Saflufenacil (BAS 800H) is a new herbicide being developed by BASF for PRE broadleaf weed control in corn. Field studies were conducted at two Ontario locations in 2006 and 2007 to evaluate the tolerance of field corn to PRE and POST (spike and two- to three-leaf corn) applications of saflufenacil at 50, 100, and 200 g ai/ha with and without an adjuvant (surfactant blend + solvent [petroleum hydrocarbons]; 1% v/v). Saflufenacil applied PRE reduced corn height by as much as 12% with the highest rate of 200 g/ha; however, corn yield was not affected. When saflufenacil was applied without an adjuvant to corn at the spike stage, injury was as much as 12%, 7 d after treatment (DAT). However, corn height and yield were not affected. Saflufenacil applied POST to two- to three-leaf corn at 50 to 200 g/ha without an adjuvant resulted in as much as 25% injury and reduced corn height 31% but did not affect yield. Adding an adjuvant to POST applications of saflufenacil caused as much as 4 and 99% injury, reduced corn height 13 and 77%, and reduced corn yield 0 and 59% when applied to corn at the spike and at the two- to three-leaf stages, respectively. Based on these results, saflufenacil applied PRE can be safely used in corn at rates up to 200 g/ha. Saflufenacil applied to corn at the spike and two- to three-leaf stage at 50 or 100 g/ha without an adjuvant demonstrated acceptable corn tolerance and may allow for the use of saflufenacil beyond the proposed PRE use pattern. In contrast, applying saflufenacil POST with an adjuvant to spike and two- to three-leaf stage corn resulted in unacceptable injury and yield losses in field corn.

Field studies were conducted in 2007 and 2008 to evaluate fall applications of herbicides to control glyphosate-resistant (GR) horseweed before planting cotton. Fall treatments were compared with spring treatments for control of GR horseweed and effect on seed cotton yield. Fall and spring treatments with and without residual herbicides were also compared. No differences were observed for control of GR horseweed or seed cotton yield between fall and spring application timings. However, a difference was observed between fall applications with and without a residual herbicide. Fall applications that contained residual herbicides provided 86% control of GR horseweed and yielded 2,360 kg/ha of seed cotton. Fall applications that did not contain a residual herbicide only provided 70% control of GR horseweed and yielded 2,010 kg/ha of seed cotton. No benefit was observed from spring applications that contained a residual herbicide. This research indicates that glyphosate-resistant horseweed can be controlled with fall- or spring-applied burndown herbicides, and fall applications should include a residual herbicide for best results.

Saflufenacil is a new herbicide being developed for preplant burndown and PRE broadleaf weed control in field crops, including corn, soybean, sorghum, and wheat. Field experiments were conducted in 2006 and 2007 at Concord, in northeast Nebraska, with the objective to describe dose–response curves of saflufenacil applied with several adjuvants for broadleaf weed control. Dose–response curves based on log-logistic model were used to determine the effective dose that provides 90% weed control (ED90) values for six broadleaf weeds (field bindweed, prickly lettuce, henbit, shepherd's-purse, dandelion, and field pennycress). Addition of adjuvants greatly improved efficacy of saflufenacil. For example, the ED90 values for field bindweed control at 28 d after treatment were 71, 20, 11, and 7 g/ha for saflufenacil applied alone, or with nonionic surfactant (NIS), crop oil concentrate (COC), or methylated seed oil (MSO), respectively. MSO was the adjuvant that provided the greatest enhancement of saflufenacil across all species tested. COC was the second-best adjuvant and provided control similar to MSO on many weed species. NIS provided the least enhancement of saflufenacil. These results are very similar to the proposed label dose of saflufenacil for burndown weed control, which will range from 25 to 100 g/ha with MSO or COC. We believe that such a dose would provide excellent burndown control of most broadleaf weed species that emerge in the fall in Nebraska.

Field trials were conducted from 2005 to 2007 at two locations in southwestern Ontario to investigate how weed control in corn was affected by the time of day that herbicides were applied. Weed control following the application of six POST herbicides (atrazine, bromoxynil, dicamba/diflufenzopyr, glyphosate, glufosinate, and nicosulfuron) at 06:00, 09:00, 12:00, 15:00, 18:00, 21:00, and 24:00 h was assessed. For many weed species herbicide efficacy was reduced when applications were made at 06:00, 21:00, and 24:00 h. Velvetleaf was the most sensitive to the time of day effect, followed by common ragweed, common lambsquarters, and redroot pigweed. Annual grasses were not as sensitive to application timing; however, control of barnyardgrass and green foxtail was reduced in some environments at 06:00 h and after 21:00 h. Only in the most severe cases was the grain yield of corn reduced due to decreased weed control. Daily changes in air temperature, relative humidity, and light intensity that cause species-specific physiological changes may account for the variation in weed control throughout the day. The results of this research suggest that there is a strong species-specific influence of ambient air temperature, light intensity, and leaf orientation on the efficacy of POST herbicides. These results should aid growers in applying herbicides when they are most efficacious, thus reducing costs associated with reduced efficacy.

