When tank mixed with certain boadleaf-selective herbicides, fluazifop {(+)-2-[4-[[5-(trifluoromethyl)-2-pyridinyl] oxy] phenoxy] propanoic acid}, sethoxydim {2-[1-(ethoxyimino)butyl]-5-[2-(ethylthio)propyl]-3-hydroxy-2-cyclohexen-1-one}, haloxyfop {2-[4-[[3-chloro-5-(trifluoromethyl)-2-pyridinyl] oxy] phenoxy] propanoic acid}, and fluazifop-P {(R)-2-[4-[[5-trifluoromethyl)-2-pyridinyl] oxy] phenoxy] propanoic acid} were less effective in controlling two annual grasses, Texas panicum (Panicum texanum Buckl. #3 PANTE) and large crabgrass [Digitaria sanguinalis (L.) Scop. # DIGSA]. These herbicides were applied alone or were combined with the broadleaf-selective herbicides bentazon {3-(1-methylethyl)-(1H)-2,l,3-benzothiadiazin-4(3H)-one-2,2-dioxide} and/or 2,4-DB [4-(2,4-dichlorophenoxy)butanoic acid]. The herbicide combinations controlled smooth pigweed (Amaranthus hybridus L. # AMACH) and yellow nutsedge (Cyperus esculentus L. #CYPES). Increasing the rates of the grass-selective herbicides in the mixture reduced the adverse effects of 2,4-DB or bentazon.

Flumioxazin plus metolachlor mixtures preemergence (PRE) were evaluated with or without postemergence (POST) herbicides for weed control and peanut (Arachis hypogaea) response in three North Carolina studies. Metolachlor PRE at 2.24 kg ai/ha controlled goosegrass (Eleusine indica) and yellow nutsedge (Cyperus esculentus) 93 and 80%, respectively, and control was not improved with flumioxazin or norflurazon. Metolachlor plus flumioxazin PRE at 0.07 or 0.11 kg ai/ha controlled common lambsquarters (Chenopodium album); entireleaf (Ipomoea hederacea var. integriuscula), ivyleaf (I. hederacea), and pitted morningglory (I. lacunosa); and prickly sida (Sida spinosa) better than metolachlor plus norflurazon PRE at 1.34 kg ai/ha. Morningglories (Ipomoea spp.) were controlled 77 and 86% with flumioxazin PRE at 0.07 and 0.11 kg/ha, respectively, and control was increased to nearly 100% with acifluorfen plus 2,4-DB or lactofen plus 2,4-DB POST. Peanut injury by flumioxazin and norflurazon was observed at one location in 1997; however, yields were not reduced. Peanut treated with metolachlor plus flumioxazin PRE at either rate yielded at least 3,750 kg/ha compared to 3,120 kg/ha with metolachlor plus norflurazon PRE or 1,320 kg/ha with metolachlor PRE.

The potential for yellow nutsedge (Cyperus esculentus L. var. leptostachyus Boeck. # CYPES) regrowth was reduced by increasing plant age and by glyphosate [N-(phosphonomethyl)glycine] and oxyfluorfen [2-chloro-1-(3-ethoxy-4-nitrophenoxy)-4-(trifluoromethyl)benzene]. Of the amount of glyphosate transported to underground parts, most was found in the tubers, with immature rhizomes, roots, and tubers having 2 to 3 times higher concentrations than comparable mature tissues. Addition of unlabeled oxyfluorfen as a tank mixture with glyphosate increased absorption and translocation, mainly into leaves and new tubers, of radioactivity from 14C-glyphosate in 30-day-old plants. In contrast to the younger plants, the addition of oxyfluorfen decreased 14C-glyphosate detected in 60-day-old plants. The greater effectiveness of glyphosate when applied with oxyfluorfen on yellow nutsedge at the early growth stage has important implications in the field because the tuberization process must be stopped early in the development of the plant for successful control.

In field studies, mefluidide {N-[2,4-dimethyl-5-[[(trifluoromethyl)sulfonyl] amino] phenyl] acetamide} was most effective as an enhancing agent for bentazon [3-(1-methylethyl)-(1H)-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide] and/or acifluorfen {5-[2-chloro-4-(trifluoromethyl)phenoxy]-2-nitrobenzoic acid} when applied as a tank mixture compared to sequential applications. The influence of mefluidide rate on weed control was not consistent. Additives improved the control of several weed species evaluated, but mefluidide generally was only equal to petroleum oil concentrate (phytobland petroleum oil plus emulsifiers in an 83:17 ratio) as an enhancing agent for bentazon and/or acifluorfen.

