Glyphosate is the leading herbicide used in glyphosate-resistant (GR) crops and no-till production systems. Evolved resistance to glyphosate in kochia was first reported in Kansas in 2007. Shortly thereafter, GR kochia became prevalent in western Kansas. An online survey of crop consultants was conducted in fall 2012 to gain their perspectives on evolving glyphosate resistance in kochia in western Kansas, to gather information on how grower weed management practices have changed from before to after occurrence of GR kochia, and to assess the effectiveness of management practices used during 2011 to 2012. Results of the survey indicated increasing infestation of kochia from prior to 2007 (present in 47% of fields) through 2012 (present in 70% of fields). It was estimated that greater than one-third of the cropland in western Kansas was thought to be infested with GR kochia by 2012. Growers increased glyphosate use rates from an average of 0.8 to 1.22 kg ae ha−1 and application frequencies from 2.0 to 2.9 from the period before 2007 to 2012. The spread of GR kochia has resulted in changing weed management practices. During the survey period, growers reduced the exclusive use of glyphosate from 49 to 15% for GR crop fields and diversified weed management practices. Though other herbicides in addition to or in place of glyphosate were often applied prior to kochia emergence and were effective in more than half the fields, at least one-fourth of respondents reported inconsistent results with alternative kochia control practices other than tillage. These results are educational and helpful in developing both proactive and reactive tactics to manage GR kochia.

Purple nutsedge is a problematic weed in plasticulture vegetable production due to its ability to penetrate the plastic mulch. Experiments were conducted in the fall 2013 and spring 2014 at the Gulf Coast Research and Education Center in Balm, FL, to evaluate a range of PRE herbicides for ‘Charger' and ‘Florida 47’ tomato cultivars tolerance and herbicide efficacy on nutsedge. Fall-applied herbicides did not stunt nor damage either tomato cultivar. Tank mixes applied in the spring that contained EPTC as well as the fomesafen + S-metolachlor + napropamide tended to stunt Charger. The EPTC + fomesafen, the EPTC + fomesafen + S-metolachlor, and the fomesafen + S-metolachlor + napropamide stunted Florida 47. Crop damage in the spring was consistently higher where tank mixes were applied that contained EPTC. In the fall of 2013, S-metolachlor and fomesafen + S-metolachlor reduced nutsedge density by 84 to 90% compared to the nontreated control; in the fall of 2014, napropamide + S-metolachlor reduced nutsedge density by 88% compared to the nontreated control. In the spring of 2013 halosulfuron and a tank mix of EPTC + S-metolachlor reduced nutsedge density by 25% compared to the nontreated control. None of the herbicide treatments had a consistent effect on yield, although Florida 47 yields tended to be lower where tank mixes containing EPTC were applied.

Smooth barley has emerged as a problematic weed in cereal crops of South Australia. After the recent reports of herbicide resistance and increase in seed dormancy in smooth barley, it was considered important to determine the herbicide resistance status and seedbank behavior of field populations of this weed species. A field survey was undertaken in the Upper North and Eyre Peninsula regions of South Australia in October 2012. Of the 90 smooth barley populations screened for resistance to quizalofop, 15% exhibited some level of resistance and 85% were susceptible. Resistance to acetolactate synthase (ALS)-inhibiting herbicides was low, with only 3 and 12% of populations classified as developing resistance to imazamox + imazapyr and sulfosulfuron, respectively. No multiple resistance patterns were observed; however, two ALS-inhibiting herbicide-resistant populations had sulfonylurea-to-imidazolinone cross-resistance. At the start of the growing season, the majority of smooth barley populations emerged rapidly (median 50% time to emergence [T50] = 8 d). In contrast, some populations of smooth barley displayed an extremely slow emergence pattern, with T50 of > 20 d. No direct linkage between seed dormancy and herbicide resistance was observed. However, two acetyl coenzyme A carboxylase-inhibiting herbicide-resistant populations were highly dormant and exhibited delayed emergence. The majority of smooth barley populations showed low-level or no seedbank persistence, but a few populations persisted for 1 yr. However, some weed populations had up to 20% seedbank persistence from 1 yr to the next. Overall there was a strong negative relationship between smooth barley seedling emergence and the level of seed persistence (R2 = 0.84, P < 0.05). This association indicated that greater seed dormancy could be responsible for extended persistence of the seedbank of this weed species. The study provides valuable insights into the general pattern of herbicide resistance and the behavior of the seedbank of smooth barley populations on South Australian farms.

