David C. Hooker

Modeling effects of environment, insect damage, and Bt genotypes on fumonisin accumulation in maize in Argentina and the Philippines

Fumonisins are common contaminants of maize (Zea mays L.) grain products, especially in countries where maize is a major constituent of the diet and are harmful to human and animal health. There is a need to better define environmental conditions that favor fumonisin accumulation in the grain of maize. The impacts of biotic and abiotic factors, and hybrids containing the Cry1Ab protein from Bacillus thuringiensis (Bt), were associated with fumonisin accumulation in the grain of maize across contrasting environments in Argentina and the Philippines between 2000 and 2002. Average fumonisin concentrations in grain samples varied from 0.5 to 12 μg g−1 across field locations in Argentina, and from 0.3 to 1.8 μg g−1 across locations in the Philippines. The ratio of fumonisin B1 to fumonisin B2 was <3.0 in four of nine locations in Argentina, which proved to be due to a higher prevalence of Fusarium proliferatum in those locations. Most of the variability of total fumonisins among maize grain samples was explained by location or weather (47%), followed by insect damage severity in mature ears (17%), hybrid (14%), and with the use of Bt hybrids (11%). In Argentina, where conditions were more favorable for accumulation of fumonisin in the years considered, fumonisin concentrations were lower in Bt hybrids compared to their genetic isolines by an average of 40%. A model was developed to predict fumonisin concentration using insect damage to ears and weather variables as predictors in the model. Four periods of weather around silking were identified as critical for fumonisin concentrations at harvest. The model accounted for 82% of the variability of total fumonisin across all locations in 2 years of the study.

Effect of previous crop, tillage, field size, adjacent crop, and sampling direction on airborne propagules of Gibberella zeae/Fusarium graminearum, fusarium head blight severity, and deoxynivalenol accumulation in winter wheat

The objective of this study was to determine the relative importance of previous and adjacent crop, tillage, field size, and sampling direction on the number of viable airborne propagules of Gibberella zea/Fusarium graminearum trapped at anthesis, fusarium head blight (FHB) index, percentage of seeds infected with F. graminearum, and deoxynivalenol (DON) accumulation in seed of winter wheat from commercial fields across southwestern Ontario. More viable airborne propagules of G. zeae/F. graminearum were trapped in wheat fields that were planted on corn or wheat stubble than in wheat fields in which previous crops were nonhosts. Previous crop, field size, and tillage interacted to affect the FHB index, DON accumulation, and percentage of seeds infected with F. graminearum; large fields where corn was planted one year previous to wheat with minimum or no tillage had the highest values. Adjacent crops (nonhost, corn, and wheat) affected the number of viable airborne propagules trapped, FHB index, and percentage of seeds infected with F. graminearum. Sampling direction (east–west) did not have a significant effect on any variable. The number of viable airborne propagules trapped at wheat anthesis was not predictive of FHB symptoms or DON accumulation in grain.

Agronomic and environmental impacts on concentrations of deoxynivalenol and fumonisin B1 in corn across Ontario

Relative effects of year, weather, and cultural practices on concentrations of deoxynivalenol (DON) and fumonisin B1 (FB1) were compared in grain that was harvested from corn fields across Ontario, Canada, from 1993 to 2000. Overall, between 59% and 88% of grain samples were contaminated with DON ≥ 0.2 μg g−1 in each year of the survey. From 1997 to 2000, between 17% and 56% of samples were contaminated with FB1 = 1.0 μg g−1, which is higher than first reported for fumonisins in 1993 in Ontario (9%). Deoxynivalenol and FB1 were mostly associated with corn hybrid and year-to-year effects caused by weather or geographical differences in the 8-year study. Among all cultural practices, corn hybrid was the most influential for both DON and FB1 accumulation, accounting for 25% (P < 0.0001) of the variation in both toxins across years. The effect due to year (or to weather, perhaps) accounted for 12% (P < 0.0001) of the variation in concentration of DON and 19% of the variation in FB1. When the effects of hybrid and year were considered in the same model, 42% of the variability of both toxins was accounted for in the model. A higher incidence of DON and fumonisin was detected for corn grown after wheat than for corn after corn. These results demonstrate that predictive models for DON in corn need to include the sensitivity of corn hybrids to infection by Fusarium spp. or mycotoxin accumulation, in addition to the response caused by weather. In practice, the best chance for corn growers to reduce DON and FB1 in harvested grain, when comparing cultural practices, is to select hybrids that are known to have more resistance to fusarium ear rots or mycotoxin accumulation than others.

Corn yield loss estimates due to diseases in the United States and Ontario, Canada from 2012 to 2015.

