Prostrate water primrose is a troublesome weed in rice paddy fields. A study was conducted to determine the influence of environmental and agronomic factors on its emergence. The efficacy of herbicides on this species was also examined. The germination percentage of mature seeds remained above 90% within 180 d after harvest, indicating a low primary dormancy of this species. Light stimulated seed germination. Seeds buried deeper than 0.5 cm did not form seedlings. These results suggest that stale seedbed practices and deep tillage operations can mitigate the occurrence of this species in paddy fields. The optimum temperature for germination varied from 25/15 C to 35/25 C. The osmotic potential and salt concentration needed to inhibit 50% of maximum germination were −0.4 MPa and 197 mM, respectively. Seeds were tolerant to flooding and did not germinate at pH 8 to 10. The preemergence herbicides oxadiazon, oxadiargyl, and butachlor had excellent control efficacy on prostrate water primrose, with a 95.4% to 100% reduction in seedling number and a 99.2% to 100% reduction in biomass, respectively. The postemergence herbicides MCPA-Na + bentazone, bentazone, MCPA-Na, and fluroxypyr applied at the 2- to 3-leaf stage of prostrate water primrose provided a 90.6% to 100% reduction in seedling number and a 99.3% to 100% reduction in biomass. The results of this study can help in developing sustainable and effective integrated weed management strategies for controlling prostrate water primrose in paddy fields.

Herbicide-resistant (HR) kochia is a growing problem in the Great Plains region of Canada and the United States. Resistance to up to four herbicide sites of action, including photosystem II inhibitors, acetolactate synthase inhibitors, synthetic auxins, and the 5-enolpyruvylshikimate-3-phosphate synthase inhibitor glyphosate have been reported in many areas of this region. Despite being present in the United States since 1993/1994, auxinic-HR kochia is a recent and growing phenomenon in Canada. This study was designed to characterize 1) the level of resistance and 2) patterns of cross-resistance to dicamba and fluroxypyr in 12 putative auxinic-HR kochia populations from western Canada. The incidence of dicamba-resistant individuals ranged among populations from 0% to 85%, while fluroxypyr-resistant individuals ranged from 0% to 45%. In whole-plant dose-response bioassays, the populations exhibited up to 6.5-fold resistance to dicamba and up to 51.5-fold resistance to fluroxypyr based on visible injury 28 d after application. Based on plant survival estimates, the populations exhibited up to 3.7-fold resistance to dicamba and up to 72.5-fold resistance to fluroxypyr. Multiple patterns of synthetic auxin resistance were observed, in which one population from Cypress County, Alberta, was resistant to dicamba but not fluroxypyr, whereas another from Rocky View County, Alberta, was resistant to fluroxypyr but not dicamba based on single-dose population screening and dose-response bioassays. These results suggest that multiple mechanisms may confer resistance to dicamba and/or fluroxypyr in Canadian kochia populations. Further research is warranted to determine these mechanisms. Farmers are urged to adopt proactive nonchemical weed management practices in an effort to preserve efficacy of the remaining herbicide options available for control of HR kochia.

Herbicide management information is lacking for recently developed turf-type bahiagrass germplasm. The objective of this study was to evaluate the herbicide tolerance of nine experimental bahiagrass genotypes compared to the industry standard ‘Argentine’. The experimental entries included Argentine and ‘Wilmington’ mutants, and wild-type breeding lines. Plants were grown under greenhouse conditions, and 12 herbicides were applied at 1× and 2× labeled rates. Bentazon, bromoxynil, carfentrazone + 2,4-D + MCPP + dicamba, and carfentrazone were classified as safe. Fluroxypyr, halosulfuron, and triclopyr + clopyralid reduced growth >50% when applied at twice the label rate. Fenoxaprop, sulfentrazone + imazethapyr, and thiencarbazone + iodosulfuron + dicamba reduced growth and caused turfgrass injury above an acceptable threshold (≥20%). In general, the Argentine mutants showed greater herbicide injury compared to the Wilmington mutants. However, metsulfuron exceeded the acceptable injury threshold and stopped growth in all the genotypes, Argentine and genotype WT6 were the least injured by this herbicide. The experimental genotype WT6 consistently showed the greatest herbicide tolerance. Except for one genotype (WT4), the experimental genotypes responded similarly or better than Argentine to the tested herbicides, except for metsulfuron.

