Greenhouse trials were conducted to determine Hooker's evening primrose transplant tolerance to POST-applied herbicides. Herbicide treatments consisted of glyphosate at 1.68 kg ae ha−1, glufosinate at 0.84 kg ai ha−1, fenoxaprop at 0.10 kg ai ha−1, fluazifop at 0.45 kg ai ha−1 + a nonionic surfactant (NIS) at 0.25% v/v, sulfosulfuron at 0.06 kg ai ha−1 + NIS at 0.25% v/v, quinclorac at 0.42 kg ae ha−1 + methylated seed oil (MSO) at 0.5% v/v, mesotrione at 0.21 kg ai ha−1, and the combination of quinclorac + mecoprop + dicamba at 0.42 + 0.21 + 0.06 kg ae ha−1 + MSO at 0.5% v/v. Fluazifop (14%) and fenoxaprop (19%) treatments did not result in any significant phytotoxicity 7 d after treatment (DAT) compared with the nontreated check. Hooker's evening primrose exhibited 26 to 37% phytotoxicity in response to quinclorac, glyphosate, or sulfosulfuron 7 DAT. Phytotoxicity ≥ 50% was observed for mesotrione, glufosinate, and the combination of quinclorac + mecoprop + dicamba 7 DAT. Phytotoxicity increased for all treatments 28 DAT. Fluazifop (21%) was the only treatment that did not exhibit phytotoxicity symptoms different from the nontreated check 28 DAT. Hooker's evening primrose exhibited 31 to 40% phytotoxicity with applications of fenoxaprop, glyphosate, or glufosinate 28 DAT. Phytotoxicity was ≥ 58% with all other treatments 28 DAT. Fluazifop exhibited similar above-ground (12.4 g) and below-ground (16.4 g) biomass as the nontreated check (10.8 and 14.7 g, respectively) 28 DAT. All other treatments resulted in 1.6 to 5 g of above-ground biomass and 0.8 to 4.3 g of below-ground biomass 28 DAT. Fluazifop (24.3) and fenoxaprop (18.8) applications resulted in a plant growth index (PGI) that was not significantly different from the nontreated check (24.7) 28 DAT. A PGI ≤ 16.2 was observed for all other treatments 28 DAT.

Simulated drift rates of bromoxynil followed by an in-crop application of metribuzin were applied to processing tomato in eight field studies conducted from 2008 to 2010 in Ridgetown, Ontario, Canada, to determine if a synergistic interaction occurred due to the cumulative herbicide application. A transient synergistic response was observed 7 d after treatment (DAT) when bromoxynil drift rates of 8.5, 17, and 34 g ai ha−1 were followed 3 to 5 d later by metribuzin at 250 g ai ha−1. By 28 DAT, visible injury ratings were additive for 8.5, 17, and 34 g ha−1 bromoxynil followed by metribuzin treatments. However, when bromoxynil at 68 g ha−1 (20% of field rate) was followed by metribuzin, a synergistic interaction was evident and remained through harvest. Based on Colby's equation there was greater visible injury than expected at 7, 14, and 28 DAT when bromoxynil at 68 g ha−1 was followed by metribuzin. A corresponding synergistic reduction of plant dry weight and marketable tomato yield, compared with the nontreated control, was identified. Marketable yields were expected to be 65% of the control according to Colby's equation, but observed yield reductions were 49% when bromoxynil at 68 g ha−1 was followed by metribuzin. In general, tomato plants sprayed with metribuzin after bromoxynil drift had greater injury than treatments sprayed with bromoxynil alone.