Annual decreases in corn yield caused by diseases were estimated by surveying members of the Corn Disease Working Group in 22 corn-producing states in the United States and in Ontario, Canada, from 2012 through 2015. Estimated loss from each disease varied greatly by state and year. In general, foliar diseases such as northern corn leaf blight, gray leaf spot, and Goss’s wilt commonly caused the largest estimated yield loss in the northern United States and Ontario during nondrought years. Fusarium stalk rot and plant-parasitic nematodes caused the most estimated loss in the southernmost United States. The estimated mean economic loss due to yield loss by corn diseases in the United States and Ontario from 2012 to 2015 was

Farm-level profitability analysis of alternative tillage systems on clay soils

76.51 USD per acre. The cost of disease-mitigating strategies is another potential source of profit loss. Results from this survey will provide scientists, breeders, government, and educators with data to help inform and prioritize research, policy, and educational efforts in corn pathology and disease management. M U E L L E R E T A L . , P L A N T H E A L T H P R O G R E S S 1 7 (2 0 1 6 )

The effect of artificial selection on phenotypic plasticity in maize

Crop yields, production costs, and net returns for seven alternative conservation tillage (including five reduced tillage and two no-till) treatments were compared with a conventional tillage (CT) treatment for a corn (Zea mays L.) – soybean (Glycine max L. Merr) rotation for two clay soils in southwestern Ontario. There was no significant difference in corn and soybean yields between the CT and the conservation tillage systems at either location, although actual yields tended to be highest for CT management. Tillage treatments that used a common set of machinery for corn and soybean production generated savings in annual machinery costs. Variable costs were lowest for the reduced-tillage treatments and highest for the two no-till treatments due to higher equipment expenditures and additional herbicide requirements. For a given location, there was often no significant difference in net returns between CT and the conservation tillage treatments, although average net returns for the corn–soybean cropping sy...

Alternative weed management strategies in conservation tillage systems for white beans (Phaseolus vulgaris L.)

Remarkable productivity has been achieved in crop species through artificial selection and adaptation to modern agronomic practices. Whether intensive selection has changed the ability of improved cultivars to maintain high productivity across variable environments is unknown. Understanding the genetic control of phenotypic plasticity and genotype by environment (G × E) interaction will enhance crop performance predictions across diverse environments. Here we use data generated from the Genomes to Fields (G2F) Maize G × E project to assess the effect of selection on G × E variation and characterize polymorphisms associated with plasticity. Genomic regions putatively selected during modern temperate maize breeding explain less variability for yield G × E than unselected regions, indicating that improvement by breeding may have reduced G × E of modern temperate cultivars. Trends in genomic position of variants associated with stability reveal fewer genic associations and enrichment of variants 0–5000 base pairs upstream of genes, hypothetically due to control of plasticity by short-range regulatory elements.Breeding has increased crop productivity, but whether it has also changed phenotypic plasticity is unclear. Here, the authors find maize genomic regions selected for high productivity show reduced contribution to genotype by environment variation and provide evidence for regulatory control of phenotypic stability.

Glyphosate-Resistant Common Ragweed (Ambrosia artemisiifolia) Control with Postemergence Herbicides and Glyphosate Dose Response in Soybean in Ontario

White bean producers often perceive that increased herbicide inputs are required with the adoption of conservation tillage. Acceptance of conservation tillage systems for this crop would increase if effective weed management practices were assured. In 1991 and 1992, various weed management strategies were evaluated in white bean (Phaseolus vulgaris L.) grown with three tillage systems at two sites in southern Ontario. Experiments were newly established each year following corn harvested for grain. Primary tillage treatments were fall moldboard plowing, fall chisel plowing, and first-year no-till. Combinations of mechanical weeding, metobromuron [3–(4–bromophenyl)–1–methoxy–1–methylurea] herbicide broadcasted at two rates, and a band application of the herbicide were investigated in each tillage system. Timely rotary hoeing reduced weed numbers in moldboard plow and chisel plow treatments, but was not effective in no-till. Weeds were adequately controlled in all tillage systems with mechanical treatments f...