Late-season control of Palmer amaranth in postharvest wheat stubble is important for reducing the seedbank. Our objectives were to evaluate the efficacy of late-season postemergence herbicides for Palmer amaranth control, shoot dry biomass, and seed production in postharvest wheat stubble. Field experiments were conducted at Kansas State University Agricultural Research Center near Hays, KS, during 2019 and 2020 growing seasons. The study site had a natural seedbank of Palmer amaranth. Herbicide treatments were applied 3 wk after wheat harvest when Palmer amaranth plants had reached the inflorescence initiation stage. Palmer amaranth was controlled by 96% to 98% 8 wk after treatment and shoot biomass as well as seed production was prevented when paraquat was applied alone or when mixed with atrazine, metribuzin, flumioxazin, 2,4-D, sulfentrazone, pyroxasulfone + sulfentrazone, or flumioxazin + metribuzin, and with glyphosate + dicamba, glyphosate + 2,4-D, saflufenacil + 2,4-D, glufosinate + dicamba + glyphosate, and glufosinate + 2,4-D + glyphosate. Palmer amaranth was controlled by 89% to 93% with application of glyphosate, glufosinate, dicamba + 2,4-D, saflufenacil + atrazine, and saflufenacil + metribuzin resulting in Palmer amaranth shoot biomass of 15 to 56 g m−2 and production of 1,080 to 7,040 seeds m−2. Palmer amaranth control was less than 86% with application of dicamba, 2,4-D, dicamba + atrazine, and saflufenacil resulting in Palmer amaranth shoot biomass of 38 to 47 g m−2 and production of 3,110 to 6,190 seeds m−2. Palmer amaranth was controlled 63% and 72%, shoot biomass was 178 and 161 g m−2, and seed production was 35,180 and 39,510 seeds m−2, respectively, with application of 2,4-D + bromoxynil + fluroxypyr, and bromoxynil + pyrasulfotole + atrazine. Growers should use these effective postemergence herbicide mixes for Palmer amaranth control to prevent seed prevention postharvest in wheat stubble.

Three herbicide premixes have recently been introduced for weed control in wheat: halauxifen + florasulam, thifensulfuron + fluroxypyr, and bromoxynil + bicyclopyrone. The objective of this study was to evaluate these herbicides along with older products for their control of small-seeded false flax in winter wheat in Oklahoma. Studies took place during the 2017, 2018, and 2020 winter wheat growing seasons. Weed control was visually estimated every 2 wk throughout the growing season, and wheat yield was collected in all 3 yr. Small-seeded false flax diameter was approximately 6 cm at the time of application in all years. Control ranged from 96% to 99% following all treatments with the exception of bicyclopyrone + bromoxynil and dicamba alone, which controlled false flax 90%. All treatments containing an acetolactate synthase (ALS)–inhibiting herbicide achieved adequate control; therefore, resistance is not suspected in this population. Halauxifen + florasulam and thifensulfuron + fluroxypyr effectively controlled small-seeded false flax similarly to other standards recommended for broadleaf weed control in wheat in Oklahoma. Rotational use of these products allows producers flexibility in controlling small-seeded false flax and reduces the potential for development of herbicide resistance in this species.

