Florpyrauxifen-benzyl is a new synthetic auxin herbicide that will provide a novel site of action in rice production. In many areas of the United States it is common practice to plant soybeans in rotation with rice, thereby introducing the potential for herbicide carryover. Multiple field experiments were conducted in 2014 and repeated in 2015 to evaluate potential plant-back restrictions for soybean and other row crops following an application of florpyrauxifen-benzyl. In the first experiment, treatments comprised florpyrauxifen-benzyl applied at 40 followed by 40 g ai ha–1, 80 fb 80 g ai ha–1, and a nontreated check. In 2014, herbicides were applied to a silt loam soil near Stuttgart and Colt, AR, and fields remained fallow following application. The following year, corn, cotton, soybean, grain sorghum, and sunflower were planted within the previously treated area. Stand counts, crop heights, and visual injury assessments were done for each crop following planting, and aboveground biomass data were collected 28 d after planting. No significant differences were observed among the treatments for any of the parameters assessed, highlighting the rotational flexibility of common row crops 1 yr following a florpyrauxifen-benzyl application. In the second experiment, florpyrauxifen-benzyl was applied at 30 and 60 g ai ha–1 at 56, 28, 14, and 0 d before planting soybean. Injury assessments corresponded to the highest concentration of florpyrauxifen-benzyl and its metabolites recovered from soil at the time of planting. Conversely, soybean injury was reduced when florpyrauxifen-benzyl was applied at increasing intervals before planting. At the end of each season, soybean yield was similar to the nontreated control when florpyrauxifen-benzyl at 30 or 60 g ai ha–1 was applied 56 d before planting, whereas all other treatments reduced yield. These results support a relatively short replant interval for soybean after florpyrauxifen-benzyl application to rice.

Imazapyr and imazamox are frequently applied postemergence to control grass and broadleaf weeds in imidazolinone-resistant sunflower in Argentina. Herbicide carryover to rotational crops represents a disadvantage of these herbicides, particularly in regions with low rainfall during the months prior to rotational crop sowing. Between 2009 and 2012, field and greenhouse studies were conducted on four important sunflower-cropped areas of Argentina. The objective was to quantify the effects of imazapyr alone and imazamox plus imazapyr applied in sunflower crops on the subsequent establishment, growth, and yield of barley, oat, and wheat. In all field experiments, imazapyr alone and imazamox plus imazapyr were applied at recommended rates (80 gha–1 and 66 plus 30 gha–1, respectively), and also, in some experiments, at double the recommended rates. Soil bioassays were also conducted in the greenhouse to study the effect of these herbicides on barley, oat, and wheat seedlings. The mixture of imazamox plus imazapyr was safer for rotational crops than imazapyr applied alone, because of the reduced rate of imazapyr in the mixture treatments. Barley was more sensitive to imidazolinones, particularly imazapyr, than the other winter cereals. Imazapyr at double rate (160 gha–1) reduced barley yield by 45% when seeds were sown 165 d after herbicide application and with 240 mm rainfall after herbicide application.

Triclopyr is a synthetic auxin herbicide currently available as a triethylamine salt, butoxyethyl ester, pyridinyloxyacetic acid, or choline salt. The formulation of a herbicide has the potential to impact its activity; therefore, the objective of this study was to determine the relative activity of these four triclopyr formulations. Greenhouse dose–response studies were conducted twice at the University of Florida in 2015. The four formulations were foliar applied at rates ranging from 17 to 1,121 g ae ha−1 to 2- to 3-leaf soybean, sunflower, tomato, and cotton. The amine salt formulation provided the lowest ED50 values in tomato and sunflower (22.87 and 60.39 g ha−1, respectively); whereas in soybean, amine and choline formulations provided the lowest ED50 values (22.56 and 20.95 g ha−1, respectively). No differences between formulations were observed in cotton. These data suggest that (1) the amine salt formulation of triclopyr might be more active than the others on tomato and sunflower, and (2) the amine and choline salt formulations might be more active than the others on soybean. Further work must be conducted to determine whether there are differences among these formulations under a range of field conditions and target species. In addition, other important management factors such as applicator safety, volatility potential, and cost should be considered when choosing the best formulated product to be applied.

