Joan A. Dusky

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 ≥u200980% 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 (<u200963%) 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.

Above- and belowground interference of purple and yellow nutsedge (Cyperus spp.) with tomato

Abstract Studies were conducted to determine the extent of full and partitioned interference of two nutsedge species with tomato. For full interference, the crop and the weed were transplanted in the same container. For belowground interference, tomato and either weed species were grown in the same container, but the canopies were separated. For aboveground interference, tomato and nutsedges were grown in separate containers placed adjacently, whereas for the no-interference treatment, tomato and nutsedge plants were grown in individual containers. Full interference by yellow nutsedge was more detrimental to tomato shoot dry weight accumulation (34% reduction) than was full interference by purple nutsedge (28% reduction). Belowground interference by purple nutsedge reduced tomato shoot dry weight (18%) more than did aboveground interference (9%). Yellow nutsedge interference above- or belowground reduced tomato shoot dry weight to a similar extent (19%). The belowground interference of both nutsedges with tomato resulted in deficient concentrations of nitrate in the sap of tomato (>u200918% reduction). The growth of purple nutsedge was influenced more strongly by tomato shading than by belowground interference from the crop, whereas yellow nutsedge growth was equally affected by tomato above- and belowground. According to these results, shoot dry weight accumulation in tomato was affected to the same extent by belowground interference from purple and yellow nutsedge, and the higher effect of full interference by yellow nutsedge may be attributed to increased aboveground competition between tomato and yellow nutsedge. Nomenclature:u2003Purple nutsedge, Cyperus rotundus L. CYPRO; yellow nutsedge, Cyperus esculentus L. CYPES; tomato, Lycopersicon esculentum Mill. ‘Solimar’.

Influence of common lambsquarters (Chenopodium album) densities and phosphorus fertilization on lettuce

Abstract Field trials were conducted in organic soils to determine the effects of different phosphorus fertilization programs and common lambsquarters ( Chenopodium album L.) densities on ‘South Bay’ lettuce ( Lactuca sativa L.) yield loss. Phosphorus was applied either banded (125xa0kg P/ha) or broadcast (250xa0kg P/ha) prior to lettuce planting. Common lambsquarters population densities of 0, 2, 4, 8 or 16 plants/6xa0m row (5.4xa0m 2 ) interfered with lettuce for 10 weeks. Two rectangular hyperbola models characterized the relationship between common lambsquarters density and lettuce yield loss. When phosphorus was applied broadcast, predicted lettuce yield losses were 39%, 50%, 59% and 65% for 2, 4, 8 and 16 common lambsquarters plants/6xa0m row, respectively. However, when the phosphorus rate was reduced by 50% and was applied in bands beneath lettuce rows, these predicted losses were 23%, 30%, 35%, and 38% for the same common lambsquarters densities. Based on the lettuce yield loss models, if a single common lambsquarters plant interferes with lettuce every 6xa0m row, then predicted lettuce yield losses could be approximately 27% and 16% for broadcast and banded phosphorus applications, respectively.

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.

Purple Nutsedge (Cyperus rotundus) Control with Glyphosate in Soybean and Cotton1

Studies were conducted at the University of Florida, West Florida Research and Education Center to determine the effect of glyphosate on purple nutsedge control and nutsedge tuber production when glyphosate was applied to the same plots over 3 y in glyphosate-resistant soybean and cotton. Greater than 90% control of purple nutsedge foliage was achieved with a single POST application of glyphosate at 0.9 kg ai/ha in soybean or a sequential glyphosate application of 1.1 kg/ha POST followed by 0.6 kg/ha POST-directed in cotton. By the end of the third year of the study, these same treatments reduced purple nutsedge tuber density to less than 0.2% of the nontreated. In cotton, cultivation alone reduced tuber numbers by greater than 90%. Viability of tubers was also reduced by 80% in soybean and by 65% in cotton in the glyphosate-treated plots. Comparison treatments of imazaquin PRE followed by imazaquin POST in soybean or norflurazon PRE followed by cyanazine plus MSMA POST-directed in cotton also reduced purple nutsedge tuber density by ≥85% after three consecutive years of treatment. Nomenclature: Cyanazine; glyphosate; fluometuron; imazaquin; MSMA; norflurazon; pendimethalin; purple nutsedge, Cyperus rotundus L., #3 CYPRO; cotton, Gossypium hirsutum L. ‘Delta Pine 5415 RR’; soybean, Glycine max L. ‘Hartz 7555RR’. Additional index words: CYPRO, transgenic cotton, cultivation, purple nutsedge population dynamics. Abbreviations: DAP, days after planting; POST-directed, postemergence directed; Early-POST, early postemergence.

