acceptable control of redroot pigweed. 1,3-Dichloropropene + oxadiazon did not control yellow nutsedge, purple nutsedge, or Coastal bermudagrass. Similarly, this combination treatment failed to control carpetweed but did provide 83% control of the winter annual weed species, 71% control of alexandergrass and broadleaf signalgrass, and ≥ 80% control of tall morningglory, sharppod morningglory, and redroot pigweed. Dazomet + combination treatments provided control of Coastal bermudagrass at Jay; however, control of common bermudagrass, alexandergrass, and broadleaf signalgrass was not acceptable at Arcadia. Sedge species control with dazomet + combinations was poor (< 63%) at both sites. Iodomethane, a treatment not yet registered by the U.S. Environmental Protection Agency (EPA), controlled weedy grass species, sedge species, and broadleaf weeds present at the two locations under different environmental conditions. Metam-sodium alone and MS + chloropicrin, tarped and untarped, and MS + 1,3-D provided acceptable weed control; however, MS + chloropicrin covered with a plastic tarp for 48 h was the best MS treatment. Metam-sodium + chloropicrin, with plastic tarp, controlled weedy grass and broadleaf species equal to MeBr; however, unacceptable sedge species control at Jay and Arcadia was 56 and 79%, respectively. Metam-sodium applied alone failed to control redroot pigweed; however, MS + combinations provided control. These studies confirm that no EPA-registered fumigant alternative to MeBr, applied alone or in combination for preplant turf soil fumigation, exists. Consequently, until such time that an effective alternative is identified, turf managers will be forced to forego fumigation, or they will have to choose a less-effective alternative and accept the consequences of contamination. Nomenclature: Chloropicrin (trichloronitromethane); dazomet; 1,3-dichloropropene; iodomethane; metam-sodium; methyl bromide; oxadiazon; potassium azide; alexandergrass, Brachiaria plantaginea (Link) A.S. Hitchc. #3 BRAPL; bermudagrass, Cynodon dactylon (L.) Pers. # CYNDA; broadleaf signalgrass, Brachiaria platyphylla (Griseb.) Nash # BRAPP; carpetweed, Mollugo verticillata L. # MOLVE; purple nutsedge, Cyperus rotundus # CYPRO; redroot pigweed, Amaranthus retroflexus L. # AMARE; sharppod morningglory, Ipomoea cordatotriloba Dennstedt # IPOTC; tall morningglory, Ipomoea purpurea L. # IPOPU; yellow nutsedge, Cyperus esculentus L. # CYPES. Additional index words: Fumigation, sod, turf. Abbreviations: 1,3-D, 1,3-dichloropropene; EPA, Environmental Protection Agency; IM, iodomethane; MeBr, methyl bromide; MITC, methyl isothiocyanate; MS, metam-sodium; PA, potassium azide; WAT, weeks after treatment.

Control of Purple Nutsedge (Cyperus rotundus) with Herbicides and Mowing1

Purple nutsedge management with herbicides (halosulfuron, imazaquin, MSMA, S-metolachlor, and sulfentrazone) and mowing was investigated in a bare ground homogenous purple nutsedge field site. Mowing at 5 cm increased control of purple nutsedge by 6% compared to not mowing. Sequential applications of halosulfuron, MSMA, and sulfentrazone provided at least 80% control of purple nutsedge shoots, whereas imazaquin controlled purple nutsedge shoots less than 65%. All herbicide treatments reduced purple nutsedge total and viable tuber densities at least 40%. S-metolachlor PRE reduced total and viable tuber densities 65 and 69%, respectively. Sequential applications of sulfentrazone or MSMA reduced total and viable tubers 80%. Early postemergence (EPOST) or EPOST followed by late-postemergence applications of halosulfuron and imazaquin reduced total and viable tuber densities 52 and 59%, respectively. Data indicate that S-metolachlor PRE and sequential applications of MSMA and sulfentrazone may be viable treatments for control of purple nutsedge shoots and tubers. Nomenclature: Halosulfuron; imazaquin; MSMA; S-metolachlor; sulfentrazone; purple nutsedge, Cyperus rotundus L. #3 CYPRO. Additional index words: Purple nutsedge control, purple nutsedge tuber viability. Abbreviations: EPOST, early postemergence; LPOST, late-postemergence; WALP, weeks after late-postemergence; WAT, weeks after treatment.