Nonsynthetic herbicides offer a potentially useful addition to the suite of weed management tools available to organic growers, but limited information is available to guide the optimal use of these products. The objectives of this research were to (1) evaluate the efficacy of clove oil– and vinegar-based herbicides on weeds across multiple states, and (2) assess the potential role of temperature, relative humidity (RH), and cloud cover in explaining inter-state variations in results. From 2006 to 2008, a total of 20 field trials were conducted in seven states using an identical protocol. Seeds of brown mustard were sown and herbicides applied to both mustard and emerged weeds when mustard reached the three- to four-leaf stage. Treatments included clove oil at 2.5, 5, 7.5, and 10% v/v concentrations at 54 L ha−1, and vinegar at 5, 10, 15, and 20% v/v concentrations at 107 L ha−1. Results varied widely across trials. In general, concentrations of at least 7.5% for clove oil and 15% for vinegar were needed for adequate control of mustard. Both products were more effective at suppressing mustard than Amaranthus spp. or common lambsquarters. Poor control was observed for annual grasses. No significant effects of cloud cover on the efficacy of either product were detected. In contrast, RH was positively correlated with control of brown mustard by both clove oil and vinegar with improved control at higher RH. Temperature had no detectable effect on the efficacy of clove oil, but higher temperatures improved control of brown mustard by vinegar.

Aminocyclopyrachlor will control a variety of invasive weeds but may injure sensitive plant species if seeded into treated soil too soon after application. Aminocyclopyrachlor 50% dissipation time (DT50) ranged from 3 to > 112 d in four soils from the Northern Great Plains. The DT50 was dependent on several factors including soil type, moisture content, and temperature. Across four different soil textures, aminocyclopyrachlor dissipation generally increased as soil moisture content increased, but moisture had less of an impact in sandy soils. Aminocyclopyrachlor dissipation also increased as temperature increased in the four soils. The most rapid dissipation occurred in soils with higher clay content, which also had the highest organic matter content of the soils evaluated, and an average DT50 of less than 20 d. Seeding sensitive pasture, range, or crop species after aminocyclopyrachlor applications should be done with caution since the herbicide has potential for long persistence in the soil.

This study determined the potential of the tortoise beetle (Coleoptera: Chrysomelidae) to control Canada thistle (Asteraceae) in Iran. Genetic analysis of the tortoise beetle, based on mitochondrial DNA, confirmed the presence of the species in Iran. A field experiment using five insect densities (0 to 20 larvae plant−1) showed a positive correlation between the number of larvae transferred and impact. Feeding by 20 larvae reduced total biomass of Canada thistle by 78% and the number of capitula by 94%. More important, when grown in competition with wheat, four and eight egg batches (corresponding to approximately 12 and 24 larvae) per Canada thistle plant increased wheat ear weight by 46 and 82%, respectively. Host range studies with 22 crop and 21 weed species using no-choice and multiple-choice tests under laboratory and field conditions and parallel data from a field survey showed that joint feeding and oviposition were restricted to Canada thistle and a few other weed species. Limited feeding, without oviposition, was recorded on an additional seven weed species but also on safflower (10 to 15% reduction in biomass), and common sunflower (< 10%); the latter only under no-choice conditions. The growing period of either crop species, however, does not coincide with the feeding period of the tortoise beetle in the field. Findings indicate that the tortoise beetle is a promising biological control agent for Canada thistle in arable crops and grasslands in Iran. Other complementary methods will likely be needed to prevent substantial yield losses.

Japanese bindweed was found to be one of the most abundant and most difficult-to-control weed species during a 2-yr weed survey in more than 100 winter wheat fields in the North China Plain region. Multivariate data analysis showed that Japanese bindweed is most abundant at sites with comparative low nitrogen (N) fertilization intensities and low crop densities. To gain deeper insights into the biology of Japanese bindweed under various N fertilization intensities, winter wheat seeding rates, herbicide treatments, and their interactions, a 2-yr field experiment was performed. In nonfertilized plots, a herbicide efficacy (based on density reduction) of 22% for 2,4-D, and of 25% for tribenuron-methyl was found. The maximum herbicide efficacy in Nmin-fertilized plots (target N value based on expected crop yield minus soil mineral nitrogen content, ) was 32% for 2,4-D and 34% for tribenuron-methyl. In plots fertilized according to the farmer's practices, a maximum herbicide efficacy of 72% for 2,4-D and of 64% for tribenuron-methyl could be observed. Furthermore, medium and high seeding rates improved the herbicide efficacy by at least 39% for tribenuron-methyl and 44% for 2,4-D compared to the low seeding rate. Winter wheat yield was not significantly affected by seeding rate itself, whereas at low and medium seeding rates, Nmin fertilization was decreasing winter wheat yield significantly compared to the farmer's usual fertilization practice. At the highest seeding rate, Nmin fertilization resulted in equal yields compared to the farmer's practices of fertilization.

