Imazethapyr dose response curves were developed under laboratory and field conditions with the imazethapyr-resistant and -susceptible corn hybrids Pioneer 3180IR, IR denoting a hybrid homozygous for the XA17 gene conferring resistance to imazethapyr, and normal Pioneer 3180, respectively, and their F1 progeny to establish methods of measuring the presence of the XA17 gene and quantifying its impact. At two field locations, absorption of photosynthetically active radiation was a sensitive index of corn injury caused by imazethapyr. Imazethapyr, at 35 g/ha (one half the labeled rate), reduced absorption of photosynthetically active radiation in Pioneer 3180 by 8.3% at 1 wk after treatment. Plant height also was a sensitive index of injury. The minimum rate at which imazethapyr injury was detected in the Pioneer 3180IR/Pioneer 3180 F1 hybrid differed with location. Pioneer 3180IR was not injured by 280 g/ha of imazethapyr. The Pioneer 3180IR/3180 F1 hybrid was injured slightly by imazethapyr at 140 g/ha, but recovered within 5 wk after treatment, and grain yield was not reduced by 280 g/ha of imazethapyr. A seedling assay reliably detected differences between progeny of Pioneer 3180IR and Pioneer 3180IR/3180 F1.

Atrazine detection in drinking water has raised questions about how to reduce levels of this herbicide. Field experiments were conducted near Ottawa, KS, to determine atrazine levels in runoff from grain sorghum grown under three tillage systems in three growing seasons. Atrazine at 1.12 kg ai/ha was applied several weeks before planting to areas where no-till (NT), ridge-till (RT), and chisel-disk (CD) systems were used, followed by an additional 0.56 kg ai/ha applied at planting. Surface-water runoff was collected from enclosed metal frames within each tillage system, and total water runoff and atrazine concentration were determined and used to compute total atrazine loss. Atrazine loss was less from CD than from the other tillage systems in years when atrazine was soil incorporated. Atrazine loss was highly variable among years and tillage systems. This suggests that other factors besides till systems influenced atrazine runoff.

Field studies were conducted from 1985 through 1987 to evaluate control of wild jujube, a deciduous, thorny shrub that causes complete wheat and other crop loss by preventing harvest operations. Initial herbicide or sweep tillage treatments were applied in late June or July, as plants approached maximum foliar development, to wild jujube regrowth from plants cut at ground level the previous fall. Nearly 1 yr after treatment, over 97% reduction of wild jujube regrowth was achieved with initial treatments of 7.2 and 10.7 g ae/L of the isopropylamine salt of glyphosate, 2.4 and 3.6 g ae/L of the potassium salt of picloram, and mixtures of glyphosate plus picloram at half those concentrations, followed 2 to 3 mo later with a repeat herbicide treatment or sweep tillage. About 60% reduction in wild jujube regrowth was achieved with two sweep tillage operations 25 cm deep. Mixtures of half rates of glyphosate plus picloram were less costly than full rates of glyphosate alone and had less carryover to wheat than full rates of picloram alone.

Japanese honeysuckle (Lonicera japonica Thunb. # LONJA) vines can smother young trees, presenting problems in nursery, parkland, and woodlot management. The tardy-deciduous nature of honeysuckle provides an application window for its selective control with glyphosate [N-(phosphonomethyl)-glycine] or dichlorprop [(±)-2-(2,4-dichlorophenoxy)propanoic acid] plus 2,4-D [2,4-dichlorophenoxy)acetic acid] immediately after fall defoliation of hardwood species. Glyphosate at 1.5% v/v (5.4 g ae/L) applied in December killed mature, woody honeysuckle vines and eliminated most regrowth from basal and subterranean buds 28 months after treatment. Dichlorprop plus 2,4-D at 1.5% v/v (3.6 g ae/L of each herbicide), when applied shortly after the first freezing temperatures in October, was as effective as glyphosate but was less effective when applied in December. Tuliptree (Liriodendron tulipifera L.), American beech (Fagus grandifolia Ehrh.), and Scotch pine (Pinus sylvestris L.) suffered minimal and temporary injury from these herbicides.