Intensive cultivation in organic peanut is partially effective, but in-row weed control remains problematic. In an attempt to improve in-row weed control, irrigated trials were conducted from 2011 to 2013 near Ty Ty, GA to determine the feasibility of early-season cultivation perpendicular to row direction using a tine weeder when integrated with other weed-control practices. Combinations of perpendicular cultivation (cultivation perpendicular to row direction), parallel cultivation (cultivation in the same direction of the rows), and banded applications of herbicides derived from natural sources were compared. Perpendicular cultivation improved overall weed control and peanut yield (two years of three), but this benefit was independent of weed control from any form of parallel cultivation. Additionally, tractor tire tracks from perpendicular cultivation across the rows repeatedly crushed peanut seedlings. Parallel cultivation with the tine weeder was generally more effective than parallel cultivation with sweeps, particularly for southern crabgrass and Texas millet. Herbicides derived from natural products were inconsistent in controlling dicot weeds, ineffective in controlling annual grasses, and did not protect peanut yield from weed interference.

Crop producers might be able to better manage field bindweed, an aggressive perennial weed, by utilizing tillage to bring roots to the surface where they can be consumed by ruminant livestock. The objectives of this study were to provide first perspectives on forage nutritive value of field bindweed roots and to determine root chemistry responses to Aceria malherbae, an eriophyid mite that has been released for field bindweed biocontrol in the western United States and Canada. To accomplish these objectives, root systems were sampled from A. malherbae-infested and noninfested plants occurring in an agricultural field in eastern New Mexico. Sampling took place during autumn and spring of each year for 3 consecutive yr. Results indicated that A. malherbae reduced taproot diameter and increased root concentrations of Ca, P, and Mg. However, A. malherbae did not affect root concentrations of acid detergent fiber, nonfiber carbohydrates, neutral detergent fiber (NDF), crude protein (CP), and total digestible nutrients (TDN). Overall means for NDF (33.8%), CP (11.6%), and TDN (72.1%) were similar to those reported for forages commonly grown in the region, suggesting that field bindweed roots might positively contribute to nutritional programs of ruminant livestock. These results justify subsequent studies on livestock responses to field bindweed roots and field bindweed responses to targeted root grazing.

Interest in the cultivation of bioenergy feedstocks has increased the need for information in this rapidly developing sector of agriculture. Many fast-growing, large-statured perennial grasses have been selected because of their high biomass production potential, competitive nature, and ability to tolerate marginal growing conditions. However, weed pressure in the establishment phase can be detrimental to crop yield. Weed control is one of the most costly and resource-intensive aspects of bioenergy crop establishment. Unfortunately, little information exists on practical weed management techniques for the majority of these new crops. The tolerance of switchgrass, big bluestem, reed canarygrass, sorghum, giant reed, eulaliagrass, and giant miscanthus (sterile and seeded) to 22 PRE and 22 POST herbicides were evaluated. Plants were grown in the greenhouse and evaluated for injury, height, and aboveground biomass after 5 or 7 wk for PRE and POST applications, respectively. PRE and POST application of 2,4-D, bentazon, bromoxynil, carfentrazone, dicamba, halosulfuron, and topramezone did not significantly injure any species. Giant miscanthus was more tolerant to PRE herbicides when established from rhizomes compared with seed establishment. Supporting previous research, all eulaliagrass and switchgrass cultivars demonstrated comparable tolerance to PRE application of all 22 herbicides. With the information gained in this study a suite of herbicides may have potential for use in bioenergy crops; however, they should be tested on larger-scale field trials over multiple growing seasons to validate initial findings.

