A field study evaluated the effects of green kyllinga establishment method (seed vs. stolon), two mowing heights (2.5 and 5.0 cm), and three nitrogen (N) rates (0, 24, and 49 kg/ha/mo) on green kyllinga infestation in ‘Tifway’ bermudagrass turf. The study was initiated in vigorous and newly established or “weak” bermudagrass turf in May 1997 and continued until December 1998. The green kyllinga area was measured periodically each year and plant dry weight (g/500 cm2) was calculated in December 1997 and 1998. In 1997, stolon established green kyllinga plots were twice as large as seeded plots in vigorous turf and four times larger in weak turf. Method of establishment, however, was less important in 1998 as seedling populations became more established. In weak turf, increasing N rate to 49 kg/ha/mo decreased green kyllinga spread by 50% in 1997 and by 40% in 1998 compared to no N. In vigorous turf, mowing height influenced green kyllinga infestation more than N. Low mowing height (2.5 cm) increased green kyllinga infestations nearly twofold in vigorous turf in 1997 and more than fivefold in 1998. Golf course fairways are often maintained at clipping heights shorter than 2.5 cm, and green kyllinga is a prevalent weed at these sites. Green kyllinga may gain a competitive advantage in bermudagrass turf at lower mowing heights.

The effect of adding a spray adjuvant to SAN 582H tank mixtures with fluazifop-P, imazethapyr, and sethoxydim was evaluated. SAN 582H synergistically increased broadleaf signalgrass control with reduced rates of all three postemergence (POST) herbicides when no spray adjuvant was used and when crop oil concentrate was added. For example, broadleaf signalgrass control increased from 50% to 83% when SAN 582H was tank-mixed with 52 g ai/ha sethoxydim and crop oil concentrate. In another experiment, several formulations of SAN 582H, including blank solvent-only formulations (no SAN 582H), were evaluated in combination with a reduced rate of sethoxydim to determine the source of synergism from tank mixtures. The SAN 582H molecule, not the carrier solvents in formulated product, was determined to be the source of synergism. The synergistic properties of SAN 582H were compared to other chloroacetamides. Synergism from acetochlor was similar to SAN 582H when applied POST with a reduced rate of either fluazifop-P, imazethapyr, or sethoxydim for grass control. Metolachlor also synergistically increased the control of grasses with the POST herbicides; however, metolachlor caused considerable phytotoxicity when applied alone and synergistic interactions were detected less frequently. The efficacy of sethoxydim mixed with SAN 582H was evaluated under different soil moisture conditions. Broadleaf signalgrass control increased from 81% to 93% under dry, moisture-stressed conditions when 210 g/ha sethoxydim was tank- mixed with SAN 582H.

Field experiments were conducted to determine the effect of selected rice pesticides on the mycoherbicide Colletotrichum gloeosporioides (Penz.) Sacc. f. sp. aeschynomene (designated as C.g.a.) for northern jointvetch control in dry-seeded rice. Sequential treatments of pencycuron at 0.56 kg ai/ha, SN-84364 at 0.40 kg ai/ha applied 7 and 14 days after C.g.a., or pencycuron sprayed sequentially after a tank mixture of C.g.a. plus actifluorfen did not reduce infectivity of C.g.a. Also, propiconazol at 0.60 kg ai/ha or pencycuron applied 7 days before and after C.g.a. did not reduce fungus development on northern jointvetch. Sequential treatments of benomyl at 0.56 kg ai/ha or propiconazol applied 7 and 14 days after C.g.a. reduced pathogen activity on northern jointvetch.