Research in Kansas from 1983 to 1986 evaluated early preplant (30 to 45 days) and late preplant (10 to 14 days) herbicide treatments for weed control before ridge-till planting in a soybean and sorghum rotation. Control of fall panicum and common lambsquarters at planting time averaged at least 95% for all early preplant and 92% for late preplant treatments. Where no preplant treatment was used, heavy weed growth in spring delayed soil dry-down, which resulted in poor ridge-till planting conditions and reduced plant stands, and ultimately reduced sorghum grain yields by 24% and soybean yields by 12%. Horsenettle population declined significantly, and honeyvine milkweed population increased. Smooth groundcherry populations fluctuated from year to year with no overall change.

Field studies were conducted in central Missouri and central Kansas to evaluate the crop tolerance and efficacy of various combinations of atrazine, flufenacet + isoxaflutole, flumetsulam + clopyralid, isoxaflutole, and S-metolachlor applied PPI or PRE in conventional-till corn. Application technique did not influence crop injury in Kansas. In Missouri, greater crop injury was observed with treatments containing isoxaflutole when applied PPI vs. PRE. Application technique influenced giant foxtail, ivyleaf morningglory, large crabgrass, Palmer amaranth, and common waterhemp control. In dry years, control of these weeds was usually either same or greater with PPI than it was with PRE treatments. In years with average to above average precipitation, isoxaflutole provided greater control as a PRE application than as a PPI application. Palmer amaranth and common waterhemp control was usually greater with atrazine, isoxaflutole, and S-metolachlor applied PRE than it was applied PPI. Differences in control of all weeds between PPI and PRE applications were less obvious with two or three herbicides compared with treatments with a single herbicide. In general, the corn yield was greater with most of the treatments having two, three, or four herbicides than it was with treatments having a single herbicide, which was due to better weed control with the tank-mixtreatments.

Research was conducted to determine the effects of management practices and precipitation on herbicide loss in surface water runoff. A field runoff experiment was conducted in 1999 and 2000 in Manhattan, KS. Some plots received only natural precipitation, whereas others received natural precipitation plus additional precipitation from a rainfall simulator. Atrazine was applied at 0.9 and 1.8 kg ha−1, S-metolachlor at 0.7 and 1.4 kg ha−1, and isoxaflutole at 0.05 and 0.11 kg ha−1 to field corn grown under conventional tillage and no-till. Runoff volumes and herbicide concentrations were determined for each runoff event. Across all precipitation, tillage, and placement variables, atrazine, S-metolachlor, and isoxaflutole and diketonitrile (DKN) (soil metabolite of isoxaflutole), hereafter referred to as isoxaflutole/DKN, losses were similar at 5.0, 4.1, and 4.1% of applied, respectively. Additional precipitation increased runoff 2.5-, 2.2-, and 3.4-fold for atrazine, S-metolachlor, and isoxaflutole/DKN, respectively. Preplant soil incorporation reduced atrazine, S-metolachlor, and isoxaflutole/DKN losses in runoff by 67, 69, and 57%, respectively, compared with soil surface applications. Lower preplant rainfall in 2000 resulted in sharply reduced runoff losses despite postplant precipitation similar to that in 1999. These findings suggest that the best management practices for atrazine can be used to manage S-metolachlor and isoxaflutole/DKN loss in surface water runoff.

Field experiments were conducted in 1997 and 1998 near Rossville in northeast Kansas to evaluate control of imazethapyr-resistant common sunflower with selected herbicides in corn and soybean. In soybean, common sunflower control was unacceptable with imazethapyr, chlorimuron, CGA-277476, and cloransulam applied alone. Lactofen or acifluorfen applied with these herbicides slightly improved control, whereas glyphosate applied with them controlled more than 97% of common sunflower. All herbicides reduced common sunflower populations in the corn. The greatest reductions occurred when atrazine was applied with dicamba, 2,4-D, RPA 201772, or CGA-152005 plus primisulfuron. These herbicide combinations also stunted common sunflower that survived treatment. Several herbicide alternatives are available to control imazethapyr-resistant common sunflower in corn. However, glyphosate was the only herbicide that gave adequate control in soybean.

