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Martin M. Williams II

Sweet corn is planted over a 3-month period in the north central United States to extend availability for fresh market and processing; however, the extent to which development and growth of sweet corn changes during this period is unreported. Field experiments were conducted in 2006 and 2007 to determine the effect of five planting dates, ranging from mid-April to early July, on sweet corn establishment, growth, and yield components. Day length at the time of silking decreased from 15.1 h in the mid-April planting to 13.7 h in the early July planting. Development took 13 to 25 fewer days from emergence to silking for the hybrid ‘BC0805’, an 82-day augmented sugar enhancer endosperm type, as planting was delayed from mid-April to early July. Maximum height generally increased through planting dates with as much as 23% taller plants in early July versus mid-April planted sweet corn. While leaf mass was unaffected by planting date, maximum leaf number and rate of leaf appearance steadily decreased with later planting dates. Lower reproductive and total biomass at silking as well as marketable ear yield components were lowest in the early July planting date and were associated with presence of maize dwarf mosaic virus in leaf samples. In response to environmental conditions, the crop canopy undergoes distinct morphological changes as planting is delayed, and those changes may have implications for crop production.

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Martin M. Williams II

Improvements in plant density tolerance have played an essential role in grain corn yield gains for ≈80 years; however, plant density effects on sweet corn biomass allocation to the ear (the reproductive ‘sink’) is poorly quantified. Moreover, optimal plant densities for modern white-kernel shrunken-2 (sh2) hybrids are unknown. The objectives of the study were to 1) quantify the effect of plant density and hybrid on the reproductive sink of sweet corn and 2) determine optimal plant densities for white-kernel sh2 sweet corn. Field experiments were conducted across 2 years on 10 white-kernel sh2 hybrids grown at plant densities ranging from 4.3 to 8.6 plants/m2. Increasing plant density negatively influenced reproductive sink characteristics of individual sweet corn plants, including linear decreases in ear shoots/plant, marketable ears/plant, ear length, filled ear length, ear mass/plant, and kernel mass/plant. Reproductive traits varied widely among hybrids, including ear mass (15.6–20.6 Mt·ha−1) and recovery (32.3% to 42.4%), which is the contribution of fresh kernel mass to total ear mass. Hybrids had a common response to plant density, whereby ear yield was optimized at 5.5 plants/m2 and gross profit margin was optimized at 6.1 plants/m2. Plant density data from 586 growers’ fields suggest current seeding rates have optimized the reproductive sink size for today’s white-kernel sh2 hybrids. However, room exists for improving plant density tolerance, yield, and profitability.

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Martin M. Williams II

Yield stability (simply “stability”) is a crop genotype’s performance over a range of environmental conditions, such that a specific genotype may be less sensitive to environmental change (i.e., above-average stability) or more sensitive to environmental change (i.e., below-average stability) relative to other genotypes. The ideal genotype for most crops is believed to have both above-average yield and above-average stability. The objective of the study was to determine the pattern of genotype adoption and use of processing sweet corn in relation to yield and stability. I hypothesized that if yield and stability influence decision-making on genotype choice, then differences among commercial genotypes in such traits would relate to the pattern of adoption and use of those genotypes. Stability analyses of ear mass and case production were conducted on processing sweet corn genotypes grown in varied environments of the United States’ Upper Midwest and Pacific Northwest. Yield and stability of the 12 most tested genotypes were then related to the extent of their adoption and use by a sweet corn processing company over a 20-year period. Although some genotypes exhibited above-average yield or above-average stability, data revealed there was no evidence of both traits in individual genotypes currently used in processing sweet corn. Adoption of genotypes with below-average yield or stability was less than other genotypes. Genotype adoption pattern of case production showed the greatest proportion of adoption of above-average stability genotypes. Stable case production across all environments is a more important trait in a genotype to the sweet corn processor than a genotype with record yields under favorable conditions. This conclusion is consistent with the industry’s need to have a predictable level of performance in the processing facility, through which all raw product must flow, on a daily basis for the about three-month window of harvest in the northern United States.

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Martin M. Williams II and Carl A. Bradley

Poor crop establishment is a major problem in edamame (Glycine max), a specialty type of soybean produced in locations throughout the United States. The objective of this research was to quantify the extent to which seed treatment with fludioxonil + mefenoxam improves seedling emergence of edamame. Emergence characteristics of fludioxonil + mefenoxam-treated and nontreated seed of 30 cultivars were characterized in field conditions over 2 years. Edamame cultivars used in the study exhibited poor field emergence in a previous study despite high germinability. Seed treatment with fludioxonil + mefenoxam at 2.5 and 3.75 g/100 kg seed, respectively, improved crop emergence 33% to 47% more than the nontreated control. The emergence rate (days to 50% emergence) was improved the most by the seed treatment for several cultivars that were generally slow to emerge. Crop establishment is essential for further development of domestic edamame production. Seed treatment with fludioxonil + mefenoxam, at the rate currently registered for use on grain-type soybean, offers one approach to help vegetable growers improve edamame seedling emergence.

