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Charles L. Webber III and James W. Shrefler

Although CGM has been identified as an organic herbicide for weed control in turf and established vegetable plants, direct contact with vegetable seeds can decrease crop seedling development and plant survival by inhibiting root and shoot development. The objective of this research was to determine the impact of banded corn gluten meal applications on squash plant survival and yields. This factorial field study was conducted during Summer 2005 on 81-cm-wide raised beds at Lane, Okla., with two application configurations (banded and solid), two CGM formulations (powdered and granulated), two incorporation treatments (incorporated and nonincorporated), and three application rates (250, 500, and 750 g·m–2). The two CGM formulations at three application rates were uniformly applied in both banded and solid patterns on 19 Aug. The banded application created a 7.6-cm wide CGM-free planting zone in the middle of the raised bed. The CGM applications were then either incorporated into the top 2.5 to 5.0 cm of the soil surface with a rolling cultivator or left undisturbed on the soil surface. `Lemondrop' summer squash (Cucurbita pepo L.) was then direct-seeded into the center of the raised beds. When averaged across the other factors, there was no significant difference between powdered and granulated CGM formulations or incorporating and nonincorporating the CGM for either squash plant survival or yields. As the CGM application rates increased the plant survival and yields decreased. Banded application resulted in significantly greater crop safety (90% plant survival) and yields (445 cartons/ha) than the broadcast (solid) applications (45% plant survival and 314 cartons/ha). The research demonstrated the potential usefulness of CGM in direct-seeded squash production, if used in banded application configuration.

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Charles L. Webber III and James W. Shrefler

Corn gluten meal (CGM) has been identified as a potential organic preemergence and preplant-incorporated herbicide. It is an environmentally friendly material that has demonstrated ability to decrease seedling development and plant survival by inhibiting root and shoot development. Unfortunately, CGM can also decrease the development and plant survival of direct-seeded vegetable crops. As a result, the use of CGM is not recommended in conjunction with direct-seeded vegetables. The development of equipment to apply CGM in banded configurations has created an opportunity to investigate whether banded CGM applications will provide significant crop safety for direct-seeded vegetables. The objective of this research was to determine the impact of banded CGM applications on squash plant survival and yields. A factorial field study was conducted during the summer of 2004 on 81-cm-wide raised beds at Lane, Okla., with two application configurations (banded and solid), two CGM formulations (powdered and granulated), two incorporation treatments (incorporated and non-incorporated), and three application rates (250, 500, and 750 g·m–2). The two CGM formulations at three application rates were uniformly applied in both banded and solid patterns on 18 Aug. The banded application created a 7.6-cm-wide CGM-free planting zone in the middle of the raised bed. The CGM applications were then either incorporated into the top 2.5 to 5.0 cm of the soil surface with a rolling cultivator or left undisturbed on the soil surface. `Lemondrop' summer squash (Cucurbita pepo L.) was then direct-seeded into the center of the raised beds. When averaged across the other factors, there was not a significant difference between powdered and granulated CGM formulations or incorporating and non-incorporating the CGM for either squash plant survival or yields. CGM application rates made a significant difference for both squash survival and yields, when averaged across all other factors. As the CGM application rate increased, the plant survival and yields decreased. When averaged across all other factors, the banded application resulted in significantly greater crop safety (59% plant survival) and yields (228 cartons/ha) than the solid applications (25% plant survival and 118 cartons/ha). The research demonstrated the potential usefulness of CGM in direct-seeded squash production, if used in a banded application configuration. Additional research should further investigate the interaction of CGM application rates and the width of the CGM-free zone on crop safety for various vegetables.

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Charles L. Webber and James W. Shrefler

