Two trials were conducted to evaluate the effects of herbicide and mulch on weed management and strawberry yield. Napropamide at rates of 4.50, 6.75, or 9.00 kg ai/ha; oxyfluorfen at 0.57 kg ai/ha; and napropamide plus oxyfluorfen at 4.50 plus 0.57 kg/ha were applied pretransplant on pressed beds covered with either low-density polyethylene mulch or virtually impermeable film. There was no herbicide by mulch interaction. Mulch types had no influence on weed counts and fruit yield, whereas herbicides affected both variables. The napropamide plus oxyfluorfen treatment resulted in the highest fruit number and weight, increasing yield by 20% with respect to the nontreated control. This herbicide combination provided the best weed suppression.

Glyphosate-resistant (GR) Italian ryegrass is one of the most troublesome weeds in Mississippi row crop production. Fall-applied residual herbicide applications are recommended for control of GR Italian ryegrass. However, carryover of residual herbicides applied in fields for rice production can have a negative impact on rice performance. Field studies were conducted in Stoneville, MS, to determine the effects of fall-applied residual herbicides on rice growth and yield. Herbicide treatments included suggested use rates (1×) of clomazone at 840 g ai ha–1, pyroxasulfone 170 g ai ha–1, S-metolachlor 1,420 g ai ha–1, and trifluralin 1,680 g ai ha–1, and two times (2×) the suggested use rates in the fall before rice seeding. Pooled across application rate, pyroxasulfone, S-metolachlor, and trifluralin injured rice to an extent 28% to 36% greater than clomazone 14 d after emergence (DAE). Rice seedling density and height 14 DAE and rice maturity were negatively affected by all fall-applied herbicides except clomazone. Applications at 2× rates reduced rough rice yields in plots treated with pyroxasulfone, S-metolachlor, and trifluralin compared with clomazone. Pyroxasulfone applied at the 2× rate reduced rough rice yield 22% compared with the 1× rate. Rough rice yield was 90% or greater of the nontreated control in plots treated with either rate of S-metolachlor, and these were comparable with rough rice yields from plots treated with both rates of trifluralin and the 1× rate of pyroxasulfone. Early-season injury and reductions in seedling density and height 14 DAE, would preclude even 1× applications of pyroxasulfone, S-metolachlor, and trifluralin from being viable options for residual herbicide treatments targeting GR Italian ryegrass in the fall before rice seeding. Of the herbicides evaluated, only clomazone should be utilized as a fall-applied residual herbicide treatment targeting GR Italian ryegrass before seeding rice.

The objective of this research was to explore the influence that weed decision threshold (DT; expressed as plants m−2), weed spatial distribution patterns, and spatial resolution of sampling have on potential reduction in herbicide use under site-specific weed management. As a case study, a small plot located in a typical corn field in central Spain was used, constructing very precise distribution maps of the major weeds present. These initial maps were used to generate herbicide prescription maps for each weed species based on different DTs and sampling resolutions. The simulation of herbicide prescription maps consisted of on/off spraying decisions based on information from two different approaches for weed detection: ground-based vs. aerial sensors. In general, simulations based on ground sensors resulted in higher herbicide savings than those based on aerial sensors. The extent of herbicide reductions derived from patch spraying was directly related to the density and the spatial distribution of each weed species. Herbicide savings were potentially high (up to 66%) with relatively sparse patchy weed species (e.g., johnsongrass) but were only moderate (10 to 20%) with abundant and regularly distributed weed species (e.g., velvetleaf). However, DT has proven to be a key factor, with higher DTs resulting in reductions in herbicide use for all the weed species and all sampling procedures and resolutions. Moreover, increasing DT from 6 to 12 plants m−2 resulted in additional herbicide savings of up to 50% in the simulations for johnsongrass and up to 28% savings in the simulations for common cocklebur. Nonetheless, since DT determines the accuracy of patch spraying, the consequences of using higher DTs could be leaving areas unsprayed, which could adversely affect crop yields and future weed infestations, including herbicide-resistant weeds. Considering that the relationship between DT and accuracy of herbicide application depends on weed spatial pattern, this work has demonstrated the possibility of using higher DT values in weeds with a clear patchy distribution compared with weeds distributed regularly.

