Studies were conducted at three locations in North Carolina in 2004 to evaluate density-dependent effects of glufosinate-resistant (GUR) corn on GUR cotton growth and lint yield. GUR corn was taller than GUR cotton as early as 11 d after planting, depending on location. A GUR corn density of 5.25 plant/m of crop row reduced late-season cotton height by 38, 43, and 43% at Clayton, Lewiston-Woodville, and Rocky Mount, NC, respectively, compared with weed-free cotton height. GUR corn dry biomass per meter of crop row and GUR corn seed biomass per meter of crop row decreased linearly with increasing GUR corn density at all locations. The relationship between GUR corn density and GUR cotton yield loss was described by the rectangular hyperbola model with the asymptote (a) constrained to 100% maximum yield loss. The estimated coefficient i (yield loss per unit density as density approaches zero) was 7, 5, and 6 at Clayton, Lewiston-Woodville, and Rocky Mount, respectively. Percentage of GUR cotton lint yield loss increased 4, 5, and 8 percentage points at Clayton, Lewiston-Woodville, and Rocky Mount, respectively, with each 500 g increase in weed biomass/m of crop row. The examined GUR corn densities had a significant effect on cotton yield but not as significant as many other problematic grass and broadleaf weeds.

Research on weed management in furrow-irrigated rice is needed as water availability becomes more limited in rice production regions of Arkansas. Research was conducted at Keiser and Pine Tree, AR, with the objectives being to determine (1) whether the addition of clomazone to imazethapyr would improve PRE weed control in furrow-irrigated, imidazolinone-tolerant rice, and (2) whether increasing the imazethapyr rates would improve weed control without injuring rice. Imazethapyr was applied at 70, 87.5, and 105 g ai/ha PRE with and without clomazone followed by imazethapyr POST at the same rate as used PRE. No rice injury was observed during the growing season at either site. Clomazone plus imazethapyr applied PRE did not improve early season control of Palmer amaranth, pitted morningglory, prickly sida, barnyardgrass, or broadleaf signalgrass over imazethapyr alone. Increasing the PRE imazethapyr rate to 105 g/ha did not improve Palmer amaranth or pitted morningglory control. Imazethapyr applied PRE on a clay soil generally provided lower weed control than on the silt loam soil. Increasing the imazethapyr rate did not improve rice yields.

Experiments were conducted in the greenhouse and the field to evaluate the efficacy of various sulfonylurea herbicides applied with mesotrione or mesotrione + atrazine. The addition of mesotrione or mesotrione + atrazine to sulfonylurea herbicides had no adverse effects on the control of large crabgrass or velvetleaf in a controlled environment. Tank mixing mesotrione or mesotrione + atrazine with nicosulfuron or foramsulfuron, however, antagonized nicosulfuron and foramsulfuron control of green foxtail and shattercane. Field experiments conducted in 2004 and 2005 also indicated that addition of mesotrione + atrazine to a sulfonylurea herbicide decreased herbicidal efficacy on green foxtail, yellow foxtail, and shattercane, compared with the sulfonylurea herbicide applied alone. In addition, increasing mesotrione application from 53 to 105 g/ha decreased efficacy of sulfonylurea herbicide in the tank mix on selected grass species. This research showed that the addition of mesotrione to sulfonylurea herbicides resulted in decreased efficacy of sulfonylurea herbicides on green foxtail, yellow foxtail, and shattercane. The addition of atrazine to the tank mix or an increased mesotrione rate will further decrease herbicide efficacy of sulfonylurea herbicides on shattercane and foxtail species.