Field studies were conducted in 1996, 1997, and 1998 at Clinton, NC, to determine the influence of Palmer amaranth establishment and removal periods on the yield and quality of plasticulture-grown ‘Mountain Spring' fresh market tomato. Treatments consisted of 14 Palmer amaranth establishment and removal periods. Half of the treatments were weed removal treatments (REM), in which Palmer amaranth was sowed at the time tomato transplanting and allowed to remain in the field for 0 (weed-free all season), 2, 3, 4, 6, 8, or 10 wk after transplanting (WAT). The second set of the treatments, weed establishment treatments (EST), consisted of sowing Palmer amaranth 0 (weedy all season), 2, 3, 4, 6, 8, or 10 WAT and allowing it to grow in competition with tomato the remainder of the season. Tomato shoot dry weight was reduced 23, 7, and 11 g plant−1 for each week Palmer amaranth removal was delayed from 0 to 10 WAT in 1996, 1997, and 1998, respectively. Marketable tomato yield ranged from 87,000 to 41,000 kg ha−1 for REM of 0 to 10 WAT and 28,000 to 88,000 kg ha−1 for EST of 0 to 6 WAT. Percentage of jumbo, large, medium, and cull tomato yields ranged from 49 to 33%, 22 to 31%, 2 to 6%, and 9 to 11%, respectively, for REM of 0 to 10 WAT and 30 to 49%, 38 to 22%, 3 to 2%, and 12 to 9%, respectively, for EST of 0 to 6 WAT. To avoid losses of marketable tomato yield and percentage of jumbo tomato fruit yield, tomato plots must remain free of Palmer amaranth between 3 and 6 WAT. Observed reduction in marketable tomato yield was likely due to competition for light as Palmer amaranth plants exceeded the tomato plant canopy 6 WAT and remained taller than tomato plants for the remainder of the growing season.

Field research was conducted in 2010 and 2011 to investigate the efficacy of herbicides for dallisgrass control when applied at various growing (GDD) or cooling degree day (CDD) –based application timings. Herbicide treatments included fluazifop-p-butyl (fluazifop; 105 g ai ha−1), mesotrione (280 g ai ha−1), tembotrione (92 g ai ha−1), topramezone (37 g ai ha−1), and tank mixtures of fluazifop plus mesotrione, tembotrione, or topramezone. Herbicide treatments were applied at either 75, 175, 375, 775 GDD, or 5 CDD. Treated plots were subjected to three tall fescue interseeding regimes: no seeding, seeding in spring, or seeding in fall (0, 353, and 353 kg pure live seed ha−1, respectively). In 2010, dallisgrass control from fluazifop applied at 75, 375, and 775 GDD was poor (< 50%) by 52 wk after treatment (WAT); in 2011, control from fluazifop application at these timings was higher (62 to 72%). When applied at 175 GDD or 5 CDD in 2010 and 2011, dallisgrass control from fluazifop ranged from 79 to 93% at 52 WAT. The addition of mesotrione, tembotrione, or topramezone to fluazifop did not affect dallisgrass control at any application timing, and control provided by these herbicides alone was low (< 65%). Interseeding tall fescue in the fall improved dallisgrass control from herbicides applied at 75 GDD in 2010 and 175, 375, and 775 GDD at 52 WAT in both years. Results suggest that timing of fluazifop applications at 175 GDD and 5 CDD enhances dallisgrass control.

