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Warren Roberts, Jim Duthie and Jonathan Edelson

Soils in eastern Oklahoma have low N and P levels. The poultry industry in the area produces large amounts of poultry litter. Horticultural producers could benefit from using the poultry litter as a fertilizer for various crops, but many horticultural crops require a fertilizer with a ratio of about 2:1:3 (N: P2O5: K2O). Poultry litter has an approximate ratio of 1:1:1. Poultry litter applied at a rate to supply all needed N or K will supply more P than is needed by the current crop, although low P soils can accumulate significant amounts of P before the P levels are excessive. Poultry litter at different rates and synthetic fertilizers have been applied for 3 years to a field in which cucumbers were produced. Poultry litter rates supplied N at as much as 500 kg·ha–1 and P2O5 at as much as 300 kg·ha–1. Cucumber yields were recorded, and soil tests were conducted three times a year for N, P, K, Ca, Mg, Mn, Cu, Pb, Zn, and Fe. Cucumber yields from plots fertilized with poultry litter were equal to or greater than yield from plots that received commercial fertilizer. There appears to be a trend toward increasing levels of soil P with all treatments. and decreasing levels of soil Zn with all treatments. After 3 years, there is no evidence of detrimental levels of any of the monitored elements.

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Warren Roberts, Jonathan Edelson, Benny Bruton, Jim Shrefler and Merritt Taylor

Plots were established at the Lane Agricultural Center in Lane, Okla., in 2003 for the purpose of conducting research in certified organic vegetable production. A field was selected that had been in pine timber since 1985. The field was cleared, plowed, disked, and land-planed. To establish a baseline for future reference, soil samples were collected on a 30 × 30 ft grid. Lime was added to adjust the pH. Poultry litter was added to the field as a fertilizer, and was incorporated by disking. Turnips were grown as a cover crop during the winter of 2003–04. In Spring 2004, the field was divided into four equal sections, which were planted with either tomatoes, sweet corn, watermelons, or southern peas. Tomatoes were planted using both determinate and indeterminate types. Plants were selected based on reported properties of interest to organic growers, such as disease resistance, pest resistance, or heat-set capabilities. The cultivars with greatest yield were Sunny, Solar Set, Classica, Sun Leaper, and Mountain Fresh. Visual disease ratings were taken throughout the season. Copper sulfate was used as a fungicide. The cultivars with the lowest disease ratings were Amelia, Peron, Celebrity, Florida 91, and Mountain Fresh. The major insect pest throughout the season was aphids. Aphid counts reached 6.9 aphids per leaf on 11 June. Two applications of AzaDirect, a neem extract, reduced aphid populations to 1.0 aphid per leaf on 17 June, 0.1 aphid per leaf on 25 June, and 0 aphids on 9 July.

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Warren Roberts, Jim Duthie, Jonathan Edelson and Jim Shrefler

Poultry litter is readily available in eastern Oklahoma. Poultry litter contains most of the essential elements for plant growth, and has long been used as a fertilizer for various crops. The ratio of N-P-K is about 1-1-1. In some areas, litter has been used excessively, and buildups of certain nutrients have occurred. There are concerns that a buildup of phosphorus (P) will lead to excessive amounts of P in water systems, which will affect water quality. There are also concerns that nitrogen (N) will leach or run off into water systems and also lower the water quality. Oklahoma has enacted legislation that will control how much litter can be applied to a given field, and regulations are being set in place to monitor and control the applications of litter. Studies have been conducted at the Lane Agricultural Center in southeastern Oklahoma over the past 6 years to determine vegetable production and soil nutrient changes when different litter application strategies are followed. In general, poultry litter has produced yields of cucumbers, collards, and corn that are equal to or greater than yields of the same crops fertilized with conventional synthetic fertilizers. Buildups of certain nutrients, particularly P, are occurring. At this time, the buildups are considered beneficial. The highest rate of litter application has resulted in levels of soil P that are about half the maximum amount allowed under present legislation.