Annual bluegrass is one of the most diverse plant species in the world and is the most problematic winter annual weed in commercial turfgrass. Continuous application of the same herbicide mechanism of action for annual bluegrass control on golf courses has increased herbicide-resistant populations. The purpose of this research was to simulate six herbicide-use strategies to evaluate the risk of annual bluegrass resistance evolution to glyphosate. In a worst-case scenario of yearly glyphosate applications at dormancy, resistance evolved within 10 yr and was predicted to evolve in > 90% of populations by yr 20. When glyphosate was rotated on alternate years with a unique mechanism of action, resistance was delayed for 12 to 15 yr. Season-long control of annual bluegrass often requires multiple herbicide applications. Therefore, additional strategies were simulated in which glyphosate was applied at dormancy with combinations of PRE and/or POST herbicides at various timings. Resistance was most effectively delayed with a PRE application in late summer, a POST application in fall, and alternating glyphosate with a different POST option at dormancy. This delayed resistance by 25 yr and a 35% risk was predicted after 50 yr. Strategies utilizing three annual herbicide applications with unique mechanisms of action were more effective for controlling population growth compared to other strategies. Resistance was predicted to evolve within 35 yr for each of the strategies simulated. However, these results indicate annual bluegrass herbicide resistance can be managed by using an integrated herbicide program, rotating unique mechanisms of action as frequently as possible.

Alligatorweed is a perennial, invasive weed in southern United States rice production, but knowledge on effective management of this weed is limited, especially in conventional (non-imidazolinone-resistant) rice fields. Field studies were conducted in multiple environments in southeastern Texas to evaluate different herbicide options involving penoxsulam, propanil, triclopyr, halosulfuron, bispyribac-sodium, bensulfuron, and quinclorac for alligatorweed control in conventional drill-seeded rice when applied at early POST (EPOST), late POST (LPOST), or both. Among the herbicide options evaluated, penoxsulam alone (up to 83%), penoxsulam plus triclopyr (up to 87%), or bispyribac-sodium plus triclopyr (92%) provided superior alligatorweed control. Plots treated with penoxsulam plus triclopyr EPOST produced the highest yields (9,550 kg ha−1), which were comparable to plots receiving penoxsulam plus triclopyr LPOST (9,320 kg ha−1), penoxsulam alone EPOST (9,280 kg ha−1), and penoxsulam plus halosulfuron LPOST (9,180 kg ha−1). Considering both weed control and rice grain yields, penoxsulam plus triclopyr applied EPOST was found to be the best option among the treatments tested. The treatments bensulfuron alone, bensulfuron plus propanil, penoxsulam plus propanil, triclopyr plus propanil, and bispyribac-sodium plus propanil provided poor (≤ 65%) alligatorweed control. Results also suggest the likelihood for antagonistic interactions when tank-mix combinations tested in this study included propanil.

Metribuzin has a 60-d preharvest interval (PHI) in potato, which limits utility of metribuzin POST in potato. In certain years, the potato may not fully cover the area between the potato rows. This allows for late-season weed emergence and subsequent yield reduction through direct competition or harvest interference. Field experiments were conducted in 2011 at Castle Hayne, NC; Freeville, NY; Hasting, FL; and Plymouth, NC to determine the effect of a 30-d PHI on potato crop tolerance. The cultivars planted were ‘Superior' and ‘Yukon Gold' in Castle Hayne and Plymouth, ‘Castille' and Yukon Gold in Freeville, and ‘Atlantic' in Hastings. Treatments included metribuzin at 278 g ai ha−1 PRE, 30, and 60 d before harvest (DBH), and metribuzin at 556 g ha−1 at 30 and 60 DBH. Split application treatments included metribuzin at 556 g ha−1 at PRE followed by metribuzin at 556 g ha−1 30 or 60 DBH and metribuzin at 842 g ha−1 PRE followed by metribuzin at 278 g ha−1 at 30 or 60 DBH. Potato injury was ≤ 8% at all locations, and injury was transient. There were no differences observed between metribuzin rate or application date for individual potato grades or total yield. Reducing the PHI in potato to 30 d would have no effect on yield and would provide a longer period for controlling broadleaf weeds.