Field studies were conducted from 1991 through 1994 in several locations of Southern Spain to determine the efficacy of imazapyr as late postemergence application in sunflower for broomrape control and the crop response to this herbicide under weed-free conditions. Single applications of imazapyr at 10 to 15 g/ha on sunflower plants at about the V12 (12 leaves) to V19 (19 leaves) growth stages, infected with broomrape plants at the predominant growth stages “c” (small nodule with shoot bud visible) and “d” (shoot bud and roots well developed), resulted in effective control without damaging the crop. Double applications of imazapyr at 10 + 10 g/ha at about the same crop growth stages V12 to V19, at a time interval of 12 to 14 d between single applications, were also efficacious and well tolerated by the crop. The same herbicide treatments applied to weed-free sunflower did not adversely affect the biomass, head diameter or yield of the crop as compared with the nontreated check. As a result of the low rate of imazapyr required for broomrape control, the herbicide treatments are economical (about $3 to $6/ha), non-residual and not affected by the type of soil texture and rainfall conditions.

Experiments were conducted to determine the effect of triglycerides, free fatty acids (FFA), and fatty acid methyl esters (FAME) on the foliar absorption, translocation, and phytotoxicity of quizalofop. Absorption, translocation, and phytotoxicity of quizalofop in oats were greater when quizalofop was applied with FFA or FAME than with their respective triglycerides. Triglycerides and FFA generally enhanced quizalofop absorption and translocation more when they contained unsaturated than saturated fatty acids. Methylation of the fatty acids reduced differences among fatty acids, but methyl stearate and methyl linolenate enhanced absorption of quizalofop less than the other FAME for oats and yellow foxtail. Quizalofop absorption and phytotoxicity to oats were greater when applied with sunflower oil, sunflower oil FFA, and sunflower oil FAME than with the corresponding linseed oil derivatives. Emulsifier generally reduced differences between linseed oil and sunflower oil derivatives in their enhancement of absorption, translocation, and phytotoxicity of quizalofop.

The response of oat, foxtail millet, proso millet, and sunflower to atrazine and clomazone applied the previous fall was investigated two years in field studies near Akron, CO and Sidney, NE. Foxtail millet biomass, and proso millet and sunflower grain yields were not reduced when these crops were seeded into soil that had been treated the previous fall with atrazine and/or clomazone at rates of 0.6 or 1.1 kg ai/ha. Forage yield of oat was reduced 11 to 18% by some treatments, but this effect was not consistent over years or sites. Treatments containing 1.1 kg/ha of atrazine provided 1 to 5 wk of residual weed control in foxtail millet, proso millet, and sunflower. The study indicated that producers have flexibility in crop selection when using atrazine and clomazone in reduced- and no-till production systems.

Field experiments were conducted during 1984 and 1985 to determine the influence of 2,4-D and MCPA amine and ester formulations on control of foxtail millet with diclofop. Foxtail millet control increased as the diclofop rate increased from 0.6 to 1.7 kg ai/ha whether diclofop was applied alone or with 2,4-D or MCPA amine and ester formulations; however, foxtail millet control was lower when diclofop was applied with 2,4-D or MCPA amine and ester formulations compared to diclofop applied alone. MCPA ester, MCPA amine, 2,4-D ester, or 2,4-D amine at 0.14 kg ai/ha added to a diclofop spray mixture reduced foxtail millet control 8, 15, 20, and 30% compared to diclofop applied alone, averaged over diclofop rates of 0.6, 0.8, 1.1, 1.4, and 1.7 kg/ha. Adding a petroleum oil to diclofop increased foxtail millet control with diclofop at 0.6 kg/ha but not at 0.8 kg/ha. The petroleum oil additive did not overcome the antagonism of foxtail millet control when diclofop at 0.6 kg/ha was applied with 2,4-D or MCPA amine and ester formulations. The amount of 14C-diclofop absorbed by oats was greater when diclofop was applied with the ester formulations of 2,4-D or MCPA compared to the amine formulations. Either once-refined sunflower oil or sunflower oil methyl ester applied with 14C-diclofop increased the amount of 14C absorbed and translocated in oat plants compared to 14C-diclofop applied alone.