Water is the primary carrier for herbicide application, and carrier-water–related factors can influence herbicide performance. In a greenhouse study, premixed formulation of glyphosate plus dicamba was mixed in deionized (DI) water at 5, 18, 31, 44, or 57 C and applied immediately. In a companion study, glyphosate and dicamba formulation was mixed in DI water at temperatures of 5, 22, 39, or 56 C and sprayed after the herbicide solution was left at the respective temperatures for 0, 6, or 24 h. In both studies, glyphosate plus dicamba was applied at 0.275 plus 0.137 kg ae ha−1 (low rate), and 0.55 plus 0.275 kg ha−1 (high rate), respectively, to giant ragweed, horseweed, Palmer amaranth, and pitted morningglory. Glyphosate plus dicamba applied at a low rate with solution temperature of 31 C provided 14% and 26% greater control of giant ragweed and pitted morningglory, respectively, compared to application at solution temperature of 5 C. At both rates of glyphosate and dicamba formulation, giant ragweed and pitted morningglory control was 15% or greater at solution temperature of 44 C compared to 5 C. Weed control was not affected with premixture of glyphosate and dicamba applied ≤ 24 h after mixing herbicide. When considering solution temperature, glyphosate and dicamba applied at low rate provided 13 and 6% greater control of Palmer amaranth and pitted morningglory, respectively, with solution temperature of 22 C compared to 5 C. Similarly, giant ragweed control was 8% greater with solution temperature of 39 C compared to 5 C. Glyphosate and dicamba applied at high rate provided 8% greater control of giant ragweed at solution temperature of 22 or 39 C compared to 5 C. Therefore, activity of premixed glyphosate and dicamba could be reduced with spray solution at lower temperature; however, the result is dependent on weed species.

Field experiments were conducted at Warooka and Rudall on the Yorke and Eyre Peninsula of South Australia during 2004 and 2005 to investigate the effectiveness of metribuzin for the selective control of rigid brome in no-till sown barley. Metribuzin (135 to 203 g ai/ha) incorporated by sowing (IBS) was more effective in controlling rigid brome (> 67%) than the same herbicide dose applied POST. Although IBS metribuzin at the highest rate (270 g/ha) provided effective weed control (82 to 90%), it was more phytotoxic to barley, reducing crop density by 23% relative to the nontreated control at Rudall. Soil at Rudall had low clay and organic matter content. In contrast, tank mixtures of metribuzin (203 g/ha) with pendimethalin, applied IBS, provided reliable rigid brome control (89 to 93%) and resulted in little crop damage (< 5%). Over the site-by-year combinations studied, all herbicide-treated barley at Warooka and Rudall yielded 6 to 50% more grain than the nontreated crop. Although metribuzin provides growers with an opportunity to selectively control rigid brome in no-till barley, high rates (≥ 203 g/ha) of this herbicide on sandy textured soils can result in significant crop damage.

The adaptation of herbicides to control the encroachment of one warm-season grass into another species is an important management practice. A field study was conducted in Georgia to determine the rates and frequency of herbicide applications needed to suppress three seashore paspalum cultivars and determine what effects these treatments will have on three bermudagrass cultivars. MSMA plus triclopyr plus clopyralid applied at a total of 2.7 kg/ha in each of three applications for a cumulative total of 8.1 kg/ha effectively suppressed (> 70%) ‘Sea Isle 1’ and ‘Sea Isle 2000’ for 13 wk during 1998 and 1999 and ‘K-3’ during 1998. The suppression of K-3 in 1999 was 56%. The suppression was higher in all instances when MSMA was applied with triclopyr plus clopyralid than when it was not included (< 45%). Four-way combinations of MSMA plus 2,4-D plus mecoprop plus dicamba applied at a total of 5.3 kg/ha in each of three applications for a cumulative total of 15.9 kg/ha suppressed K-3 from 37 to 66%, Sea Isle 2000 from 55 to 66%, and Sea Isle 1 from 59 to 65% for 13 wk. The suppression of three paspalum cultivars at 13 wk from tank mixes of MSMA plus 2,4-D plus dicamba applied at a total of 4.5 kg/ha in each of three applications for a total cumulative of 13.5 kgsol:ha was 7 to 12% lower using the four-way combination treatments. Injury to the bermudagrass cultivars from herbicide treatments was not a problem. In some instances, all herbicides caused some degree of bermudagrass injury on selected dates of treatment. Maximum injury from the herbicides ranged from 18 to 40% for ‘common’ bermudagrass, 18 to 39% for ‘Tifway’ and 30% for ‘TifEagle’ bermudagrass. When injury occurred, bermudagrass recovery was within 1- to 2-wk following treatments.

