Journal of Agricultural Science; Vol. 9, No. 8; 2017 ISSN 1916-9752 E-ISSN 1916-9760 Published by Canadian Center of Science and Education 81 Impact of Mustard Seed Meal Applications on Direct-Seeded Cucurbits and Weed Control Charles L. Webber III 1 , Paul M. White Jr. 1 , Rick A. Boydston 2 & James W. Shrefler 3 1 USDA, Agriculture Research Service, Sugarcane Research Unit, Houma, LA, USA 2 USDA, Agriculture Research Service, Grain Legume Genetics Physiology Research, Prosser, WA, USA 3 Extension Service, Oklahoma State University, Durant, OK, USA Correspondence: Charles L. Webber III, USDA, Agriculture Research Service, Sugarcane Research Unit, Houma, LA 70360, USA. E-mail: chuck.webber@ars.usda.gov Received: June 8, 2017 Accepted: July 4, 2017 Online Published: July 15, 2017 doi:10.5539/jas.v9n8p81 URL: https://doi.org/10.5539/jas.v9n8p81 Abstract Weed control in organic production systems can be a labor intensive and expensive process. Mustard seed meal (MSM) is phytotoxic and a potential pre-emergent and preplant-incorporated organic herbicide for controlling germinating and emerging weed seedlings: unfortunately, MSM may also adversely impact seedling survival of certain direct-seeded vegetable crops. Field research was conducted in southeast Oklahoma (Lane, OK) to determine the phytotoxic impact of MSM on indigenous weeds and seedling establishment of cantaloupe (Cucumis melo L.) var. ‘PMR-45’, cucumber (Cucumis sativus L.) var. ‘Marketmore 76’, yellow squash (Cucurbita pepo L.) var. ‘Crookneck’, and watermelon (Citrullus lanatus L.) var. ‘Dixie’. The factorial experiment included 2 MSM incorporation levels (no incorporation and incorporation), 2 MSM application rates (2.25 and 4.5 mt/ha), 2 application patterns (banded and solid), 2 experimental control treatments (1 for each incorporation method) and four replications. The soil [Bernow fine sandy loam, 0-3% slope (fine-loamy, siliceous, thermic Glossic Paleudalf)] was prepared for planting by plowing, fertilizing, and forming raised beds. MSM was applied to raised beds 3 m-long on 0.76 m-centers. The banded application produced a 10.2 cm-wide MSM-free area in the bed center where the crop would later be direct-seeded. The MSM was then either left on the surface or incorporated into the top 2.5-5.0 cm and then direct-seeded with cantaloupe, cucumber, yellow squash, and watermelon. Plant stands and weed control ratings were collected during the experimental period. Twenty-eight days after planting, the entire plot was harvested and the fresh and dry plant weights determined. Although applications of MSM provided sufficient broadleaf, grass, and total weed control, cucurbit establishment and development, the application of MSM at 2.25 and 4.5 mt/ha severely reduced crop establishment of direct-seeded cucurbits. Further research should address banded applications of MSM with either established direct-seeded or transplanted cucurbits and other vegetable crops in the same manner as others have done with corn gluten meal. Keywords: agricultural by-products, certified organic, organic weed control, pestiphytology 1. Introduction 1.1 Organic Weed Control Weed control is often considered a major production concern for producers, whether they use conventional (Pimental et al., 2001; Zimdahl, 2002) or organic (McDade & Christians, 2000; Walz, 2011) production systems. Weed research was rated as the number one priority by organic producers (Walz, 2011). Research has been conducted to develop weed control strategies that would qualify as natural, organic, and/or sustainable (Webber & Shrefler, 2008). Naturally occurring chemicals found within plants offer an excellent potential source for natural herbicides for weed control in crops (Rice, 1984). 1.2 Mustard Seed Meal Field incorporation of yellow mustard as a cover crop reduced redroot pigweed (Amaranthus retroflexus) germination and establishment, but did not adversely impact green bean (Phaseolus vulgaris) (Haramoto & Gallandt, 2005). Mustard (Sinapis alba L.) plants contain glucosinolates (Ildikó et al., 2006), mainly in the seeds, which are considered allelopathic compounds (Kobayashi, 2004). Mustard seed is processed for the extraction of