Torpedograss (Panicum repens) Control with Quinclorac in Bermudagrass (Cynodon dactylon × C. transvaalensis) Turf1

Torpedograss is a serious problem in southern turfgrass, especially along the U.S. gulf coast. Studies were conducted during 1998, 1999, and 2000 to evaluate quinclorac for torpedograss control in bermudagrass turf. Three applications of quinclorac at 0.6 kg/ha spaced 21 d apart provided better torpedograss control (88%) than two applications at 0.8 kg/ha (69%) or one application at 1.7 kg/ha (69%). Two applications of quinclorac (0.8 kg/ha) plus diclofop (0.8 kg/ha) provided better torpedograss control (82%) than either herbicide applied alone when evaluated after a single season of application. Increasing the mowing interval prior to quinclorac application to allow for more foliage to be present did not improve control. Nitrogen application prior to quinclorac treatment did not improve torpedograss control. Long-term control will most likely require quinclorac applications for more than one season. Nomenclature: Diclofop; quinclorac; bermudagrass, Cynodon dactylon (L.) Pers. × C. transvaalensis Burtt-Davey ‘Tifway’; torpedograss, Panicum repens L. #3 PANRE. Additional index words: Application frequency, cultural practices, mowing interval, nitrogen fertility, turfgrass. Abbreviations: LSD, least significant difference; POST, postemergence; WAIT, weeks after initial treatment.

Control of Torpedograss (Panicum repens) with Trifloxysulfuron-Sodium in Bermudagrass (Cynodon dactylon x Cynodon transvaalensis) Turf

Torpedograss is a serious problem in southern turfgrass, especially along the U.S. gulf coast. Studies were conducted in 1999, 2000, 2002, and 2003 to evaluate single and sequential applications of trifloxysulfuron-sodium for torpedograss control in bermudagrass turf. In 1999/2000, single applications of trifloxysulfuron-sodium at 75 g ai/ha provided at least 10% better torpedograss control than 25 g/ha 7 and 15 wk after initial treatment (WAIT). When evaluated 15 WAIT, sequential applications of trifloxysulfuron-sodium provided 87% control, similar to 84% control observed with quinclorac + diclofop-methyl, each applied at 840 g ai/ha. Both treatments controlled torpedograss better than a single trifloxysulfuron-sodium application (61%) in 1999/2000. Torpedograss control was less in 2002/2003 than in 1999/2000 because of high rainfall, which encouraged aggressive torpedograss growth and possible movement of trifloxysulfuron-sodium below its rooting zone. No differences were noted among trifloxysulfuron-sodium rates or number of applications in 2002/2003. Quinclorac + diclofop-methyl controlled torpedograss greater than trifloxysulfuron-sodium 15 WAIT in 2002/2003, but neither treatment provided greater than 45% control. These results suggest that trifloxysulfuron-sodium controls torpedograss when rainfall is not excessive. Nomenclature: Bermudagrass, Cynodon dactylon (L.) Pers. × Cynodon transvaalensis Burtt-Davey ‘Tifway’; torpedograss, Panicum repens L. #3 PANRE. Additional index words: Application rate, application frequency. Abbreviations: WAIT, weeks after initial treatment.

Tolerance of 'Salam' seashore paspalum (Paspalum vaginatum) to postemergence herbicides.