Kochia accessions (designated as KS-4A and KS-4H) collected from a corn field near Garden City, KS, have previously shown multiple resistance to glyphosate, dicamba, and fluroxypyr. These accessions were also suspected as being resistant to photosystem II (PS II) inhibitors. The main objectives of this research were to 1) confirm the coexistence of cross-resistance to PS II inhibitors (atrazine and metribuzin) applied PRE and POST, 2) investigate the underlying mechanism of PS II-inhibitor resistance, and 3) determine the effectiveness of alternative POST herbicides for control of these multiple herbicide–resistant (MHR) kochia accessions. Results from dose-response experiments revealed that the KS-4A and KS-4H kochia accessions were 23-fold to 48-fold resistant to PRE- and POST-applied atrazine and 13-fold to 18-fold resistant to POST-applied metribuzin compared to a known susceptible kochia accession (KS-SUS). Both accessions also showed putative resistance to PRE-applied metribuzin that needs to be confirmed. Sequence analyses of the psbA gene further revealed that all samples from the KS-4A and KS-4H kochia accessions had a Ser264Gly point mutation. A pretreatment with malathion followed by a POST application of atrazine at 1,120 g ha−1 or metribuzin at 630 g ha−1 did not reverse the resistance phenotypes of these MHR accessions. In a separate greenhouse study, alternative POST herbicides, including bicyclopyrone + bromoxynil; bromoxynil + pyrasulfotole; paraquat alone or in combination with atrazine, metribuzin, 2,4-D, or saflufenacil; and saflufenacil alone or in combination with 2,4-D effectively controlled the KS-4H accession (≥97% injury). To our knowledge, this research reports the first case of kochia accessions with cross-resistance to PRE-applied atrazine and POST-applied metribuzin. Growers should adopt diversified weed control strategies, including the use of competitive crops, cover crops, targeted tillage, and harvest weed seed control along with effective alternative PRE and POST herbicides with multiple sites of action to control MHR kochia seedbanks on their production fields.

Horseweed is a competitive summer or winter annual weed that produces up to 230,000 small seeds per plant that are capable of traveling more than 500 km via wind. Giant ragweed is a tall, highly competitive summer annual weed. Glyphosate-resistant (GR) horseweed and GR giant ragweed pose significant challenges for producers in the United States and Ontario, Canada. It is thought that an integrated weed management (IWM) system involving herbicide rotation is required to control GR biotypes. Halauxifen-methyl is a new selective broadleaf POST herbicide registered for use in cereal crops; there is limited information on its efficacy on horseweed and giant ragweed. The purpose of this research was to determine the efficacy of halauxifen-methyl applied POST, alone and in a tank mix, for the control of GR horseweed and GR giant ragweed in wheat across southwestern Ontario. For each weed species, an efficacy study consisting of six field experiments was conducted over a 2-yr period (2018, 2019). At 8 wk after application (WAA), halauxifen-methyl, fluroxypyr/halauxifen-methyl, fluroxypyr/halauxifen-methyl + MCPA EHE, fluroxypyr + MCPA ester, 2,4-D ester, clopyralid, and pyrasulfotole/bromoxynil + ammonium sulfate controlled GR horseweed >95%. Fluroxypyr and MCPA provided only 86% and 37% control of GR horseweed, respectively. At 8 WAA, fluroxypyr, fluroxypyr/halauxifen-methyl, fluroxypyr/halauxifen-methyl + MCPA EHE, fluroxypyr + MCPA ester, fluroxypyr/halauxifen-methyl + MCPA EHE + pyroxsulam, 2,4-D ester, clopyralid, and thifensulfuron/tribenuron + fluroxypyr + MCPA ester controlled GR giant ragweed 87%, 88%, 90%, 94%, 96%, 96%, 98%, and 93%, respectively. Halauxifen-methyl and pyroxsulam provided only 45% and 28% control of GR giant ragweed, respectively. Halauxifen-methyl applied alone POST in the spring controlled GR horseweed but not GR giant ragweed in winter wheat.