Pesticide bans in Canada have resulted in a requirement for municipal turfgrass managers to use cultural methods of weed control to provide a safe playing surface for athletes. A field study was conducted to determine if overseeding provides enough competition to decrease weed populations in Kentucky bluegrass athletic turf typically used in municipal parks for recreation. Perennial ryegrass was overseeded at 2, 4, and 8 kg/100 m2 in May, July, or September, and all permutations of these timings in nonirrigated and irrigated trials at the Guelph Turfgrass Institute (GTI) field station in Guelph, and on in-use soccer fields at the University of Guelph campus and in the town of Oakville, Ontario, Canada over 2 yr. Plant cover by species was recorded every other month using a randomized point quadrat method throughout the growing seasons of 2005 and 2006. Weed populations were not affected by overseeding in 2005, a dry growing season. However, when weed populations were high and normal growing conditions existed in 2006, overseeding applications in May/July/September at 4 and 8 kg/100 m2 decreased perennial weed cover, specifically white clover in the irrigated trial and dandelion in the nonirrigated trial at the GTI. An increase in perennial ryegrass was observed in all plots that received an overseeding treatment. Treatments applied on the in-use soccer fields in Oakville and Guelph, which included May/September and May only overseedings, had no effect on weed populations or perennial ryegrass populations compared to the weedy control. Over the short term, high-rate and frequent overseeding with perennial ryegrass appears to provide competition against perennial weeds when weed cover is high and should be considered an important part of a weed management program for municipal turfgrass managers.

Field studies were conducted near Knoxville, TN, from 2003 to 2005 to evaluate the response of ‘Thermal Blue’, a new interspecific hybrid Kentucky bluegrass to commonly applied PRE and POST herbicides for weed management. Dithiopyr, oryzalin, oxadiazon, pendimethalin, prodiamine, quinclorac, and trifluralin applied at seeding injured hybrid bluegrass greater than 81% and reduced hybrid bluegrass cover greater than 57%. In a second study, established hybrid bluegrass was treated POST with acetolactate synthase–inhibiting herbicides including bispyribac-sodium, chlorosulfuron, foramsulfuron, halosulfuron, imazapic, imazaquin, metsulfuron, rimsulfuron, sulfosulfuron, and trifloxysulfuron at low and high rates (one and two times the suggested use rates in Kentucky bluegrass or other turfgrasses). By 5 wk after treatment (WAT), foramsulfuron at 88 g ai/ha and trifloxysulfuron at 35 g ai/ha injured hybrid bluegrass greater than 26% and reduced visually estimated quality and chlorophyll meter indices. However, hybrid bluegrass injury was no longer evident at 10 WAT. In a third study, established hybrid bluegrass was treated with clethodim, diclofop-methyl, fluazifop-p-butyl, and sethoxydim applied at low, medium, and high rates (0.5, 1, and 2 times the registered Kentucky bluegrass or other turfgrass use rates). Clethodim applied at 280 and 560 g ai/ha, fluazifop at 420 g ai/ha, and sethoxydim at 630 g ai/ha injured hybrid bluegrass 5 WAT. These treatments also reduced quality (to less than 5 on a scale of 1 to 9) and chlorophyll meter indices (24 to 37%) when compared to the untreated control. By 10 WAT, only clethodim at 560 g ai/ha caused injury (14%). By 10 WAT, hybrid bluegrass had recovered and injury was only observed in plots treated with clethodim at 560 g ai/ha. No differences in chlorophyll indices or quality were observed at 10 WAT for any POST graminicides.

Research trials conducted at two locations in the spring of 2004 evaluated the effect of soil temperature as an indicator for application timings of certain sulfonylurea herbicides for perennial ryegrass control while maintaining acceptable turfgrass quality during bermudagrass spring transition. Herbicide application timings began when soil temperatures reached 17 C (April 14, 2004). Greater perennial ryegrass control 4 wk after initial treatment (WAIT) was achieved when sulfonylurea herbicides were applied at 26 C soil temperature compared to 17 or 21 C. Bermudagrass density 6 WAIT increased with treatments applied at 26 C soil temperature compared to cooler soil temperatures. There was a decrease in overall turfgrass quality 2 WAIT when treatments were applied at 17 C. However, by 4 WAIT all application timings provided overall turfgrass quality comparable to the untreated control. Acceptable turfgrass quality and maximum perennial ryegrass control was achieved by delaying transition-aid herbicide applications until soil temperatures reached 26 C and growing conditions were more conducive to bermudagrass growth.

Bahiagrass grown for foundation seed had become infested primarily with knotroot foxtail, and secondarily with yellow foxtail. Seed from both foxtail species are mechanically inseparable to certified seed standards from bahiagrass seed. Studies were conducted to determine if pendimethalin applied PRE, in combination with multiple POST applications of diclofop would sufficiently control and/or suppress foxtail seed head production so as to prevent contamination of the harvested bahiagrass seed. Neither pendimethalin nor multiple applications of diclofop were detrimental to bahiagrass seed head production. Although pendimethalin had no effect of knotroot foxtail seed head production, diclofop was effective. Depending on the year, between one and three POST applications of diclofop at 1.12 kg/ha each were effective in reducing, but not completely eliminating, knotroot foxtail seed head production in bahiagrass.

