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.

A growth chamber study was conducted to evaluate the effects of temperature and soil moisture on the absorption and translocation of the new sulfonylurea herbicide, MON 37500, in wheat, jointed goatgrass, wild oat, and downy brome. Treatment combinations of temperatures—25/23, 15/13, and 5/3 C—and soil moistures of one-third, two-thirds, and full field capacities were assigned to the germinated plants. Radiolabeled MON 37500 was applied to the second leaf of plants at the three-leaf stage. The plants were then harvested at 6, 24, and 96 h after application. The plants absorbed MON 37500 in the greatest quantity during the first 6 h; however, absorption did continue to increase over time. Absorption was highest in wheat and lowest in wild oat. Temperature influenced absorption, while soil moisture status appeared to have no effect. Translocation of radiolabeled material out of the treated leaf increased over time; however, 90 to 97% of absorbed radioactivity remained in the treated leaf 96 h after treatment. Temperature affected translocation differently in each species, but increasing soil moisture increased translocation.

Kochia is a troublesome weed throughout the western United States. Although glyphosate effectively controls kochia, poor control was observed in several no-till fields in Kansas. The objectives of this research were to evaluate kochia populations response to glyphosate and examine the mechanism that causes differential response to glyphosate. Glyphosate was applied at 0, 54, 109, 218, 435, 870, 1305, 1740, 3480, and 5220 g ae ha−1 on 10 kochia populations. In general, kochia populations differed in their response to glyphosate. At 21 d after treatment, injury from glyphosate applied at 870 g ha−1 range from 4 to 91%. In addition, glyphosate rate required to cause 50% visible injury (GR50) ranged from 470 to 2149 g ha−1. Differences in glyphosate absorption and translocation and kochia mineral content were not sufficient to explain differential kochia response to glyphosate.

Spray application of 24 and 46 g ha−1 MON 37500 was used in efficacy studies, and vacuum infiltration or droplet application of radiolabeled MON 37500 was used in metabolism studies to evaluate temperature and soil moisture on MON 37500 efficacy and metabolism. Day/night temperatures before vs. after application of MON 37500 of 25/23 vs. 25/23, 25/23 vs. 5/3, 5/3 vs. 25/23, and 5/3 vs. 5/3 C were evaluated for the efficacy study, whereas day/night temperatures of 5/3 and 25/23 C were used for the metabolism study. Soil moisture of one-third and full pot capacities was evaluated for both studies. No Triticum aestivum injury was observed at the different temperatures or soil moistures because of rapid metabolism of MON 37500 by T. aestivum. Weed control was greater when the temperature after application was 25/23 C or soil moisture was at full pot capacity than when the temperature was at 5/3 C after application or soil moisture was at one-third pot capacity. Susceptibility to MON 37500 was greatest for Bromus tectorum, moderate for Avena fatua, and least for Aegilops cylindrica. This pattern of susceptibility for the weed species was related to their ability to metabolize MON 37500. Aegilops cylindrica metabolized more MON 37500 in the first 24 h than did A. fatua, whereas B. tectorum metabolized the least MON 37500. Cool air temperatures decreased MON 37500 metabolism in all species, whereas soil moisture had no effect.

Pyroxasulfone (KIH-485) is a seedling growth-inhibiting herbicide developed by Kumiai America that has the potential to control weeds in sunflower. However, little is known about how this herbicide will interact with various soil types and environments when combined with sulfentrazone. The objective of this research was to evaluate sunflower injury and weed control with pyroxasulfone applied with and without sulfentrazone across the Great Plains sunflower production area. A multisite study was initiated in spring 2007 to evaluate sunflower response to pyroxasulfone applied PRE at 0, 167, 208, or 333 g ai ha−1. In 2008, pyroxasulfone was applied alone and in tank mixture with sulfentrazone. In 2007, no sunflower injury was observed with any rate of pyroxasulfone at any location except Highmore, SD, where sunflower injury was 17%, 4 wk after treatment (WAT) with 333 g ha−1. In 2008, sunflower injury ranged from 0 to 4% for all treatments. Adding sulfentrazone did not increase injury. Sunflower yield was only reduced in treatments in which weeds were not effectively controlled. These treatments included the untreated control and pyroxasulfone at 167 g ha−1. Sunflower yield did not differ among the other treatments of pyroxasulfone or sulfentrazone applied alone or in combination. The addition of sulfentrazone to pyroxasulfone improved control of foxtail barley, prostrate pigweed, wild buckwheat, Palmer amaranth, and marshelder, but not large crabgrass or green foxtail. The combination of pyroxasulfone and sulfentrazone did not reduce control of any of the weeds evaluated.

