Brian L. S. Olson

Efficacy and metabolism of MON 37500 in Triticum aestivum and weedy grass species as affected by temperature and soil moisture

Abstract 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. Nomenclature: MON 37500, 1-(2-ethylsulfonylimidazo[1,2-a]pyridin-3-ylsulfonyl)-3-(4,6-dimethoxypyrimidin-2-yl)urea; Triticum aestivum L., spring wheat ‘Len’; Aegilops cylindrica Host. AEGCY, jointed goatgrass; Avena fatua L. AVEFA, wild oat; Bromus tectorum L. BROTE, downy brome.

Differential Kochia (Kochia scoparia) Populations Response to Glyphosate

Abstract 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. Nomenclature: Glyphosate; kochia, Kochia scoparia (L.) Schrad.

Soil and crop response to stover removal from rainfed and irrigated corn

Excessive corn (Zea mays L.) stover removal for biofuel and other uses may adversely impact soil and crop production. We assessed the effects of stover removal at 0, 25, 50, 75, and 100% from continuous corn on water erosion, corn yield, and related soil properties during a 3‐year study under irrigated and no‐tillage management practice on a Ulysses silt loam at Colby, irrigated and strip till management practice on a Hugoton loam at Hugoton, and rainfed and no‐tillage management practice on a Woodson silt loam at Ottawa in Kansas, USA. The slope of each soil was <1%. One year after removal, complete (100%) stover removal resulted in increased losses of sediment by 0.36–0.47 Mg ha−1 at the irrigated sites, but, at the rainfed site, removal at rates as low as 50% resulted in increased sediment loss by 0.30 Mg ha−1 and sediment‐associated carbon (C) by 0.29 kg ha−1. Complete stover removal reduced wet aggregate stability of the soil at the irrigated sites in the first year after removal, but, at the rainfed site, wet aggregate stability was reduced in all years. Stover removal at rates ≥ 50% resulted in reduced soil water content, increased soil temperature in summer by 3.5–6.8 °C, and reduced temperature in winter by about 0.5 °C. Soil C pool tended to decrease and crop yields tended to increase with an increase in stover removal, but 3 years after removal, differences were not significant. Overall, stover removal at rates ≥50% may enhance grain yield but may increase risks of water erosion and negatively affect soil water and temperature regimes in this region.

Skip-Row Planting Patterns Stabilize Corn Grain Yields in the Central Great Plains

The highly variable climate of the central Great Plains makes dryland corn (Zea mays) production a risky enterprise. Twenty-three field trials were conducted across the central Great Plains from 2004 through 2006 to quantify the effect of various skip-row planting patterns and plant populations on grain yield in dryland corn production. A significant planting pattern by plant population interaction was observed at only one of 23 trials, suggesting that planting pattern recommendations can be made largely irrespective of plant population. In trials where skip-row planting patterns resulted in increased grain yields compared to the standard planting pattern treatment (every row planted using a 30-inch row spacing), the mean grain yield for the standard planting treatment was 44 bu/acre. In those trials where skip-row planting resulted in decreased grain yield compared to the standard planting pattern, the mean yield was 135 bu/acre. The plant two rows, skip two rows planting pattern is recommended for riskaverse growers in the central Great Plains where field history or predictions suggest likely grain yields of 75 bu/acre or less. Planting one row and skipping one row is recommended for growers with moderate risk-aversion and likely yield levels of 100 bu/acre or less.

Pyroxasulfone with and without Sulfentrazone in Sunflower (Helianthus annuus)

Abstract 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. Nomenclature: Pyroxasulfone (KIH-485); sulfentrazone; foxtail barley, Hordeum jubatum L. HORJU; green foxtail, Setaria viridis (L.) Beauv. SETVI; large crabgrass, Digitaria sanguinalis (L.) Scop. DIGSA; marshelder, Iva xanthifolia Nutt. IVAXA; Palmer amaranth, Amaranthus palmeri S. Wats. AMAPA; prostrate pigweed, Amaranthus blitoides S. Wats AMABL; wild buckwheat, Polygonum convolvulus L. POLCO; sunflower, Helianthus annuus L

Preemergence Herbicide Efficacy and Phytotoxicity in Grain Sorghum

Abstract 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. Nomenclature: Acetochlor; atrazine; flufenacet; KIH-485, 3-[(5-difluoromethoxy-1-methyl-3-trifluoromethylpyrazol-4-yl)methylsulfonyl]-4,5-dihydro-5,5-dimethylisoxazole; s-metolachlor; green foxtail, Setaria viridis (L.) Beauv. SETVI; large crabgrass, Digitaria sanguinalis (L.) Scop. DIGSA; shattercane, Sorghum bicolor (L.) Moench SORVU; grain sorghum, Sorghum bicolor (L.) Moench.

MON 37500 efficacy as affected by rate, adjuvants, and carriers.

