Richard K. Zollinger

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

A Test Method for Evaluating Water Conditioning Adjuvants

Glyphosate is a weak acid herbicide and can bind with antagonistic salts in the spray carrier. Diammonium sulfate (AMS) is commonly used as an adjuvant with glyphosate to enhance activity and overcome antagonistic salts. Water conditioning (WC) adjuvants are used at low rates and are used as AMS replacement adjuvants. However, an ASTM approved method for testing WC adjuvants has not been established. Appropriate research parameters were used to test the water conditioner definition. Glyphosate plus NIS and glyphosate plus AMS and nonionic surfactant (NIS) were used as standards from comparing WC adjuvants. WC were compared to NIS and AMS plus NIS to determine the potential to reduce or eliminate antagonism between glyphosate and antagonistic cations. Velvetleaf was a good indicator to show antagonism, the ability for AMS and WC adjuvants to overcome antagonism, and also show greater bioefficacy. Velvetleaf, a mixture of broadleaf species, and a mixture of grass species all showed similar response to WC adjuvants. Studies to test water conditioning adjuvants were conducted at multiple locations provided a high degree of precision.

Influence of Adjuvants on Weed Control from Tribenuron

Tribenuron is a slow acting sulfonylurea herbicide that becomes more soluble as spray solution pH increases. Data from field research show differences in adjuvant enhancement of tribenuron. The most effective adjuvants with tribenuron were methylated seed oil and basic pH blend adjuvants, but the greatest activity occurred when applied together. The order of tribenuron enhancement from adjuvants was: methylated seed oil & basic pH blend>methylated seed oil=basic pH blend>crop oil concentrate=nonionic surfactant & organosilicone>nonionic surfactant=nonionic surfactant&water conditioner>nonionic surfactant&organosilicone. Methylated seed oil & basic pH blend adjuvant did not entirely overcome tribenuron antagonism of quizalofop. Tribenuron, applied as a soluble granule (SG) formulation and having properties to increase spray solution pH, provided similar weed control at a reduced rate as compared to the commercial extruded paste (XP) formulation of tribenuron. Limited research suggests that applying adjuvants on an area basis provides greater adjuvant enhancement than if applied on a percent volume basis. This would be especially important as spray volume decreases. These results generally support the concept that herbicide solubilization and absorption are necessary to maximize foliar activity.

Weed Management in 2050: Perspectives on the Future of Weed Science

Abstract The discipline of weed science is at a critical juncture. Decades of efficient chemical weed control have led to a rise in the number of herbicide-resistant weed populations, with few new herbicides with unique modes of action to counter this trend and often no economical alternatives to herbicides in large-acreage crops. At the same time, the world population is swelling, necessitating increased food production to feed an anticipated 9 billion people by the year 2050. Here, we consider these challenges along with emerging trends in technology and innovation that offer hope of providing sustainable weed management into the future. The emergence of natural product leads in discovery of new herbicides and biopesticides suggests that new modes of action can be discovered, while genetic engineering provides additional options for manipulating herbicide selectivity and creating entirely novel approaches to weed management. Advances in understanding plant pathogen interactions will contribute to developing new biological control agents, and insights into plant-plant interactions suggest that crops can be improved by manipulating their response to competition. Revolutions in computing power and automation have led to a nascent industry built on using machine vision and global positioning system information to distinguish weeds from crops and deliver precision weed control. These technologies open multiple possibilities for efficient weed management, whether through chemical or mechanical mechanisms. Information is also needed by growers to make good decisions, and will be delivered with unprecedented efficiency and specificity, potentially revolutionizing aspects of extension work. We consider that meeting the weed management needs of agriculture by 2050 and beyond is a challenge that requires commitment by funding agencies, researchers, and students to translate new technologies into durable weed management solutions. Integrating old and new weed management technologies into more diverse weed management systems based on a better understanding of weed biology and ecology can provide integrated weed management and resistance management strategies that will be more sustainable than the technologies that are now failing.