Field studies were conducted to assess the tolerance of seashore paspalum (‘Salam’) to postemergence (POST) herbicides in Florida in 2000 and 2001. POST applications of bentazon (2,200 g/ha), clopyralid (420 g/ha), dicamba (280 g/ha), halosulfuron (70 g/ha), imazaquin (420 g/ha), mecoprop + 2,4-D + dicamba (160 + 180 + 40 g/ha), metsulfuron (30 g/ha), and quinclorac (1,700 g/ha) resulted in ≤10% injury 7 and 15 d after treatment (DAT), indicating their safety for POST application. Clethodim (280 g/ha) and sethoxydim (310 g/ha) caused 67 and 46% injury, respectively, 15 DAT averaged across 2000 and 2001. Ethofumesate was inconsistent between years, causing 30 and 60% injury 7 and 15 DAT, respectively, in 2000, but only 5 and 13% 7 and 15 DAT, respectively, in 2001. Imazapic and trifloxysulfuron-sodium caused an average of 47% injury 7 DAT in 2000 and 45% injury 15 DAT in 2001. Clethodim, ethofumesate, imazapic, sethoxydim, and trifloxysulfuron-sodium can not be safely applied POST to Salam seashore paspalum; however, bentazon, clopyralid, dicamba, halosulfuron, imazaquin, mecoprop + 2,4-D + dicamba, metsulfuron, and quinclorac are safe. Nomenclature: Bentazon, clethodim, clopyralid, dicamba, ethofumesate, halosulfuron, imazapic, imazaquin, mecoprop + 2,4-D + dicamba, metsulfuron, quinclorac, sethoxydim, trifloxysulfuron-sodium; seashore paspalum, Paspalum vaginatum Swartz ‘Salam’ #3 PASVA. Additional index words: Turfgrass tolerance, turfgrass injury. Abbreviations: DAT, days after treatment; OCGC, Old Collier Golf Club; WFREC, West Florida Research and Education Center.

St. Augustinegrass Fertilizer Trials

ABSTRACT Research was conducted to verify the current fertilization recommendations for St. Augustinegrass (Stenotaphrum secundatum Walt. Kuntze) lawns. Currently, a range from 100 to 300 kg nitrogen (N) ha− 1 per growing season is suggested, based on factors such as location in the state, desired maintenance level, soil conditions, etc. Research was conducted at the G.C. Horn Turfgrass Field Laboratory in Gainesville, FL from 2000 to 2002, utilizing medium to high management levels and at a sod farm in Bradenton, FL from 2001 and 2002, under low management conditions. Nitrogen (N) and potassium (K) treatments were arranged in a randomized complete block design with three replications in both locations. In Gainesville, best visual quality was generally obtained with medium (MN) or high nitrogen rates (HN). In Bradenton, MN, and HN rates provided best visual quality responses in 2002 and 2003, but higher rates of N were required than in Gainesville to maintain acceptable quality. This higher N requirement could be due to the longer growing season in Bradenton or to poor turfgrass growth resulting from inadequate pest control. In the absence of biotic or abiotic stresses, the highest rates of N were not necessary to maintain an acceptable quality lawn.

Tropical signalgrass (Urochloa subquadripara) control with preemergence- and postemergence-applied herbicides.

Tropical signalgrass is one of the most serious weed problems in the St. Augustinegrass sod production in Florida, and its presence increases production costs and lowers turfgrass quality. The objectives of our research were to: (1) evaluate herbicides preemergence and postemergence for control of tropical signalgrass and (2) compare control of tropical signalgrass and other problem weeds (torpedograss, blanket crabgrass, and India crabgrass) with postemergence herbicides. In preemergence herbicide field trials, only benefin + oryzalin, imazapic, imazapic + 2,4-D, and oryzalin provided ≥75% tropical signalgrass control 8 wk after application (WAA). By 11 WAA, only benefin + oryzalin and imazapic + 2,4-D provided ≥75% tropical signalgrass control. In greenhouse experiments, eight herbicide treatments were applied postemergence to tropical signalgrass seedlings at the two-, four-, six-, and eight-leaf stages. Asulam and CGA 362622 provided ≥89% tropical signalgrass control at all application timings. Imazaquin controlled tropical signalgrass ≥98% when applied before the eight-leaf stage. However, in field trials with mature tropical signalgrass (>20 cm stolons), none of the 20 herbicide treatments applied postemergence provided acceptable control. Nomenclature: Asulam; benefin; CGA 362622, N-[[(4,6-dimethoxy-2-pyrimidinyl)amino]carbonyl]-3-(2,2,2-trifluoroethoxy)-2-pyridinesulfonamide; 2,4-D; imazapic; imazaquin; oryzalin; blanket crabgrass, Digitaria serotina (Walt.) Michx. #3 DIGSO; India crabgrass, Digitaria longiflora (Retz.) Pers. # DIGLO; St. Augustinegrass, Stenotaphrum secondatum (Walt.) Kuntz; torpedograss, Panicum repens L. # PANRE; tropical signalgrass, Urochloa subquadripara (Trin.) R. D. Webster # BRASU. Additional index words: BRASU, DIGLO, DIGSO, PANRE. Abbreviation: WAA, weeks after application.