Field and greenhouse experiments were conducted to evaluate the efficacy and safening of metsulfuron applied with dicamba, 2,4-D, clopyralid, and fluroxypyr with and without nonionic surfactant. Greenhouse data showed that 2,4-D and dicamba, but not fluroxypyr, safened grain sorghum from metsulfuron injury. In the field study, grain sorghum injury from metsulfuron was decreased when tank mixed with 2,4-D or dicamba but not when tank mixed with clopyralid or fluroxypyr. Tank mixes of 2,4-D or dicamba with metsulfuron did not reduce ivyleaf morningglory or velvetleaf control. At 4 wk after treatment (WAT), ivyleaf morningglory was controlled 95, 84, 59, and 91%, and velvetleaf was controlled 88, 82, 78, and 95% when metsulfuron was tank mixed with 2,4-D, dicamba, clopyralid, and fluroxypyr, respectively. In a separate field study, differential grain sorghum hybrid responses to a tank mix of metsulfuron + 2,4-D was examined. In general, a tank mix of metsulfuron and 2,4-D caused visible injury to all hybrids at 1 and 2 WAT, but grain sorghum recovered and most hybrids appeared normal at the end of the growing season. Differential hybrid responses to metsulfuron + 2,4-D were observed at 1 and 2 WAT in 2000 and 4 WAT in 2001. The most susceptible hybrid was ‘Mycogen 1506’, and the least susceptible hybrids were ‘NK KS-310’ and ‘Pioneer 87G57’. This study demonstrates the potential for 2,4-D or dicamba to safen metsulfuron injury of sorghum without compromising weed control.

Field studies were conducted at 35 sites throughout the north-central United States in 1998 and 1999 to determine the effect of postemergence glyphosate application timing on weed control and grain yield in glyphosate-resistant corn. Glyphosate was applied at various timings based on the height of the most dominant weed species. Weed control and corn grain yields were considerably more variable when glyphosate was applied only once. The most effective and consistent season-long annual grass and broadleaf weed control occurred when a single glyphosate application was delayed until weeds were 15 cm or taller. Two glyphosate applications provided more consistent weed control when weeds were 10 cm tall or less and higher corn grain yields when weeds were 5 cm tall or less, compared with a single application. Weed control averaged at least 94 and 97% across all sites in 1998 and 1999, respectively, with two glyphosate applications but was occasionally less than 70% because of late emergence of annual grass and Amaranthus spp. or reduced control of Ipomoea spp. With a single application of glyphosate, corn grain yield was most often reduced when the application was delayed until weeds were 23 cm or taller. Averaged across all sites in 1998 and 1999, corn grain yields from a single glyphosate application at the 5-, 10-, 15-, 23-, and 30-cm timings were 93, 94, 93, 91, and 79% of the weed-free control, respectively. There was a significant effect of herbicide treatment on corn grain yield in 23 of the 35 sites when weed reinfestation was prevented with a second glyphosate application. When weed reinfestation was prevented, corn grain yield at the 5-, 10-, and 15-cm application timings was 101, 97, and 93% of the weed-free control, respectively, averaged across all sites. Results of this study suggested that the optimum timing for initial glyphosate application to avoid corn grain yield loss was when weeds were less than 10 cm in height, no more than 23 d after corn planting, and when corn growth was not more advanced than the V4 stage.