We conducted a series of field experiments to determine the role of several factors that might contribute to the inconsistent control of common lambsquarters with glyphosate. Experiments in 2006 and 2007 determined common lambsquarters response to glyphosate under a wide range of measured environmental conditions. Glyphosate was applied at 0.84 kg ae ha−1 plus 3.8 kg ha−1 ammonium sulfate (AMS) to 10-cm-tall plants on 18 dates in each year and to 20-cm-tall plants on 18 dates in 2007. Control was less for six application dates relative to control for 48 other dates. Poor control was attributed to rainfall on one of these six dates, but for the other five dates, regression analysis did not identify any significant relationships between environmental conditions (relative humidity, temperature at time of treatment, or minimum and maximum temperature pre- and posttreatment) and control, even though a wide range of conditions occurred. To determine the effects of plant growth stage on control, glyphosate was applied at 0.1 to 3.2 kg ha−1 plus 3.8 kg ha−1 AMS to 10- and 20-cm-tall plants at four sites. The glyphosate ED50 value (the effective dose that reduced shoot mass by 50% relative to nontreated plants) was 1.9 to 3.0 times greater for 20- than 10-cm-tall plants in three site-years, but was not affected by plant height in one site-year. We also conducted experiments to determine the effect of rainfall on glyphosate efficacy. Across years, common lambsquarters control increased from 44 to 75% as the interval between glyphosate application (0.84 kg ha−1 + 3.8 kg ha−1 AMS) and simulated rainfall increased from 0.5 to 4.0 h, respectively. Our results did not identify environmental conditions that explained reduced glyphosate efficacy in all cases, but they suggest that rainfall after application and plant height can be important factors contributing to the inconsistent control of common lambsquarters.

In field experiments, nicosulfuron at 35 g ai/ha controlled itchgrass in corn 28 d after treatment better than primisulfuron at 39 g ai/ha (80 vs. 44%). Control with both herbicides was greater when applied to six-leaf itchgrass than to 10-leaf and with the addition of nonionic surfactant than with an organosilicone surfactant and methylated seed oil blend. Weed control for nicosulfuron plus nonionic surfactant resulted in corn yield approximately 1.5 times that of primisulfuron plus nonionic surfactant and 1.6 times that of nicosulfuron plus an organosilicone surfactant and methylated seed oil blend. When primisulfuron was applied with organosilicone surfactant and methylated seed oil rather than nonionic surfactant, corn yield was reduced by 25%. For nicosulfuron with nonionic surfactant, corn yield averaged approximately twice that of the nontreated check. In other field experiments, itchgrass control 28 d after treatment with nicosulfuron was enhanced with addition of an organosilicone and nonionic surfactant blend or methylated seed oil (83 and 78%, respectively) compared with nonionic surfactant (69%). Nicosulfuron was less effective when applied with crop oil concentrate or organosilicone surfactants compared with nonionic surfactant.

Field bindweed is a major weed problem for wheat producers across the Great Plains and for Oklahoma hard red winter wheat producers. Herbicides have demonstrated limited efficacy, with retreatment often suggested on labels. However, little data are available to verify efficacy with repeated treatments in Oklahoma wheat fields. Annual treatment with dicamba + 2,4-D, the prepackaged mixture (premix) glyphosate + 2,4-D, premix quinclorac + 2,4-D at two different rates, or picloram + 2,4-D to actively growing field bindweed for three consecutive years reduced stem density up to 88% at Lahoma and up to 96% at Stillwater for several months after treatment. However, by 12 to 14 mo after the last treatment, stem densities returned to 47% or more of the nontreated. Treatments applied in June or July were not more effective than treatments applied in September. These results suggested a need to shift the intent of herbicide application from multiyear control to single-year control with treatments designed to control field bindweed throughout one growing season. To field test this approach, nine farmer cooperators in 1998 to 1999 and seven cooperators in 1999 to 2000 applied either premixed glyphosate + 2,4-D or dicamba in late summer or early fall after the field bindweed was allowed to grow 5 wk or more without disturbance. Of the participants, 88% reported little field bindweed present at wheat harvest, whereas 12% reported considerable field bindweed present at harvest. Cooperators were generally satisfied with the reduction in field bindweed canopy through harvest.