Hairy fleabane is an important weed in orchards and vineyards of California. Populations of glyphosate-resistant (GR) and glyphosate-paraquat-resistant (GPR) hairy fleabane have been documented in California but very little information is available on the efficacy of other POST herbicides on these populations. Greenhouse and field experiments were conducted to evaluate the efficacy of several POST herbicides registered in almond orchards on GPR, GR, and glyphosate/paraquat-susceptible (GPS) hairy fleabane plants. Plants were treated at the 8- to 12-leaf stage in greenhouse experiments, and at the bolting to flowering stage in field experiments. A sequential application of glyphosate (1,100 g ae ha−1) followed by paraquat (500 g ai ha−1) 14 d later did not control the GPR plants in any of the studies, but was effective in controlling the GR and GPS plants. Glufosinate at 1,050 g ai ha−1 or saflufenacil at 48.8 g ai ha−1 resulted in 90% or greater control of all populations in all studies, whereas glyphosate (1,100 g ae ha−1) + 2,4-D (1,090 g ae ha−1) resulted in inconsistent control (58 to 100%). The GPR population was not resistant to other common POST herbicide modes of action used in California tree nut orchards, and glufosinate and saflufenacil can provide growers effective management options for hairy fleabane in these crops.

Buckhorn plantain is a perennial weed in turfgrass and efficacy of POST herbicides is often inconsistent for control in spring. Indaziflam is a cellulose biosynthesis inhibitor used for PRE control of annual weeds in turf and applications have shown to be injurious to established buckhorn plantain. The objectives of this research were to evaluate (1) effects of indaziflam application rate and placement on buckhorn plantain injury; (2) effects of tank-mixing indaziflam with POST herbicides for buckhorn plantain control; and (3) physiological effects of indaziflam on absorption and translocation of 14C-2,4-D in buckhorn plantain. In greenhouse experiments, indaziflam reduced buckhorn plantain shoot mass 61 to 75% from the nontreated at 4 wk after treatment (WAT) and hierarchical rank of application placements were: foliar + soil ≥ soil ≥ foliar. Differences in biomass reduction from application rates (27.5 and 55 g ai ha−1) were not detected. In field experiments, indaziflam at 55 g ha−1 controlled buckhorn plantain 34% at 9 WAT but enhanced the speed of control from all herbicides tested in tank mixtures. Exclusive applications of 2,4-D or 2,4-D + dicamba + MCPP provided poor control (< 70%) of buckhorn plantain at 9 WAT, but tank mixtures with indaziflam provided 81 and 98% control, respectively. Fluroxypyr and simazine alone controlled buckhorn plantain < 38% but tank mixtures with indaziflam enhanced control more than twice as much from exclusive applications. Tank-mixing indaziflam with metsulfuron did not improve control from metsulfuron alone after 9 wk. Bermudagrass injury was not detected from any treatment. In laboratory experiments, 14C-2,4-D absorption and translocation in buckhorn plantain was similar with or without indaziflam tank mixtures at 72 and 168 h after treatment. Overall, indaziflam may improve buckhorn plantain control from POST herbicides by providing additive phytotoxicity in tank mixtures in spring.

Tomato grafting has gained increased attention in the United States as an alternative to methyl bromide to control soilborne pests and diseases. Although several herbicides are registered in tomato production, a lack of information exists on the effect of herbicides on grafted tomato. Greenhouse and field experiments were conducted to determine herbicide tolerance of grafted tomato. In greenhouse experiments, halosulfuron (27, 54, and 108 g ai ha−1), metribuzin (280, 560, and 1,120 g ai ha−1), and S-metolachlor (1,070, 2,140, and 3,200 g ai ha−1) were applied posttransplant to nongrafted ‘Amelia' and Amelia scion grafted onto ‘Maxifort' or ‘RST-04-106-T' tomato rootstocks. Although herbicide injury was observed, no differences were observed in grafted and nongrafted tomato response including visible injury assessments, plant height, and fresh weight. Tomato injury at 3 wk after herbicide application increased from 3 to 12, 1 to 87, and 0 to 37% as rate of halosulfuron, metribuzin, and S-metolachlor increased, respectively. In field experiments under plasticulture, herbicides applied pretransplant included fomesafen (280 and 420 g ai ha−1), halosulfuron (39 and 54 g ha−1), metribuzin (280 and 560 g ha−1), napropamide (1,120 and 2,240 g ha−1), S-metolachlor (800 and 1,070 g ha−1), and trifluralin (560 and 840 g ai ha−1). Amelia was used as the scion and the nongrafted control. ‘Anchor-T', ‘Beaufort', or Maxifort tomato were used as rootstocks for grafted plants. Fomesafen, halosulfuron, napropamide, and trifluralin initially caused greater injury to grafted tomato than to nongrafted tomato regardless of rootstock (Anchor-T, Beaufort, or Maxifort). However, by 4 wk after treatment, all grafted and nongrafted plants had recovered from herbicide injury. A transplant type-by-herbicide interaction was not observed for yield, but grafted A-Maxifort tomato produced greater total and marketable yield than nongrafted Amelia tomato. Grafted tomato exhibited similar tolerance as nongrafted tomato for all herbicides applied post- and pretransplant.

