Mustard Meal Weed Control.

Weed control in organic production systems can be a labor intensive and expensive process. Mustard meal (MM) is phytotoxic and a potential pre-emergent and preplant-incorporated organic herbicide for controlling germinating and emerging weed seedlings: unfortunately, MM 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 MM on seedling establishment of cantaloupe (Cucumis melo  L.).  The factorial experiment included 2 MM incorporation levels (no incorporation and incorporation), 2 MM application rates (1 and 2 t/a), 2 application patterns (banded and solid), 2 controls (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.  MM was applied to raised beds 10 ft-long on 3 ft-centers.  The banded application produced a 4 in-wide MM-free area in the bed center where the crop would later be direct-seeded.  The MM was then either left on the surface or incorporated into the top 1-2 in and then direct-seeded with ‘PMR-45’ cantaloupe.  Plant stands and weed control ratings were collected during the experimental period.  Twenty-eight days after planting (DAP), the entire plot was harvested and the fresh and dry plant weights determined.  Total weed control ranged from good (greater than 80%) to excellent (greater than 90%) for all MM weed control treatments.  Unfortunately, all MM applications adversely affected seedling establishment independently of application rate, incorporation level, and application pattern.  Injury and morality occurred prior to seedling emergence.  MM was clearly phytotoxic to germinating and emerging weed species and cantaloupe.   MM has potential as an organic pre-emergent and preplant-incorporated organic herbicide, but application rates and application methods must be further refined to control weeds while protecting direct-seeded crops such as cantaloupe.