Imazamethabenz is a selective herbicide used to control wild oat in small grains. The effects of rate, volume of carrier, and surfactant concentration on the efficacy of this herbicide in controlling wild oat were studied in field experiments. As each of the variables increased, wild oat control increased; the greatest degree of wild oat growth inhibition occurred at the highest herbicide rate, highest volume of carrier, and highest surfactant concentration.

In field studies in 1991, 1992, and 1993, rimsulfuron at 26 and 35 g ai/ha, sequentially at 26 g/ha, at 26 g/ha plus metribuzin at 280 g ai/ha, and metribuzin at 280 g/ha were evaluated POST for weed control in transplanted ‘Agriset’ tomato. Common lambsquarters was controlled by rimsulfuron at 35 g/ha. Rimsulfuron plus metribuzin gave consistent control of common ragweed, but jimsonweed control was inconsistent and goosegrass control was generally low. Rimsulfuron treatments caused slight (< 12%) temporary injury to new terminal growth of tomato. Yield of tomato fruit was consistently high in the metribuzin, metribuzin plus rimsulfuron, and rimsulfuron sequential treatments. In greenhouse studies, giant foxtail and large crabgrass control by rimsulfuron was above 95 and 85%, respectively, but goosegrass was not controlled. Height of four tomato cultivars was not reduced, but dry weight of ‘Floradade’ and ‘Sunbeam’ was reduced by rimsulfuron.

Field research was conducted to evaluate the effectiveness of herbicides and carrot mowing for swamp dodder control. Herbicide evaluation indicated the highest carrot yield and lowest crop injury with pendimethalin compared to the industry standard linuron. Swamp dodder control with pendimethalin was greater than 80% at 56 and 70 d after planting (DAP). Other herbicides controlled swamp dodder, but crop injury was unacceptable. Carrot yield was greater where pendimethalin or s-metolachlor was applied compared to all other herbicides. Carrot mowing once 72, 86, or 100 DAP and mowing twice (72 plus 100 DAP) reduced the percentage of carrots infected with swamp dodder. Carrot infection level was least when mowed 100 DAP, and mowing did not increase yield compared to the non-treated check. These results suggest that the integration of pendimethalin for early-season swamp dodder control, followed by mowing 100 DAP, could reduce the impact of swamp dodder on carrots.

A high proportion of viable pollen grains must germinate to study the physiology of pollen growth to reduce the confounding effects of environmental influences on pollen germination. The objectives of this study were to evaluate the nuclear state and develop a suitable medium and culture method for in vitro germination of johnsongrass pollen. Johnsongrass pollen was trinucleate, and in vitro tests for pollen viability using Alexander's stain and a fluorochromatic reaction method (FCR) indicated johnsongrass pollen was viable (92.6 to 98.4%). A factorial treatment arrangement of four concentrations of sucrose, two concentrations of boric acid, and two concentrations of calcium nitrate were used to determine the optimum pollen-germination medium composition in suspension culture, agar culture, and cellophane membrane culture. Germination was highest in a suspension culture with a medium containing 0.3 M sucrose, 2.4 mM boric acid, and 3 mM calcium nitrate. Pollen germination using this medium was 78.9% when anthers were harvested just before anthesis.

The objective of this 2-yr study was to determine the optimal length of time between stale-seedbed preparation and planting that maximized weed control along with growth, development, and yield of cucumbers, compared with conventional seedbeds. Stale-seedbeds were prepared 40, 30, 20, and 10 d before planting (DBP), with an additional treatment of 40-DBP seedbed that received an application of glyphosate at 0.9 kg ae/ha, 20 DBP (40 and 20 DBP). The control (0 DBP) was prepared at planting. Glyphosate plus glufosinate ammonium at 1.26 and 0.042 kg ae/ha were applied after cucumber seeding to kill any emerged weeds. The experiment was a split-plot design in which one half of the main plots were treated with a preemergence application of clomazone at 0.42 kg ai/ha after cucumber seeding. Management of the stale-seedbed influenced the level of weed control and final crop yield. Generally, the 40-DBP seedbed had the highest weed biomass at planting and the lowest at harvest. Cucumber density, leaf number, and vine length were reduced in this treatment, and flowering was delayed because of the high weed biomass present during seedling emergence. All stale-seedbeds, with the exception of the 40-DBP stale-seedbed, had greater yields compared with the control (0 DBP) seedbed. The optimal timing of stale-seedbed preparation was 20 to 30 DBP. Seedbed preparation could be expanded to 40 DBP; however, an application of glyphosate at 20 DBP would be required to optimize yield. The stale-seedbed in combination with herbicides was a superior integrated weed management tool compared with conventional weed management practices.