Field experiments were conducted in Georgia to evaluate weed control and crop tolerance with glufosinate applied to ‘PHY 485 WRF®’ cotton. This glyphosate-resistant cotton also contains a gene, used as a selectable marker, for glufosinate resistance. Three experiments were maintained weed-free and focused on crop tolerance; a fourth experiment focused on control of pitted morningglory and glyphosate-resistant Palmer amaranth. In two experiments, PHY 485 WRF cotton was visibly injured 15 and 20% or less by glufosinate ammonium salt at 430 and 860 g ae/ha, respectively, applied POST two or three times. In a third experiment, glufosinate at 550 g/ha injured cotton up to 36%. Pyrithiobac or glyphosate mixed with glufosinate did not increase injury compared to glufosinate applied alone; S-metolachlor mixed with glufosinate increased injury by six to seven percentage points. Cotton injury was not detectable 14 to 21 d after glufosinate application, and cotton yields were not reduced by glufosinate or glufosinate mixtures. A program of pendimethalin PRE, glyphosate applied POST twice, and diuron plus MSMA POST-directed controlled glyphosate-resistant Palmer amaranth only 17% late in the season. S-metolachlor included with the initial glyphosate application did not increase control, and pyrithiobac increased late-season control by only 13 percentage points. Palmer amaranth was controlled 90% or more when glufosinate replaced glyphosate in the aforementioned system. Pitted morningglory was controlled 99% by all glufosinate programs and mixtures of glyphosate plus pyrithiobac. Seed cotton yields with glufosinate-based systems were at least 3.3 times greater than yields with glyphosate-based systems because of differences in control of glyphosate-resistant Palmer amaranth.

Herbicide rotations and mixtures are widely recommended to manage herbicide resistance. However, little research has quantified how these practices actually affect the selection of herbicide resistance in weeds. A 4-yr experiment was conducted in western Canada from 2004 to 2007 to examine the impact of herbicide rotation and mixture in selecting for acetolactate synthase (ALS) inhibitor resistance in the annual broadleaf weed, field pennycress, co-occurring in wheat. Treatments consisted of the ALS-inhibitor herbicide, ethametsulfuron, applied in a mixture with bromoxynil/MCPA formulated herbicide (photosystem-II inhibitor/synthetic auxin), or in rotation with the non-ALS inhibitor at an ALS-inhibitor application frequency of 0, 25, 50, 75, and 100% (i.e., zero to four applications, respectively) over the 4-yr period. The field pennycress seed bank at the start of the experiment contained 5% ethametsulfuron-resistant seed. Although weed control was only marginally reduced, resistance frequency of progeny of survivors increased markedly after one ALS-inhibitor application. At the end of the experiment, the level of resistance in the seed bank was buffered by susceptible seed, increasing from 29% of recruited seedlings after one application to 85% after four applications of the ALS inhibitor. The level of resistance in the seed bank for the mixture treatment after 4 yr remained similar to that of the nontreated (weedy) control or 0% ALS-inhibitor rotation frequency treatment. The results of this study demonstrate how rapidly ALS-inhibitor resistance can evolve as a consequence of repeated application of herbicides with this site of action, and supports epidemiological information from farmer questionnaire surveys and modeling simulations that mixtures are more effective than rotations in mitigating resistance evolution through herbicide selection.