A field experiment was conducted in 2009–2010 at Pennsylvania and Maryland locations, and repeated it in 2010–2011 to test the effectiveness of POST-applied herbicides at fall and spring timings on seeded hairy vetch in winter wheat. A total of 16 herbicide treatment combinations was tested that included synthetic auxins, acetolactate synthase (ALS) inhibitors, and a protoporphyrinogen oxidase inhibitor. Spring applications tended to be more effective than fall applications. Among synthetic auxins, clopyralid (105 g ae ha−1) and treatments containing dicamba (140 g ae ha−1) were effective at both timings, resulting in greater than 90% hairy vetch control at wheat harvest. Pyroxsulam and prosulfuron applied at 18 g ai ha−1 provided the most effective hairy vetch control (> 90%) at both application timings among ALS inhibitors. Spring applications of several herbicides provided moderate (> 80%) to high (> 90%) levels of hairy vetch control, including: 2,4-D amine (140 g ae ha−1), mesosulfuron-methyl (15 g ai ha−1), tribenuron-methyl (13 g ai ha−1), and thifensulfuron/tribenuron-methyl treatments (16 and 32 g ai ha−1). Winter wheat injury was evaluated, but symptoms were negligible for most treatments. Winter wheat yields declined with increasing hairy vetch biomass. Fall herbicides may be prioritized to reduce hairy vetch competition during the fall and early spring growing season. Our research has established that several synthetic auxin and ALS-inhibiting herbicides, applied POST in fall or spring, can be safely used in winter wheat to control hairy vetch in an integrated weed management program.

Energycane has been proposed as a potential, perennial bioenergy crop for lignocellulosic-derived fuel production in the United States. Herbicides currently used in sugarcane and other crops can potentially be used in energycane if there is acceptable tolerance. Also, to limit future invasion of energycane escapes, herbicides used for perennial grass control could potentially be used for management of escapes. In container studies conducted outside, aboveground and belowground biomass of energycane was measured to evaluate energycane tolerance to 9 PRE and 19 POST herbicides used in sugarcane and other crops. PRE application of atrazine, diuron, mesotrione, metribuzin, pendimethalin, and S-metolachlor at rates labeled for sugarcane did not significantly injure (< 3%) or reduce energycane biomass compared with the nontreated plants 28 and 56 d after treatment (DAT). Injury from clomazone (54%), flumioxazin (7%), and hexazinone (29%) was observed 28 DAT. Injury from flumioxazin was transient and was not observed at 56 DAT. At 56 DAT, energycane injury increased to 71 and 98%, respectively, for clomazone and hexazinone. Hexazinone and clomazone applied PRE significantly reduced biomass compared with the nontreated plants. At 28 DAT, POST application of 2,4-D amine, ametryn, asulam, atrazine, carfentrazone, dicamba, halosulfuron, mesotrione, metribuzin, and trifloxysulfuron at labeled rates for sugarcane did not injure or significantly reduce energycane biomass compared with the nontreated plants. Injury was observed when clethodim (99%), clomazone (51%), diuron (51%), flumioxazin (21%), glufosinate (84%), glyphosate (100%), hexazinone (100%), paraquat (66%), and sethoxydim (100%) were applied POST, and each of these treatments reduced energycane biomass compared with the nontreated plants. These results show that several PRE and POST herbicides used for weed management in sugarcane may potentially be used in energycane for weed control. Also, based on our results, clethodim, glyphosate, and sethoxydim would be effective for management of energycane escapes.