Field research was conducted at Fargo, Langdon, and Prosper, ND to determine carryover of clopyralid applied at 70 to 560 g ae ha-1 in soil as indicated by response of crops planted 1 yr after application. Flax, potato, and safflower growth at Fargo were not affected by clopyralid residues. At Fargo, soybean height, stand, and yield were reduced by residues from clopyralid at 560 g ha-1, and sunflower heads ha-1 and yield were reduced by residues from clopyralid at 280 and 560 g ha-1 and 560 g ha-1, respectively. Potato and sunflower at Langdon and Prosper and lentil at Langdon were not affected by clopyralid residues. Soybean yield at Prosper was not affected by clopyralid residues, but plant height was reduced by residues from clopyralid at 280 and 560 g ha-1. These results indicate that residues from clopyralid applied at labeled cropland rates, of 280 g ha-1 or less, in silty clay, clay loam, and silty clay loam soils in North Dakota probably will not adversely affect the dicot crops tested in these experiments planted 11 mo or more after application.

AC 222,293, a postemergence herbicide for wild oat control in wheat, barley, and sunflower, was applied at five rates at three locations in Montana in the spring of 1985. Twelve and 11 crops were seeded into treated soil in 1985 and 1986, respectively. Sugarbeet, lentil, and rape were injured by residual levels of AC 222,293 14 months after application. Injury was significantly greater at one location, indicating herbicide bioavailability varied by location. Soil pH was correlated negatively with crop injury, indicating the herbicide persists longer on lower pH soils.

Field studies were conducted from 1990 through 1997 to evaluate the long-term effect of 2- and 3-yr rotations on the control of downy brome, jointed goatgrass, and feral rye in winter wheat. At the completion of the study, jointed goatgrass and feral rye densities averaged 8 plants/m2 and < 0.1 plant/m2 for the 2- and 3-yr rotations, respectively. Downy brome densities averaged < 0.5 plant/m2 for both the 2- and 3-yr rotations, with no treatment differences observed. Winter annual grasses were not eradicated after two cycles of the 3-yr rotations, but weed densities were reduced 10-fold compared to densities after one cycle and more than 100-fold compared with the 2-yr rotations. Wheat grain contamination with dockage and foreign material followed a similar trend. The 3-yr rotations were economically competitive with 2-yr rotations and provided superior control of the winter annual grass weeds.

We compared applications of trifluralin or ethalfluralin granules incorporated with a sweep plow or pendimethalin (ec) applied without incorporation to incorporating trifluralin (ec) by tandem-disk harrowing for sunflower production. The study was established in winter wheat stubble at three sites in the northern and central Great Plains. Crop residues on the soil surface following sunflower planting was greater than 30% (level required to protect soil from erosion) with all conservation-tillage strategies, but not with disk incorporation. Weed control and sunflower seed yield with conservation-tillage strategies were similar to the disk incorporation practice, demonstrating that producers can use these strategies for sunflower production and to protect soil from erosion.

Producers in the northern Great Plains are exploring alternative crop rotations, with the goal of replacing spring wheat-fallow. We characterized the weed associations occurring with tillage system and nitrogen level in two rotations, spring wheat (SW)-fallow (F) and SW-winter wheat (WW)-sunflower (SUN). Weed density was measured 10 yr after initiation of the study. With both rotations, weed community density was highest with no-till. For SW-F, green foxtail, yellow foxtail, and fairy candelabra comprised 99% of the weed community, whereas 13 species were observed in SW-WW-SUN. Fairy candelabra, a rangeland species, was observed only in the no-till system of SW-F. In SW-WW-SUN, no-till favored kochia, Russian thistle, and foxtails, whereas common lambsquarters and annual sowthistle were more common in tilled systems. Nitrogen fertilizer increased crop competitiveness in SW-WW-SUN with no-till, subsequently reducing weed density. Cultural strategies that disrupt weed associations will aid producers in managing weeds.

Diammonium sulfate often is used as an adjuvant with glyphosate. Experiments were conducted in the greenhouse to determine the effectiveness of diammonium sulfate in overcoming calcium antagonism of glyphosate toxicity to wheat, sunflower, kochia, and soybean. Each species was a separate experiment and treatments varied with the experiment. Diammonium sulfate at 0.5% (w/v) in a spray carrier containing calcium chloride (500 ppm calcium) overcame calcium antagonism of glyphosate toxicity to wheat, overcame antagonism and enhanced toxicity to sunflower, but only partly overcame calcium antagonism of toxicity to kochia and soybean. With glyphosate at 100 g ae ha–1, diammonium sulfate at 2% (w/v) in a distilled water spray carrier enhanced toxicity to sunflower from a 11% to a 55% fresh weight reduction but was antagonistic to glyphosate toxicity to kochia and soybean.