Field experiments were conducted in Georgia in 2004 and 2005 to evaluate the effects of S-metolachlor on summer squash fruit yield. Main treatment effects included summer squash cultivar (yellow or zucchini), planting method (seeded or transplanted) and herbicide program (nontreated control, S-metolachlor applied at planting and prior to transplanting [PRE] at 0.5 and 1.0 kg ai/ha, S-metolachlor applied postemergence [POST] 3 wk after planting [WAP] at 0.5 and 1.0 kg/ha, and S-metolachlor applied PRE at 0.5 kg/ha followed by POST at 0.5 kg/ha [PRE fb POST]). Fruit number and weight were measured 12 times during each growing season and the harvests combined into early (harvests 1 to 4), middle (harvests 5 to 8), late (harvests 9 to 12), and cumulative (harvests 1 to 12) yield categories. Mixed-models analyses were used to evaluate the effects of herbicide rate and timing, squash cultivar, and planting method on squash yield for each harvest period. Summer squash cultivar and planting method did not affect squash response to S-metolachlor. Averaged over squash cultivar and planting method, S-metolachlor applied PRE and PRE fb POST reduced fruit number and weight at the early harvest between 35 and 60%, middle harvest between 14 and 30%, and cumulative harvest between 14 and 22%. S-metolachlor applied POST at 0.5 kg/ha did not impact squash yield compared to the nontreated control at any harvest period, whereas 1.0 kg/ha reduced fruit number and weight at the middle harvest 14 and 20%, respectively. We propose that POST applications of S-metolachlor at 0.5 kg/ha or lower can be adopted for use in summer squash production in Georgia.

Field and laboratory experiments were conducted in New Jersey to investigate the influence of spray adjuvants on foliar absorption and efficacy of bispyribac–sodium on annual bluegrass, creeping bentgrass, and perennial ryegrass. In laboratory experiments on annual bluegrass, 14C–bispyribac–sodium without an adjuvant had 25% foliar absorption by 8 h after treatment, whereas absorption increased to 45, 46, and 75% when applied with crop oil concentrate, nonionic surfactant, and methylated seed oil, respectively. In creeping bentgrass fairways, sequential bispyribac–sodium applications at 37 g ai/ha with spray adjuvants controlled annual bluegrass similarly to 74 g ai/ha applied sequentially without adjuvants. In perennial ryegrass, treatments with methylated seed oil and nonionic surfactant required 25 and 41% lower bispyribac–sodium rates, respectively, to obtain annual bluegrass control levels comparable to bispyribac–sodium rates without adjuvants. Spray adjuvants did not exacerbate turf-grass discoloration from bispyribac–sodium. Overall, spray-adjuvant use with bispyribac–sodium may allow practitioners to reduce application rates and enhance efficacy for annual bluegrass control.

Several field observations and limited research have confirmed that sulfonylurea herbicides commonly used in warm-season turf can laterally relocate via turf equipment and injure neighboring cool-season grasses. This phenomenon is referred to as ‘tracking’ among turf managers and often occurs when mowers traverse treated areas and adjacent creeping bentgrass putting greens, fairways, and tee boxes while foliage is wet with dew. Tracked flazasulfuron and metsulfuron at 9 and 42 g/ha, respectively, caused little injury to creeping bentgrass. Flazasulfuron at 26 and 53 g/ha, and foramsulfuron at 28 g ai/ha tracked while dew was present 20 h after treatment (HAT) resulted in the most noticeable creeping bentgrass injury when tracked. Flazasulfuron at higher rates and foramsulfuron tracked 20 HAT on dew-covered turf reduced turf color compared to nontracked turf. When the mower traversed dry turf at 6 HAT and wet turf at 68 HAT, turf color was reduced less than wet turf tracked 20 HAT. Length of track and creeping bentgrass injury decreased with flazasulfuron rate. When using flazasulfuron at rates between 9 and 53 g/ha, a 1.5- and 4.5-m border, respectively, around creeping bentgrass would eliminate most injury from tracked herbicide.