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Warren Roberts, Jim Shrefler, Jim Duthie and Jonathan Edelson

A study was conducted in southeastern Oklahoma to determine treatments or combinations of treatments that provided the best weed control and crop yield for watermelon. `Allsweet' watermelons were grown with different combinations of mechanical and chemical weed control. Treatments included naptalam, clomazone, naptalam + clomazone, bensulide, naptalam + bensulide, napropamide, trifluralin, dcpa, ethalfluralin, sethoxydim, paraquat, glyphosate, cultivation, cultivation + hoeing, cultivation + paraquat, cultivation + glyphosate, and one treatment with no weed control. Glyphosate and paraquat were applied as wipe-on when weeds were taller than watermelons. The five treatments with greatest yields were (in descending order) cultivation + hoeing, trifluralin, cultivation + paraquat, cultivation, and dcpa. The treatments with lowest yield were the control, paraquat, glyphosate, and naptalam. A visual rating (0–10, 0 is poor, 10 is ideal) was taken about 5 weeks after seeding. Treatments with a visual rating of 6 or more were trifluralin (9.4), cultivation + hoeing (9.3), napropamide (9.3), cultivation + glyphosate (7.5), cultivation + paraquat (6.8), dcpa (6.7), and cultivation (6.5). With the exception of the cultivation + hoeing, all plots were weedy at harvest time. Suppression of selected weeds by a herbicide usually allowed rapid growth of the remaining weeds.

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Robert Wiedenfeld, B. Scully, Marvin Miller, Jonathan Edelson and Jiandong Wang

Purple blotch (Alternari a porri) and thrips (Thrips tabaci) can seriously reduce yields of short day onions in South Texas. The level of injury caused by these organisms is influenced by the concentration of nitrogen in leaf tissue. Lower levels of tissue nitrogen increase susceptibility to A. porri but decrease susceptibility to thrips. The purpose of this study was to evaluate the effect of tissue N levels on joint susceptibility of 4 onion cultivars to A. porri and thrips. Foliage was fertilized at 0, 4, 8, 12 or 16 lbs N/ac/wk for 6 weeks. Nitrogen concentrations in onion leaves varied over time and by leaf age, but showed very little effect due to foliar fertilization. Significant differences in thrips were noted among cultivars, but not among leaf N concentrations with cultivars. Purple blotch outbreak occurred late in the growing season and was not related to leaf N levels. Total N uptake failed to respond to foliar fertilization, therefore overall use efficiency of the foliar N applied averaged only about 10% relative to the amount taken up in the check plots.

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James A. Duthie, James Shrefler, Warren Roberts and Jonathan V. Edelson

In each of seven field experiments, density of watermelon (cultivar Sugar Baby) plants was varied over the range 1000-9000 plants/ha by varying the distance between plants in single-row, replicate plots. Per unit area, reproductive biomass and marketable yield each increased linearly with density. An upper limit on these response variables at high density was not detected in any experiment. The rate of increase per 1000 plants/ha ranged from 1.1 to 3.2 Mg·ha-1, for reproductive biomass, and from 0.5 to 1.1 Mg·ha-1, for marketable yield. The linear effect of density explained >90% of the increase in reproductive biomass in most experiments. The effect on marketable yield was more variable because the marketable fraction of reproductive biomass often was highly variable. In most experiments, the marketable fraction did not vary systematically with density. The linear rate of change in the marketable fraction with density did not exceed 3% per 1000 plants/ha on average in any experiment. Intraspecific competition intensified rapidly as density was increased in some experiments. Intensity of competition appeared to vary among environments.

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Warren Roberts, Jim Shrefler, Jim Duthie, Jonathan Edelson and Wes Watkins

Watermelon is the major fresh-market vegetable grown in Oklahoma, but growers have few labeled herbicides from which to choose. Grower surveys in Oklahoma have identified weed control as the major production problem facing watermelon producers. In 1995 and 1996, various mechanical and chemical weed control strategies have been explored. `Allsweet' watermelons were grown with various combinations of labeled and unlabeled herbicides, as well as mechanical control treatments. Treatments included bensulide, clomazone, DCPA, ethalfluralin, glyphosate, halosulfuron, napropamide, naptalam, paraquat, pendimethalin sethoxydim, and trifluralin. Certain chemicals were used in combination. Paraquat and glyphosate were used as wipe-on materials. Glyphosate and paraquat could not be applied until weeds were taller than the watermelon foliage, causing serious weed competition. In general, superior results were obtained from hand-weeded plots, trifluralin, and DCPA. Halosulfuron gave superior control of broadleaf weeds, but had a negligible effect on grasses. Napropamide gave good control of grasses and broadleaf weeds other than solanaceous weeds. No chemical, when used alone, gave satisfactory control throughout the growing season. Early cultivation, followed by chemical application at layby, appears to be one of the better treatments.