Influence of Clethodim Formulation and Oil Adjuvants on Weed Control and Overcoming Herbicide Antagonism

Clethodim is a non-residual, foliar-applied herbicide that controls grass weeds in many major and minor crops in the United States. Grass control was evaluated in field trials conducted in 2003 and 2004 using commercial clethodim formulations of Select (240 g/L), Arrow (240 g/L), and Prism (113 g/L), and experimental clethodim formulations of V-10117 (226 g/L), V-10139 (192 g/L), and V10137 (113 g/L). Petroleum oil (PO) adjuvant was added to all clethodim treatments except V-10137. The V-10137 formulation of clethodim without petroleum oil (PO) adjuvant gave greater and faster grass control than other formulations of clethodim with PO. Adding PO adjuvant to V-10137 reduced activity except at reduced rates when additional PO or nonionic surfactant increased grass control. All clethodim formulations except Prism and V-10137 caused significant canola injury when applied at post-bolting. V-10137, without additional adjuvants, with less active ingredient concentration, and likely a higher adjuvant load has more grass activity at equivalent rates than other clethodim formulations with PO. Tribenuron applied with clethodim antagonized grass control from Select, Arrow, V-10117, and V-10139, but not V-10137. Grass control was reduced from 99 % when clethodim formulations (except V-10137) were applied alone, to 50 %–80 % when applied with tribenuron. Grass control from V-10137 applied alone or with tribenuron, with or without PO, was greater than 96 %. The K salt of glyphosate was antagonistic to Select and V-10137, but V-10137 overcame most of the antagonism. These results suggest V-10137 activity is greater than commercial clethodim formulations of Select or Arrow, may not require additional oil adjuvant for grass control, is effective with glyphosate, and can overcome tribenuron antagonism. Including an oil adjuvant with V-10137 may not increase grass control in some uses.

Spray droplet size and carrier volume effect on dicamba and glufosinate efficacy: Drop size and carrier volume efficacy effect

BACKGROUND Pesticide applications using a specific droplet size and carrier volume could maximize herbicide efficacy while mitigating particle drift in a precise and efficient manner. The objectives of this study were to investigate the influence of spray droplet size and carrier volume on dicamba and glufosinate efficacy, and to determine the plausibility of droplet-size based site-specific weed management strategies. RESULTS Generally, across herbicides and carrier volumes, as droplet size increased, weed control decreased. Increased carrier volume (187 L ha-1 ) buffered this droplet size effect, thus greater droplet sizes could be used to mitigate drift potential while maintaining sufficient levels of weed control. To mitigate drift potential and achieve satisfactory weed control (≥ 90% of maximum observed control), a 900 µm (Ultra Coarse) droplet size paired with 187 L ha-1 carrier volume is recommended for dicamba applications and a 605 µm (Extremely Coarse) droplet size across carrier volumes is recommended for glufosinate applications. Although general droplet size recommendations were created, optimum droplet sizes for weed control varied significantly across site-years. CONCLUSION Convoluted interactions occur between droplet size, carrier volume, and other application parameters. Recommendations for optimizing herbicide applications based on droplet size should be based on a site-specific management approach to better account for these interactions.

Effect of Hard Water and Ammonium Sulfate on Weak Acid Herbicide Activity

Glyphosate is a weak acid herbicide and can bind with calcium in the spray carrier. Diammonium sulfate is commonly used as an adjuvant with glyphosate to enhance phytotoxicity and overcome antagonistic effect of these cations. Most postemergence herbicides are also weak acid herbicides. Data is limited for other weak acid herbicides and the effect of diammonium sulfate in enhancing herbicide activity and overcoming antagonism. Field studies were conducted with aminopyralid, tembotrione, dicamba plus diflufenzopyr, and glufosinate to determine if (1) these weak acid herbicides are enhanced by ammonium, (2) if they are antagonized by calcium and magnesium in the spray solution, (3) if diammonium sulfate overcomes salt antagonism, and (4) if a previously published equation for the amount of ammonium sulfate required to overcome salt antagonism of glyphosate based on cation concentration in spray water correctly predicts to other weak acid herbicides. The activity of the four weak acid herbicides increased with the addition of ammonium to the spray solution, all were antagonized by calcium and magnesium, and diammonium sulfate overcame the antagonism. The previously published equation to calculate the amount the diammonium sulfate needed to overcome 500 and 1000 ppm hardness was accurate and can be used for these herbicides and possibly other weak acid herbicides.