Halauxifen plus florasulam, thifensulfuron plus fluroxypyr, and bromoxynil plus bicyclopyrone are three, relatively new POST premix herbicides developed for control of broadleaf weeds in winter wheat. These herbicides, along with older products, were evaluated for their control of horseweed in Altus, Perkins, and Ponca City, Oklahoma, during the spring of 2017 and 2018. Horseweed has become a critical weed in Oklahoma because of its extensive germination window, changes in tillage practices, and increase in herbicide-resistant horseweed biotypes. Visual weed control was estimated every 2 wk throughout the growing season and wheat yield was collected from three of the six site-years. Horseweed size ranged from 5 to 20 cm at time of application. The halauxifen plus florasulam, and thifensulfuron plus fluroxypyr combinations were effective at controlling a wide range of horseweed rosette sizes across all locations, whereas control with other treatments varied depending on presence of herbicide resistance, weed size at time of application, and mix partner.

Glyphosate-resistant (GR) kochia has been reported across the western and midwestern United States. From 2011 to 2014, kochia seed was collected from agronomic regions across Colorado to evaluate the frequency and distribution of glyphosate-, dicamba-, and fluroxypyr-resistant kochia, and to assess the frequency of multiple resistance. Here we report resistance frequency as percent resistance within a population, and resistance distribution as the percentage and locations of accessions classified as resistant to a discriminating herbicide dose. In 2011, kochia accessions were screened with glyphosate only, whereas from 2012 to 2014 kochia accessions were screened with glyphosate, dicamba, and fluroxypyr. From 2011 to 2014, the percentages of GR kochia accessions were 60%, 45%, 39%, and 52%, respectively. The percentages of dicamba-resistant kochia accessions from 2012 to 2014 were 33%, 45%, and 28%, respectively. No fluroxypyr-resistant accessions were identified. Multiple-resistant accessions (low resistance or resistant to both glyphosate and dicamba) from 2012 to 2014 were identified in 14%, 15%, and 20% of total sampled accessions, respectively. This confirmation of multiple glyphosate and dicamba resistance in kochia accessions emphasizes the importance of diversity in herbicide site of action as critical to extend the usefulness of remaining effective herbicides such as fluroxypyr for management of this weed.

Evolution and rapid spread of herbicide-resistant (HR) kochia has become a significant challenge for growers in the U.S. Great Plains. The main objectives of this research were to confirm and characterize the response of putative auxinic HR (Aux-HR) kochia accessions (designated as KS-4A, KS-4D, KS-4H, KS-10A, KS-10-G, and KS-10H) collected from two different corn fields near Garden City, KS, to dicamba and fluroxypyr and to determine the EPSPS gene copy number to detect whether those accessions were also resistant to glyphosate. Single-dose experiments indicated that putative Aux-HR kochia accessions had 78% to 100% and 85% to 100% survivors when treated with dicamba (560 g ae ha−1) and fluroxypyr (235 g ae ha−1), respectively. Whole-plant dicamba dose–response studies revealed that the selected Aux-HR accessions had 2.9- to 15.1- and 3.1- to 9.4-fold resistance to dicamba relative to two susceptible accessions (MT-SUS and KS-SUS). In a separate fluroxypyr dose–response experiment, the selected Aux-HR accessions also exhibited 3.8- to 7.3- and 3.0- to 8.6-fold resistance to fluroxypyr on the basis of shoot fresh and dry weight responses, respectively. The confirmed Aux-HR kochia accessions also had 3 to 13 EPSPS gene copies relative to MT-SUS and KS-SUS accessions (each with 1 EPSPS gene copy). These results suggest that the putative Aux-HR kochia accessions from Kansas had developed moderate to high levels of cross-resistance to dicamba and fluroxypyr and low to high levels of resistance to glyphosate. This is the first confirmation of kochia accessions with cross-resistance to dicamba and fluroxypyr in Kansas. Growers should use diverse kochia control programs, including the proper use of dicamba and fluroxypyr stewardship, use of cover crops, occasional tillage, diversified crop rotations, and alternative effective herbicides to prevent further evolution and spread of Aux-HR kochia on their fields.