Abstract: Field research was conducted to determine effects of application rate, spray adjuvants, and spray carriers on visible control of downy brome, jointed goatgrass, and cheat and potential injury to wheat by MON 37500. MON 37500 at 24 and 46 g/ha with and without a methylated seed oil or nonionic surfactant and carriers of water, urea ammonium nitrate (UAN), and a 1:1 water/UAN combination were applied to the weeds at the one- to four-leaf stage. Cheat was the most susceptible weed to MON 37500, with control consistently above 87% with all treatments except MON 37500 at 24 g/ha in water 26 weeks after treatment. Downy brome control was more variable, with ratings ranging from 50 to 99% among treatments. For jointed goatgrass, only moderate stunting was observed from all MON 37500 applications. Both wheat varieties showed early season injury after MON 37500 was applied with UAN and either adjuvant; however, no visible injury or yield reduction to either wheat variety was noticed at harvest. Nomenclature: MON 37500, 1-(2-ethylsulfonylimidazo[1,2-a]pyridin-3-ylsulfonyl)-3-(4,6-dimethoxypyrimidin-2-yl)urea; UAN, urea ammonium nitrate–28% N; jointed goatgrass, Aegilops cylindrica Host. #3 AEGCY; cheat, Bromus secalinus L. # BROSE; downy brome, Bromus tectorum L. # BROTE; hard-red winter wheat, Triticum aestivum L.; Jagger; ‘2137’. Abbreviations: WAT, weeks after treatment.

Alachlor and metolachlor transformation pattern in corn and soil

Abstract 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. Nomenclature: Alachlor; metolachlor; corn, Zea mays ‘Patriot 6168’.

Weed Control and Crop Safety with Premixed Pyrasulfotole and Bromoxynil in Grain Sorghum

Abstract 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. Nomenclature: Atrazine; bromoxynil; dicamba; pyrasulfotole; 2,4-D; common lambsquarters; Chenopodium album L.; common sunflower; Helianthus annuus L.; ivyleaf morningglory; Ipomoea hederacea Jacq.; kochia; Kochia scoparia (L.) Schrad.; Palmer amaranth; Amaranthus palmeri S. Wats.; puncturevine; Tribulus terrestris L.; redroot pigweed; Amaranthus retroflexus L.; tumble pigweed; Amaranthus albus L.; velvetleaf; Abutilon theophrasti Medik.; grain sorghum; Sorghum bicolor (L.) Moench. Resumen Se realizaron experimentos de campo con sorgo para grano, en cinco localidades en Kansas en 2009 y 2010, para evaluar la eficacia y la seguridad en el cultivo de aplicaciones tempranas a intermedias POST (EMPOST) y tardías POST (LPOST) de pre-mezclas de pyrasulfotole y bromoxynil (PYRA&BROM) en combinaciones en mezclas en tanque con atrazine o atrazine más 2,4-D ester o dicamba comparadas a bromoxynil más atrazine. PYRA&BROM a 244 ó 300 g ai ha−1 más atrazine a 560 g ai ha−1 aplicado EMPOST controló especies de amaranto (Amaranthus palmeri, Amaranthus albus, y Amaranthus retroflexus), Kochia scoparia, Abutilon theophrasti, Helianthus annuus, Ipomoea hederacea y Chenopodium album 93% o más. El control de Tribulus terrestris en tres localidades varió entre 85 y 99%. El control de la mayoría de las especies de malezas no mejoró al incrementar la dosis PYRA&BROM de 244 a 300 g ai ha−1 o al mezclar en tanque 2,4-D o dicamba con PYRA&BROM más atrazine. Sin embargo, el control de I. hederacea fue mejorado en LPOST al agregar 2,4-D o dicamba a 140 g ai ha−1. En ninguna instancia, ninguno de los tratamientos PYRA&BROM brindaron un control de malezas mayor al brindado por bromoxynil más atrazine 281 + 560 g ha−1 cuando se aplicó EMPOST, pero en la mayoría de las instancias los tratamientos PYRA&BROM fueron más efectivos que bromoxynil más atrazine aplicados LPOST. Generalmente, los tratamientos PYRA&BROM fueron más efectivos cuando se aplicaron EMPOST que LPOST, especialmente cuando se agregó 2,4-D o dicamba. Los tratamientos PYRA&BROM más atrazine causaron blanqueamiento foliar en el sorgo a 7 ± 3 días después del tratamiento, pero este se recuperó completamente en 2 a 4 semanas y los rendimientos de grano no se redujeron. El mezclar en tanque dicamba con PYRA&BROM y atrazine ocasionalmente redujo la respuesta visible del cultivo en comparación con PYRA&BROM más atrazine. Nuestros resultados indican que PYRA&BROM más atrazine con o sin 2,4-D o dicamba controla selectivamente malezas de hoja ancha problemáticas en el sorgo para grano. El blanqueamiento foliar de hojas de sorgo puede ocurrir, pero los síntomas son transitorios, y las reducciones en rendimientos de grano son poco probables.

Volunteer corn in fallow

Introduction Volunteer corn is a common weed in the fallow phase of wheat-corn-fallow in western Kansas and the west central Great Plains. No-till increases precipitation storage, reduces soil erosion, and often increases crop yields when compared to conventional-till. As a result, many producers have adopted no-till cropping systems that use glyphosate extensively for weed control in fallow. Because most of the corn grown is herbicide-tolerant, volunteer corn in fallow may not be controlled with glyphosate. Failing to control weeds in fallow can reduce soil moisture storage and subsequent crop yield.