Grafting is a widely-adopted cultural method to incorporate desired traits of rootstock with those of the scion and has been used successfully to address many biotic and abiotic stresses, including drought/waterlogging, insects, and diseases. However, it is not known if a herbicide resistance trait can be transferred across a graft union. Using Roundup Ready® (RR; glyphosate-resistant) soybean grafted with conventional (CN; nontransgenic and glyphosate-sensitive) soybean, we show that grafting is capable of transferring glyphosate resistance from RR rootstocks to CN scions. Grafts of CN/CN (scion/rootstock), CN/RR, RR/CN, and RR/RR were treated with potassium salt of glyphosate at 0.28, 0.84 and 1.68 kg ae ha−1. The CN/RR plants survived glyphosate treatment at 0.84 and 1.68 kg ha−1 while CN/CN plants were killed, indicating that glyphosate resistance is systemically mobile across the graft union. Intraspecies transfer of glyphosate resistance was unidirectional from root to shoot, since RR/CN plants were killed by glyphosate. The glyphosate resistance trait is conferred by CP4 5-enolpyruvylshikimate-3-phosphate synthase (CP4-EPSPS); therefore, we further examined whether CP4-EPSPS played a role in the phenomenon. CP4-EPSPS was detected in the CN scion of CN/RR plants by enzyme-linked immunosorbent assay (ELISA) but only 0.001% of that detected in RR leaf. This concentration is unlikely to have contributed significantly to the glyphosate resistance observed in CN/RR plants. Amino acid systemic trafficking and/or tissue specific glyphosate resistance are more likely the reasons for this phenomenon. These results show that grafting a transgenic herbicide-resistant rootstock to a nonresistant scion can confer resistance to the entire plant.

A survey questionnaire was sent to cotton consultants of Arkansas and Mississippi through direct mail and Louisiana and Tennessee consultants through on-farm visits in fall of 2011. The survey was returned by a total of 22 Arkansas, 17 Louisiana, 10 Mississippi, and 11 Tennessee cotton consultants, representing 26, 53, 13, and 38% of total cotton planted in these states in 2011, respectively. Collectively, the area planted to glyphosate-resistant (Roundup Ready®, RR) cotton was 97%, glyphosate plus glufosinate-resistant (Widestrike® Flex, WRF) cotton was 30%, and glufosinate-resistant (Liberty Link, LL) cotton was 2.6% of the total cotton surveyed in 2011. Seventy percent of area in all states is still under continuous RR/WRF cotton. Average cost of herbicides in RR systems was $114 ha−1 and in LL systems was $137 ha−1. Across the states, cotton planted under no-tillage, conservation tillage, and conventional tillage was 31, 36, and 33%, respectively, of total scouted cotton. Area under conventional tillage increased and conservation tillage decreased in Arkansas compared with a previous survey conducted in 2006. Palmer amaranth, morningglories, and horseweed in the order of listing were the most problematic weeds of cotton across Arkansas, Mississippi, and Tennessee. In Louisiana, however, morningglories were the most problematic weed followed by Palmer amaranth and common waterhemp. Glyphosate-resistant (GR) Palmer amaranth infested only 13% of scouted cotton area in Louisiana compared with 75% in the remaining three states, and consequently, hand-weeding to control GR Palmer amaranth is practiced on only 2.5% of total scouted area of Louisiana and 49% of the scouted area of the remaining three states. Hand-weeding added an additional $12 to 371 ha−1 to weed-management costs. One-half (50%) of the cotton consultants emphasized the need for more research on residual herbicides that can control GR Palmer amaranth effectively.