Field experiments were conducted from 1989 to 1992 in Balcarce, Tandil, and San Cayetano, all in Buenos Aires province (Argentina), to evaluate clethodim, fenoxaprop-P-ethyl, fluazifop-P, haloxyfop, propaquizafop, and quizalofop-P-ethyl for bermudagrass control in sunflower, soybean, and potato. The highest levels of bermudagrass control 60 days after treatment (DAT) were generally obtained with fenoxaprop-P-ethyl, haloxyfop, propaquizafop, and quizalofop-P-ethyl. Late season bermudagrass control, based on biomass of stolons and rhizomes, suggested that the most consistent treatments in potato and sunflower were haloxyfop at 180 g ai/ha and quizalofop-P-ethyl at 54 g ai/ha. In soybean, clethodim at 336 g ai/ha, haloxyfop at 180 g/ha, propaquizafop at 100 g ai/ha, and quizalofop-P-ethyl at 54 g/ha provided the greatest reductions in bermudagrass biomass. All of the postemergence (POST) graminicide treatments increased crop yields when compared to a nontreated check. However, little or no difference in yield was obtained when herbicide rate was increased.

The effect of imazethapyr and imazamethabenz on following crops was tested in southern Alberta, on Dark Brown and Brown Chernozemic soils, to assess the potential restrictions placed on cropping sequences by the use of these herbicides. Imazamethabenz reduced the yield of sugarbeet seeded one year after application. After imazethapyr application there is risk of yield loss with flax, corn, meadow bromegrass, mustard, sunflower, timothy, and wheat seeded one year later; canola seeded up to two years later; and sugarbeet and potato seeded up to three years later. Legume crops and intermediate wheatgrass may be seeded the year after application with little risk of yield loss. The required recropping intervals limit the use of imazethapyr for weed control in pea, alfalfa, or dry bean in cropping sequences that include sugarbeet, canola, or potato.

Integrated weed management practices, such as crop rotation and increased seeding rates, potentially improve weed management. Yet, few studies compare competitive interactions of weeds with different crops. This research quantified the impact of Persian darnel on spring wheat, canola, and sunflower yield across different seeding rates. Increasing crop density increased yield when Persian darnel affected crop yield early in physiological development. Crop yield loss was estimated to reach 83, 70, and 57% for spring wheat, canola, and sunflower, respectively, at high Persian darnel densities. Persian darnel reduced spring wheat yield by limiting the number of tillers per plant and seed per tiller; reduced canola yield by limiting the number of branches per plant, pods per branch, and seed per pod; and reduced sunflower yield by limiting the number of seed per plant. Persian darnel affected crop growth early in physiological development, indicating that interspecific interference occurred early in the growing season. Cultural and resource management aimed at reducing Persian darnel impact on resource availability and crop yield components will reduce Persian darnel impact on crop yield.

Protoporphyrinogen oxidase (protox)-inhibiting herbicides damage cell membranes, resulting in electrolyte leakage. A whole-plant dose-response study and a rapid assay that measured electrolyte leakage was used to determine the response of wild mustard, soybean, and protox inhibitor–susceptible and protox inhibitor–resistant common waterhemp to increasing doses of three protox inhibitors: acifluorfen, fomesafen, and sulfentrazone. For the dose-response study, whole plants were treated with the three protox-inhibitor herbicides. Electroconductivity assay 1 consisted of cutting discs from leaf tissue and submerging them in an incubation medium containing concentrations of acifluorfen, fomesafen, or sulfentrazone. In electroconductivity assay 2, the entire leaf was treated with solutions containing acifluorfen, fomesafen, or sulfentrazone. The whole-plant dose-response study showed increasing visible injury with increasing herbicide rates for all species and all herbicides. The order of visible injury was wild mustard > susceptible common waterhemp > resistant common waterhemp > soybean. In assay 1, electrolyte leakage from leaf discs treated with acifluorfen or fomesafen increased with increasing herbicide concentrations, and was similar for all species. In contrast, electrolyte leakage from leaf discs treated with sulfentrazone did not increase with increasing herbicide concentrations for any species. In assay 2, only wild mustard leaf discs increased in electrolyte leakage with increasing herbicide rates of acifluorfen, fomesafen, and sulfentrazone and followed the regression curves established by the whole-plant dose-response study. However, assay 2 was not able to distinguish between susceptible wild mustard and tolerant soybean, or between susceptible and resistant waterhemp.