Across the southeastern United States, pyridine carboxylic acid herbicides are widely used for broadleaf weed control in permanent grass pastures. This family of herbicides has proved very successful for controlling most broadleaf weeds commonly present in southeastern pastures and hayfields. In the southern United States, producers have expressed concern when overseeding legume species into warm-season perennial sods following application of commonly used pyridine carboxylic acid herbicides, as legumes are generally highly sensitive to this herbicide family. Field experiments were established to evaluate two herbicide treatment programs (residual vs nonresidual) on crimson clover overseeded into bermudagrass sod. The residual herbicide program included aminopyralid plus 2,4-D (0.09 + 0.7 kg ae ha–1), and the nonresidual program included triclopyr plus fluroxypyr (0.63 + 0.21 kg ae ha–1) plus 2,4-D (1.12 kg ae ha–1). Herbicide programs were applied at two key timings: in spring (May) and early summer (June). Spring applications were also evaluated when used in single vs repeated annual application. Our results did not indicate soil residual herbicide issues for crimson clover planted in the fall following spring or early-summer application of aminopyralid + 2,4-D at either location. Additionally, there were no cumulative negative impacts on crimson clover following 2 yr of spring herbicide application. Crimson clover cover, however, strongly decreased as grass and weed cover increased––an event that may be related to greater interspecific competition at higher levels of grass and weed cover. Soil fertility, weather, and competition from resident annual grasses and weeds strongly influenced productivity, suggesting that changes in pasture dynamics had a greater influence on clover productivity than did herbicide treatment or timing of application.

A 3-yr study investigated highbush blackberry control in bahiagrass turf using selective herbicides. Triclopyr applied alone at ≤ 0.56 kg/ha and in combination with other herbicides provided best (75 to 95%) control for up to 52 wk after treatment with minimal damage to bahiagrass turf. Triclopyr formulations (3A vs 4EC) provided similar highbush blackberry control and bahiagrass tolerance. The addition of either 2,4-D, dicamba, hexazinone, or sulfometuron to triclopyr provided slightly better blackberry control, but increased bahiagrass turf damage. Fluroxypyr applied at 0.14 to 0.28 kg/ha provided 60 to 80% control of highbush blackberry 12 WAT. Glyphosate and glufosinate treatments provided unacceptable highbush blackberry control and/or unacceptable bahiagrass turf injury. The addition of oxadiazon for residual control of subsequent highbush blackberry emergence was ineffective.

A false cleavers population that survived treatment with triasulfuron/bromoxynil in 1996 was identified in central Alberta, Canada, in a field that had been treated with acetolactate synthase (ALS) inhibitors in 3 of the previous 6 yr. In greenhouse studies, this biotype was highly resistant to the ALS inhibitors triasulfuron, thifensulfuron/tribenuron, and sulfometuron and moderately resistant to imazethapyr; GR50, values were > 16, > 5, > 1.0, and 9.9, respectively. In addition, cross-resistance was identified to the auxin-type herbicide quinclorac (GR50 value > 6.7) but not to fluroxypyr (GR50 value 1) or MCPA/mecoprop/dicamba. Quinclorac had not been used previously in this field. Analysis of ALS extracted from the resistant biotype and a susceptible biotype from a nearby location indicated that resistance to ALS inhibitors was due to an altered target site with reduced sensitivity to a broad range of ALS inhibitors. The ALS I50 values for triasulfuron, metsulfuron, chlorsulfuron, thifensulfuron, and imazethapyr were 36, 34, 92, 96, and 14 times higher, respectively, for the resistant compared to the susceptible biotype. The mechanism of resistance to quinclorac is unknown. This is the first report of high-level herbicide resistance in this weed species.

In field studies effective dogfennel control was obtained with glyphosate, dicamba + 2,4-D, triclopyr + 2,4-D, and fluroxypyr at rates of 1.68, 0.44 + 1.25, 0.56 + 1.12, and 0.28 kg ai/ha, respectively, applied after dogfennel was 75 cm tall. Mowing alone reduced dogfennel regrowth by 81% and when combined with dicamba + 2,4-D or triclopyr + 2,4-D regrowth was reduced over 94%. Triclopyr, dichlorprop, and sulfometuron also controlled dogfennel greater than 90% but metsulfuron did not.