Whole-plant bioassays using sugar beet, lettuce, cucumber, green bean, pea, and soybean as test crops were used to detect mesotrione residues in the soil. The test crops were planted in soil treated with mesotrione in the field the previous year at rates of 0 to 560 g ai ha−1 and in nontreated soil from the same field, with mesotrione added at concentrations of 0 to 320 μg kg−1. Experiments were conducted in the greenhouse for a 21-d period. Values for the dose giving a 50% response (I50) were predicted using a log-logistic nonlinear regression model. I50 values (mean ± SE) of 8.6 ± 1.8, 14.9 ± 2.0, 29.8 ± 11.0, 41.6 ± 7.3, 52.9 ± 6.4, and 67.9 ± 30.3 g ai ha−1 for sugar beet, lettuce, green bean, cucumber, pea, and soybean, respectively, indicate that these crops were effective bioassay test species for quantifying mesotrione residues. A greenhouse bioassay was a simple and sensitive tool to detect mesotrione at concentrations of less than 1.0 μg kg−1 with sugar beet and lettuce being the most sensitive test species. The I50 values for soil treated with known concentrations of mesotrione were lower than for field soil treated with mesotrione the previous year. Knowing the level of mesotrione residues in the soil, growers have flexibility in crop rotations following mesotrione use on corn. Growers can use this information to minimize risk of crop injury by choosing appropriate rotation crops that suffer little or no yield reduction.

A late-summer survey of herbicide-resistant (HR) weeds was conducted in Alberta in 2007, Manitoba in 2008, and Saskatchewan in 2009, totaling 1,000 randomly selected annually cropped fields. In addition, we screened 1,091 weed seed samples (each sample from one field) submitted by Prairie growers between 2007 and 2011. Of 677 fields where wild oat samples were collected, 298 (44%) had an HR biotype. Group 1 (acetyl CoA carboxylase inhibitor)-HR wild oat was confirmed in 275 fields (41%), up from 15% in previous baseline surveys (2001 to 2003). Group 2 (acetolactate synthase)-HR wild oat was found in 12% of fields (vs. 8% in 2001 to 2003). Group 8 (triallate, difenzoquat)-HR wild oat was identified in only 8% of fields (not tested in 2001 to 2003); the frequency of occurrence of group 1+2-HR wild oat was similar (8%, vs. 3% in 2001 to 2003). Group 1-HR green foxtail was found in 27% of 209 fields sampled for the weed (vs. 6% in 2001 to 2003). Group 2-HR spiny sowthistle was confirmed in all Alberta fields sampled (vs. 67% in 2001); common chickweed was found mainly in Alberta in 40% of fields (vs. 17% in 2001). Group 2-HR weed biotypes not previously detected in the baseline surveys included false cleavers mainly in Alberta (17% of fields) and Saskatchewan (21%), Powell amaranth in Manitoba (16% of fields), wild mustard (three populations in Saskatchewan and Manitoba), and wild buckwheat (one population in Alberta). No sampled weed populations across the Prairies were found to be resistant to herbicides from group 4 (synthetic auxins), group 9 (glyphosate), or group 10 (glufosinate). Based on the proportion of total field area at each site infested with HR weeds, it is estimated that 7.7 million ha (29% of annually cropped land) are infested with HR weeds (eight-fold increase from 2001 to 2003), in a total field area of 9.9 million ha (37%)—over a two-fold increase. Of 816 cases of HR wild oat identified from submitted samples, 69% were group 1-HR, 15% group 2-HR, and 16% group 1+2-HR. Additionally, there were 10 populations of group 1-HR green foxtail in Saskatchewan or Manitoba, and six populations of group 1-HR Persian darnel in southern Alberta and Saskatchewan. Various group 2-HR broadleaf weeds were identified, including 17 wild mustard populations mainly from Saskatchewan and 39 cleavers populations across the three Prairie provinces. Herbicide-use data from 2006 to 2010 indicated continued reliance on group 1 herbicides in cereal crops and group 2 herbicides in pulse crops.