Data on the efficacy of alternative fumigants to methyl bromide for weed control in perennial crop nurseries in California are needed because few herbicides are registered for this purpose. Field studies were conducted from 2003 to 2006 in four commercial perennial crop nurseries in California. Treatments included a nonfumigated control; methyl bromide (98%) (MeBr) with high-density polyethylene (HDPE) film; iodomethane (50%) + chloropicrin (50%) with HDPE film; 1,3-dichloropropene (1,3-D) with HDPE film; 1,3-D (61%) + chloropicrin (35%) with HDPE film; 1,3-D (62%) + chloropicrin (35%) subsurface drip; and 1,3-D (61%) + chloropicrin (35%) with virtually impermeable film (VIF). All the fumigants reduced the seed viability of common purslane, johnsongrass, and tall morningglory but were not as effective on little mallow and field bindweed. Although total weed densities and the level of control provided by each fumigant differed between locations, weed density was generally reduced by all the fumigation treatments, compared to the nonfumigated control. At three locations, alternative fumigation treatments usually resulted in hand-weeding time similar to MeBr. Reductions in weed seed viability, weed emergence, and weed densities suggest that these alternative fumigants will provide weed control similar to MeBr in perennial nurseries.

Crabgrass species are problematic weeds in bermudagrass turf that can be controlled by PRE herbicide applications. Because of the difficulty in predicting crabgrass emergence and other prevailing management constraints, PRE herbicide applications are not always properly timed. Mesotrione controls crabgrass both PRE and POST; however, relatively short soil-residual activity limits its use as a PRE herbicide. Two experiments were conducted to evaluate smooth crabgrass control with PRE applications of mesotrione plus prodiamine. The first experiment evaluated the influence of application timing on the efficacy of mesotrione-plus-prodiamine combinations. Applications were made every 2 wk from March 15 to May 24. Mesotrione plus prodiamine controlled smooth crabgrass more consistently across all application dates than either mesotrione or prodiamine applied alone. The second experiment evaluated mesotrione along with current PRE and early POST herbicide treatments used for control of crabgrass. When applied at one to two tillers growth stage, mesotrione plus prodiamine controlled smooth crabgrass 99% when rated on August 31. Bermudagrass injury from mesotrione ranged from 9 to 44%, but did not result in any reduction in turf plant density. Mesotrione plus prodiamine is an effective tank mixture when prodiamine alone is not applied in a timely fashion; however, variable and excessive turf injury is a potential impediment to mesotrione use on bermudagrass turf.

Twelve winter cover crops were planted in Citra and Live Oak, FL, in 2004, to evaluate their potential for use as living mulches in organic vegetable production: black oat, rye, annual ryegrass, hard fescue, two cultivars of white clover, berseem clover, crimson clover, subterranean clover, arrowleaf clover, barrel medic, and a hybrid disc × strand medic cultivar. The best canopy development and weed suppression occurred with black oat, rye, and annual ryegrass. In 2005, black oat, two rye cultivars, and annual ryegrass were evaluated as living mulches in broccoli at Citra and Live Oak, using organic production methods. ‘Florida 401’ (FL 401) rye was tallest, black oat was intermediate, and ‘Wrens Abruzzi’ (WA) rye and ‘Gulf’ ryegrass were of similar height and were the shortest living mulches. Biomass harvested at 12 and 13 wk after planting at Citra and Live Oak, respectively, was greatest with FL 401 rye. At Live Oak, the three other mulches had similar amounts of biomass; however, at Citra, black oat biomass was greater than that of WA rye, and biomass of ryegrass was lowest. The greatest weed infestation occurred with the weedy control. Weed biomass was highest with the weedy control, intermediate with ryegrass, and lowest with rye and black oat. However, the biomass of the weedy control was lower than that of the living mulches plus any associated weeds. Marketable broccoli yield was highest with the weed-free control. Yields with black oat, WA rye, and ryegrass were similar to that of the weedy control, whereas yield with the FL 401 rye was lower than with the weedy control. Suppression of living mulches by mowing at 3 and 7 wk after planting had no effect on broccoli growth or yield.