Multiple weed species in the field combine to cause yield losses and can be described using one of several empirical models. Field studies were conducted to compare observed corn yield loss caused by common sunflower and shattercane populations with predicted yield losses modeled using a multiple species rectangular hyperbola model, an additive model, or the yield loss model in the decision support system, WeedSOFT, and to derive competitive indices for common sunflower and shattercane. Common sunflower and shattercane emerged with corn and selected densities established in field experiments at Scandia and Rossville, KS, between 2000 and 2002. The multiple species rectangular hyperbola model fit pooled data from three of five location–years with a predicted maximum corn yield loss of 60%. Initial slope parameter estimate for common sunflower was 49.2 and 4.2% for shattercane. A ratio of these estimates indicated that common sunflower was 11 times more competitive than shattercane. When common sunflower was assigned a competitive index (CI) value of 10, shattercane CI was 0.9. Predicted yield losses modeled for separate common sunflower or shattercane populations were additive when compared with observed yield losses caused by low-density mixed populations of common sunflower (0 to 0.5 plants m−2) and shattercane (0 to 4 plants m−2). However, a ratio of estimates of these models indicated that common sunflower was only four times as competitive as shattercane, with a CI of 2.5 for shattercane. The yield loss model in WeedSOFT underpredicted the same corn losses by 7.5%. Clearly, both the CI for shattercane and the yield loss model in WeedSOFT need to be reevaluated, and the multiple species rectangular hyperbola model is proposed.

The selection of herbicide-resistant weeds in grain sorghum production has prompted researchers to explore alternative herbicides to prevent, delay, and manage herbicide-resistant weed biotypes. Greenhouse and field experiments were conducted to evaluate the differential response of sorghum hybrids to POST application of mesotrione. In a greenhouse experiment, 85 sorghum hybrids were treated with 0, 52, 105, 210, and 315 g ai/ha mesotrione when plants were at the three- to four-leaf collar stage. Sorghum response ranged from susceptible to tolerant sorghum hybrids. ‘Pioneer 84G62’, ‘Pioneer 85G01’, and ‘Triumph TR 438’ were the three most susceptible, whereas ‘Dekalb DKS35-70’, ‘Frontier F222E’, and ‘Asgrow Seneca’ were the three most tolerant hybrids. One week after treatment (WAT), the mesotrione rate causing 50% visible injury ranged from 121 to 184 and 64 to 91 g/ha in the most tolerant and susceptible hybrids, respectively. Mesotrione dose–response studies were conducted under field conditions on four sorghum hybrids. One WAT, injury symptoms were greater (up to 23%) in Pioneer 85G01 than in Asgrow Seneca (< 14%). However, all plants appeared normal by the end of the growing season. In addition, sorghum yields were not reduced by mesotrione treatments as verified by correlation coefficient analysis.

Field experiments were conducted from 1996 to 2000 near Manhattan, KS, to determine the effects of application timing on atrazine loss in surface water runoff. In addition, Groundwater Loading Effects of Agricultural Management Systems (GLEAMS) was run to compare simulated loss with actual loss in the field. Atrazine treatments were fall plus preemergence (FALL + PRE), early preplant plus PRE (EPP + PRE), PRE at a low rate (PRE-LOW), and PRE at a full (recommended) rate (PRE-FULL). Ridge-till furrows served as mini watersheds for the collection of surface water runoff. Water runoff volumes and herbicide concentrations were determined for each runoff event. Across four sampling years, mean atrazine runoff loss was 1.7, 4.3, and 1.7% of applied for FALL + PRE, EPP + PRE, and the mean of the PRE treatments, respectively. Thus, actual average losses from FALL + PRE and EPP + PRE treatments were somewhat higher than that predicted by GLEAMS. For PRE treatments, actual average losses were significantly lower than that predicted by GLEAMS, with measured losses falling below the bottom of the graph in 3 of 4 yr. These findings suggest that in certain parts of the Great Plains, FALL + PRE split applications of atrazine offer acceptably low atrazine runoff loss potential; EPP + PRE is more vulnerable to loss than FALL + PRE; and the GLEAMS model may overestimate atrazine runoff potential for PRE applications.