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Laura E. Crawford and Martin M. Williams II

Edamame growers currently rely heavily on planting depth recommendations for grain-type soybean, despite stark differences in seed characteristics between the two types of cultivars, most notably seed size. Therefore, the objective of the study was to determine the effects of planting depth and seed size on edamame emergence. A popular edamame cultivar used in commercial production was sorted into “small” (23.7 g/100-seed) and “large” (36.8 g/100-seed) seed-size classes, then planted at depths of 1.0, 2.0, 3.0, and 5.0 cm in field experiments. Experiments were conducted in four environments as a split-plot experimental design with four replications. Seed size did not influence total emergence; however, small seed emerged 10% faster than large seed. Although planting depth recommendations for grain-type soybean are 3.2 to 4.5 cm, our results showed edamame emerged more completely and quicker at the shallowest depths examined. The research could be expanded to capture greater diversity in growing environments and crop cultivars; however, the vegetable industry now has research-based information to guide preliminary recommendations regarding appropriate planting depth of edamame.

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Daljeet S. Dhaliwal and Martin M. Williams II

Consumer demand for edamame [Glycine max (L.) Merr.], the vegetable version of soybean (Glycine max), has grown during the past decade in North America. Domestic production of edamame is on the rise; however, research to guide fundamental crop production practices, including knowledge useful for developing appropriate recommendations for crop seeding rate, is lacking. Field experiments near Urbana, IL, were used to quantify edamame response to plant density and determine the economically optimal plant density (EOPD) of machine-harvested edamame. Crop growth and yield responses to a range of plant densities (24,700 to 395,100 plants/ha) were quantified in four edamame cultivars (AGS 292, BeSweet 292, Gardensoy 42, and Midori Giant) across 2 years. Plots were harvested with the Oxbo BH100, a fresh market bean harvester. In general, as plant density increased, branch number and the ratio of pod mass to vegetative mass decreased, while plant height and leaf area index increased. Recovery, the percent of marketable pods in the machine-harvested sample, varied among cultivars from 86% to 95%. Results identified the EOPD for machine-harvested edamame ranged from 87,000 to 120,000 plants/ha. When considering the effect of plant density on plant morphology, as well as seeding cost, harvester efficiency, recovery, and marketable pod yield, edamame EOPDs are considerably lower than seeding rates of up to 344,200 seeds/ha recommended in recent publications.

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Martin M. Williams II, Rick A. Boydston and Adam S. Davis

Research in dent corn has found significant variation in crop/weed competition for light among hybrids. However, little has been published on the extent of variation in sweet corn competitive ability. Field studies were conducted under weed-free conditions to quantify canopy development and light environment among three sweet corn hybrids and to determine associations among canopy characteristics to crop yield. An early-season hybrid (Spirit) and two midseason hybrids (WHT2801 and GH2547) were grown at experimental sites located near Urbana, Ill., and Prosser, Wash., in 2004 and 2005. Maximum leaf area index (LAI) and intercepted photosynthetically active radiation (PAR) was typically highest for GH2547 and lowest for Spirit. Most differences in vertical LAI among hybrids was observed above 60 and 150 cm in Illinois and Washington, respectively, with WHT2801 and GH2547 having leaf area distributed higher in the canopy than Spirit. Both number and mass of marketable ears were positively correlated with maximum relative growth rate (correlation coefficients 0.60–0.81), leaf area duration (0.68–0.79), total LAI (0.56–0.74) at R1, and intercepted PAR (0.74–0.83) at R1. Differences in canopy properties and interception of solar radiation among Spirit, WHT2801, and GH2547 lead us to hypothesize that variation in weed-suppressive ability exists among hybrids. Future testing of this hypothesis will provide knowledge of interactions specific to sweet corn useful for developing improved weed management systems.

