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Bielinski M. Santos, James P. Gilreath, Camille E. Esmel and Myriam N. Siham

second only to tomato ( Lycopersicon esculentum ) in total value, representing $187 million ( U.S. Department of Agriculture, 2007 ). Yellow nutsedge and purple nutsedge interference in polyethylene-mulched bell pepper can cause significant yield

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Yan Chen, Ronald E. Strahan and Regina P. Bracy

Yellow nutsedge is one of the most troublesome and widespread perennial weeds in managed landscapes in the United States ( Gao et al., 1999 ; Wilcut et al., 1991 ). Its upright growth habit and pale green leaf color are a prominent distraction and

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John W. Wilcut, Charles H. Gilliam, Glenn R. Wehtje, T. Vint Hicks and Diane L. Berchielli

Preplant-incorporated, preemergence, and postemergence herbicides were evaluated for yellow nutsedge (Cyperus esculentus L.) control and for phytotoxicity to four container-grown woody plants. Preplant-incorporated or preemergence applications of chlorimuron at 0.07 kg a.i./ha or imazaquin at 1.12 kg a.i./ha provided the greatest control of yellow nutsedge. Imazaquin applied at 0.28, 0.56, 0.84, or 1.12 kg a.i./ha suppressed growth of Rhododendron × `Copperman' azalea and Lagerstroemia indica ×sfauriai `Natchez'. All other herbicides tested were safe on the four woody plants evaluated. Chlorimuron provided the best combination of yellow nutsedge control and tolerance on woody ornamental. Chemical names used: 2-[[[[(4-chloro-6-methoxy-2-pyrimidinyl)amino]carbonyl]amino]sulfonyl]benzoic acid (chlorimuron); 2-[4,5-dihydro-4-methyl-4-(1-methylethyl)-5-oxo-1H-imidazol-2-yl]-3-quinolinecarboxylic acid (imazaquin).

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Timothy N. Motis, Salvadore J. Locascio and James P. Gilreath

Yellow nutsedge (Cyperus esculentus L.) interference with bell pepper (Capsicum annuum L.) has become an important concern because of the phase-out of methyl bromide as a soil fumigant. The critical period for yellow nutsedge control in pepper was determined in two adjacent experiments (removal and plant-back) conducted twice in separate fields each Spring and Fall 2000 in Gainesville, Fla. In the removal experiment, nutsedge was planted with pepper in all but the full-season (13 weeks) weed-free controls and removed at 1, 3, 5, and 7 weeks after pepper transplanting (WAPT). Full-season weedy control plots in the removal experiment were obtained by never removing nutsedge planted with pepper (0 WAPT). In the plant-back experiment, all but the full-season weed-free controls received nutsedge with nutsedge planted at 0 (full-season weedy control), 1, 3, 5, and 7 WAPT. Sprouted nutsedge tubers were planted at a density of 45 tubers/m2. Results indicated that a nutsedge-free period from 3 to 5 WAPT in spring and 1 to 7 WAPT would prevent >10% yield reductions of large and marketable peppers. Full-season nutsedge interference reduced pepper yields by >70%. When planted with pepper, nutsedge shoots grew taller than pepper plants with nutsedge heights at 5 WAPT up to two times greater in fall than spring. Results indicated that yellow nutsedge control practices should be initiated earlier and continue longer in fall than spring due to faster early-season nutsedge growth in fall than spring.