This research explored the use of downy brome (BROTE) as a cover crop in irrigated corn. Although BROTE is a difficult weed to control, it could not be maintained as a cover crop in no-till irrigated corn for more than one season. A 10-fold reduction in BROTE occurred in the second year of corn. By the fourth year, only one BROTE plant could be found at the two locations. Because BROTE did not persist across years, soil coverage decreased 5 to 18% in the later location-years. At one location, normal herbicide rates decreased Johnsongrass biomass more than 22-fold both years it was applied. Increasing herbicide input decreased Palmer amaranth density more than 3-fold, but only in a single location-year. In three of six location-years, level of herbicide input had no significant effect on evapotranspiration (ET). Increased BROTE biomass decreased ET 0.033 to 0.083 cm/d during the first season at both locations. Increased irrigation increased corn yield by 240 to 1,900 kg/ha in five of six location-year combinations. Half rates of in-season herbicides reduced yield only in one of six location-years. High BROTE density reduced ET but did not translate into increased crop yield. In three of six location-year combinations, high BROTE density decreased yield by 300 to 1,000 kg/ha. In a single location-year, increased surface residues provided by BROTE increased yield by 560 kg/ha. Increased irrigation inputs decreased water use efficiency (WUE) by 6.3 kg/ha-cm in a single location-year and increased WUE by 10.8 to 121.6 kg/ha-cm in four of six location-years. Increased herbicide inputs increased WUE by 10.3 kg/ha-cm in one location-year. BROTE density had no significant effect on WUE at location 1. At location 2 in the first 2 yr, WUE was increased 9.4 to 22.2 kg/ha-cm.

Field studies were conducted to determine if mesotrione alone or in combinations with other corn herbicides would control horseweed and other winter annual weeds associated with no-till corn. Mesotrione alone controlled horseweed 52 to 80% by 3 wk after treatment (WAT); however, by 7 WAT control diminished to between 37 to 68%, depending on mesotrione rate. Mesotrione at 0.16 kg ai/ha plus atrazine at 0.28 kg ai/ha controlled 99% of horseweed and annual bluegrass and 88% of yellow woodsorrel. Combinations of mesotrione at 0.16 kg/ha plus acetochlor at 1.79 kg ai/ha plus 1.12 kg ai/ha glyphosate (trimethylsulfonium salt of glyphosate) or 0.7 kg ai/ha paraquat provided 93% or greater control of all three weed species. Glyphosate alone also controlled all weed species 97 to 99%, while paraquat alone provided 99% control of annual bluegrass, 72% control of horseweed, and 36% control of yellow woodsorrel. Mixtures of paraquat plus acetochlor improved control of horseweed (93%) and yellow woodsorrel (73%) over control with either herbicide applied alone.

A 3-yr field study was conducted from 2005 to 2007 at Stoneville, MS, to determine efficacy of in-crop and autumn-applied glyphosate on purple nutsedge density and yield of no-till glyphosate-resistant (GR) corn and GR soybean. Separate experiments were conducted in GR corn and GR soybean in areas maintained under a no-tillage system after the autumn of 2004. Each experiment was conducted in a split-plot arrangement of treatments in a randomized complete-block design with and without autumn application of glyphosate at 1.68 kg ae/ha as main plots and in-crop herbicide application (glyphosate- and nonglyphosate-based programs) as subplots with three replications. In GR corn, glyphosate applied in the autumn reduced purple nutsedge density by 40 to 67% compared with no glyphosate during 3 yr. In GR corn, glyphosate applied in-crop reduced purple nutsedge shoot density by 48% in 2005, 92% in 2006, and 100% in 2007 compared with no herbicide. However, GR corn yields were unaffected by either in-crop or autumn-applied glyphosate. In GR soybean, glyphosate applied in the autumn reduced purple nutsedge shoot density by 64 to 83% compared with no glyphosate during 3 yr. Glyphosate applied in-crop in GR soybean reduced purple nutsedge density by 81% in 2005 and by 100% in 2006 and 2007 compared with no herbicide. GR soybean yields were similar in 2005, but yields were 34 and 18% higher in 2006 and 2007, respectively, with autumn-applied glyphosate compared with no glyphosate. GR soybean yields were higher with glyphosate applied in-crop compared with no herbicide in 2 of 3 yr. These results indicate that purple nutsedge density could be reduced with glyphosate applied in-crop in no-till GR corn and GR soybean. In addition, autumn-applied glyphosate was effective in reducing purple nutsedge populations following harvest of crops and could be an effective purple nutsedge management strategy regardless of GR trait.