Growth characteristics and competitive relationships of cotton and three perennial weeds (johnsongrass, purple nutsedge, and yellow nutsedge) were investigated at the USDA Cotton Research Station in Shafter, CA. In growth analysis experiments, yellow nutsedge and johnsongrass had highest values for height, biomass, leaf area production, growth rate, and photosynthetic efficiency. The weeds exhibited greater overall resource use and production efficiency than cotton, while cotton attained greater leafiness and canopy closure than weeds over the 10-wk experiment. Linear correlation indicated that most growth variables were significantly correlated with aggressivity (competitiveness); however, all correlation coefficients were less than 0.80. Stepwise multiple regression, using aggressivity as the dependent variable, defined 4 growth variables out of 12 that best described competitiveness. These were unit leaf rate (ULR), height, relative growth rate (RGR), and initial propagule weight (PWT). Thus, parameters of light utilization (ULR, height) and early establishment (RGR, PWT) were best predictors of competitive success in this system.

Yellow nutsedge (Cyperus esculentus L. # CYPES) was treated with unlabeled and 14C-labeled glyphosate [N-(phosphonomethyl)glycine] to study the toxicity and translocation of glyphosate into parent tubers of this weed. When plants of 2 and 4 weeks of age were treated with 0.6 kg ai/ha of glyphosate, fewer parent tubers from treated plants resprouted (14 and 32%) than tubers from control plants (73 and 59%, respectively) of equal age. Also, fewer tubers resprouted from 2-week than from 4-week-old treated plants. The radioactivity of parent tubers from plants treated at 2 weeks of age, which exceeded that of tubers from plants of 4 and 6 weeks of age, indicated that translocation of 14C into parent tubers decreased as the treated plants increased in age. The differential amounts of 14C translocated appear to explain why applications of glyphosate were more effective in suppressing resprouting of parent tubers from 2-week than 4-week-old plants.

Field and greenhouse experiments were conducted to evaluate postemergence (POST) soybean injury and weed control with CGA-277476 and cloransulam-methyl alone and in tank mixtures. In the field, visible soybean injury was 12 to 14% from CGA-277476 and 9 to 13% from cloransulam-methyl 7 d after treatment. Tank mixtures of either herbicide with acifluorfen or acifluorfen plus thifensulfuron were more injurious than CGA-277476 or cloransulam-methyl applied alone. Both CGA-277476 and cloransulam-methyl reduced velvetleaf dry weight 82%, and cloransulam-methyl reduced common ragweed dry weight 92%. Neither herbicide adequately controlled common lambsquarters, redroot pigweed, nor eastern black nightshade. The addition of acifluorfen to the spray solution improved common ragweed, common lambsquarters, redroot pigweed, and eastern black nightshade control with CGA-277476 and improved common lambsquarters, redroot pigweed, and eastern black nightshade control with cloransulam-methyl. Tank mixing thifensulfuron with CGA-277476 or cloransulam-methyl increased common lambsquarters and redroot pigweed control. In the greenhouse, CGA-277476 at 20 g ai/ha reduced velvetleaf dry weight 98%, and 79 g/ha was required to reduce common ragweed dry weight 93%. Cloransulam-methyl at 4.4 g ai/ha reduced velvetleaf dry weight 98% and common ragweed dry weight 94% at 8.8 g/ha. Chlorimuron reduced yellow nutsedge dry weight more than CGA-277476 or cloransulam-methyl. Antagonism of POST graminicide activity by CGA-277476 was grass species and graminicide related. CGA-277476 reduced giant foxtail control by clethodim but not by quizalofop. Cloransulam-methyl tank mixed with clethodim or quizalofop controlled giant foxtail.