A study was conducted in three locations in Louisiana to evaluate interactions of imazethapyr at 0 and 70 g ai ha−1 mixed with propanil at 0, 1,120, 2,240, 3,360, and 4,480 g ha−1 for the control of red rice, barnyardgrass, and hemp sesbania. According to Blouin’s modified Colby’s, a synergistic response occurred for red rice treated with imazethapyr mixed with propanil at 4,480 g ha−1 for all evaluations. Observed control was 93% to 95% compared with expected control of 81% to 87%. An antagonistic response occurred for barnyardgrass control with imazethapyr mixed with propanil at 1,120 g ha−1 at 35 and 49 d after treatment (DAT), with control of 75% and 64%, respectively, compared with expected control of 89% and 78%. However, a neutral response occurred for barnyardgrass control when treated with all other imazethapyr plus propanil combinations. An antagonistic interaction occurred for hemp sesbania when treated with imazethapyr plus propanil at 3,360 and 4,480 g ha−1 at 21 DAT with an observed control of 89% compared with an expected control of 96%; however, a neutral response occurred at all other evaluation dates. An increase in rice yield was observed with an imazethapyr plus propanil at 4,480 g ha−1 mixture compared with a single application of imazethapyr or propanil at any rate evaluated.

During the 2017 to 2019 growing seasons, samples of waterhemp and Palmer amaranth that had reportedly survived field-rate applications of protoporphyrinogen oxidase (PPO)–inhibiting herbicides were collected from the American Midwest and tested for target-site mutations known at the time to confer resistance. Target-site resistance was identified in nearly all (135 of 145) tested common waterhemp populations but in only 8 of 13 Palmer amaranth populations. Follow-up research on one population of Palmer amaranth (W-8), which tested negative for all such mutations, confirmed it was resistant to lactofen, with a magnitude of resistance comparable to that conferred by the ΔG210 PPO2 mutation. Gene sequences from both isoforms of PPO (PPO1 and PPO2) were compared between W-8 and known PPO inhibitor–sensitive sequence. A glycine-to-alanine substitution at the 399th amino acid position (G399A) of PPO2, recently identified to reduce target-site herbicide sensitivity, was observed in a subset of resistant W-8 plants. Because no missense mutation completely delimited resistant and sensitive sequences, we initially suspected the presence of a secondary, non-target-site resistance mechanism in this population. To isolate G399A, a segregating F2 population was produced and screened with a delimiting rate of lactofen. χ2 goodness-of-fit analysis of dead/alive ratings indicated single-locus inheritance of resistance in the F2 population, and molecular markers for the W-8 parental PPO2 coding region co-segregated tightly, but not perfectly, with resistance. More research is needed to fully characterize Palmer amaranth PPO inhibitor–resistance mechanisms, which appear to be more diverse than those found in common waterhemp.

Dissipation of S-metolachlor, a soil-applied herbicide, on organic and mineral soils used for sugarcane production in Florida was evaluated using field studies in 2013 to 2016. S-metolachlor was applied PRE at 2,270 g ha−1 on organic and mineral soils with 75% and 1.6% organic matter, respectively. The rate of dissipation of S-metolachlor was rapid on mineral soils compared with organic soils. Dissipation of S-metolachlor on organic soils followed a negative linear trend resulting in half-lives (DT50) ranging from 50 to 126 d. S-metolachlor loss on organic soils was more rapid under high soil-moisture conditions than in corresponding low soil-moisture conditions. On mineral soils, dissipation of S-metolachlor followed an exponential decline. The DT50 of S-metolachlor on mineral soils ranged from 12 to 24 d. The short persistence of S-metolachlor on mineral soils was likely attributed to low organic matter content with limited adsorptive capability. The results indicate that organic matter content and soil moisture are important for persistence of S-metolachlor on organic and mineral soils used for sugarcane production in Florida.