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W.C. Porter

Yellow nutsedge (YNS) can be a serious problem where vegetables are grown on polyethylene mulch. YNS will rapidly cover the row and become a nuisance. This study was conducted to determine the effect of various population densities of YNS on the yield response of yellow squash grown on black polyethylene. Presprouted YNS tubers were planted at densities of 0, 10, 20, 40, and 50/m2 the day after `Superpik' yellow squash was planted. In 1996 the YNS did not produce tubers. Top growth increased up to 40/m2, but root growth increased to 50/m2. In 1997 top and root growth increased up to 20/m2. Tuber production increased up to 40/m2. In 1998 top, root, and tubers dry weight increased as the YNS density increased to 50 tubers/m2. There were no differences in weight of the squash plants or fruit yields any year. In experiments over three growing seasons, YNS at the densities tested did not interfere with the yield of yellow summer squash grown on black polyethylene mulch. The rapid growth of the squash and its dense canopy provide too much shade for the YNS to grow competitively. The yield of the YNS was greater in wet years than in dry years. The increased supply of YNS tubers could cause squash yield reductions in future plantings because of potential densities greater than those use in this study. YNS competition could also be a problem in rotational crops that are less competitive.

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Milton E. McGiffen Jr., David W. Cudney, Edmond J. Obguchiekwe, Aziz Baameur and Robert L. Kallenbach

Yellow and purple nutsedge are problem perennials that resist common control measures. High temperatures, irrigation, and relatively non-competitive crops combine to greatly increase the severity of nutsedge infestations in the Southwest. We compared the growth and susceptibility of purple and yellow nutsedge to chemical and cultural control measures at several locations in southern California. When not controlled, low initial populations of either species led to heavy infestations later in the season. Purple nutsedge was far more prolific in both tuber production and above-ground growth. Summer rotations that included crops with dense canopies severly decreased nutsedge shoot and tuber growth. Cool-season crops planted into heavy nutsedge infestations in the fall are generally unaffected because nutsedge infestations in the fall are generally unaffected because nutsedge soon enters dormancy and ceases growth. Solarization, or pasteurization of the upper soil layers, was effective in decreasing tuber formation. Tillage effectively spread local infestations over larger areas.

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Bielinski M. Santos, James P. Gilreath, Camille Esmel and Myriam N. Siham

Field trials were conducted in Bradenton, Fla., to determine the effect of purple and yellow nutsedge (Cyperus rotundus and C. esculentum) time of emergence on the area of influence of each weed on bell pepper (Capsicum annuum). Each weed-bell pepper complex was studied separately. A single weed was transplanted 1, 2, 3, 4, and 5 weeks after bell pepper transplanting (WAT) and bell pepper yield was collected at 0, 30, 60, and 90 cm from each weed. Bell pepper yield data indicated that yellow nutsedge was more aggressive than purple nutsedge interfering with bell pepper. When yellow nutsedge emerged 1 WAT, bell pepper yield losses were between 32 and 57% for plants at 0 and 30 cm away from the weed, respectively, which represents at least a density of approximately 3.5 plants/m2. For purple nutsedge, one weed growing since 1 WAT between two bell pepper plants (0 cm; 10 plants/m2) produced a yield reduction of 31%. These results indicated that low nutsedge densities, which are commonly believed to be unimportant, can cause significant bell pepper yield reductions.

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J.P. Morales-Payan, W.M. Stall, D.G. Shilling, J.A. Dusky and T.A. Bewick

Field trials were conducted in Gainesville, Fla., to determine the influence of nitrogen fertilization on the interference effect of purple or yellow nutsedge on the yield of fresh tomato. Nitrogen (N) rates of 50, 100, 150, 200, 250, 300, and 350 kg·ha–1 were applied broadcast to the soil. Before transplanting, 1-m-wide soil beds were covered with plastic and fumigated with methyl bromide to suppress the growth on undesired weeds. Nutsedge-free and purple or yellow nutsedge-infested tomato plots were separately established. `Solar Set' tomatoes were transplanted in the middle of the soil beds, 50 cm apart in a single row. In nutsedge-infested plots, weed densities known to cause significant yield reduction in tomato (100 purple nutsedge plants/m2 and 50 yellow nutsedge plants/m2) were uniformly established perforating the plastic and transplanting viable tubers in the perforations. Purple and yellow nutsedge tubers were transplanted the same day as tomatoes and were allowed to interfere during the whole crop season. Results indicate that N rates had a significant effect on tomato fruit yield in both nutsedge-free and nutsedge-infested treatments. The presence of either purple or yellow nutsedge significantly reduced the fruit yield of tomato at all N rates. As N rates increased, tomato fruit yield reduction caused by the interference of either nutsedge species also increased. When yellow nutsedge was allowed to interfere with tomato, fruit yield loss was as low as 18% at 50 kg N/ha and as high as 42% at 350 kg N/ha. In purple nutsedge-infested tomato, fruit yield reductions ranged from 10% at 50 kg N/ha to 27% at 350 kg N/ha. N effects on nutsedge-free and nutsedge-infested tomato yields were described by quadratic equations, with maximum tomato fruit yield values being reached between 200 and 250 kg N/ha in both nutsedge-free and nutsedge-infested treatments.

