Chloropicrin and Inline Dose-Response Under VIF
and HDPE Film: Weed Control Results in California

S. Fennimore¹, Z. Kabir¹, H. Ajwa¹, O. Daugovish², K. Roth,¹ and J. Valdez^1
1University of California, Davis, Salinas, CA 93905
²University of California, Ventura, CA 93003

Virtually impermeable films (VIF) have been tested for several years. These films may reduce fumigant emissions and increase fumigant efficacy by retaining lethal fumigant concentrations for longer times. However, we know of no field dose response studies to evaluate whether VIF improves fumigant efficacy on weeds. The objective of this work is to determine if VIF improves the weed control efficacy of chloropicrin (Pic) and Inline under VIF and standard film.

Methods

Pic and Inline were applied at 50, 100, 200, 300, and 400 lbs. per acre in water through the drip irrigation system on September 16, 2002 near Oxnard, CA and on October 1, 2002 near Watsonville, CA. Methyl bromide/chloropicrin (MBPic) was shank-applied at 350 lbs. per acre. Two types of film were used: standard high-density polyethylene (HDPE) and VIF (Bromostop). Each treatment was replicated four times and arranged in a randomized complete block design. Gas permeable bags containing yellow nutsedge tubers were buried 6 inches deep in the center of the beds prior to fumigation and retrieved prior to strawberry transplanting. Similarly, bags containing burclover, common chickweed, common purslane, little mallow, and knotweed seed were buried at 2 and 6 inches deep in the center and at the edge of the bed prior to fumigation. After retrieval, the nutsedge samples were germinated in greenhouse pots to test viability and weed seed viability was determined with tetrazolium. Strawberry ‘Camarosa’ was planted on October 7 at Oxnard and on October 25 at Watsonville. Weed counts, weed fresh weights, and weeding times were measured within 100 ft. long subplots on November 26, 2002, January 15, February 25, March 26, and May 8, 2003 at Oxnard and within 90 ft. long subplots at Watsonville on December 5, 2002, February 24, April 3, and May 1, 2003.

Results and Discussion

Tarp type did not affect native weed biomass and weeding times at Oxnard (table 1). However, at Watsonville, VIF reduced native weed biomass and weeding times (table 2). Impermeable films appear to improve weed control with Inline more than Pic. At Watsonville, weeding times with Inline at 200 lbs. per acre were 40 hours per acre under VIF and 91 hours per acre under HDPE (table 2). Generally, Pic and Inline killed more chickweed, knotweed and purslane seed under VIF than under HDPE (table 3 and table 4). Based on 50% growth reduction (GR50), the Inline doses at Oxnard required to kill half the nutsedge samples were 101 lbs. per acre (80, 122, lower and upper 95% confidence intervals, respectively) under VIF and > 400 lbs. per acre under HDPE. Nutsedge GR50s at Watsonville for Inline were 147 (137, 156) under VIF and 262 (236, 295) under HDPE. The GR50s for Pic at Oxnard on nutsedge were 185 lbs. per acre (156, 216) under VIF and 362 lbs. per acre (288, 515) under HDPE. Nutsedge GR50s for Pic at Watsonville were 128 lbs. per acre (121, 136) under VIF and 218 lbs. per acre (194, 247) under HDPE.

Conclusion

These results suggest that Inline and Pic generally provide better weed control under VIF than HDPE. VIF improves control of difficult-to-control weeds, such as yellow nutsedge, compared to HDPE.

Last Updated: June 24, 2005