Field studies were conducted from 2000 through 2002 to evaluate the effects of atrazine, pendimethalin, and trifluralin applied alone or in combination followed by cultivation when weeds and grain sorghum were less than 7 cm tall (early postemergence [EPOST]) or when weeds and grain sorghum were 10 to 15 cm tall (late postemergence [LPOST]). Atrazine plus pendimethalin applied EPOST caused 9 to 14% sorghum stunting all 3 yr while atrazine plus trifluralin applied EPOST caused 1 to 4% grain sorghum stunting. When applied LPOST, atrazine plus pendimethalin or trifluralin resulted in no greater than 3% stunting. Tumble pigweed was controlled at least 99% with atrazine plus pendimethalin or trifluralin applied EPOST or LPOST, whereas Texas panicum was controlled at least 97% with atrazine plus pendimethalin or trifluralin applied EPOST, and 76 to 100% with LPOST application. Sorghum yields were reduced with atrazine plus pendimethalin applied EPOST when compared with all herbicide combinations in one of 3 yr.

Field experiments were carried out from 1987 to 1990 to develop an integrated weed control management system for the control of blackgrass in winter wheat in Greece. The weed control treatments included both herbicides and cultural measures. The performance of preemergence (PRE) herbicides against blackgrass was better than postemergence (POST) herbicides; selectivity was dependent on application rate. Late timing of wheat sowing resulted in significant reduction of the blackgrass population competing with wheat. The critical period for blackgrass infestation occurred 4.0 to 5.5 wk after wheat emergence. Blackgrass density of 170 to 1,170 plants/m2 caused wheat yield reduction equal to 10 and 30%, respectively. A quadratic relationship describing the percent reduction of wheat yield due to competition with different blackgrass densities was developed. The economic threshold level for blackgrass varied between 100 and 125 plants/m2. The results emphasize the importance of using a combination of chemical and cultural controls, including critical periods for herbicide application in maintaining an integrated approach for blackgrass control in wheat.

Control of two perennial weeds, quackgrass and Canada thistle, and the differential sensitivities of three imidazolinone-resistant (IMI) corn hybrids and their sensitive isolines to various acetolactate synthase (ALS)-inhibiting herbicides were evaluated in greenhouse studies. The postemergence sulfonylurea herbicides nicosulfuron and primisulfuron controlled quackgrass > 80%. The imidazolinone herbicides imazapyr and imazamox applied postemergence controlled quackgrass 70 and 74%, respectively. Canada thistle control was 89% with the sulfonylurea herbicide metsulfuron. Primisulfuron, chlorsulfuron, and tribenuron controlled Canada thistle > 70%. The imidazolinonesensitive corn hybrids did not tolerate the imidazolinone herbicides imazethapyr, imazaquin, imazapyr, AC 263,222, and imazamox; the sulfonylurea herbicides chlorimuron, chlorsulfuron, metsulfuron, tribenuron, and triflusulfuron; and the pyrimidinylthiobenzoate herbicide pyrithiobac applied postemergence. The ‘Ciba 4393 IMR’ corn hybrid, homozygous for an unknown allele, was resistant to all of the various ALS-inhibiting herbicides that injured its sensitive isoline. The magnitude of resistance for this hybrid was greater than the other IR corn hybrids. The ‘Pioneer 3751 IR’ corn hybrid, homozygous for the XA-17 ALS allele, was also resistant to a number of ALS-inhibiting herbicides. The ‘ICI 8692 IT’ corn hybrid, heterozygous for the Mut2 allele, was only resistant to the imidazolinone herbicides.