Field studies were conducted near Clayton, Lewiston, and Rocky Mount, NC in 2005 to evaluate weed control and cotton response to preemergence treatments of pendimethalin alone or in a tank mixture with fomesafen, postemergence treatments of glufosinate applied alone or in a tank mixture with S-metolachlor, and POST-directed treatments of glufosinate in a tank mixture with flumioxazin or prometryn. Excellent weed control (> 91%) was observed where at least two applications were made in addition to glufosinate early postemergence (EPOST). A reduction in control of common lambsquarters (8%), goosegrass (20%), large crabgrass (18%), Palmer amaranth (13%), and pitted morningglory (9%) was observed when residual herbicides were not included in PRE or mid-POST programs. No differences in weed control or cotton lint yield were observed between POST-directed applications of glufosinate with flumioxazin compared to prometryn. Weed control programs containing three or more herbicide applications resulted in similar cotton lint yields at Clayton and Lewiston, and Rocky Mount showed the greatest variability with up to 590 kg/ha greater lint yield where fomesafen was included PRE compared to pendimethalin applied alone. Similarly, an increase in cotton lint yields of up to 200 kg/ha was observed where S-metolachlor was included mid-POST when compared to glufosinate applied alone, showing the importance of residual herbicides to help maintain optimal yields. Including additional modes of action with residual activity preemergence and postemergence provides a longer period of weed control, which helps maintain cotton lint yields.

This study measured weed interference in soybean and corn as affected by residue management tactics following a sequence of oat and winter wheat. Residue management tactics compared were conventional tillage, no-till, and no-till plus cover crops. Treatments were split into weed-free and weed-infested conditions; prominent weeds were green and yellow foxtail and common lambsquarters. Grain yield of soybean did not differ between weed-free and weed-infested conditions with no-till, whereas weeds reduced yield 25% in the tilled system. Corn responded inconsistently to treatments, with more than 40% yield loss due to weed interference in 1 yr with all treatments. Cover crops did not improve weed management compared with no-till in either crop. Seedling emergence of the weed community differed between tillage and no-till; density of weed seedlings was fivefold higher with tillage, whereas seedling emergence was delayed in no-till. The initial flush of seedlings occurred 2 to 3 wk later in no-till compared with the tilled system. Designing rotations to include cool-season crops in a no-till system may eliminate the need for herbicides in soybean to manage weeds.

Mesosulfuron is often applied to wheat at a time of year when top-dress nitrogen is also applied. Current labeling for mesosulfuron cautions against applying nitrogen within 14 d of herbicide application. Soft red winter wheat response to mesosulfuron and urea ammonium nitrate (UAN) applied sequentially and in mixtures was determined at three locations in North Carolina and Georgia during 2005 and 2006. Mesosulfuron at 0, 15, and 30 g ai/ha was applied in water to wheat at Feekes growth stage (GS) 3 followed by UAN at 280 L/ha 2 h, 7 d, 14 d, and 21 d after mesosulfuron. Mesosulfuron applied in UAN was also evaluated in 2006. Mesosulfuron injured wheat 6 to 9% in 2005 and 12 to 23% in 2006 when UAN was applied 2 h or 7 d after the herbicide. Wheat injury did not exceed 8% when UAN was applied 14 or 21 d after the herbicide. Greatest injury, 35 to 40%, was noted when mesosulfuron and UAN were combined. Wheat yield was unaffected by mesosulfuron or time of UAN application in 2005. In 2006, yield was affected by the timing of UAN application relative to mesosulfuron; wheat yield increased as the interval, in days, between UAN and herbicide applications increased. To avoid crop injury and possible yield reduction, mesosulfuron and UAN applications should be separated by at least 7 to 14 d. These findings are consistent with precautions on the mesosulfuron label.

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.

Field studies were conducted from 2004 to 2006 to evaluate the tolerance of three annual medic species (bur, black, and barrel medic) to selected POST herbicides. 2,4-DB at 0.56 and 1.12 kg/ha caused the most stunting across all three species. Imazethapyr at 0.1 kg/ha stunted all three annual medics in 1 of 3 yr whereas flumetsulam at 0.04 kg/ha stunted black and barrel medics in 1 of 3 yr. Clethodim at 0.28 kg/ha did not cause any medic stunting. Imazethapyr, imazamox, and 2,4-DB at 0.56 kg/ha reduced henbit dry matter composition compared to the untreated check whereas clethodim, flumetsulam, and 2,4-DB at 1.12 kg/ha did not. In 2004, 2,4-DB at 1.12 kg/ha reduced dry weight yield of bur and barrel medic but not black medic when compared with the untreated check. Black medic treated with imazethapyr at 0.05 and 0.1 kg/ha and clethodim at 0.28 kg/ha produced higher dry weight yield than the untreated check. In 2006, both rates of 2,4-DB and flumetsulam at 0.04 kg/ha reduced dry weight yield of bur medic compared to the untreated check. Barrel medic dry weight yields were reduced by both rates of 2,4-DB and flumetsulam compared to untreated check. No herbicides reduced dry weight yields of black medic.