Greenhouse and field experiments were conducted to evaluate herbicidal efficacy on tropical soda apple and bahiagrass. Acifluorfen, clopyralid, dicamba, fluroxypyr, picloram, and triclopyr were the most effective postemergence herbicides, providing > 90% control of tropical soda apple plants with no injury to bahiagrass 145 days after treatment (DAT). Glyphosate and imazapyr resulted in effective (> 90%) control of both seedling and mature tropical soda apple plants. However, these herbicides caused severe (> 90%) damage to bahiagrass. Control of tropical soda apple with 2,4-D, AC-263,222, diuron, fomesafen, lactofen, MSMA, sulfometuron, and triasulfuron was unacceptable (> 90%).

Fringed sagebrush is a native, drought-resistant, increaser species in Saskatchewan pastures and rangelands. Conventional control by cultivating and reseeding is neither highly effective nor sustainable. Two field experiments were conducted in 1988 and 1989 through 1991 to develop a management plan for fringed sagebrush. Comparison of fringed sagebrush control using various applications of clopyralid, dicamba, dichlorprop, fluroxypyr, picloram, triclopyr and 2,4-D, showed control was sufficient using the low-cost herbicide 2,4-D isooctyl ester at 1.5 kg ai/ha. Total yield of crested wheatgrass plus smooth brome was compared and the plots subjected to two applications of 2,4-D yielded the greatest accumulation of grass over the length of the experiments. The economic threshold of fringed sagebrush is the density at which yield is reduced by approximately 290 kg/ha; above this density it is economically viable to use 2,4-D at 1.5 kg/ha to control fringed sagebrush. Grazing practices can aid greatly in management of fringed sagebrush by allowing the forage to out-compete fringed sagebrush.

Two putative glyphosate-resistant (GR) Russian-thistle accessions were collected from fallow fields (wheat-fallow rotation): one from Choteau County, MT (MT-R), and a second from Columbia County, WA (WA-R) in summer/fall of 2015. Greenhouse and outdoor/field whole-plant dose-response studies were conducted to confirm and characterize the levels of glyphosate resistance in these GR accessions relative to known glyphosate-susceptible accessions (MT-S and WA-S from MT and WA, respectively). Based on GR50 values of the progeny plants, the MT-R accession exhibited 4.5-fold and 5.9-fold resistance to glyphosate relative to the MT-S accession under greenhouse and outdoor conditions, respectively. The WA-R accession showed 3.0- to 5.0-fold resistance relative to the WA-S accession in greenhouse experiments, and 1.9- to 7.5-fold resistance in multi-site field experiments. In a separate greenhouse study on alternative POST herbicides to control GR Russian-thistle, bicyclopyrone plus bromoxynil, bromoxynil plus fluroxypyr, bromoxynil plus pyrasulfotole, bromoxynil plus MCPA, paraquat alone, paraquat plus metribuzin, saflufenacil alone, saflufenacil plus 2,4-D, and 2,4-D plus bromoxynil plus fluroxypyr provided effective control (≥95%) and shoot dry weight reduction (up to 98%) of GR accessions. This research confirms the first global case of field-evolved GR Russian-thistle. Best management practices (BMPs); including alternative, effective herbicide programs (based on multiple mechanisms of action highlighted in this study) need immediate implementation to prevent further spread of GR or evolution of multiple HR Russian-thistle populations in this region.