Field experiments were conducted at Belleville, Colby, Hays, Hesston, Garden City, and Manhattan, KS, to determine grain sorghum response to POST application of mesotrione at three application timings. Mesotrione was applied at 52, 105, 157, and 210 g ai/ha in combination with 280 g ai/ha atrazine to grain sorghum at heights of 5 to 8, 15 to 20, and 30 cm, which correspond to early POST (EPOST), mid-POST (MPOST), and late POST (LPOST), respectively. All mesotrione rates caused injury at all application timings. Overall, grain sorghum injury from mesotrione was greatest at 1 wk after treatment (WAT); plants partially recovered from injury by 4 WAT. Mesotrione applied EPOST injured grain sorghum more than when applied at MPOST and LPOST timings. The EPOST application injured grain sorghum 19 to 88%, whereas injury from MPOST and LPOST application was 1 to 66% and 0 to 69%, respectively, depending on rate. Mesotrione injury was least at Belleville and most at the Hesston and Garden City (irrigated) sites regardless of growth stage. Correlation coefficient analyses indicated that observed mesotrione injury symptoms were not well correlated with grain sorghum yield; thus, mesotrione injury to grain sorghum did not influence grain yield. However, initial grain sorghum injury was severe, and this will likely be a major concern to producers.

Field experiments were conducted across the north-central United States to determine the benefits of various weed control strategies in corn. Weed control, corn yield, and economic return increased when a preemergence (PRE) broad-spectrum herbicide was followed by (fb) postemergence (POST) herbicides. Weed control decisions based on field scouting after a PRE broad-spectrum herbicide application increased weed control and economic return. Application of a PRE grass herbicide fb a POST herbicide based on field scouting resulted in less control of velvetleaf and morningglory species, corn yield, and economic return compared with a PRE broad-spectrum herbicide application fb scouting. Cultivation after a PRE broad-spectrum herbicide application increased weed control and corn yield compared with the herbicide applied alone, but economic return was not increased. An early-postemergence herbicide application fb cultivation resulted in the highest level of broadleaf weed control, the highest corn yield, and the greatest economic return compared with all other strategies. Weed control based on scouting proved to be useful in reducing the effect of weed escapes on corn yield and increased economic return compared with PRE herbicide application alone. However, economic return was not greater than the PRE fb planned POST or total POST strategies.

Field studies conducted from 2005 to 2007 in Kansas compared the effects of KIH-485 and flufenacet to acetochlor and s-metolachlor applied PRE in grain sorghum. All treatments were combined with 1.12 kg/ha of atrazine for broadleaf weed control. KIH-485 and flufenacet, each at one time (1×) and two times (2×) the labeled rates, controlled large crabgrass 55 to 76% in 2005 and 94% or more in 2006 and 2007. In 2005, all herbicides controlled shattercane less than 20%, and only KIH-485 at the 2× rate controlled shattercane more than 70% in 2006 and 2007. Averaged over herbicides, green foxtail was controlled 98% in 2005, 77% in 2006, and 79% in 2007. Most herbicides controlled foxtail 86% or more when averaged over experiments, however, s-metolachlor at 1×, flufenacet at either rate, or atrazine alone did not. Sorghum was not stunted with KIH-485 or flufenacet in two of seven experiments. However, sorghum growth was reduced 23 to 54% with the 2× rates of KIH-485, flufenacet, or acetochlor in four experiments. Compared to the weed free control, sorghum stand establishment was reduced 18% with the 2× rate of flufenacet at Colby in 2006. At Hays in 2005, stand reductions occurred with acetochlor or KIH-485 at the 2× rates and either rate of flufenacet. Averaged over experiments, grain yields were reduced 9 and 10% with KIH-485 and flufenacet at the 2× rates, respectively. Where precipitation was greatest during the 2 wk following herbicide application, weed control was the best with these herbicides, but sorghum injury was also greatest.

Field experiments were conducted at four locations in Kansas in 1999 and 2000 to evaluate grain sorghum response to simulated drift rates of four herbicides. Imazethapyr, glufosinate, glyphosate, and sethoxydim were applied at 1/3, 1/10, 1/33, and 1/100 of the use rate when plants were 10 to 20 cm tall. Visible crop injury increased as rates of each herbicide increased. Glyphosate and imazethapyr caused the most injury and glufosinate the least. Data show that some plants that were significantly injured 2 wk after treatment (WAT) recovered 8 WAT. However, some plants that received the highest rate of imazethapyr or glyphosate died. Grain sorghum yields were reduced only when injury was severe. This research showed that the potential for sorghum injury from off-target herbicide drift is greater from imazethapyr and glyphosate than from sethoxydim or glufosinate.