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Jim Shrefler, Mike Bourne, John Damicone, Jonathan Edelson, S. Pair, Warren Roberts and Merritt Taylor

Geographical dispersion of production hampers watermelon integrated pest management (IPM) information delivery in Oklahoma. Melon Pest Manager (MPM) was created to educate and provide advisory information on IPM. Available at, the site emphasizes information relevant to the area. MPM was conceived as Internet availability grew and was recognized to have potential for enhancing IPM implementation. Survey of producers suggested the value of Web-based information may depend on how easily it can be accessed. MPM was designed to provide easy access to watermelon IPM information. Compared to printed literature, web-based format is easier to revise and suited to presentation of information that applies yearly as well as that which may change frequently. MPM provides general discussion of melon IPM tactics and pest-identification and time sensitive information such as pest advisories and pesticide registration changes. MPM offers opportunity for novel presentation of educational information such as the real-time posting of field demonstrations. An initial challenge was to balance site development, promotion and education. Promotion and education followed placement of watermelon IPM tactic information on MPM but preceded advisory and pest identification. Pest identification links to existing sources are enhanced by material prepared for MPM. Progress is slowed by the need for expert intervention and the availability of images and descriptive information. Education on use of advisory resources (e.g., disease forecasters) is a high priority. However, availability and applicability of such products is dependent on the home site. The original concept envisaged mapping of pest activity using grower, extension agent and expert input. Time demands of other components of the site delay development of this aspect. Pest alerts are posted and distributed to county extension offices.

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Warren Roberts, Penny Perkins-Veazie, Jonathan Edelson, Jim Shrefler and Lynn Brandenberger

Forty-one watermelon cultivars were compared for yield and fruit size. Fields were prepared with raised beds 1 m wide covered with black plastic and equipped with drip irrigation. Plots were 2.7 m wide × 15.2 m long, with 10 plants being spaced 2.7 m apart in the row, and the remaining 6.1 m of each plot being used as a buffer zone. There were 4 replications of each plot, arranged as a randomized complete block. Seeds were placed in pre-moistened Jiffy-9 pellets in a greenhouse on 16 June 2003. Germinated seedlings were transplanted to the field on June 30. There were 27 triploid cultivars grown, with an average yield of 34.3 t·ha–1, and 14 diploid cultivars grown, also with an average of 34.3 t·ha–1. The three highest yielding diploids were `Gold Strike' with 51.7 t·ha–1, `Jamboree' with 44.8 t·ha–1, and `Dulce'with 43.0 t·ha–1. The three highest yielding triploids were `Sweet Slice' with 49.1 t·ha–1, `Sweet Delight' with 46.6 t·ha–1, and `Samba' with 45.0 t·ha–1. Small, personal sized melons are gaining popularity in the markets, and several small sized cultivars were included in this study. The cultivars with the smallest fruit, and their average fruit sizes, were `HA 5133', 2.6 kg; `HA 6007', 2.7 kg; `HA 5109', 2.8 kg; `Minipol', 3.0 kg; `WD-02-05', 3.4 kg; `HA 6008', 3.4 kg; `HSR 2920', 3.5 kg; `HA 6009], 3.7 kg; `HA 5116', 3.7 kg; and `WT-03-05', 4.2 kg.

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Warren Roberts, Benny Bruton, Jonathan Edelson, Wenhua Lu, Penny Perkins-Veazie, Jim Shrefler and Michael E. Stanghellini

Forty-one cultivars of triploid and diploid watermelons (Citrullus lanatus) were grown at Lane, Oklahoma in 2003. Seeds were placed in Jiffy-9 pellets in a greenhouse on 21 May. Fields were prepared with raised beds 1 m wide covered with black plastic. Plots were 3 m wide by 15 m long, with 4 replications, arranged as a randomized complete block. Seedlings were transplanted to the field on 4 June. From 4–9 June, rainfall occurred 5 days. Maximum soil temperatures at 5 cm, under bare soil, from 1–9 June were 34, 34, 35, 26, 22, 26, 31, 29, and 32 °C, respectively. On 9 June, 84% of the seedlings were dead. Lesions were observed on the roots and stems and isolations were made from symptomatic tissues. The predominant pathogen isolated from the seedlings was Pythium aphanidermatum. Some of the cultivars appear to have some degree of resistance to P. aphanidermatum. Mortality among the cultivars, averaged across all replications, ranged from 33% to 100%. The cultivars with the lowest mortality were “Tri-X Carousel” (33%), `Sunny' (40%), `WT-02-31' (53%), `Ole' (58%), and `Tri-X Palomar' (68%). New seeds were seeded in the greenhouse on 16 June, and transplanted to the field on June 30. The replacement seedlings were planted in the same field, in the same location as the previous plants. Maximum soil temperatures for the two week interval following the second planting ranged from 33 to 39 °C, with only one rain of 0.8 cm occurring 10 days after planting. There was no apparent plant loss due to P. aphidermatum in the second planting.