In Alaska Conservation Reserve Program (CRP) lands, succession of fields planted with grass and clover to shrubs and small trees is resulting in program compliance problems related to ease of reconversion to crop lands. Standard practice for slowing this succession is mowing every 2 to 3 yr, which does not kill the woody vegetation. A field study was conducted at three sites over 2 yr to determine if 2,4-D (2.2 kg ae ha−1 2-ethylhexyl ester) or triclopyr (2.2 kg ae ha−1 butoxyethyl ester) applied broadcast or 2,4-D (2.2 kg ae ha−1 2,4-D dimethylamine salt) or triclopyr (1.7 kg ae ha−1 triclopyr triethylamine salt) applied with a Diamond Wet Blade™ mower (DWB) would result in longer shrub control compared to mowing. Mowing was conducted at both 15 and 45 cm above ground level and herbicides were applied with the DWB at three rates. Measurements 2 yr after treatment (YAT) confirmed that both herbicides reduced shrub cover about 50% compared to controls. Reduced rates of the herbicides applied with the DWB did not result in decreased shrub control. Grass cover was negatively correlated with shrub cover. Typically, mower height did not alter treatment effects. Treatments had little impact on forb cover and composition 2 YAT, with the exception of fireweed, which was generally reduced where herbicides were applied. Application of 2,4-D and triclopyr does not decrease the frequency of shrub control in CRP lands in Alaska. Use of 2,4-D and triclopyr with or without mowing resulted in no widespread improvement over the current practice of mowing to 15 cm every 2 to 3 yr.

In fall 2011, cotton and soybean consultants from Arkansas, Louisiana, Mississippi, and Tennessee were surveyed through direct mail and on-farm visits, and rice consultants from Arkansas and Mississippi were surveyed through direct mail to assess the importance and level of implementation of herbicide resistance best management practices (HR-BMPs) for herbicide-resistant weeds. Proper herbicide timing, clean start with no weeds at planting, application of multiple effective herbicide modes of action, use of full labeled herbicide rates, and prevention of crop weed seed production with importance rating of ≥ 4.6 out of 5.0 were perceived as the most important HR-BMPs in all crops. Purchase of certified rice seed was on 90% of scouted hectares. In contrast, least important HR-BMPs as perceived by consultants with importance ratings of ≤ 4.0 in cotton, ≤ 3.7 in rice, and ≤ 3.8 in soybean were cultural practices such as manual removal of weeds; tillage including disking, cultivation, or deep tillage; narrow (≤ 50 cm)-row crops, cover crops, and altered planting dates. Narrow crop rows and cover crops in cotton; altered planting dates in cotton and soybean; and cleaning of farm equipment and manual weeding in rice and soybean is currently employed on ≤ 20% of scouted hectares. Extra costs, time constraints, adverse weather conditions, lack of labor and equipment, profitability, herbicide-related concerns, and complacency were perceived as key obstacles for adoption of most HR-BMPs. With limited adoption of most cultural practices that reduce risks of herbicide-resistant weeds, there are opportunities to educate growers concerning the proactive need and long-term benefits of adopting HR-BMPs to ensure sustainable weed management and profitable crop production.

As the amount of methyl bromide approved for use in Florida strawberry diminishes, growers are faced with a forced transition to alternative fumigants. Many of these methyl bromide alternatives have been associated with reductions in weed control, requiring additional but complementary measures. POST herbicide options for annual strawberry are limited, resulting in significant portions of the strawberry acreage in Florida being hand-weeded when troublesome weeds escape conventional control methods. Strawberry has shown acceptable tolerance to clopyralid in other areas and production systems; however, its integration into the Florida production system and ramifications of applications during fruiting warrants further research. Eight trials were conducted, with three common strawberry cultivars grown in West Central Florida subjected to POST spray and drip-tape-injected applications of clopyralid. Formation of new strawberry leaves was not affected by clopyralid application, except for a reduction in new leaves of the cultivar ‘Strawberry Festival' at the highest rate of application of 261 g ae ha−1 in comparison with the nontreated control. Strawberry leaf malformation was best explained by an exponential growth equation, whereas marketable yield followed the trend of a Weibull peak. At the maximum labeled rate (66 g ha−1), leaf malformation was less than 5% for all cultivars tested, and marketable yield was estimated at 104% of the nontreated control.