2,4-DB ester had been widely used for winter annual broadleaf weed control in seedling alfalfa in the western United States, but was replaced commercially by the amine formulation in 1990. Field studies conducted in the high desert region of southern California confirmed previous reports that 2,4-DB amine is not as effective as the ester formulation. Two methods were found to improve the weed control performance of 2,4-DB amine: 1) application at earlier alfalfa growth stages and 2) the addition of adjuvant. Applications made at the three-trifoliate leaf stage of the alfalfa were more than three times as effective as applications made at the eight-trifoliate leaf stage. When adjuvants were added to the amine formulation, weed control was improved 50 to 97%.

Greenhouse research was conducted to evaluate shoot and root growth response of imidazolinone-tolerant (IT) rice cultivars to imazethapyr applied postemergence at various rates and application timings. Imazethapyr was applied at 70, 140, and 280 g ai/ha to IT cultivars ‘CL 121’ and ‘CL 161’ in the one- to two-leaf and three- to four-leaf growth stages. Imazethapyr applied to one- to two-leaf or three- to four-leaf rice at 70, 140, and 280 g/ha was more injurious to CL 121 than to CL 161. At 3 wk after treatment (WAT), CL 121 was injured 23 to 38% regardless of application timing. In contrast, CL 161 was injured no more than 11% at 3 WAT. Shoot:root ratio for CL 161 was not affected by imazethapyr application. For CL 121, shoot:root ratio was lower following imazethapyr at 280 g/ha than at 70 or 140 g/ha. Based on shoot fresh weight following imazethapyr at 70 g/ha, CL 161 was 1.8 times more tolerant than CL 121 at 2 WAT and 1.3 times more tolerant at 3 WAT. The IT rice cultivar CL 161 is inherently more tolerant to imazethapyr than is CL 121 based on visual injury and shoot and root growth.

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

Quinclorac was registered for weed control in wheat (Triticum spp.) for western Canada in 1997. Residues from quinclorac may persist in the soil and may damage following crops; therefore, field and growth chamber experiments were conducted to determine the tolerance of several following rotational crops. Cereals and bromegrass (Bromus biebersteinii) were sufficiently tolerant that they could be seeded within 16 d of quinclorac application without risk of injury. At the other extreme, marketable and total potato (Solanum tuberosum) yields were reduced by quinclorac on irrigated land 1 yr after application. Growth chamber experiments were used to rank crops in order of their tolerance of quinclorac residues and to compare the tolerance of crops that were grown in the field with additional crops. Quinclorac injured several legume and oilseed crops when the crops were seeded immediately after application, but quinclorac did not reduce the dry matter yield of two of the most sensitive legumes, faba bean (Vicia faba) and alfalfa (Medicago sativa), 1 yr after application on irrigated land. However, based on a previous study, one can conclude that injury to these crops may occur in the field under drought conditions in rain-fed agricultural systems.

Efficacy of primisulfuron and reduced rates of nicosulfuron on woolly cupgrass, wild-proso millet, and giant foxtail in field corn was evaluated in 1994 and 1995. Nicosulfuron was applied at 18, 27, and 36 g ai/ha alone and with 20 g ai/ha primisulfuron. Woolly cupgrass control from nicosulfuron at 18 and 27 g/ha was less than control from 36 g/ha (79% and 84% vs. 90%, respectively). Woolly cupgrass control was 5% greater when primisulfuron was combined with nicosulfuron at 27 and 36 g/ha than when nicosulfuron was applied alone. Corn grain yields were similar among all nicosulfuron plus primisulfuron treatments applied to control woolly cupgrass in 1994. In 1995, corn grain yield was increased 900 kg/ha when primisulfuron was combined with nicosulfuron at 18 g/ha compared to nicosulfuron applied at the same rate alone. Wild-proso millet control 3 WAT with nicosulfuron at 18 g/ha was less than control with nicosulfuron at 36 g/ha. Wild-proso millet control 8 WAT with nicosulfuron alone was greater than when nicosulfuron at any rate was applied with primisulfuron. No differences in corn grain yields were observed across nicosulfuron rates or combinations with primisulfuron to control wild-proso millet either year. Giant foxtail control and corn grain yield were not affected by nicosulfuron rate or combined applications of nicosulfuron and primisulfuron either year.

