2013 Annual Report
1a.Objectives (from AD-416):
Improve fumigation efficacy with alternatives to methyl bromide for almond orchard replanting using low permeability tarps.
1b.Approach (from AD-416):
Two field trials will be conducted to collect soil fumigant (1,3-D, chloropicrin and methyl iodide) and pest control (e.g., nematode, pathogen, and weed) data under low permeability tarps such as TIF. Fields with naturally occurring nematode and pathogen populations will be selected for fumigation. Treatments will include: control (no fumigation), full rate (maximum allowed) in bare soil, under standard tarp, and TIF tarp, and reduced rates (2/3 and 1/2 of full rate) under TIF. Soil-gas concentrations will be monitored at pest sampling locations and depths. Correlation between fumigant dosage and pest control, and treatment effects will be statistically analyzed. Tarp permeability will be measured before and after installation. Fumigant change in the air under tarp will be monitored to estimate the proper time for the safe removal of TIF tarps to minimize exposure.
This project addresses the in-house project (NP 211) Objective 5: Develop various application methods, soil amendments, and physical barriers to reduce the emissions and enhance efficacy of the chemical alternatives to methyl bromide. This project is conducted through collaboration with University of California Cooperative Extension farm adviser in Merced County, California, and researchers or extension specialists in University of California, Davis. This is a subcontract from the Agreement No: 5302-13000-011-26R between ARS and California Department of Food and Agriculture. Detailed reports can be found under Project No. 5302-13000-011-26R.
One large and comprehensive field fumigation trial was conducted from 29 Nov. 2012 through 3 Jan. 2013. The trial was conducted in an almond orchard near Merced, California. After trees were pulled out following harvest in fall 2012, the soil was prepared for fumigation. The treatments included three surface sealing methods [bare, standard polyethylene (PE), and totally impermeable film (TIF)] and four application rates (full, 2/3, 1/3, and 0 rates) of Telone C35 (35% CP, 63% 1,3-D, and 2% other ingredients). A total of 12 treatments with 6 replicates were applied in a randomized complete block design. The fumigant was applied through shank injection to 18 inch depth with spacing of 20 inches between shanks. Fumigant emissions from PE and TIF tarped plots as well as near the edge of the TIF tarp, changes of fumigant concentrations in soil profile, and air fumigant concentrations under tarp from different application rates were all determined for about 6 weeks. Soil samples before and after fumigation treatment were collected for residential nematode population count. In addition, bioassay bags containing soils infested with citrus nematodes and pathogens were buried in soil before fumigant application and retrieved at the end of the trial for survival count.
All field samples have been processed and the data are being compiled. The emission data illustrated again that TIF tarp can significantly reduce emission peak flux compared to the standard PE tarp. For all three fumigant application rates, fumigant concentration in air under the tarp reached a peak in 2 days under PE, but in 6 days under TIF before starting to decline. This can be explained by the ability of TIF to retain fumigants that can easily pass through PE film as emission loss. Large field variability was observed and no differences in fumigant concentrations could be identified between PE tarped and TIF tarped plots treated at the same rate. The field varied in topography and soil water content. The field showed high nematode population (chiefly pin and some ring nematode and spiral nematode detected) with the highest population below 3 ft. All full rate treatments and the 2/3 rate under TIF provided 100% kill for residential nematodes in the top 3 ft soil, i.e., the 2/3 rate under bare and PE and all 1/3 rates as well as non-fumigated controls showed much higher survival of residential nematodes. However, from 3 to 5 ft depth, all treatments including the full rate under TIF showed survival of nematodes. The data suggest again that the difficulties in controlling nematodes in deeper soil continue to be a challenging task in replanting orchard. The poor efficacy data in the deeper soil were supported by low fumigant concentrations in the soil-gas phase. Almond trees were planted early spring 2013. Tree response to the fumigation treatment is being monitored.