Field experiments were conducted in grain sorghum at five locations in Kansas in 2009 and 2010, to evaluate the efficacy and crop safety of early- to mid-POST (EMPOST) and late-POST (LPOST) applications of premixed pyrasulfotole and bromoxynil (PYRA&BROM) in tank mix combinations with atrazine or atrazine plus 2,4-D ester or dicamba compared to bromoxynil plus atrazine. PYRA&BROM at 244 or 300 g ai ha−1 plus atrazine at 560 g ai ha−1 applied EMPOST controlled pigweed species (Palmer amaranth, tumble pigweed, and redroot pigweed), kochia, velvetleaf, common sunflower, ivyleaf morningglory, and common lambsquarters 93% or greater. Puncturevine control among three locations ranged from 85 to 99%. Control of most weed species was not improved by increasing PYRA&BROM rate from 244 to 300 g ha−1 or by tank mixing 2,4-D or dicamba with PYRA&BROM plus atrazine. However, ivyleaf morningglory control was improved at the LPOST timing by adding 2,4-D or dicamba at 140 g ae ha−1. In no instance did any PYRA&BROM treatment provide greater weed control than bromoxynil plus atrazine at 281 + 560 g ha−1 when applied EMPOST, but in most instances PYRA&BROM treatments were more effective than bromoxynil plus atrazine when applied LPOST. Generally, PYRA&BROM treatments were more effective when applied EMPOST than LPOST, especially when 2,4-D or dicamba was added. PYRA&BROM plus atrazine treatments caused foliar bleaching in sorghum within 7 ± 3 d after treatment, but recovery was complete within 3 to 4 wk and grain yields were not reduced. Tank mixing dicamba with PYRA&BROM and atrazine occasionally reduced visible crop response compared to PYRA&BROM plus atrazine. Our results indicate that PYRA&BROM plus atrazine with or without 2,4-D or dicamba selectively controls several troublesome broadleaf weeds in grain sorghum. Foliar bleaching of sorghum leaves can occur but the symptoms are transient, and grain yields are not likely to be reduced.

Guar production in the United States is limited to a relatively small region in the semiarid southern Great Plains of Texas and Oklahoma. The lack of POST broadleaf herbicides is a potential limiting factor to increased production. A greenhouse study was initiated in 2001 at the Texas A&M Research Center near Vernon, TX to evaluate guar tolerance to 10 POST herbicides typically used in soybean or cotton. Guar seedlings were grown in pots, and herbicides with appropriate adjuvants were applied to 3-wk-old seedlings at the registered rate (1×) and twice (2×) the registered rate for soybean or cotton. The study was repeated twice, with six replications in each run. Twenty-eight d after treatment (DAT), visual injury and aboveground dry weight of viable biomass were recorded for each plant. Significant differences (P = 0.05) were noted among herbicides for visual injury and viable biomass. Little or no differences in visual injury and aboveground dry weight were observed between the control (no herbicide applied) and the 1× rate of 4-(2,4-dichlorophenoxy)butanoic acid, bentazon, or imazethapyr 28 DAT. A 1× application rate of acifluorfen, imazamox, thifensulfuron, or bromoxynil caused minor visual injury of 7 to 9% and a reduction in dry weight of 8 to 23%. Pyrithiobac and chlorimuron caused 38 and 47% visible injury and a 35 and 58% reduction in dry weight, respectively. Guar was most sensitive to lactofen, with the 1× rate causing 100% visual injury and no recoverable aboveground biomass. This greenhouse study identified three POST herbicide candidates with potential to control broadleaf weeds in guar without noticeable plant injury, and offers data to support herbicide registrations for this minor crop.

Experiments were conducted in a growth chamber to study alachlor and metolachlor metabolism in soil and corn and to determine if alachlor and metolachlor and their metabolites are exuded from corn roots to the growth medium. Alachlor was more readily absorbed by corn than was metolachlor. The absorption of alachlor and metolachlor was 72 and 55%, respectively, 10 d after seedling emergence (DAE). Alachlor and metolachlor were rapidly metabolized in corn, although metabolism rates were higher with metolachlor than with alachlor. Ten similar alachlor metabolites were detected in roots and shoots. In addition, two metabolites were detected only in the shoots, and one metabolite was detected only in the roots. Metolachlor metabolism in corn produced fewer metabolites than did alachlor metabolism. At 5 DAE, 10 and 9 metabolites were detected in shoots and roots, respectively. The metabolism of alachlor and metolachlor in soil showed patterns similar to the metabolism in corn but produced fewer metabolites. One unique alachlor metabolite appeared in soil but not in corn. Roots of corn seedlings treated with 14C-alachlor or 14C-metolachlor released significant amounts of radioactivity to the surrounding growth medium 5 d after treatment. Plants treated with alachlor released more radioactivity than did plants treated with metolachlor.

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.