Postemergence Southern Crabgrass (Digitaria Ciliaris) Control with Sulfonylurea Herbicides

Southern crabgrass is a major weed in turfgrass and it primarily is controlled through preemergence herbicide application. Separate studies were conducted to evaluate the efficacy of trifloxysulfuron and flazasulfuron alone and in tank mixtures for southern crabgrass control in bermudagrass as MSMA alternatives. In 2001, two applications of trifloxysulfuron at 0.03 kg ai/ha 6 wk apart controlled southern crabgrass equal to MSMA applied twice at 2.2 kg ai/ha 7 d apart (91% compared to 90%, respectively) 90 d after initial treatment (DAIT), but provided greater control than MSMA in 2002 (80 versus 74%, respectively) 90 DAIT. Two applications of trifloxysulfuron at 0.02 kg/ha tank mixed with MSMA at 1.1 kg/ha controlled southern crabgrass 90%, greater than either two applications of trifloxysulfuron or MSMA applied alone (80% and 74%, respectively). In the second study, flazasulfuron applied at 0.05 kg ai/ha tank mixed with prodiamine at 1.1 kg ai/ha, pendimethalin at 1.6 kg ai/ha, or quinclorac at 0.84 kg ai/ha controlled southern crabgrass greater than a single application of MSMA at 2.2 kg/ha 60 DAT. In both 2005 and 2006 flazasulfuron applied alone provided similar or greater southern crabgrass control compared to a single application of MSMA at 2.2 kg/ha 60 DAT. At the conclusion of these studies, trifloxysulfuron and flazasulfuron alone or in tank mixtures controlled southern crabgrass similar to or better than MSMA; therefore these would be effective alternatives to MSMA in bermudagrass. Nomenclature: flazasulfuron, trifloxysulfuron. bermudagrass, Cynodon dactylon Pers. (L.) x. transvaalensis Burtt-Davy, ‘Tifway 419’, southern crabgrass, Digitaria ciliaris L. DIGSP

Timing of Oxadiazon and Quinclorac Application on Newly Sprigged Turfgrass Species

Abstract Tolerance of sprigged ‘Tifsport’ and ‘Tifdwarf’ bermudagrass, ‘Meyer’ zoysiagrass, and ‘Salam’ seashore paspalum to oxadiazon (2,240 g/ha) or quinclorac (840 g/ha) applied 1 wk before sprigging (WBS), at sprigging (AS), 2 wk after sprigging (WAS), and 4 WAS was investigated in the field. Weed control was also evaluated. For both herbicides only the AS application timing injured the turfgrass greater than 22%, and injury for the other application timings ranged from 9 to 19% 5 WAS. When evaluated 8 WAS turfgrass injury following the AS application timing remained at 19%, and injury for all other timings was 8% or less. Eight WAS the 1 WBS, AS, 2 WAS, and 4 WAS application timings achieved 89, 79, 94, and 99% plot coverage, respectively, when averaged over all turfgrass species/cultivars and herbicides. By 13 WAS, all species/cultivars achieved at least 90% plot coverage. Presprigging applications of oxadiazon provided 98 to 100% goosegrass and old world diamond-flower control. Quinclorac applied AS provided greater than 70% control of these weeds. Results indicate that oxadiazon and quinclorac applied AS will cause unacceptable turfgrass injury. If goosegrass and/or old world diamond-flower are problematic, oxadiazon is a feasible choice for control of these weeds, but quinclorac is not. Nomenclature: Oxadiazon; quinclorac; goosegrass, Eleusine indica (L.) Gaertn.; old world diamond-flower, Oldenlandia corymbosa L.; bermudagrass, Cynodon dactylon (L.) Pers. × Cynodon transvaalensis Burtt-Davey ‘Tifsport’, ‘Tifdwarf’ CYNDA; zoysiagrass, Zoysia japonica L. ‘Meyer’ ZOYJA; seashore paspalum, Paspalum viginatum Swartz, ‘Salam’ PASVA