Research was conducted in 2012 and 2013 to evaluate the response of the rice cultivars ‘Cheniere', ‘CL151′, ‘Caffey', ‘CL261′, and ‘CLXL745′ response to POST applications of saflufenacil. Treatments included a nontreated control, saflufenacil at 50 g ai ha−1, and carfentrazone at 35 g ai ha−1 applied mid-POST (MPOST) to rice in the three- to four-leaf stage. Pooled across cultivars, injury was greatest at 3 and 7 d after treatment (DAT), 21 and 17%, respectively. Rice injury was only 5% at 14 DAT and 1% at 28 DAT. Hybrid long-grain cultivar CLXL745 was injured more than inbred long-grain cultivars CL151 and Cheniere. Cheniere was more tolerant than inbred medium-grain cultivars CL261 and Caffey. All cultivars exhibited tolerance to saflufenacil as evidenced by similar normalized difference vegetative index (NDVI), maturity, mature plant height, and rice yield (rough, whole, and total milled rice).

Giant ragweed has become an increasingly important weed of arable land in many parts of North America. It is now a common weed of row crop production systems, a fact that can be attributed to earlier crop planting dates, reduced tillage, and the development of resistance to Group 2 and 9 herbicides. The propagation of giant ragweed seedlings for experimental purposes is a lengthy process because up to 90 d of stratification is often required to alleviate primary seed dormancy. The objective of this research was to evaluate physical, chemical, and cold stratification methods for alleviating seed dormancy in giant ragweed and reducing the length of cold stratification required. Results indicate that the most effective method for alleviating dormancy in seed of giant ragweed is to excise the embryo from its covering structures. By excising the embryo, 96% of viable giant ragweed seeds germinated with no stratification. In contrast, untreated seeds required a minimum of 6 wk of stratification to alleviate dormancy in a similar proportion of the population. Although excising embryos requires time and effort, the time savings relative to stratification make it an attractive method for propagating giant ragweed seedlings.

Field studies were conducted to evaluate Italian ryegrass control and winter wheat tolerance to applications of diclofop, mesosulfuron plus methylated seed oil (MSO) alone or with 30% urea ammonium nitrate (UAN), mesosulfuron plus thifensulfuron plus tribenuron plus MSO, mesosulfuron plus MCPA plus MSO, or flufenacet plus metribuzin. Treatments were applied to wheat PRE, two- to three-leaf wheat (2–3 LF) at Feekes stage 1.0 or to one- to two-tiller wheat (TILL) at Feekes stage 3.0, depending on label recommendations. Studies were conducted in Williamson, GA, and Plains, GA, from autumn 2003 to spring 2005. Italian ryegrass control was variable, depending on location and year. Maximum and most-consistent Italian ryegrass control (> 90%) occurred with mesosulfuron plus MSO and UAN. Without UAN, control of Italian ryegrass with mesosulfuron varied from 44 to 97%. That variability was partially attributed to unfavorable environmental conditions associated with cold night time temperatures at or below 0 C, following applications. Wheat injury observed in response to herbicide treatments was minimal (< 15%) and transient; wheat recovered with no differences in yield.