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Yim F. So, Martin M. Williams II and Jerald K. Pataky

Knowledge of cultivar-specific information on crop tolerance, the ability of the crop to endure competitive stress from weeds, has garnered recent interest in organic crop production. Twenty-five commercial sweet corn hybrids from nine seed companies were grown in the presence and absence of wild-proso millet (Panicum miliaceum L.) to 1) quantify tolerance in crop growth and yield to weed interference; 2) determine associations between tolerance in crop growth and yield; and 3) identify hybrids differing in tolerance to weed interference. Despite large differences in canopy architecture among hybrids, crop height and leaf uprightness were minimally affected by weed interference. In contrast, wild-proso millet interference reduced ear number 11% to 98% and ear mass 24% to 82% depending on the hybrid. The ability of a hybrid to make small growth adjustments in the presence of wild-proso millet appeared to have no relationship to yield tolerance. The least competitive hybrids were ‘ACX1413’, ‘Optimum’, ‘Quickie’, ‘Spring Treat’, and ‘Sugar Buns’. The most competitive hybrids were ‘Code128’, ‘Coho’, ‘El Toro’, ‘EX 8716622’, and ‘Legacy’. Although some exceptions were observed, in general, the longer-maturity processing hybrids were more competitive with wild-proso millet than the earlier-maturing fresh market hybrids.

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Jerald K. Pataky, Michael D. Meyer, Joseph D. Bollman, Chris M. Boerboom and Martin M. Williams II

Some sweet corn (Zea mays L.) hybrids and inbreds can be severely injured or killed after postemergence applications of certain P450-metabolized herbicides. Consequently, existing hybrids are regularly evaluated for tolerance to new herbicides, and new hybrids are evaluated for tolerance to existing herbicides. In 2005 and 2006, the University of Wisconsin Cooperative Extension Service coordinated 12 trials in six states in which a total of 149 sweet corn hybrids were evaluated for tolerance to three cytochrome P450-metabolized herbicides: nicosulfuron, foramsulfuron, and mesotrione. Hybrid responses differed substantially within and among locations. The objective of this study was to determine if alleles affecting herbicide sensitivity (e.g., cytochrome P450 alleles) were associated with differences in levels of injury to sweet corn hybrids in these trials. Based on responses of F2 progeny to nicosulfuron, foramsulfuron, and mesotrione, 95 hybrids were classified as homozygous for alleles conditioning herbicide tolerance; 47 hybrids were classified as heterozygous with one allele each conditioning tolerance and sensitivity; and two hybrids were classified as homozygous for alleles conditioning sensitivity. When trial mean levels of injury after applications of mesotrione, nicosulfuron, and foramsulfuron in the herbicide trials were above 1%, 4%, and 5%, respectively, the response of the three genotypic classes of hybrids followed a consistent pattern. Homozygous-sensitive hybrids were injured most severely and often were killed by the two acetolactate synththase-inhibiting herbicides, nicosulfuron and foramsulfuron. Heterozygous hybrids had an intermediate response to all three herbicides that was more similar to homozygous-tolerant hybrids than homozygous-sensitive hybrids; however, injury to heterozygous hybrids was 1.5 to 2.3 times greater and significantly (P < 0.05) different from homozygous-tolerant hybrids based on t tests of group means and comparisons of predicted values from regressions of genotypic means on trial means. Based on responses of the 149 hybrids in this trial, the potential for and level of crop injury from use of nicosulfuron, mesotrione, and foramsulfuron on any specific sweet corn hybrid is conditioned largely by alleles at a single locus.

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Martin M. Williams II, Loyd M. Wax, Jerald K. Pataky and Michael D. Meyer

Over the last two decades, sweet corn injury from postemergence herbicides has resulted in routine screening of combinations of new and existing hybrids and herbicides. Sensitivity of sweet corn to several cytochrome P450-metabolized herbicides is simply inherited and has a common genetic basis, a single P450 locus that may account for a large amount of the variation in sweet corn injury commonly observed among screening trials. Using data from 13 hybrid-herbicide screening trials, the objective of this work was to determine the extent to which injury from P450-metabolized herbicides was associated with the genotypes of hybrids at a locus affecting herbicide sensitivity. Of the 703 hybrids evaluated in the University of Illinois sweet corn hybrid nurseries from 2002 to 2007, previous work showed that a total of 104, 70, and nine of the hybrids were known to be homozygous-tolerant, heterozygous, or homozygous-sensitive, respectively, for an allele affecting herbicide response. Nurseries from 2002 to 2007 included six trials with mesotrione, three trials with nicosulfuron, and one trial each with foramsulfuron, tembotrione, halosulfuron, and carfentrazone. When means of hybrids in genotypic classes were compared, homozygous-sensitive hybrids were consistently injured more severely than homozygous-tolerant and heterozygous hybrids. When environmental conditions favored crop injury, heterozygous hybrids had an intermediate response that was closer to homozygous-tolerant hybrids than homozygous-sensitive hybrids. These data are further evidence that the probability of injury from several P450-metabolized herbicides, including mesotrione, nicosulfuron, foramsulfuron, tembotrione, halosulfuron, and carfentrazone, is highest in homozygous-sensitive hybrids and least in homozygous-tolerant hybrids and that variability of responses among sweet corn hybrids to these P450-metabolized herbicides can be explained largely by the genotype of a hybrid at a single locus.