Producers and researchers are interested in pelargonic acid (nonanoic acid) as a broad-spectrum postemergence or burn-down herbicide. Pelargonic acid is a fatty acid naturally occurring in many plants and animals, and present in many foods we consume. The objective of this research was to determine the effect of pelargonic acid concentration, adjuvants, and application timing on weed control efficacy as a burn-down herbicide. Field research was conducted at Lane, Okla. (southeast Oklahoma), during the 2005 growing season. One month prior to spraying the weed control treatments, the land was cultivated to kill the existing weeds and provide a uniform seed bed for new weed growth. The factorial weed control treatments included three application concentrations of Scythe (57.0% pelargonic acid) applied at 3%, 6.5%, and 10%; three adjuvants (none, orange oil, and non-ionic surfactant); and two application dates. All herbicide treatments were applied with an application volume of 935 L/ha to seedling weeds. The experiment had a high weed density with multiple species of grass and broadleaf weeds. Weed control across species increased as the herbicide concentrations increased from 0% to 10%. At all concentrations applied, pelargonic acid produced greater weed control for a longer time period for the broadleaf weeds than the grass weeds. Visual damage to the weeds was often apparent within a few hours after application. There was a significant increase in weed control when applied to the younger weeds. In this research, pelargonic acid was effective in controlling both broadleaf and grass weeds as a burn-down herbicide, although crabgrass was tougher to control.

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Charles L. Webber III, Merritt J. Taylor, and James W. Shrefler

Squash (Cucurbita pepo) producers could benefit from additional herbicide options that are safe to the crop and provide effective weed control. Research was conducted in southeastern Oklahoma (Atoka County, Lane, OK) during 2010 and 2011 to determine the impact of pelargonic acid (PA) on weed control efficacy, crop injury, and squash yields. The experiment included PA applied unshielded postdirected at 5, 10, and 15 lb/acre, plus an untreated weedy control and an untreated weed-free control. ‘Enterprise’ yellow squash was direct-seeded in single rows into raised beds. Weeds included smooth crabgrass (Digitaria ischaemum), cutleaf groundcherry (Physalis angulata), spiny amaranth (Amaranthus spinosus), and yellow nutsedge (Cyperus esculentus). Pelargonic acid was applied each year in mid-July and then reapplied 8 days later. The maximum smooth crabgrass control (98%), broadleaf weed control (94%), and yellow nutsedge control (41%) was observed with the 15-lb/acre PA treatment at 9 days after initial spray treatment (DAIT), 1 day after sequential treatment (1 DAST). Pelargonic acid at 15 lb/acre provided equal or slightly greater smooth crabgrass and broadleaf (cutleaf groundcherry and spiny amaranth) control compared with the 10-lb/acre application, and consistently greater control than the 5-lb/acre rate and the weedy control. Pelargonic acid was less effective at controlling yellow nutsedge than smooth crabgrass and broadleaf weeds. Yellow nutsedge control peaked at 9 DAIT (1 DAST) with 10-lb/acre PA (41%). As the rate of PA increased from 5 to 15 lb/acre, yellow nutsedge control also increased significantly for all observation dates, except for 28 DAIT. Increasing the PA application rate increased the crop injury rating at 1 and 3 days after each application (1 and 3 DAIT, 1 and 3 DAST). Maximum squash injury occurred for each application rate at 9 DAIT (1 DAST) with 4.4%, 8.0%, and 12.5% injury for PA rates 5, 10, and 15 lb/acre, respectively. The 10-lb/acre PA treatment produced the highest squash yields (kilograms per hectare) and fruit number (fruit per hectare) compared with either the 5- or 15-lb/acre rates, and equivalent yields and fruit number as the hand-weeded weed-free treatment. The 10-lb/acre PA rate applied in a timely sequential application has the potential of providing good weed control with minimal crop injury resulting in yields equivalent to weed-free hand-weeding conditions.

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Charles L. Webber III, Merritt J. Taylor, and James W. Shrefler

