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ARS Home » Pacific West Area » Salinas, California » Crop Improvement and Protection Research » Research » Publications at this Location » Publication #316359
Title: Light intensity is the main factor affecting fresh market spinach tolerance for Phenmedipham

Author
item LATI, RAN - University Of California
item Mou, Beiquan
item RACHUY, JOHN - University Of California
item FENNIMORE, STEVEN - University Of California

Submitted to: Weed Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/25/2015
Publication Date: 1/1/2016
Citation: Lati, R.N., Mou, B., Rachuy, J.S., Fennimore, S.A. 2016. Light intensity is the main factor affecting fresh market spinach tolerance for Phenmedipham. Weed Science. 64:146-153. doi: 10.1614/WS-D-15-00056.1.

Interpretive Summary: There are few available herbicides for fresh-market spinach that do not provide adequate weed control, and there is need for additional herbicides tools for growers. Spin-Aid (phenmedipham) herbicide is registered for use in processing spinach but not in fresh-market spinach due to its crop injury potential and short time window from application to harvest. The objectives of this study were to evaluate the tolerance level of fresh spinach varieties for Spin-Aid, find a tolerance mechanism, and study the impact of light and temperature on tolerance of spinach to the herbicide. In the greenhouse, nine spinach varieties were treated with Spin-Aid (0.55 kg active ingredient per hectare). Spinach exhibited a wide range of tolerance to the herbicide, and reduction in dry weights of treated plants ranged from 40% to 78% compared to untreated control. Based on the tolerance screen, two varieties with low (Nordic) and high (Regal) tolerance levels were treated with Spin-Aid, then exposed to half and full sun light intensities, followed by photosynthesis function and biomass evaluations. Nordic plants treated with the herbicide and exposed to full sun had 65% lower dry weight compared to similarly treated plants exposed to half sun intensity, suggesting that spinach tolerance to Spin-Aid was mainly affected by light. The evaluation of photosynthesis function suggests that faster detoxification is the main tolerance mechanism. In the field, Spin-Aid was applied under varied light and temperature conditions. The impact of light intensity on yield of treated spinach was greater than the impact of temperature. Spin-Aid applied under high light conditions was more injurious than when applied under low light conditions, suggesting that the application of the herbicide in the evening or night might be safer. Results from this study can contribute to successful integration of Spin-Aid into currently used fresh-market spinach weed-management systems, which in turn can allow more efficient production of this crop.

Technical Abstract: The few available herbicides for fresh market spinach do not provide adequate weed control, and there is need for additional herbicide tools. Phenmedipham is registered for use in processing spinach but not in fresh spinach due to its crop injury potential and short time window from application to harvest. The study objectives were to evaluate the tolerance level of fresh spinach varieties for phenmedipham, suggest a tolerance mechanism and characterize the impact of light and temperature on tolerance of spinach to phenmedipham. In the greenhouse, nine spinach varieties were treated with phenmedipham (0.55 kg ai ha-1). Spinach exhibited a wide range of tolerance and reduction in dry weights of treated plants ranged between 40% to 78% compared to control. Based on the phenmedipham tolerance screen, two varieties with low (Nordic) and high (Regal) tolerance levels were treated with phenmedipham, then exposed to half and full sun light intensities, followed by photosystem II function and biomass evaluations. Nordic plants treated with phenmedipham and exposed to full sun had 65% lower dry weight compared to similarly treated plants exposed to half sun, suggesting that spinach tolerance to phenmedipham was mainly affected by light. The maximum PSII photochemical potential values of Regal treated with phenmedipham were higher than similarly treated Nordic, suggesting that faster detoxification is the main tolerance mechanism. In the field, phenmedipham was applied under varied light and temperature conditions. The impact of light intensity on yield of treated spinach was greater than the impact of temperature. Phenmedipham applied under high light conditions was more injurious than when applied under low light conditions. Results from this study can contribute to successful integration of phenmedipham into currently used fresh spinach weed-management, which in turn can allow more efficient production of this crop.