Field experiments were conducted to determine the critical period of weed interference in glyphosate- and glufosinate-resistant sugar beet, and to determine if PRE herbicides increased weed control or sugar beet root yield when glufosinate, glyphosate, or conventional POST herbicides were applied. Glyphosate- and glufosinate-resistant sugar beet root yields were reduced by up to 66 and 67%, respectively, when weeds remained all season in the weedy control treatment compared with yields when weed removal occurred as soon as the weeds were 2.5 cm tall, approximately 2 to 3 wk after planting (WAP). A critical period of weed interference did not occur in this research. The critical time of weed removal was approximately 8 WAP in 1998 and beyond 11 WAP in 1999. Weeds averaged 20 cm in height at 8 WAP and weed densities were greater in 1998 compared with 1999. The critical weed-free period for glyphosate- and glufosinate-resistant sugar beet was 4.5 to 5 WAP in 1998. In 1999, the critical weed-free period at the Michigan Sugar location was 1.5 WAP in glyphosate-resistant sugar beet, and 6.5 WAP in glufosinate-resistant sugar beet for the Michigan Sugar site. Glyphosate or glufosinate POST provided better weed control and resulted in greater sugar beet root yield compared with conventional POST herbicides when data were combined over PRE herbicide treatments. PRE herbicides improved the control of common lambsquarters and Amaranthus species in some of the site-years when data were combined over POST treatments, but sugar beet yield did not increase. Our research suggests that PRE herbicides will not be necessary in glyphosate- or glufosinate-resistant sugar beet. To avoid sugar beet yield loss, multiple POST applications of glyphosate or glufosinate will be needed until 6 to 9 WAP to prohibit yield loss from weeds emerging after the last POST application.

Bispyribac-sodium is an efficacious herbicide for annual bluegrass control in creeping bentgrass fairways, but turf tolerance and growth inhibition may be exacerbated by low mowing heights on putting greens. We conducted field and greenhouse experiments to investigate creeping bentgrass putting green tolerance to bispyribac-sodium. In greenhouse experiments, creeping bentgrass discoloration from bispyribac-sodium was exacerbated by reductions in mowing height from 24 to 3 mm, but mowing height did not influence clipping yields or root weight. In field experiments, discoloration of creeping bentgrass putting greens was greatest from applications of 37 g/ha every 10 d, compared to 74, 111, or 222 g/ha applied less frequently. Chelated iron effectively reduced discoloration of creeping bentgrass putting greens from bispyribac-sodium while trinexapac-ethyl inconsistently reduced these effects. Overall, creeping bentgrass putting greens appear more sensitive to bispyribac-sodium than higher mowed turf, but chelated iron and trinexapac-ethyl could reduce discoloration.

There is an urgent need to accelerate the development and implementation of effective organic-compliant herbicides that are environmentally safe and that help the producer meet increasing consumer demand for organic products. Therefore, greenhouse experiments were conducted to evaluate the effectiveness of acetic acid (5%), acetic acid (30%), citric acid (10%), citric acid (5%) + garlic (0.2%), citric acid (10%) + garlic (0.2%), clove oil (45.6%), and corn gluten meal (CGM) compounds as natural-product herbicides for weed control. The herbicides were applied to the broadleaf weeds stranglervine, wild mustard, black nightshade, sicklepod, velvetleaf, and redroot pigweed and to narrowleaf weeds crowfootgrass, Johnsongrass, annual ryegrass, goosegrass, green foxtail, and yellow nutsedge. The herbicides were applied POST at two weed growth stages, namely, two to four and four to six true-leaf stages. CGM was applied PPI in two soil types. Citric acid (5%) + garlic (0.2%) had the greatest control (98%) of younger broadleaf weeds, followed by acetic acid (30%) > CGM > citric acid (10%) > acetic acid (5%) > citric acid (10%) + garlic (0.2%), and clove oil. Wild mustard was most sensitive to these herbicides, whereas redroot pigweed was the least sensitive. Herbicides did not control narrowleaf weeds except for acetic acid (30%) when applied early POST (EPOST) and CGM. Acetic acid (30%) was phytotoxic to all broadleaf weeds and most narrowleaf weeds when applied EPOST. Delayed application until the four- to six-leaf stage significantly reduced efficacy; acetic acid was less sensitive to growth stage than other herbicides. These results will help to determine effective natural herbicides for controlling weeds in organic farming.