Pepper (Capsicum annuum) producers would benefit from additional herbicide options that are safe to the crop and provide effective weed control. Research was conducted in southeastern Oklahoma (Atoka County, Lane, OK) during 2010 and 2011 to determine the impact of pelargonic acid on weed control efficacy, crop injury, and pepper yields. The experiment included pelargonic acid applied unshielded postdirected at 5, 10, and 15 lb/acre, plus an untreated weedy control and an untreated weed-free control. ‘Jupiter’ sweet bell pepper, a tobacco mosaic virus-resistant sweet pepper with a 70-day maturity, was transplanted into single rows on 3-ft centered raised beds with 18 inches between plants (9680 plants/acre) on 28 May 2010 and 27 May 2011, respectively. Weeds included smooth crabgrass (Digitaria ischaemum), cutleaf groundcherry (Physalis angulata), spiny amaranth (Amaranthus spinosus), and yellow nutsedge (Cyperus esculentus). Pelargonic acid was applied postdirected each year in mid-June and then reapplied 8 days later. The 15-lb/acre pelargonic acid treatment resulted in the maximum smooth crabgrass control (56%) and broadleaf weed control (66%) at 1 day after the initial spray treatment (DAIT), and 33% yellow nutsedge control at 3 DAIT. Pelargonic acid at 15 lb/acre provided equal or slightly greater smooth crabgrass and broadleaf (cutleaf groundcherry and spiny amaranth) control compared with the 10-lb/acre application, and consistently greater control than the 5-lb/acre rate and the weedy control. Pelargonic acid was less effective at controlling yellow nutsedge than smooth crabgrass and broadleaf weeds. As the rate of pelargonic acid increased from 5 to 15 lb/acre, yellow nutsedge control also increased significantly for all observation dates. Increasing the pelargonic acid application rate increased the crop injury rating. The maximum crop injury occurred for each application rate at 1 DAIT with 7%, 8.0%, and 13.8% injury for pelargonic acid rates 5, 10, and 15 lb/acre, respectively. There was little or no new crop injury after the second postdirected application of pelargonic acid and crop injury following 3 DAIT for application rates was 2% or less. Only the 15-lb/acre pelargonic acid application produced greater fruit per hectare (4784 fruit/ha) and yields (58.65 kg·ha−1) than the weedy control (1196 fruit/ha and 19.59 kg·ha−1). The weed-free yields (7176 fruit/ha, 178.11 kg·ha−1, and 24.82 g/fruit) were significantly greater than all pelargonic acid treatments and the weedy control. Pelargonic acid provided unsatisfactory weed control for all rates and did not significantly benefit from the sequential applications. The authors suggest the pelargonic acid be applied to smaller weeds to increase the weed control to acceptable levels (>80%).

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Charles L. Webber III, James W. Shrefler, and Merritt J. Taylor

Corn gluten meal (CGM) is a non-selective preemergence or preplant-incorporated herbicide that inhibits root development, decreases shoot length, and reduces plant survival. The development of a mechanized application system for the banded placement of CGM between crop rows (seed row not treated) has increased its potential use in organic vegetable production, especially in direct-seeded vegetables. The objective of this research was to determine the impact of CGM applications (formulations, rates, incorporation, and banded applications) on direct-seeded squash (Cucurbita pepo) plant survival and yields. Neither CGM formulation (powdered or granulated) nor incorporation method (incorporated or non-incorporated) resulted in significant differences in plant survival or squash yields. When averaged across all other factors (formulations, incorporation method, and banding), CGM rates of 250 to 750 g·m−2 reduced squash survival from 70% to 44%, and squash yields from 6402 to 4472 kg·ha−1. However, the banded application (CGM placed between rows) resulted in significantly greater crop safety (75% survival) and yield (6402 kg·ha−1) than the broadcast (non-banded) applications (35% survival and 4119 kg·ha−1 yield). It was demonstrated that banded applications of CGM can be useful in direct-seeded squash production and other organic direct-seeded vegetables.

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Charles L. Webber, Vincent M. Russo, and James W. Shrefler

Non-pungent jalapeño peppers are used for making commercial picante sauces (salsas) and have a potential for outstanding yields in Oklahoma. There is incomplete information on the crop safety of certain herbicides that may not specifically address their use with non-pungent jalapeño peppers. The objective of this research was to determine the weed control efficacy and safety of a combination of preplant incorporated herbicides on transplanted non-pungent jalapeño pepper production. A field study was conducted during the Summer 2005 on 91-cm-wide raised beds at Lane, Okla. The herbicides in the study included napropramide (2.2 kg a.i./ha), clomazone (1.1 kg a.i./ha), bensulide (6.7 kg a.i./ha), and trifluralin (1.1 kg a.i./ha) used separately and in combination with one of the other herbicides. All herbicides were applied preplant-incorporated just prior to transplanting `Pace 105' non-pungent jalapeño peppers on 6 May 2005. Fruit were harvested on 21 July 2005, 76 days after transplanting. Plants treated with clomazone used by itself produced the greatest yields (16.4 t/ha) compared to plants treated with the other herbicides used individually, although it was not significantly greater than napropramide, 9.2 t/ha. Four of the five top-yielding herbicide treatments included the use of clomazone. The tank mixture of napropramide and bensulide produced the second greatest yield (16.2 t/ha). The weed-free treatment produced 17.5 t/ha compared to 86% yield reduction for the weedy check. These results demonstrated that clomazone, used individually or in combination with certain other herbicides, can maintain non-pungent jalapeño yields equivalent to weed-free levels.