Mechanisms of interference of smooth pigweed (Amaranthus hybridus) and common purslane (Portulaca oleracea) on lettuce as influenced by phosphorus fertility

Abstract Greenhouse studies were conducted to assess the intensity of smooth pigweed and common purslane aboveground interference (AI) and belowground interference (BI) with lettuce and to determine primary mechanisms of interference of each species as affected by P fertility rates. Lettuce was transplanted in mixtures with either smooth pigweed or common purslane according to four partitioning regimes: no interference, full interference, BI, and AI. Soil used was low in P for optimum lettuce yields, therefore P was added at rates of 0, 0.4, and 0.8 grams of P per liter of soil. Shoot and root biomass and plant height were measured for each species, as well as P tissue content. The data obtained indicated that smooth pigweed interfered with lettuce primarily through light interception by its taller canopy. A secondary mechanism of interference was the absorption of P from the soil through luxury consumption, increasing the P tissue content without enhancing smooth pigweed biomass accumulation. In contrast, common purslane competed aggressively with lettuce for P. Because the weed grew taller than lettuce, light interception was a secondary interference factor. Nomenclature:u2003Common purslane, Portulaca oleracea L. POROL; smooth pigweed, Amaranthus hybridus L. AMACH; lettuce, Lactuca sativa L.

Competition of giant smutgrass (Sporobolus indicus) in a bahiagrass pasture

Abstract Field experiments were established in 1998 and 1999 to evaluate the effect of giant smutgrass competition and hexazinone application on bahiagrass forage yield. The experimental design was a split-plot, with low (<u200920% groundcover), medium (20 to 70% groundcover), and high (>u200970% groundcover) giant smutgrass density as the main plot factors and hexazinone application or no hexazinone application as the subplot factors. In 1998, without hexazinone, bahiagrass biomass accumulation was 1,164 kg ha−1 mo−1 under low giant smutgrass infestation but 590 and 154 kg ha−1 mo−1 under medium and high giant smutgrass densities, respectively. From harvests occurring 1 yr after hexazinone application, bahiagrass yield in the weed-free area was similar to that growing under low giant smutgrass density. However, as giant smutgrass density increased to moderate or high levels, bahiagrass yield was reduced relative to the weed free. Giant smutgrass biomass accumulation was also measured over time. Giant smutgrass biomass, in both years, increased dramatically in the late summer months at the medium and high densities but not at the low density. It was concluded that bahiagrass was competing with the giant smutgrass at low density and depressed late season growth but was not capable of doing so at higher infestation levels. A rapid increase in late-season giant smutgrass growth was partially explained by the fact that bahiagrass is a short day plant that begins to flower in mid- to late summer, and aboveground biomass production decreases in late summer. This shift in carbon allocation in bahiagrass would exert less competition on giant smutgrass and thus partially be responsible for the late season increase in giant smutgrass growth. Economic analysis performed on these data illustrated that a net loss of

Phosphorus absorption in lettuce, smooth pigweed (Amaranthus hybridus), and common purslane (Portulaca oleracea) mixtures

15.20 per stocking unit (cow–calf pairs) would be realized if hexazinone were used to control low densities of giant smutgrass. However, a net gain of

Influence of method of phosphorus application on smooth pigweed (Amaranthus hybridus) and common purslane (Portulaca oleracea) interference in lettuce

29.28 and

Effect of Glyphosate and MSMA Application Timing on Weed Control, Fruiting Patterns, and Yield in Glyphosate-Resistant Cotton

55.75 per stocking unit was observed if hexazinone was used to control giant smutgrass that had reached medium or high levels of infestation, respectively. It was concluded from these data that giant smutgrass should not be controlled until densities reach approximately 35% infestation. Nomenclature:u2003Hexazinone; giant smutgrass, Sporobolus indicus (L.) R. Br. var. pyramidalis SPZIN; bahiagrass, Paspalum notatum Fluegge PASNO.