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J.D. Fry, P.H. Dernoeden, W.S. Upham and Y.L. Qian

Field studies were conducted in Kansas and Maryland to compare the safety and efficacy of halosulfuron-methyl (HM) and bentazon for topkill of yellow nutsedge (Cyperus esculentus L.). Kentucky bluegrass (Poa pratensis L.) and creeping bentgrass (Agrostis palustris Huds.) treated with single (in Kansas) or sequential (in Maryland) HM (35 to 140 g·ha–1) or bentazon (1120 or 1680 g·ha–1) applications exhibited little injury, and treated turf had acceptable quality in all studies. Bentazon caused an unacceptable reduction in perennial ryegrass (Lolium perenne L.) quality at ≥5 weeks after treatment in four of five tests. Perennial ryegrass quality declined linearly with increasing HM rates (between 35 and 140 g·ha–1). In Maryland, HM (≥70 g·ha–1) elicited unacceptable perennial ryegrass quality for 2 or 3 weeks; however, in Kansas, quality was unacceptable for ≈1 week. In Kansas, yellow nutsedge topkill by HM (70 kg·ha–1) ranged from 52% to 97%. A single HM application (35, 70, or 140 kg·ha–1) provided > 97% topkill in Maryland. Yellow nutsedge topkill by bentazon (1680 g·ha–1) generally was inferior to that by HM (70 g·ha–1). Chemical names used: 3-(1-methylethyl)-1H-2,1,3-benzothiadiazin-4 (3H)-one 2,2-dioxide (bentazon), methyl 3-chloro-5-(4,6-dimethoxypyrimidin-2-ylcarbamoylsulfamoyl)-1-methylpyrazole-4-carboxylate (halosulfuron-methyl).

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J. Pablo Morales-Payan* and William M. Stall

A field experiment was conducted in Live Oak, Fla., to determine the effect of yellow nutsedge (Cyperus esculentus L.) (YN) density and time of emergence on the yield of direct-seeded squash (Cucurbita pepo L.). YN densities (0, 20, 40, 60, and 100 plants/m2) were established from tubers planted at different times onto polyethylene-mulched beds, so that YN would emerge the same day as the crop or 5, 15, or 25 days later than the crop (DLTC). YN was not controlled after its emergence. The extent of squash yield loss was affected by YN density and time of emergence. When YN emerged the same day as the crop, the yield of squash was reduced by ≈7% (20 YN/m2) to 20% (100 YN/m2). When YN emerged 15 DLTC, crop yield loss was ≈13% at the density of 100 YN/m2>. Regardless of density, YN emerging 25 DLTC did not significantly reduce crop yield as compared to weed-free squash. Thus, in soils with high YN densities (≈100 viable tubers/m2) herbicides and/or other means of YN suppression in squash should be effective for at least 25 days after crop emergence to prevent significant yield loss. If squash yield losses <5% were acceptable, YN control may not be necessary when densities <20 YN/m2 emerge at any time during the squash season or when <100 YN/m2 emerge >25 DLTC. However, YN emerging during the first 15 days of the squash season may produce tubers, which could increase the YN population at the beginning of the following crop season.