Nutsedge control is challenging in commercial vegetable production in the absence of methyl bromide, and therefore, an effective alternative is needed. This study investigated allyl isothiocyanate (ITC) as a methyl bromide alternative for purple nutsedge control under polyethylene-mulch. Greenhouse experiments were conducted to compare the retention of allyl ITC in treated soil (3,000 nmol g−1) under low-density polyethylene (LDPE) and virtually impermeable film (VIF) mulches. Field experiments were conducted to evaluate the effectiveness of allyl ITC (6 rates: 0, 15, 75, 150, 750, 1500 kg ai ha−1) under VIF mulch against purple nutsedge. Additionally, a standard treatment of methyl bromide+chloropicrin (67 : 33%) at 390 kg ai ha−1 under LDPE mulch was included for comparison. In the greenhouse experiment, the predicted half-life of allyl ITC under LDPE and VIF mulch was 0.15 and 0.59 d, respectively. In the field experiment, it was predicted that allyl ITC at 1,240 and 1,097 kg ha−1 under VIF mulch is required to control purple nutsedge shoot and tubers equivalent to methyl bromide + chloropicrin at 4 wk after treatment (WAT). It is concluded that allyl ITC under VIF mulch would need to be applied at 2.8 to 3.2 times the standard treatment of methyl bromide + chloropicrin under LDPE mulch for commercially acceptable purple nutsedge control.

Methyl bromide (MeBr), classified as a Class I ozone-depleting substance, has been banned for ordinary agricultural uses. Weed control in commercial bell pepper production is complicated by the ban on MeBr and the lack of other available and effective soil fumigants. A field study was conducted to evaluate the effectiveness of allyl isothiocyanate (ITC) and metam sodium (methyl ITC generator) as MeBr alternatives for control of Palmer amaranth, large crabgrass, and yellow nutsedge; and for increasing marketable yields in low-density polyethylene (LDPE) –mulched bell pepper. Allyl ITC was applied at 450, 600, and 750 kg ha−1; metam sodium was applied at 180, 270, and 360 kg ha−1; and MeBr plus chloropicrin (67% and 33%, respectively) was applied at 390 kg ha−1. Allyl ITC and metam sodium did not injure bell pepper. Allyl ITC at 750 kg ha−1 or metam sodium at 360 kg ha−1 controlled Palmer amaranth (≥ 83%), large crabgrass (≥ 78%), and yellow nutsedge (≥ 80%) comparably to MeBr. Yellow nutsedge tuber density was ≤ 84 tubers m−2 in plots treated with the highest rate of allyl ITC and metam sodium and was comparable to the tuber density in MeBr-treated plots. Although allyl ITC at 750 kg ha−1 controlled weeds comparable to MeBr, total marketable bell pepper yield with allyl ITC was lower than the yield with MeBr. Conversely, total marketable bell pepper yield with the highest rate of metam sodium (53.5 ton ha−1) was equivalent to the yield (62.5 ton ha−1) in plots treated with MeBr. In conclusion, metam sodium at 360 kg ha−1 is an effective MeBr alternative for weed control in LDPE–mulched bell pepper.

Plant growth stage and temperature influence the activity of glyphosate on common lambsquarters. A biotype of common lambsquarters in Dickinson County, KS (DK) was not controlled upon treatment with glyphosate in the field. In a greenhouse dose–response study, the DK biotype expressed 1.5-fold less sensitivity to glyphosate compared to a known susceptible biotype from Riley County, KS (RL). Common lambsquarters plants were treated at different growth stages (5 to 7, 10 to 12, 15 to 17, or 19 to 21 cm tall) with glyphosate at a field rate (840 g ae ha–1), and, regardless of the biotype, plants were more susceptible to glyphosate when they were 5 to 7 cm tall. Common lambsquarters plants were treated with glyphosate (840 g ae ha–1) after growing at different temperatures (25/15, 32.5/22.5, or 40/30 C day/night), and regardless of the biotype, plants were more susceptible to glyphosate when grown at 25/15 C. The results suggest that the DK biotype exhibits reduced sensitivity to glyphosate compared to the RL biotype, and glyphosate applied at field rate would be more effective on smaller common lambsquarters plants and at cooler temperatures. Common lambsquarters seedlings tend to emerge when temperatures are cooler, early in the spring relative to other summer annual weeds. Therefore, plants should be identified and treated earlier in the growing season for best efficacy with glyphosate.