Mustard cover crops as biofumigants for organic strawberry production
Organic strawberry production requires reliable control for soil-borne pests and diseases. The land base limitations and pick-your-own marketing logistics on our farm, Little Lake Orchard, demand that some strawberry ground will be on a relatively short rotation. The short time between strawberry plantings will require near constant intensive cover cropping to replenish organic matter, nutrient levels, and reduce or eliminate residual fungus and nematode populations. Varieties of two species of mustard (Sinapis alba and Brassica juncea) have been identified as producing chemical compounds known as glucosinolates that have been shown to reduce fungus and nematodes populations when mowed and incorporated into the soil. This process is known as biofumigation.
Six varieties of mustard have been trialed to test glucosinolate production for disease and nematode control, and biomass production for organic matter and nutrient cycling. Initial results indicate that these mustard varieties can produce high levels of glucosinolates and biomass. Yield data for the strawberries will be taken in the summer of 2016 to complete the results for this project.
Six varieties of mustard were planted in the spring of 2015 to test glucosinolate production for disease and nematode control, and biomass production for organic matter and nutrient cycling. The project was implemented on one 1-acre block, instead of two 1-acre blocks due to the challenging spring weather and changing farm plans.The varieties included: Kodiak (Brassica juncea), Pacific Gold (Brassica juncea), Ida Gold (Sinapis alba), Caliente 119 (S.alba and B. juncea blend), Caliente 199 (S.alba and B. juncea blend), and Nemat (Eruca sativa– also a Brassica, bred as a nematode trap crop). Eight varieties of strawberries were then planted perpendicularly across the plots. The eight varieties planted were: ‘Wendy’, ‘Galletta’, ‘Brunswick’, ‘Jewel’, ‘Darselect’, ‘Cabot’, ‘Valley Sunset’, and ‘Record’.
The biofumigant mustard seeding rates were as follows: Kodiak (20#/ac.), Pacific Gold (20#/ac.), Ida Gold (25#/ac.), Caliente 119 (15#/ac.), Caliente 199 (15#/ac.), Nemat (10#/ac.). Soil tests were taken before planting, and after incorporation. Immediately before incorporation, yield data was measured and samples were sent to the University of Idaho for glucosinolate testing. After all measurements were taken, all the mustard plots were mowed with a rotary mower. Incorporation was accomplished with conventional tillage methods: chisel plow and disc harrow. Raised beds were then formed and black plastic was applied for the strawberry planting.
May 8: Planted mustard varieties.
June 17: Collected harvest data for ‘Idagold’
July 2: Collected harvest data for ‘Pacific Gold’
July 15: Collected harvest data for ‘Kodiak’, ‘Caliente 119’, ‘Caliente 199’, ‘Nemat’
July 30: Planted strawberries.
September: sent frozen mustard samples for freeze drying.
October: Sent freeze-dried samples to U. of Idaho for glucosinolate testing.
December: Strawberries mulched for winter.
Impacts and Contributions/Outcomes
The mustard trial was planted on May 8, 2015. All varieties grew well, and reached full bloom between June 17 and July 15. Yield measurements were taken for each variety were taken as close to full bloom as possible. The highest yielding varieties by dry weight were ‘Kodiak’ and ‘Caliente 199’, while the lowest yielding varieities were ‘Idagold’ and ‘Nemat.’
To stabilize samples for eventual glucosinolate testing, they were frozen, then freeze dried on the advice of Dr. Matt Morra of the U. of Idaho. Freeze-dried samples were tested and results were received back in October 2015. Also, it was decided to test the roots and shoots of each mustard variety. All varieties produced higher levels of glucosinolates in the shoots, but the roots produced certain compounds that the shoots did not. Overall, ‘Caliente 199’ produced the highest levels of glucosinolates. ‘Idagold’ produced some different compounds from the others, which may explain the reputed weed suppression qualities of that variety. The results from the U. of Idaho are attached. Further interpretation of the results will take place in the coming year with the help of Dr. Morra.
All strawberry varieties (‘Wendy’, ‘Galletta’, ‘Brunswick’, ‘Jewel’, ‘Darselect’, ‘Cabot’, ‘Valley Sunset’, and ‘Record’) did well after planting. There was some deer damage on the planting before mulching in mid-December 2015, but the plants looked good overall.
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