Glyphosate-resistant (GR) weeds are most challenging for growers to control in cotton in the midsouth region of the United States. As a result, growers in these states are transitioning from a glyphosate-based system to a glufosinate-based system. A field study was conducted in 2010 and 2011 in Georgia, North Carolina, and Tennessee to determine the effect of repeated glufosinate applications to WideStrike cotton applied at various application timings. One to three glufosinate applications at 594 g ai ha−1 were applied to cotton at the two-leaf, seven-leaf, bloom, or 2 wk after bloom stages. Visual estimates of crop injury were evaluated after each application, in addition to crop height, development, and yield. Crop injury after each glufosinate application typically ranged from 3 to 11%, with higher injury observed where multiple glufosinate applications were made. Crop height differences were noted after the bloom and 2 wk after bloom applications. Treatments that had one, two, or three glufosinate applications had reduced crop height when compared with the weed-free control. Node above cracked boll ratings also indicated that glufosinate treatments may have stressed the cotton. Ultimately, yield was reduced where three glufosinate treatments were applied to WideStrike cotton. In addition, one glufosinate application at the bloom stage or two glufosinate applications at the bloom and 2 wk after bloom stages reduced yield when compared with the weed-free control. Although it is a legal application, growers should use caution when applying glufosinate to WideStrike cotton because the manufacturer of glufosinate and the manufacturer of WideStrike cotton do not recommend this application. However, where GR Palmer amaranth is present, these applications may be necessary.

The chlorophyll-lacking holoparasite Egyptian broomrape is a major threat for many field crops in Israel. In carrot, a high-value crop that is grown year round in Israel, heavy infestation with broomrape can cause severe damage and even total yield loss. The objective of this study was to determine, under field conditions, selective herbicides that would effectively control Egyptian broomrape without damaging the carrots. Ten field experiments were performed between the years 2010 and 2013. The acetolactate synthase inhibitor herbicides imazapic and imazamox caused deformation of carrot taproots at low doses, and significantly reduced yield amount and quality. Glyphosate was found to be the safest herbicide for broomrape management in carrot. Carrot selectivity and broomrape control efficacy were examined with three sequential applications of nine glyphosate doses. A nonlinear log-logistic curve described the response of noninfested carrot taproot biomass to glyphosate. No significant reduction in taproot biomass was observed when glyphosate was applied at up to 149 g ae ha−1. When glyphosate was applied in an Egyptian broomrape-infested carrot field, a hormetic effect was observed, perhaps due to Egyptian broomrape control. A two-parameter exponential decay curve described the broomrape response to glyphosate. Three sequential foliar applications of glyphosate, at 108 g ha−1, completely controlled Egyptian broomrape. Our results demonstrate that glyphosate applied sequentially at a low dose on Egyptian broomrape-infested carrot can control this parasitic weed.

Hard-seeded, broadleaf, winter annual weeds in strawberry plasticulture production in Florida emerge in the crop holes in the plastic mulch and reduce berry yield and quality. Clopyralid is registered for POST control of broadleaf weeds, but herbicide damage has been observed in commercial fields, and preliminary observations suggest that effects vary with time of application. To address this issue, an experiment was conducted in 2012 to 2013 and 2013 to 2014 to evaluate clopyralid rate (0, 140, 280, and 560 g ae ha−1) and application time on strawberry vegetative and reproductive growth. Clopyralid applications at 280 and 560 g ae ha−1 on January 2 and 16, 2013 (yr 1) reduced leaf number per plant by 33 to 44% and increased the number of deformed leaves per plant compared with the nontreated control. This pattern was not observed in yr 2. In yr 1 and 2, two times the label rate of clopyralid (560 g ae ha−1) tended to reduce the total number of floral buds compared with the nontreated control by 12 to 17%. None of the herbicide rates or application times reduced the number of flowers per plant, marketable berries per plant, yield over time, or total yield. We conclude that clopyralid applications at the rates and application times tested in this study may cause leaf damage and may reduce leaf number in some situations but does not affect yield.

