Integrating Mustard Seed Meal with Steam and Anaerobic Soil Disinfestation for Weed Control In California Strawberry Production

A prior study showed that mustard seed meal (MSM) applied pre-plant at varying dose rates cannot effectively replace standard MBPic fumigation in California (CA) strawberry production. In this study initiated in 2010 in Watsonville, CA, we evaluate MSM in combination with steam or anaerobic soil disinfestation (ASD) and compare it to a standard fumigation practice. Treatment applications were made once, pre-plant, and included MSM at 3362 kg^.ha^-1, steam at ≥ 70 °C for 20 min., ASD, steam + MSM, ASD + MSM, Pic-Chlor 60 (1,3- dichloropropene [40%] and chloropicrin [60%]) at 336 kg^.ha^-1 and an untreated control. The study was arranged in a randomized complete block design with four single bed replicates. Each bed was 1.4 m wide and 12.2 m long. MSM was applied with a fertilizer applicator by shanking into the soil up to a depth of 15 cm on 7 Oct. ASD plots were treated with rice bran at 19,700 kg^.ha^-1 on 7 Oct. and were subject to a total irrigation of 2.5 acre-inches applied intermittently from 8 Oct. to 9 Nov. Steam was generated using a diesel fired steam generator and delivered to the beds using steam spikes at 0-25 cm depth to ≥ 70 °C for 20 min on 14 Oct. Pic-Chlor 60 was applied via drip system on 18 Oct. Strawberry ‘Albion’ was planted on 22 Nov. Before treatment application, weed seed bags containing 25 seeds each of common chickweed (Stellaria media (L.) Vill.), common knotweed (Polygonum arenastrum Jord. ex Boreau), common purslane (Portulaca oleracea L.), little mallow (Malva parviflora L.) and 10 tubers of yellow nutsedge (Cyperus esculentus L.) were inserted at two locations in the bed center at 15 cm depth. These bags were removed post treatment application and analyzed for their viability. Overall, the steam treatment alone, or with MSM were as effective as Pic-Chlor 60 in providing weed propagule control, where as, MSM and ASD alone were ineffective. Control of common purslane was slightly better in Pic-Chlor 60 than steam treatments, while in case of little mallow, the steam treatments provided a more effective control than Pic-Chlor 60. Weed density data taken over a 3 m long distance covered with clear tarp towards the center of each plot indicates that steam and steam + MSM were the only treatments providing weed control comparable to Pic-Chlor 60 fumigation.