Field studies were conducted from 1993 to 1995 to evaluate MON-12051 for turfgrass tolerance and control of yellow and purple nutsedges. The availability of herbicides for selective control of these weeds in turfgrass is limited. A sulfonylurea compound, MON-12051, has recently been developed for selective control of the nutsedges in turfgrass. When MON-12051 was applied at 0.07 to 0.14 kg ai/ha, the injury to Kentucky bluegrass, tall fescue, bermudagrass, and zoysiagrass was slight, with a maximum of 10% injury. At these rates, MON-12051 outperformed both bentazon and imazaquin in controlling yellow and purple nutsedges. Averaged over all tests 6 wk after treatment, yellow nutsedge control with MON-12051 was 83%. Control averaged 44% during the same period when treated with bentazon, whether applied once at 2.24 kg ai/ha or twice at 1.12 kg ai/ha. Purple nutsedge control averaged 96% when treated with MON-12051 in Kentucky bluegrass, while control was 42% with imazaquin applied at 0.19 and 0.43 kg ai/ha.

Greenhouse and laboratory studies were conducted to determine the allelopathic potential of two sweet potato [Ipomoea batatas L. (Lam.)] cultivars, ‘Regal’ and ‘SC 1149-19’. Yellow nutsedge (Cyperus esculentus L. # CYPES) and alfalfa (Medicago sativa L.) plants grown in soil from sweet potato field plots accumulated less dry matter than plants grown in soil from adjacent weedy plots. Growth of yellow nutsedge and alfalfa plants was also reduced when grown in a potting medium containing decomposing sweet potato plants in comparison to plants grown in potting medium alone. When the sweet potato potting medium mixture was incubated at 25 C and tested weekly using an alfalfa growth bioassay, inhibition was high initially but decreased over time and was not observed after a 12-week incubation. Aqueous methanol (50%)-soluble extracts of sweet potato periderm were inhibitory to yellow nutsedge root growth in vermiculite and alfalfa seed germination on filter paper. Regal extracts were inhibitory to yellow nutsedge root growth at a concentration of 2.5 mg periderm extracted/ml, but SC 1149-19 extract was inhibitory only at a concentration eight times higher. Similar differences between cultivars were observed with the alfalfa germination bioassay. Preliminary separation of the Regal periderm extract by paper chromatography indicated the presence of phenolic compounds with a wide range of polarities. Several of these UV-visible compounds were inhibitory to alfalfa germination.

Field studies at three sites in Georgia evaluated broadleaf weed and nutsedge management in peanut with PPI applications of imazethapyr and metolachlor and POST applications of paraquat in mixture with imazethapyr or bentazon. Imazethapyr at 36 g ai/ha applied PPI alone or in mixture with metolachlor at 2750 g ai/ha controlled coffee senna; entireleaf, ivyleaf, pitted, smallflower, and tall morningglories; bristly starbur; and prickly sida better than metolachlor applied PPI. Yellow nutsedge control was generally higher where metolachlor was applied PPI. Postemergence control of the aforementioned species and sicklepod was similar with paraquat plus imazethapyr and paraquat plus bentazon. Peanut yields with paraquat plus imazethapyr and paraquat plus bentazon were similar. With one exception, peanut yields from imazethapyr PPI systems were higher than metolachlor PPI systems when POST herbicides were not used. Inclusion of metolachlor with PPI application of imazethapyr increased yields only at one location.

Yellow and purple nutsedge and southern root-knot nematode are common pests in intensively managed chile pepper production. Greenhouse studies were conducted to identify relationships among nutsedge species, chile peppers, and root-knot nematode. All practical combinations of the plant species and nematodes were grown together in pots for 14 wk. Both nutsedges and root-knot nematode reduced chile pepper height over time with no interaction. Competition from purple nutsedge or either nutsedge species plus nematodes reduced chile pepper top weight more than yellow nutsedge or nematodes alone. All pest combinations reduced chile pepper root weight. Chile pepper and nematodes individually reduced rates of shoot production, as well as top and belowground weights of yellow and purple nutsedge. Chile pepper and purple and yellow nutsedge hosted root-knot nematode host race 3. Nematode egg production was greater on chile pepper roots than on either nutsedge species. Purple nutsedge growing with chile pepper increased nematode production g−1 of chile pepper root. Purple nutsedge grown with chile pepper was the most detrimental for chile pepper growth, but most efficient for maintaining the root-knot nematode population on the least amount of root biomass. Since root-knot nematode infests yellow and purple nutsedge, and few nematicides are available for nematode control, root-knot nematode cannot be managed with crop rotation if nutsedge is not controlled.