Biologically effective rate of sulfentrazone applied pre-emergence in soybean

Abstract Field trials were conducted in Ontario in 2013 and 2014 in soybean to determine the efficacy of POST herbicides on common ragweed resistant to group 2 and group 9 herbicides. Glyphosate dose-response experiments were conducted in the field on two resistant common ragweed populations and one susceptible population. None of the POST herbicides evaluated provided 80% control of glyphosate-resistant (GR) common ragweed. The most effective POST herbicide mixture was glyphosate (Monsanto Canada Inc., 67 Scurfield Blvd., Winnipeg, Manitoba, Canada) plus fomesafen(Syngenta Canada Inc., 140 Research Lane, Research Park Guelph, Ontario, Canada), which provided 68 to 98% control of GR common ragweed. Chlorimuron, cloransulam, imazethapyr, and thifensulfuron provided control similar to glyphosate alone. An application of glyphosate/fomesafen reduced biomass by as much as 95%. Glyphosate plus acifluorfen reduced GR common ragweed biomass by as much as 92%. The remaining POST herbicide tank mixes evaluated reduced GR common ragweed biomass by less than 80%. Glyphosate plus bentazon, glyphosate plus chlorimuron, and glyphosate plus thifensulfuron resulted in soybean yields similar to the weedy control, with yield reductions of 70, 62, and 73%, respectively. An application of glyphosate plus fomesafen or glyphosate/fomesafen had the lowest soybean yield reductions of 29 and 34%, respectively. The resistant biotype required a 2- to 28-fold increase in glyphosate dose compared to the susceptible population to achieve 50% control. Nomenclature: Acifluorfen; bentazon; chlorimuron; cloransulam; fomesafen; glyphosate; imazethapyr; thifensulfuron; common ragweed, Ambrosia artemisiifolia L.; soybean, Glycine max. L. Merr. Resumen En 2013 y 2014 en Ontario, se realizaron estudios de campo en soja para determinar la eficacia de herbicidas POST sobre Ambrosia artemisiifolia resistente a herbicidas de los grupos 2 y 9. Experimentos de respuesta a dosis de glyphosate fueron realizados en el campo con dos poblaciones resistentes y una población susceptible de A. artemisiifolia. Ninguno de los herbicidas POST evaluados brindó >80% de control de A. artemisiifolia resistente a glyphosate (GR). Las mezclas de herbicidas POST más efectivas fueron glyphosate más fomesafen, las cuales brindaron 68 a 98% de control de A. artemisiifolia GR. Chlorimuron, cloransulam, imazethapyr, y thifensulfuron brindaron un control similar a glyphosate solo. Una aplicación de glyphosate/fomesafen redujo la biomasa hasta 95%. Glyphosate más acifluorfen redujo la biomasa de A. artemisiifolia GR hasta 92%. Glyphosate más bentazon, glyphosate más chlorimuron, y glyphosate más thifensulfuron resultaron en rendimientos de soja similares al testigo con malezas, con reducciones en el rendimiento de 70, 63, y 73%, respectivamente. Una aplicación de glyphosate más fomesafen o glyphosate/fomesafen tuvieron las menores reducciones en el rendimiento de la soja con 29 y 34%, respectivamente. El biotipo resistente requirió un incremento de 2 a 28 veces en la dosis de glyphosate al compararse con la población susceptible para alcanzar 50% de control.

Efficacy of Saflufenacil for Control of Glyphosate-Resistant Horseweed (Conyza canadensis) as Affected by Height, Density, and Time of Day

Walsh, K. D., Soltani, N., Hooker, D. C., Nurse, R. E. and Sikkema, P. H. 2015. Biologically effective rate of sulfentrazone applied pre-emergence in soybean. Can. J. Plant Sci. 95: 339-344. Sulfentrazone is a protoporphyrinogen (PPO)-inhibiting herbicide under evaluation for use in soybean in Ontario, Canada. The primary objective of this study was to determine the dose of sulfentrazone applied pre-emergence (PRE) needed to provide 50 and 90% control of redroot pigweed, common ragweed, common lambsquarters and green foxtail. Seven field trials were conducted over a 3-yr period (2007, 2008 and 2009) in southwestern Ontario to evaluate the efficacy of sulfentrazone applied PRE at doses ranging from 26 to 1120 g a.i. ha-1. The doses of sulfentrazone applied PRE to reduce redroot pigweed, common ragweed, common lambsquarters and green foxtail dry weight by 50% were 104, 139, 15 and 65 g a.i. ha-1; doses of 241, 514, 133 and 721 g a.i. ha-1 of sulfentrazone were required for 90% reduction in above-ground biomass of those weed species, respectively. Sulfentrazone applied PRE caused soybean injury only at 560 and 1120 g a.i. ha-1, with 6 and 13% soybean injury at 4 wk after herbicide application (WAT), respectively. Weed control provided by sulfentrazone applied PRE at a dose of 600 g a.i. ha-1 was sufficient to maintain 90% of the soybean yield compared with the weed-free control. Therefore, PRE application of sulfentrazone has the potential to provide excellent (>90%) control of selected weeds with minimal to no crop injury; however, weed control varied by species, and thus broad spectrum weed control is not feasible using sulfentrazone alone.