The objective of this research was to determine the potential use of commercially available multispectral images to detect weeds at low densities during the critical period of weed control. Common lambsquarters seedlings were transplanted into plots of glyphosate-resistant corn at 0, 1, 2, and 4 plants/m2 at two sites, Agronomy Center for Research and Extension (ACRE) and Meig's Horticultural Research Farm at the Throckmorton–Purdue Agricultural Center (TPAC), in Indiana. Aerial multispectral images (12 to 16 cm pixel resolution) were taken 18 and 32 days after planting (DAP) at ACRE and 19 and 32 DAP at TPAC. Corn and common lambsquarters could not be reliably detected and differentiated at either site when weeds were 9 cm or less in height. However, economic threshold densities (2 and 4 plants/m2) of common lambsquarters could be distinguished from weed-free plots at TPAC when weeds were 17 cm in height. At this height, common lambsquarters plants were beyond the optimal height for glyphosate application, but could still be readily controlled with higher rates. Results from this study indicate that commercially available multispectral aerial imagery at current spatial resolutions does not provide consistently reliable data for detection of early season weeds in glyphosate-resistant corn cropping systems. Additional refinement in sensor spatial and spectral resolution is necessary to increase our ability to successfully detect early season weed infestations.

A study was conducted at the Louisiana State University Agricultural Center’s H. Rouse Caffey Rice Research Station in 2017 and 2018 to evaluate a prepackaged mixture of clomazone plus pendimethalin applied delayed preemergence (DPRE) or POST within an herbicide residual overlay with saflufenacil, clomazone, or quinclorac. POST applications included penoxsulam or halosulfuron in combination with the second residual application. No differences were observed in barnyardgrass control (92% to 98%) at 14 days after treatment (DAT). At 42 DAT, barnyardgrass treated with clomazone plus pendimethalin in combination with either clomazone or quinclorac at either timing was controlled 95% to 96%. However, when saflufenacil was applied PRE, regardless of the POST herbicide or when saflufenacil was applied POST with halosulfuron, barnyardgrass control was reduced to 78% to 81%, compared with 95% to 96% with the control with all other residual combinations. Yellow nutsedge and rice flatsedge control increased when treated with halosulfuron compared with penoxsulam across all evaluation dates. At 28 and 42 DAT, texasweed treated with saflufenacil PRE, regardless of POST applications, was controlled 83% and 87%, respectively, and this was greater control than provided by clomazone or quinclorac applied PRE regardless of POST herbicide program.