Weed control in organic peanut is difficult and lack of residual weed control complicates weed management efforts. Weed management systems using corn gluten meal in combination with clove oil and sweep cultivation were evaluated in a series of irrigated field trials. Corn gluten meal applied in a 30 cm band over the row at PRE, sequentially at PRE+2 wk after emergence, and PRE+2wk+4wk did not adequately control annual grasses and smallflower morningglory. Similarly, a banded application of clove oil applied POST did not adequately control weeds. The only treatment that improved overall weed control was sweep cultivation. Peanut yields were not measured in 2006 due to heavy baseline weed densities and overall poor weed control. Peanut yields were measured in 2007 and were not affected by any weed control treatment due to poor efficacy. While sweep cultivation improved weed control, weeds were controlled only in the row middles and surviving weeds in-row reduced peanut yield. Even when used in combination with sweep cultivation, corn gluten meal and clove oil were ineffective and offer little potential in a weed management system for organic peanut production.

Saflufenacil and indaziflam, POST and PRE herbicides, respectively, have been registered recently for weed control in Florida citrus. Glufosinate is under evaluation and may be registered in the future for POST weed control in citrus. Citrus growers often want to have a tank mixture of herbicides that provide broad-spectrum weed control. Saflufenacil is a broadleaf herbicide and needs to be tank mixed with other herbicide(s) to increase weed control spectrum. Information is not available on interaction of saflufenacil, glufosinate, and indaziflam applied in tank mixtures on weed control efficacy. Greenhouse and field experiments were conducted at two locations (Polk and Orange County, FL) to evaluate the efficacy and potential antagonism or synergy of saflufenacil and glufosinate applied in tank mixes, and various three-way mixes with indaziflam. The results suggested that tank mixing saflufenacil with glufosinate had no effect on grass weed control, but had additive effect on broadleaf weed control. Indaziflam tank mixed at the recommended label rate (0.073 kg ha−1) provided better residual weed control compared with the lower rate (0.05 kg ha−1). Tank mixing indaziflam with saflufenacil and glufosinate improved broadleaf and grass weed control, reduced weed density, and biomass compared with tank mixing saflufenacil and glufosinate. Tank mixing indaziflam at 0.073 kg ha−1 with saflufenacil and glufosinate provided ≥ 88% control of broadleaf and grass weeds at 30 d after treatment (DAT), and it was comparable with tank mixing saflufenacil, glyphosate and pendimethalin. This treatment combination recorded the lowest weed density (≤ 7 plants m−2) and biomass (< 80 g m−2) at 60 DAT. Glyphosate applied alone was less effective than tank mixing with saflufenacil and glufosinate for broadleaf and grass weed control. This indicates additive effect of tank mixture on glyphosate efficacy. It is concluded that saflufenacil can be tank mixed with glufosinate for control of broadleaf and grass weeds; however, addition of indaziflam in tank mixture provided long-term, broad-spectrum weed control in Florida citrus compared with other treatments.