Rhizoma et Radix Notopterygii is often used as a traditional medicine in China. In our recent work, we found that the ethanol crude extract of Rhizoma et Radix Notopterygii could reduce phytotoxicity of acetochlor on rice. The crude extract of Rhizoma et Radix Notopterygii was isolated and purified by activity-guided fractionation. Two coumarins, isopimpinellin and 5-methoxypsoralen (5-MOP) were identified, and their bioactivity was tested in a growth chamber. The results showed that the two coumarins increased herbicide tolerance of rice shoots, and 5-MOP demonstrated better protection than isopimpinellin. The treatment of 5-MOP at 50 g ai ha−1 recovered the shoot height of rice from 42.6% (treated with acetochlor only) to 81.6% of the control treated without acetochlor, whereas the phytocidal activity of acetochlor on barnyardgrass was not impaired by 5-MOP. Further study suggested that 5-MOP increases herbicide tolerance of rice by enhancing the glutathione S-transferase level of activity in rice. Our findings suggest that isopimpinellin and 5-MOP have the potential to be applied as safeners for rice.

Few herbicides are available for use in lettuce and hand weeding is required for commercially acceptable weed control. More effective herbicides are needed. Here field evaluations of pendimethalin and S-metolachlor for weed control in transplanted lettuce are reported. Pendimethalin was evaluated PRE at rates between 0.6 and 6.7 kg ai ha−1, and POST at 1.1 and 2.2 kg ha−1. Both pendimethalin PRE and POST applications were safe to transplanted lettuce and provided similar weed control. Pendimethalin PRE at rates of 1.1 kg ha−1 and higher provided better weed control than the industry standard, pronamide at 1.3 kg ha−1. S-Metolachlor PRE was evaluated at rates between 0.6 and 5.6 kg ha−1. S-Metolachlor at rates up to 2.8 kg ha−1 caused little or no crop injury or yield reduction in transplanted lettuce, and S-metolachlor at rates of 1.4 kg ha−1 and higher improved weed control compared with pronamide at 1.3 kg ha−1. Pendimethalin and S-metolachlor are not labeled for transplanted lettuce, but we suggest that labeling be pursued at rates of 1.1 and 0.7 kg ha−1, respectively. Pendimethalin at 1.1 kg ha−1 applied PRE or POST improved weed control by 57 and 42%, respectively compared with pronamide. S-Metolachlor PRE at 0.7 kg ha−1 was less effective on weeds than pendimethalin, but maintained weed control level similar to pronamide. Pendimethalin and S-metolachlor have potential for use in transplanted lettuce production and provide alternatives to current transplanted lettuce herbicides.

Niger is a potential crop for the Northern Great Plains, but not until volunteer canola can be controlled. A study at Indian Head, SK, was conducted from 2007 to 2009 to determine the tolerance of niger to flucarbazone, a herbicide that controls volunteer canola. The tolerance was determined by applying three rates of flucarbazone (19, 28.5, and 38 g ai ha−1) at four application stages (two, four, six, and eight-leaf stage). Mean injury did not exceed 22% for any year by treatment combination. Injury was most prominent in 2007, and dissipated as the growing season progressed. Increasing the rate of flucarbazone increased crop injury depending on the year, application timing, and evaluation timing. Injury under 20% in 2007 and under 10% in 2008 and 2009 was observed at the start of flowering when flucarbazone was applied at the two, four, and six-leaf stage. Injury from applications at the two, four, and six-leaf stage decreased as the growing season progressed. When the labelled rate of flucarbazone for wheat (19 g ha−1) was applied at the two, four, or six leaf stage, injury was below 10%. Injury when flucarbazone was applied at the eight-leaf stage was highest during seed filling. Volunteer canola was controlled by flucarbazone. The application of flucarbazone relative to a weedy control increased yield by about 50% (138 to 213 kg ha−1) in 2008 and 2009. Flucarbazone rate did not affect niger yield except in 2007 where yield was about 100 kg ha−1 less with the two highest rates. Delaying flucarbazone application decreased niger yield, especially in the year (2007) with most niger injury. Flucarbazone application at the two- or four-leaf niger stage at a rate of 19 g ha−1 provided a good balance of weed control and crop tolerance.