Greenhouse and field studies were conducted to determine tolerance of tomato to halosulfuron, imazosulfuron, and trifloxysulfuron herbicides applied through drip irrigation. In greenhouse studies, PRE- and POST-applied trifloxysulfuron caused greater tomato injury (14 and 54% injury, respectively) than PRE- and POST-applied halosulfuron (5 and 26% injury, respectively) or imazosulfuron (5 and 23% injury, respectively). All herbicide treatments in the greenhouse studies caused greater injury to tomato than the nontreated. Greater tomato injury was observed in the greenhouse from herbicides applied POST than when soil applied. Tomato injury from POST-applied halosulfuron, imazosulfuron, or trifloxysulfuron followed a linear relationship, with tomato injury increasing with increasing herbicide rate. Tomato photosynthetic rate did not differ among the herbicide treatments (32.7 to 55.0 μmol m−2 s−1) and the nontreated (38.0 to 55.0 μmol m−2 s−1). At 5 to 16 days after treatment (DAT), tomato treated with imazosulfuron POST (0.26 to 0.46 cm s−1) or trifloxysulfuron POST (0.27 to 0.51 cm s−1) had lower stomatal conductance compared to the stomatal conductance of the nontreated tomato (0.65 to 0.76 cm s−1). Chlorophyll content did not differ among treatments at 0 to 6 DAT. At 7 to 12 DAT, tomato treated with imazosulfuron POST (34.0 to 40.1 SPAD) and trifloxysulfuron POST (35.0 to 41.6 SPAD) had lower chlorophyll content compared to the nontreated (39.1 to 48.1 SPAD). In 2008 and 2009 field studies, no tomato injury was observed. Herbicide, herbicide application method, and herbicide rate had no effect on tomato height (73 to 77 cm 14 DAT, 79 to 84 cm 21 DAT) and total fruit yield (62,722 to 80,328 kg ha−1).

Laboratory and greenhouse studies examined effects of atrazine, alachlor, and metolachlor on growth and colonization of grain sorghum roots by Macrophomina phaseolina, causal fungus for charcoal rot disease. In laboratory studies, all three herbicides reduced fungal colony diameter and increased production of microsclerotia. Alachlor and metolachlor reduced germination of fungal microsclerotia. Atrazine did not affect microsclerotia germination, but lessened the effects of alachlor and metolachlor on germination when applied in combination. In greenhouse studies, atrazine reduced numbers of M. phaseolina microsclerotia recovered from soil after 8 wk, and this resulted in reduced colonization of roots by this fungus at harvest. Colonization of grain sorghum roots by M. phaseolina was not affected by alachlor or metolachlor. Grain sorghum growth was reduced by atrazine at all intervals and by alachlor and metolachlor at harvest, despite use of seed safened with cyometrinil.

Response of glyphosate-resistant cotton to various rates of topically applied glyphosate was investigated in growth chamber experiments to determine the relationship between glyphosate rate and boll abscission. Glyphosate at 0, 0.56, 1.12, or 2.24 kg ai/ha was applied to all exposed foliage at the 12-leaf growth stage. Immediately after this treatment, 14C-glyphosate was applied to the three uppermost fully expanded leaves at 0, 37, 74, or 148 kBq per leaf for the 0, 0.56, 1.12, or 2.24 kg/ha treatment, respectively. After glyphosate application, glyphosate accumulated in reproductive tissue, and bolls were abscised. Abscission increased as the amount of glyphosate translocated to fruiting sites increased.

Populations of eastern black nightshade suspected of being resistant to acetolactate synthase (ALS) inhibitors have been reported since 1999 in different locations in Ontario, Canada. This event has threatened the use of ALS inhibitors for control of this species. The objectives of this study were to evaluate the spectrum of resistance to different ALS-inhibiting herbicides and to examine the effectiveness of alternative modes of action herbicides. Growth room experiments were conducted to determine the response to imazethapyr and atrazine in seven suspected ALS inhibitor– resistant populations. One resistant and one susceptible population were further characterized for their response to ALS inhibitors and chloroacetamides. Seven populations were able to survive imazethapyr at 100 g ai/ha, while there was no resistance to atrazine. Compared to a susceptible (S) population, resistant (R) population SOLPT 1 had 726-, 31-, 6-, and 4-fold resistance to postemergence (POST) applied imazethapyr, imazamox, primisulfuron, and flumetsulam, respectively. Preemergence (PRE) application of imazethapyr, flumetsulam, cloransulam, nicosulfuron, prosulfuron, and rimsulfuron did not provide control of the R population, whereas they totally controlled the S population. The chloroacetamide herbicides metolachlor, dimethenamid, and flufenacet all provided at least 90% control of both R and S populations when applied PRE at the recommended field rates. The ALS inhibitors will not provide adequate control of these resistant populations, but acceptable control could be achieved with chloroacetamides or with atrazine.