Reduced-tillage systems including no-tillage and striptillage have well-known benefits for conserving and improving soils, protecting vulnerable crops from extreme weather events, and reducing labor and fuel costs associated with full-width inversion tillage (Franzluebbers 2002, 2005; Parsch et al. 2001; Pesant et al. 1987; Spargo et al. 2008). Despite these benefits, reduced-tillage has not been widely adopted in many cropping systems due in part to the increased difficulty of managing weeds when tillage is not used. Not surprisingly, adoption of reduced-tillage has occurred primarily in crops for which low-cost, effective herbicides are available, including glyphosate-resistant soybean [Glycine max (L.) Merr.], corn (Zea mays L.), cotton (Gossypium hirsutum L.), and sugarbeets (Beta vulgaris L.) (Horowitz et al. 2010; Tarkalson et al. 2012). Increased use of a narrow range of herbicides in these cropping systems has exacerbated problems of herbicide resistance (Duke and Powles 2009; Heap 2012). Conversely, adoption of reduced-tillage has been limited in crops where effective herbicides are not available (e.g. in “minor crops” like vegetables) or prohibited (e.g. in organic production systems). Research aimed at identifying nonchemical approaches to managing weeds in reduced-tillage production systems has the potential to increase adoption of reducedtillage while minimizing herbicide use and selection pressure for herbicide resistance in production systems currently using reduced tillage (Figure 1).

Greenhouse experiments were conducted in 2011 to evaluate the effect of mowing frequency and mowing height on four summer annual weed species (large crabgrass, barnyardgrass, giant ragweed, and common lambsquarters). Plants were clipped at three heights (5, 10, or 20 cm) and at two frequencies (single clipping or repeated clippings at the same height) to simulate mowing. A nonclipped control was also grown for each species. When clipped once, large crabgrass, barnyardgrass, and giant ragweed produced at least 90% of the total dry weight (DW) of the nonclipped plants, and common lambsquarters produced at least 75%. A single cut was generally not sufficient to prevent weed seed production or kill any of the weeds in this study. Repeated clipping reduced large crabgrass, giant ragweed, and common lambsquarters reproductive DW to 46, 27, and 10% respectively, of the nonclipped control. Barnyardgrass plants that were repeatedly clipped produced between 0 and 8% of the seed DW of nonclipped plants, depending on clipping height. Repeated clipping reduced weed total DW to below 40% for all species compared to nonclipped plants. Our results suggest that, unless combined with other weed management practices, repeated mowing may be necessary to limit the growth and seed production of these weed species.

Methyl bromide (MeBr), a widely used soil fumigant in tomato production, has been banned for ordinary agricultural uses. In the absence of MeBr, a viable alternative is imperative for weed control and prevention of economic loss in tomato production. A field study was conducted in the summers of 2010 and 2011 at Fayetteville, AR, to compare the efficacy and economics of herbicide programs consisting of pre-transplant followed by (fb) post-transplant herbicides in low-density polyethylene (LDPE) mulched tomato. Pre-transplant imazosulfuron at 0.112, 0.224, and 0.336 kg ai ha−1 and S-metolachlor at 1.6 kg ai ha−1 were fb a post-transplant mixture of trifloxysulfuron plus halosulfuron at 0.008 and 0.027 kg ai ha−1 at 4 wk after transplant (WATP). The standard MeBr treatment (2:1 mixture of MeBr plus chloropicrin at 390 kg ai ha−1), weed-free (hand weeding) control, and nontreated weedy check were used for comparison. Pre-transplant S-metolachlor fb post-transplant herbicides controlled Palmer amaranth ≥ 89%, large crabgrass ≥ 88%, and yellow nutsedge ≥ 90%, which was comparable to the control with MeBr. Tomato recovered the injury (≤ 19% at 6 WATP) from post-transplant herbicides in the later weeks. S-metolachlor–containing herbicide programs yielded marketable tomato fruit comparable to the yield with MeBr. Economic evaluation of the herbicide programs demonstrated a net return of $3,758.50 ha−1 from the S-metolachlor–containing herbicide program in LDPE-mulched tomato. Likewise, this herbicide program showed minimum loss of ≤ $671.61 ha−1 in net return relative to MeBr. In conclusion, a herbicide program consisting of pre-transplant S-metolachlor fb post-transplant trifloxysulfuron plus halosulfuron is a viable alternative to MeBr for weed control and marketable yield in LDPE-mulched tomato production.