Flame weeding is often used for weed control in organic production and other situations where use of herbicides is prohibited or undesirable. Response to cross-flaming was evaluated on five common weed species: common lambsquarters, redroot pigweed, shepherd's-purse, barnyardgrass, and yellow foxtail. Dose-response curves were generated according to species and growth stage. Dicot species were more effectively controlled than monocot species. Common lambsquarters was susceptible to flame treatment with doses required for 95% control (LD95) ranging from 0.9 to 3.3 kg/km with increasing maturity stage. Comparable levels of control in redroot pigweed required higher doses than common lambsquarters, but adequate control was still achieved. Flaming effectively controlled shepherd's-purse at the cotyledon stage (LD95 = 1.2 kg/km). However, the LD95 for weeds with two to five leaves increased to 2.5 kg/km, likely due to the rosette stage of growth, which allowed treated weeds to avoid thermal injury. Control of barnyardgrass and yellow foxtail was poor, with weed survival > 50% for all maturity stages and flaming doses tested. Flame weeding can be an effective and labor-saving weed control method, the extent of which is partially dependent on the weed flora present. Knowledge of the local weed flora and their susceptibility to flame weeding is vital for the effective use of this method.

Few herbicides are available for weed control in vegetable production systems using low-density polyethylene (LDPE) plastic mulch. With the elimination of methyl bromide for pest management and subsequent use of various alternative fumigants, the need for herbicides in vegetable production systems has increased. An experiment was conducted to evaluate tolerance of transplant summer squash and tomato to carfentrazone, flumioxazin, glyphosate, halosulfuron, or paraquat applied to the mulch prior to transplanting. After applying herbicides overtop of the mulch but prior to vegetable transplant, the mulch was either irrigated with 1.0 cm of water or not irrigated. Carfentrazone did not affect either crop regardless of irrigation. Irrigation readily removed glyphosate and paraquat from the mulch, as there was no adverse crop injury in these treatments. In the absence of irrigation, glyphosate and paraquat reduced squash diameter and tomato heights 18 to 34% at 3 wk after transplanting (WAT). Squash and tomato fruit numbers and fruit biomass (yield) were reduced 17 to 37%, and 25 to 33%, respectively. Halosulfuron reduced squash diameter and yield 71 to 74% and tomato heights and yields 16 to 37% when mulch was not irrigated prior to transplanting. After irrigating, halosulfuron had no affect on tomato, but reduced squash growth and yield 40 to 44%. Flumioxazin killed both crops when the mulch was not irrigated; and reduced squash yield 56% when irrigated. With irrigation, flumioxazin did not impact tomato fruit number, but did reduce tomato weight by 25%. These studies demonstrate the safety of carfentrazone, applied on mulch prior to transplanting either squash or tomato, regardless of irrigation, and also demonstrate the safety of glyphosate and paraquat if irrigated prior to transplanting. Conversely, flumioxazin should not be applied over mulch before transplanting either crop, regardless of irrigation. Halosulfuron application over mulch should be avoided before transplanting squash, regardless of irrigation, but can be applied prior to transplanting tomato if irrigated.

Diflufenzopyr is a synergist that has improved the efficacy of certain auxin-type herbicides such as dicamba on many broadleaf weed species. However, little is known regarding the activity of diflufenzopyr with other auxin-type herbicides. Russian knapweed is an invasive creeping perennial that is susceptible to certain pyridine carboxylic acids, which are auxin-type herbicides. The objective of this research was to determine if the addition of diflufenzopyr to three pyridine carboxylic acid herbicides enhances long-term control of Russian knapweed in Wyoming. All treatments were applied in the fall. Treatments included aminopyralid (0, 0.05, 0.09, and 0.12 kg ae/ha), clopyralid (0, 0.16, 0.21, 0.31, and 0.42 kg ae/ha) and picloram (0, 0.14, 0.28, 0.42, and 0.56 kg ae/ha), applied with and without diflufenzopyr (0.06 and 0.11 kg ae/ha). Twelve mo after treatment (MAT), diflufenzopyr had no significant impact on Russian knapweed control with either aminopyralid or picloram, and had significant but inconsistent impacts on knapweed control with clopyralid. At 24 MAT, diflufenzopyr did not enhance Russian knapweed control with either aminopyralid or clopyralid and was slightly antagonistic with picloram. These results indicate that the addition of diflufenzopyr does not improve Russian knapweed control with fall applications of either aminopyralid, clopyralid, or picloram.