Southern wax myrtle is a pernicious weed in south Florida pastures and this plant can eliminate all forage production under high densities. Previous work has shown that triclopyr at 1.12 kg/ha is the most effective herbicide on this species. The introduction of the Burch Wet Blade (BWB) mowing system provides an alternative application method to traditional broadcast herbicide applications. The objective of this experiment was to compare the efficacy of triclopyr and other herbicides using both broadcast and the BWB application systems. In general, broadcast applications of at least 1.1 kg/ha triclopyr provided better control than the same treatments applied with the BWB system in 1998. In 1999, control was lower overall compared to 1998, but the same trend was observed. Broadcast applications of triclopyr reduced wax myrtle densities better than when herbicides were applied with the BWB system in 1998. However, in 1999, dicamba + triclopyr, and at least 1.1 kg/ha triclopyr reduced wax myrtle densities compared to the mow-only treatment, regardless of application method. Although the BWB system provided an initial overall reduction in plant height, recovery of plants was sufficient and often outgrew those receiving broadcast applications of herbicides. Regardless of application method, retreatment of wax myrtle plants 1 yr after the initial application will likely be needed to obtain adequate control.

Flaming can be an effective nonselective, nonchemical method of weed control. It has been more effective against broadleaf weeds than grasses. Experiments were conducted with a conveyor bench burner apparatus to evaluate flaming to kill broadleaf and grass seedlings at the 0- to 2- and 2- to 4-leaf stages. Most 0- to 2-leaf green foxtail seedlings were killed when flamed at 2, 4, and 6 km/h conveyor speed. A few plants survived when flamed at 8 km/h. Green foxtail seedlings at the 2- to 4-leaf stage were more tolerant to flaming than 0- to 2-leaf green foxtail, and substantial numbers of plants survived at all flaming speeds except 2 km/h. Barnyardgrass was more tolerant to flaming than green foxtail, and many 0- to 2- and 2- to 4-leaf seedlings survived after flaming. However, fresh weight of the live plants at 14 d after treatment was reduced. Some large crabgrass plants survived flaming at both growth stages. Flaming at 2 km/h reduced seedling number and fresh weight, but there was significant regrowth. Common ragweed was more susceptible to flaming at the 2- to 4-leaf stage than at the 0- to 2-leaf stage. Redroot pigweed and common lambsquarters were susceptible to flaming at both 0- to 2- and 2- to 4-leaf stages.

Field experiments were conducted in 2004 and 2005 at Clemson, SC, and in 2004 at Clinton, NC, to quantify Palmer amaranth and large crabgrass growth and interference with plasticulture-grown bell pepper over multiple environments and develop models which can be used on a regional basis to effectively time removal of these weeds. Experiments at both locations consisted of an early and a late spring planting, with the crop and weeds planted alone and in combination. Daily maximum and minimum air temperatures were used to calculate growing degree days (GDD, base 10 C) accumulated following bell pepper transplanting and weed emergence. Linear and nonlinear empirical models were used to describe ht, canopy width, and biomass production as a function of accumulated GDD. Palmer amaranth reduced bell pepper fruit set as early as 6 wk after transplanting (WATP) (648 GDD), whereas large crabgrass did not significantly reduce fruit set until 8 WATP (864 GDD). Using the developed models and assuming Palmer amaranth and large crabgrass emergence on the day of bell pepper transplanting, Palmer amaranth was predicted to be the same ht as bell pepper at 287 GDD (20 cm tall) and large crabgrass the same ht as bell pepper at 580 GDD (34 cm tall).

Swallowwort, a twining perennial of the Asclepiadaceae family, has become increasingly invasive in cultivated fields, orchards, fence rows, natural areas, and roadsides of some provinces in Iran. The ability of this weed to establish and develop from seed was studied in laboratory and greenhouse experiments. Optimum germination temperature was 25 C. Germination did not occur at ≤ 15 C either in dark or light. In temperature fluctuation experiments, maximum germination occurred at 30/22 C, but light fluctuations had no effect on swallowwort seed germination. At pH 4 to 9 seed germination was 44 to 66%. Osmotic potential up to −0.2 MPa had little effect on germination. Seed germination was less than 5% at −0.8 Mpa. Swallowwort seeds were not able to germinate at 300 mM NaCl; however, there was 12% germination at the 200 mM concentration. Maximum emergence occurred when the seeds were planted at 1.5 cm depth. Seedlings did not emerge when planted at 6.5 cm depth. Germination percentage of the seeds kept under immersed (water) conditions was similar to those of nonimmersing periods; however, seedling growth was greater in treatments without immersing periods.