Field trials were conducted in 1997 and 1998 at two locations in Israel to evaluate the efficacy of imazapic applied postemergence (POST) to sunflower for broomrape control under irrigated and nonirrigated conditions. Two sequential treatments of imazapic at 1.5 followed by (FB) 3.0, 3.0 FB 4.5, or 4.5 FB 6.0 g ai/ha on sunflower plants 12 ± 3 and 55 ± 5 cm tall, respectively, reduced sunflower broomrape throughout the growing season under irrigated and nonirrigated conditions. Sunflower growth was not affected by imazapic treatments. It was confirmed, in accordance with an earlier report, that when sequential treatments of imazapic included an application at the sunflower inflorescence developmental stage, the herbicide decreased seed yield in proportion to the applied rate.

Pyroxasulfone (KIH-485) is a seedling growth-inhibiting herbicide developed by Kumiai America that has the potential to control weeds in sunflower. However, little is known about how this herbicide will interact with various soil types and environments when combined with sulfentrazone. The objective of this research was to evaluate sunflower injury and weed control with pyroxasulfone applied with and without sulfentrazone across the Great Plains sunflower production area. A multisite study was initiated in spring 2007 to evaluate sunflower response to pyroxasulfone applied PRE at 0, 167, 208, or 333 g ai ha−1. In 2008, pyroxasulfone was applied alone and in tank mixture with sulfentrazone. In 2007, no sunflower injury was observed with any rate of pyroxasulfone at any location except Highmore, SD, where sunflower injury was 17%, 4 wk after treatment (WAT) with 333 g ha−1. In 2008, sunflower injury ranged from 0 to 4% for all treatments. Adding sulfentrazone did not increase injury. Sunflower yield was only reduced in treatments in which weeds were not effectively controlled. These treatments included the untreated control and pyroxasulfone at 167 g ha−1. Sunflower yield did not differ among the other treatments of pyroxasulfone or sulfentrazone applied alone or in combination. The addition of sulfentrazone to pyroxasulfone improved control of foxtail barley, prostrate pigweed, wild buckwheat, Palmer amaranth, and marshelder, but not large crabgrass or green foxtail. The combination of pyroxasulfone and sulfentrazone did not reduce control of any of the weeds evaluated.

The herbicide fluridone is a soil-residual herbicide that should provide effective control of several problematic agronomic weeds, but because of herbicide persistence, injury to rotational crops is possible. In this experiment, multiple rates of fluridone were applied PRE to cotton at four irrigated locations across Arkansas to determine the risk of fluridone persisting and injuring subsequently planted wheat, corn, soybean, rice, grain sorghum, and sunflower. The multiple rates of fluridone were compared with fluometuron and evaluated for percentage of crop injury, crop density, and potential yield loss for each crop at the end of the subsequent growing season. Regardless of the location, wheat exhibited the greatest injury with 13 to 26% at Fayetteville (silt loam), 8 to 15% at Pine Tree (silt loam), 2 to 7% at Keiser (silty clay), and 3 to 8% at Rohwer (silty clay). Along with high levels of injury to wheat, fluridone at 900 g ai ha−1 caused loss of wheat stands to 29 plants m−1 row compared with fluometuron, which had stands of 49 plants m−1 row. Although injury occurred in wheat at all locations, no rate of fluridone reduced wheat yields compared with fluometuron. Injury to grain sorghum ranged from 5 to 10% from all rates of fluridone at Pine Tree. Fluridone at 900 g ha−1 (11 plants m−1 row) also reduced grain sorghum stands at Pine Tree over that of fluometuron (19 plants m−1 row). A decrease in grain sorghum yield was also observed from fluridone at 448, 673, and 900 g ha−1 compared with fluometuron at Pine Tree. At Keiser, rice exhibited significant levels of injury (1 to 13%) from fluridone 393 d after treatment. In conclusion, injury to a wheat rotational crop is more likely following an application of fluridone in cotton than is injury to other rotational crops, but yield reductions are not expected for most rotational crops when fluridone is applied to cotton at an anticipated labeled rate of 224 g ha−1.