Knowledge of weed biology is essential for development of both economically and environmentally acceptable weed management systems. Weed biology relates to plant attributes such as morphology, seed dormancy and germination, physiology of growth, competitive ability, and reproductive biology. Concepts of population biology such as seedbank dynamics for annuals and root reserves, dormancy, and longevity of vegetative propagules for perennials can be used to predict weed infestations better and to evaluate sustainable management strategies. Integrated approaches that give priority to depletion of root reserves or seedbanks through interfering with dormancy or germination requirements have great potential to enhance weed management strategies in the future.

Experiments were conducted to evaluate selective herbicides for yellow and purple nutsedge control in nursery crops. Chlorimuron at 0.03 and 0.06 kg ai ha−1 suppressed yellow and purple nutsedge shoot growth either PRE or POST and did not reduce growth of barberry, Burford holly, Compacta holly, azalea, juniper, or photinia, although shoot tip chlorosis was noted in all species except Burford holly and juniper. Imazaquin at 0.25 and 0.5 kg ha−1 and imazethapyr at 0.06 and 0.21 kg ha−1 reduced growth of azalea. Imazethapyr also reduced growth of barberry, juniper, and photinia. Chlorimuron, imazaquin, and imazethapyr inhibited liriope and daylily growth. Pyridate applied at 1.0 and 2.0 kg ha−1 POST did not control purple nutsedge. Pyridate and flurtamone applied POST did not control yellow nutsedge as effectively as chlorimuron, imazaquin, or imazethapyr. Flurtamone at 0.5 and 1.0 kg ha−1 applied PRE or POST controlled purple nutsedge. Both pyridate and flurtamone visibly injured most nursery crops tested, although plants generally outgrew the damage.

In field studies, ‘Regal’ sweet potato greatly reduced yellow nutsedge growth when the two species were grown together using standard cultural practices. At the end of the growing season, yellow nutsedge shoot dry weight per m2 in plots where the two species were planted together was less than 10% of shoot weight in plots where nutsedge was grown alone. Presence of yellow nutsedge did not markedly affect sweet potato growth. When grown together in a greenhouse experiment designed to minimize the competitive effects of sweet potato on yellow nutsedge, yellow nutsedge growth was reduced more than 50% by sweet potato 8 and 12 weeks after planting. The most polar fraction of serially extracted sweet potato periderm tissue was highly inhibitory to yellow nutsedge root growth. These results indicate that sweet potato interference with yellow nutsedge under field conditions is partially due to allelopathy.

The activity of soil-applied chlorimuron in yellow and purple nutsedge was studied in greenhouse and laboratory experiments. Soil-applied chlorimuron decreased tuber sprouting by 80% in yellow nutsedge and by 30% in purple nutsedge at 60 g ai/ha. Chlorimuron decreased shoot emergence by 53 to 83% and shoot growth by 85 to 99% in both species at rates as low as 10 g/ha. Previous exposure of tubers to chlorimuron-treated soil reduced tuber resprouting by 20 to 25% in herbicide-free soil at 60 g/ha in both species. There was no rate response in shoot emergence from tubers previously exposed to chlorimuron, but shoot dry weight decreased by 60 to 81% in both species at 60 g/ha. At 12 h after application, 47% of the total 14C applied to the shoot in yellow nutsedge and 32% of that applied in purple nutsedge were absorbed. However, less than 1% of the total 14C applied was translocated out of the shoot and into the roots and tuber in either species. In both species, 1.3% of the 14C applied to the roots and tuber was absorbed and 0.1% was translocated out of the roots and tuber into the shoot at 12 h after application. The pattern of root- and tuber-absorbed 14C distribution indicated that the 14C absorbed by the tuber remained in the tuber and that absorbed by the roots was translocated to the shoots.

Studies were conducted at the Main Agricultural Experiment Station in Fayetteville and the Vegetable Substation in Kibler, Arkansas, in 1992 and 1993 on the same plots to evaluate weed suppression by winter cover crops alone or in combination with reduced herbicide rates in no-till sweet corn and to evaluate cover crop effects on growth and yield of sweet corn. Plots seeded to rye plus hairy vetch, rye, or wheat had at least 50% fewer early season weeds than hairy vetch alone or no cover crop. None of the cover crops reduced population of yellow nutsedge. Without herbicides, hairy vetch did not suppress weeds 8 wk after cover crop desiccation. Half rates of atrazine and metolachlor (1.1 + 1.1 kg ai ha−1) reduced total weed density more effectively in no cover crop than in hairy vetch. Half rates of atrazine and metolachlor controlled redroot pigweed, Palmer amaranth, and goosegrass regardless of cover crop. Full rates of atrazine and metolachlor (2.2 + 2.2 kg ai ha−1) were needed to control large crabgrass in hairy vetch. Control of yellow nutsedge in hairy vetch was marginal even with full herbicide rates. Yellow nutsedge population increased and control with herbicides declined the second year, particularly with half rates of atrazine and metolachlor. All cover crops except hairy vetch alone reduced emergence, height, and yield of sweet corn. Sweet corn yields from half rates of atrazine and metolachlor equalled the full rates regardless of cover crops.