Minimizing inputs such as fertilizers, herbicides, or tillage may be sought by producers to satisfy economic as well as environmental goals. One of the challenges in reducing inputs, whether synthetic fertilizers or herbicides, or substituting a synthetic nutrient with an organic source, is to identify practices that will provide optimum growing conditions for the crop while maintaining an adequate level of weed control. Our objective was to measure the cumulative effects of 12 yr of nitrogen (N) and phosphorus (P) fertilization treatments applied to two tillage systems [conventional tillage (CT) vs. no tillage (NT)] in a corn–soybean rotation on weed communities and crop yields. Residual (postherbicide treatment) weed species assembly was determined by multivariate analysis and was influenced mainly by tillage, with weeds more strongly associated with NT than with CT. Diversity of weed communities as measured by richness, evenness (E), and a diversity index (H′), and total weed biomass were greater for NT than for CT. Nutrient treatments had little or no effect on these parameters. Corn yields were reduced by 70% in the absence of N and by 25% in NT compared to CT treatments. Soybean yields were reduced in NT with increasing P rates compared to other treatments, but reductions never exceeded 10%. Overall, corn and soybean had different responses to treatments, with corn yields being far more affected by fertilization and tillage than soybean yields. Conversely, the absence of tillage had a much greater effect than the absence of nutrient input on weed community assembly and biomass, suggesting the importance of a weed management program specifically tailored for NT systems.

Late-season weed infestations often do not affect yields and are allowed to mature and contribute seed to the soil seedbank, ensuring the future establishment of competitive weed complexes. Effective long-term weed management strategies must incorporate practices to reduce late-season weed seed production by weed complexes. Field studies were conducted to determine the effects of late-season glyphosate applications on seed production of barnyardgrass, Palmer amaranth, pitted morningglory, prickly sida, and sicklepod. Although sequential 0.42-kg ae/ha glyphosate applications initiated when the first weed species in the complex flowered and repeated every 10 d was the most effective treatment and reduced seed production of all species by ≥ 95%, the most practical treatment was a single 0.84-kg/ha glyphosate application at pitted morningglory flowering, suppressing seed production of barnyardgrass, Palmer amaranth, pitted morningglory, prickly sida, and sicklepod by 88, 83, 98, 95, and 99%, respectively. This research demonstrates that annual contributions by a weed complex to the soil seedbank can be significantly and practically reduced by a single late-season glyphosate application.

Indiana growers who purchase restricted-use pesticides are required to show the agrochemical dealer their private pesticide applicator license before the transaction can be completed. To keep the license current, growers may attend three private applicator recertification meetings or retake the exam every 5 yr. The meetings are county-based and must be a minimum of 2 h in length; they must include a topic mandated by the Office of the State Chemist. During the 2005/2006 private applicator recertification program (PARP) cycle, off-site movement of atrazine into surface water was the regulatory topic presented to 2,887 participants at 69 meetings. A team of individuals from different disciplines prepared educational materials to support the regulatory topic of the year. Surveys to assess grower awareness were conducted at the meetings and 1 yr later to monitor the long-term impact of the educational effort, and to evaluate which tactics were being adopted to reduce off-site movement of atrazine. Growers farming more than 800 ha had a higher degree of concern than small growers regarding the loss of atrazine as a weed management tool. Eighty-nine percent of the growers thought there would be a 314 to 1,255 kg/ha yield loss if atrazine was removed from the marketplace. Eighty-four percent of the growers estimated that weed control costs would increase $15 to $25/ha if no other products were available to replace atrazine. The three most acceptable management strategies to reduce atrazine movement were: more attention to label setback distances, establishment of grass filter strips around surface water, and reducing atrazine rates by tank mixing with other herbicides. The results of this project indicated that statewide programs such as this are effective in increasing awareness of an issue and documenting the impact of extension education programs.