A major hindrance to establishment of successful complementary forage systems that include warm-season perennial grasses and clovers is tolerance of the latter to herbicides available for weed control. Field experiments were conducted in 2013 at two locations in northeast Louisiana to evaluate simulated residual rate effects of fluroxypyr plus triclopyr and 2,4-D plus picloram applied at 0, 0.25, 0.38, and 0.5× use rates immediately after fall planting of ball, white, crimson, and red clover. For all clovers, when averaged across herbicide rates, plant population 161/171 d after planting (DAP), ground cover, and height 184/196 DAP were equivalent for fluroxypyr plus triclopyr and the nontreated control and greater than 2,4-D plus picloram. Averaged across clovers, plant height after all rates of fluroxypyr plus triclopyr was equivalent to the nontreated control (14.2 to 14.3 vs. 15.3 cm) and greater than 2,4-D plus picloram. Compared with the nontreated control, 2,4-D plus picloram at 25, 38, and 50% of the normal use rates reduced height 58, 76, and 85%, respectively. When averaged across clover species, yield for fluroxypyr plus triclopyr at all rates was equivalent to the nontreated control (2,624 to 2,840 vs. 2,812 kg ha−1). Compared with the nontreated control, 2,4-D plus picloram at the 0.25, 0.38, and 0.50× use rates reduced yield 65, 89, and 99%, respectively.

Field experiments were conducted during 3 yr in Thessaloniki, northern Greece, to determine the efficacy of various herbicides applied alone or in mixtures POST on hoary cress grown in winter wheat. Also, the efficacy of these herbicides on hoary cress generated from seed or root fragments was investigated in pot experiments. All herbicides except for ioxynil plus bromoxynil provided 90 to 100% control of hoary cress generated from seed and root fragments grown in pots. Ioxynil plus bromoxynil gave 84% control of hoary cress generated from seed, but only 66% control of plants generated from root fragments. In the field, mecoprop plus dicamba, imazamethabenz plus mecoprop plus dicamba, and triclopyr applied at the four- to eight-leaf stage provided, respectively, 87, 76, and 83% control of hoary cress (averaged over year and assessment time). Thifensulfuron plus tribenuron provided only 29% control. Chlorsulfuron plus dicamba, clopyralid plus MCPA, 2,4-D plus metosulam, and fluroxypyr provided intermediate hoary cress control. Furthermore, the least hoary cress emergence 52 wk after treatment appeared in plots treated with triclopyr. In addition, wheat grown in plots treated with mecoprop plus dicamba yielded more than wheat treated with the other herbicide treatments, and 55% more than wheat grown in nontreated plots. The results of this study indicate that very good control of hoary cress and high wheat yield can be obtained by the application of mecoprop plus dicamba at the four- to eight-leaf weed growth stage.

Volunteer potato is a major weed pest of sweet corn in regions where winter soil temperatures fail to kill tubers left in the ground after harvest. Studies were conducted in 2004 to 2005 to determine the effect of combining atrazine with mesotrione applied POST on volunteer potato control and new tuber production in sweet corn. Mesotrione at 0.035, 0.07, and 0.1 kg/ha and atrazine at 0.3, 0.6, and 1.1 kg/ha were applied alone and in all possible combinations when volunteer potato ranged from 5 to 12 cm tall. Mesotrione applied alone at all rates, atrazine at 1.1 kg/ha, or mesotrione plus atrazine combinations reduced the number of new tubers produced to ≤ 1.1 per plant compared with 11 tubers per plant in nontreated checks. Potatoes treated with atrazine alone at 0.3 or 0.6 kg/ha produced 3.3 or 1.9 tubers per plant, respectively, which could lead to volunteer potato problems in the succeeding crop. Sweet corn yield was not affected by herbicide treatment in 2004 but was reduced in 2005 when atrazine was used alone at 0.3 or 0.6 kg/ha because of poor control of volunteer potato. Additional studies were conducted from 2004 to 2006 to determine volunteer potato control in sweet corn in reduced and conventional tillage and treated with fluroxypyr, mesotrione, or no herbicide. Volunteer potato control was improved and the number and weight of tubers was reduced 79 and 91%, respectively, in conventionally tilled plots treated with fluroxypyr compared with reduced-tillage plots. Control of volunteer potato with mesotrione was greater than 98% and reduced tuber number and weight greater than or equal to all other treatments regardless of tillage level.