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James W. Shrefler, William M. Stall, and Joan A. Dusky

Three field studies on high-organic-matter soils were conducted to determine the zone of influence of spiny amaranth on lettuce head quality. Spiny amaranth reduced lettuce head firmness at all distances from the weed, ≤105 cm. Lettuce ribbiness increased at 15 and 45 cm compared with the weed-free control. Untrimmed lettuce head weight was not affected by spiny amaranth presence beyond 45 cm. Trimmed lettuce head weight was reduced at all distances compared with the control. Stem diameter and core length were not affected by spiny amaranth competition. The presence of a single spiny amaranth plant significantly influenced some lettuce quality traits at ≤105 cm.

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James W. Shrefler, Warren Roberts, Charles Webber, Jonathan Edelson, and Merritt Taylor

Commercial organic vegetable production requires using soil improvement practices and effective weed control measures. Rye (Secale cereale) cover crops are known to suppress annual weeds. Research was begun in 2004 to measure crop yield, annual weed infestation, and weed control requirements for vegetable planting systems that begin with a rye cover crop. Poultry litter was used to supply nutrients and was applied based on a soil test and commercial vegetable recommendations. Rye `Elbon' was seeded 21 Oct. 2004 on beds with 1.8-m centers. Zucchini squash (Cucurbita pepo) `Revenue' was planted the following year using three crop establishment dates, such that transplanting occurred on 6 May, 3 June, and 29 June. Planting system treatments included: conventional tillage (CT), CT and plastic mulch (P), CT with stale seedbed, mow, mow and burn-down, mow and shallow till (ST), ST and burn-down. Following field preparation, squash was transplanted in a single row at the bed center with 0.77-m plant spacing. Drip irrigation was used in all plantings. Emerging weeds were removed by hoeing. Squash was harvested from each planting over approximately 3 weeks and total marketable fruit counts were determined. Marketable yields with P were approximately double those of the CT and ST treatments in the 6 May transplanting. Yields were comparable for CT and ST in the 3 June transplanting, but were significantly lower for the P treatment. There were no significant differences among the treatments that received tillage in the 29 June planting. However, the non-tilled treatments had significantly lower yields compared to tilled treatments.

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James W. Shrefler, Charles L. Webber III, and Otis L. Faulkenberry III

Producers of organic vegetables often report that weeds are a troublesome production problem. It has been documented that corn gluten meal (CGM), a by-product of the wet-milling process of corn, is phytotoxic. As a preemergence or preplant-incorporated herbicide, CGM inhibits root development, decreases shoot length, and reduces plant survival of weed or crop seedlings. The development of a mechanized application method for CGM and the ability to apply the material in a banded pattern would increase its potential use in organic vegetable production, especially in direct-seeded vegetables. Therefore, the objective of this research was to develop a mechanized method to uniformly apply CGM to the soil surface in either a broadcast or banded pattern. An applicator was assembled using various machinery components (fertilizer box, rotating agitator blades, 12-volt motor, and fan shaped gravity-fed row banding applicators). The equipment was evaluated for the application of two CGM formulations (powdered and granulated), three application rates (250, 500, and 750 g·m–2), and two application configurations (solid and banded). Field evaluations were conducted during Summer 2004 on 81-cm-wide raised beds at Lane, Okla. Differences between CGM formulations affected the flow rate within and between application configurations. The granulated formulation flowed at a faster rate, without clumping, compared to the powdered formulation. While the CGM in the banded configuration flowed faster than the solid application. It was determined that the CGM powder used with the solid application configuration was inconsistent, unreliable, and thus not feasible for use with this equipment without further modifications. These evaluations demonstrated the feasibility of using equipment, rather than manual applications, to apply CGM to raised beds for organic weed control purposes. Several design alterations may increase the efficiency and potential usefulness of this equipment. If research determines equivalent weed control efficacy between the two CGM formulations, the granulated formulation would be the preferred formulation for use in this equipment. This equipment would be useful for evaluating the benefits of banded applications of CGM for weed control efficacy and crop safety for direct seeded vegetables.