Mustard cover crop growth and weed suppression in organic, strawberry furrows in California

Authors: Brennan, Eric; SMITH, RICHARD - University Of California - Cooperative Extension Service

Submitted to: HortScience
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/18/2017
Publication Date: 4/1/2018
Citation: Brennan, E.B., Smith, R.F. 2018. Mustard cover crop growth and weed suppression in organic, strawberry furrows in California. HortScience. 53(4):432-440. https://doi.org/10.21273/HORTSCI12576-17.
DOI: https://doi.org/10.21273/HORTSCI12576-17

Interpretive Summary: California produces most of the strawberries in the U.S. in production systems that use plastic mulch covered beds to save water and suppress weeds. But this mulch also can cause environmental problems by increasing sprinkler irrigation and rain runoff, soil erosion, and reducing ground water recharge. Growing cover crop in the furrows of strawberry beds can help reduce these problems but the cover crops need to be selected so that they can be easily killed before they impede strawberry growth. Broadleaf cover crops such as mustards may be easier to control than grass cover crops in organic strawberry furrows. This two-year experiment evaluated the growth of ‘Ida Gold’ mustard cover crops planted at two seeding rates in an organic strawberry system. Increasing seeding rate increased mustard biomass production. Mustard cover crops in the furrows reduced weed growth in the furrows by approximately 30 to 40% compared with weeds in bare furrows without cover crops. The mustard was easy to kill by mowing when it reached the height of the bed top. Additional studies are needed to improve the weed suppression in furrow cover crops.

Technical Abstract: Strawberry production in California uses plastic mulch-covered beds that provide many benefits such as moisture conservation and weed control, but also can cause environmental problems by increasing runoff of sprinkler irrigation and rain water, increasing soil erosion, and reducing ground water recharge. Planting cover crops in the furrow can help to reduce these problems and was evaluated during two years in organic strawberries in Salinas, CA with a ‘Ida Gold’ mustard (Sinapis alba) planted at two seeding rates (1x versus 3x). The mustard planting was in November or December after strawberry transplanting and resulted in average densities of 54 and 162 mustard plants per m of furrow for the 1x and 3x rates, respectively. The mustard was killed mechanically in February before it shaded the strawberry plants. Increasing seeding rate increased mustard shoot biomass, height, and C:N ratios, but usually reduced the concentrations of N, P and K in the mustard shoots. Cover cropped furrows reduced weed biomass compared with bare furrows by 29 and 40% in the 1x and 3x seeding rates, respectively, although weeds still accounted for at least 28% of the furrow biomass in the cover cropped furrows. These results show that growing mustard cover crops in furrows without irrigating the furrows worked well even during years with relatively minimal precipitation. We conclude that mustard densities of approximately 150 plants per m furrow will likely provide the most benefits due to greater biomass production, N scavenging and weed suppression. The practical implications of this best-management practice for furrow management are discussed.