Field studies were conducted from 1995 to 1997 near Tifton, GA, to determine the benefits of stale seedbed weed control in cucumber. Three stale seedbed management systems—(1) power till stale seedbeds twice (2 ×), (2) glyphosate application immediately after planting, and (3) combination system of stale seedbeds power tilled once 2 wk prior to planting followed by glyphosate application immediately after planting cucumber—were evaluated as main plots. Subplots were weed management systems after planting cucumber: intensive, basic, and cultivation alone. Weed densities were generally greater in 1996 and 1997 than in 1995. Yellow nutsedge was the overall predominant species in 1995 (46 plants m−2), with Florida pusley being the predominant species in 1996 and 1997, at 80 and 124 plants m−2, respectively. Generally, stale seedbeds shallow tilled 2 × had fewer weeds and greater cucumber yields than stale seedbeds treated with glyphosate. Glyphosate did not adequately control emerged Florida pusley on stale seedbeds, resulting in reduced cucumber yield. Clomazone preemergence and bentazon/halosulfuron postemergence were used for broadleaf weed control in the intensive weed management system. These herbicides injured cucumber plants, delayed maturity, and reduced yield. Based on our results, stale seedbeds shallow tilled 2 × can be integrated into cucumber production and provide effective cultural weed control. Furthermore, these systems will replace the need for potentially injurious herbicides.

Cloransulam-methyl applied postemergence (POST) following various preplant-incorporated (PPI) herbicides was evaluated in four experiments for weed control in North Carolina soybean over a 2-yr period at three locations. Acifluorfen plus bentazon or chlorimuron alone applied POST injured soybean more than cloransulam-methyl when following any soil-applied herbicide. When following trifluralin PPI, cloransulam-methyl controlled common ragweed, entireleaf morningglory, and pitted morningglory comparable to acifluorfen plus bentazon or chlorimuron. Common lambsquarters and prickly sida control was higher when acifluorfen plus bentazon was applied POST following trifluralin PPI compared to trifluralin PPI followed by cloransulam-methyl or chlorimuron. Acifluorfen plus bentazon or chlorimuron POST controlled yellow nutsedge and smooth pigweed more than cloransulam-methyl POST when following trifluralin PPI. When trifluralin was applied PPI in mixtures with chlorimuron plus metribuzin, flumetsulam, or imazaquin, control of most species was similar regardless of POST treatment used. Soybean treated with cloransulam-methyl yielded 250 kg/ha more than treatments with chlorimuron when these herbicides followed trifluralin plus flumetsulam or trifluralin plus imazaquin. Net returns with different herbicide systems followed trends similar to soybean yield.

A series of greenhouse studies examined the effectiveness of PRE- and POST-applied sulfentrazone in controlling purple and yellow nutsedge as influenced by selective tissue exposure. In addition, 14C-sulfentrazone was utilized to contrast absorption and translocation resulting from these exposures. Consistent control with preemergence applications to germinating tubers was obtained with a combined root and shoot zone exposure. Yellow nutsedge was more susceptible than purple nutsedge. Performance of the separate root and shoot zone exposure was soil pH- and nutsedge-species dependent. POST-foliar applications to established nutsedge were more effective when sulfentrazone was allowed to contact the soil surface. 14C-sulfentrazone was readily absorbed by the roots and translocated to the foliage of both species in hydroponic culture.

Field studies were conducted from 1986 through 1988 to evaluate various herbicides for yellow nutsedge control and peanut yields. Three applications of pyridate provided control comparable to two applications of bentazon with yellow nutsedge regrowth beginning 3 to 4 wk after application depending on moisture conditions. Crop oil concentrate did not improve the activity of pyridate. Flurtamone provided control comparable with that of metolachlor. Nutsedge control with fomesafen was erratic with peanut injury noted. Peanut yields did not reflect the competitive nature of nutsedge.