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United States Department of Agriculture

Agricultural Research Service

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Research Project: Multi-State Evaluation of Carbonated Fumigants and Low Permeable Tarps to Reduce Application Rate, Increase Efficacy, and Minimize Emissions

Location: Water Management Research

2012 Annual Report


1a.Objectives (from AD-416):
1) Replace methyl bromide with an alternative fumigant, 2) Reduce the application rates of pre-plant alternative fumigants through a combination of decreased losses by better retention with low permeability films and enhanced sub-surface dispersion by carbonation of the fumigants, and 3) To ascertain the minimum fumigation rate required to be effective in various soils in multiple states with a variety of crops under different tarping techniques.


1b.Approach (from AD-416):
Three field trials will be conducted to collect field data. Targeted cropping systems are deep-rooted perennial tree/ornamental/grapevine orchards or nurseries. Telone and chloropicrin products will be tested in all trials. The first two years will focus on filed trials to determine effective reduced rates of carbonated fumigants. In the third year, a demonstration trial will illustrate those successful fumigation methods in growers’ fields. Emission loss, fumigant distribution (or concentration change over time in soil profile), and efficacy on nematode, pathogen and weed control will all be determined. The expected outcome is an economically feasible alternative to methyl bromide by increasing use efficiency, reducing chemical input and minimizing detrimental impact on the environment.


3.Progress Report:

This project supports objective 3 of the parent project. Many perennial crops, including almonds, depend on pre-plant soil fumigation to establish productive orchards. The phase-out of methyl bromide (MeBr) and stringent environmental regulations on major alternatives, such as Telone or 1,3-dichloropropene and chloropicrin, continues to pose challenges in pest control. Low permeability tarps, such as totally impermeable films (TIF), had shown promise in emission reduction because of their effectiveness in retaining fumigants under the tarp. Earlier field trials demonstrated that TIF improves fumigant distribution uniformity, increases fumigant concentrations in soil to improve efficacy, and has the potential for using lower rates for annual crops. These benefits are uncertain for perennials because deep injection is necessary and effective dispersion of fumigants are needed in order to control pests throughout the soil profile. In fall 2011, a comprehensive field trial was conducted in a 10-year old vineyard (2.8 acres), which had vines pulled out before fumigation. The trial was designed to evaluate the effects of tarping with TIF and using a carbonation technique in combination with reduced rates on fumigant emission, distribution in soil, and efficacy on nematodes, pathogens and weeds. Carbonation refers to the process of dissolving carbon dioxide into the fumigant and using carbon dioxide as a dispersant in a soil application. A total of 11 treatments were applied including the non-treated control, standard MeBr, and various combinations of different Telone C35 (a mixture of 1,3-dichloropropene and chloropicrin) rates (full rate, 2/3 rate, and 1/3 rate) with carbonated vs. non-carbonated fumigant and different surface sealing (bare or tarped with standard polyethylene (PE) or TIF). The fumigants were applied via shank-injection to an 18 inch depth. Fumigant emissions were measured and fumigant concentrations in the soil profile were monitored for three weeks. In addition to resident nematode determinations in soil samples collected before and after fumigation, soil sample bags infested with known levels of nematodes, pathogens and weed seeds were buried prior to fumigant application and retrieved after fumigation to determine viability. TIF reduced emissions >95% relative to bare soil while standard PE tarp reduced emissions ~30%. TIF significantly increased fumigant concentration or concentration-time (CT) exposure indices at 15 cm depth relative to the PE film. In a soil profile to one meter deep, however, there was no clear indication that carbonated Telone C35 enhanced fumigant distribution. The results were possibly affected by that a reduced amount of carbon dioxide from originally planned was added to fumigant tank due to a safety concern during transportation of the tank to the field and also instead of carbon dioxide, nitrogen gas was used to deliver the fumigants during soil application due to limitations imposed by the licensed fumigators and their fumigant application rig. Soil gas data did clearly show TIF resulted in a more uniform and/or higher fumigant concentration profile using a higher application rate (2/3 vs. 1/3). The results suggest the tendency of TIF to enhance fumigant movement in the soil profile that will improve pest control in perennial fields.

The field was infested with a variety of resident plant parasitic nematodes with high populations of citrus and pin nematodes and low populations of root-knot, dagger, and ring nematodes. All Telone C35 treatments provided 100% nematode control at 30 and 60 cm soil depth. However, nematode survival was observed at 90 cm in one of the 1/3 rate treatments, and at 120 cm in three 1/3 rate and two 2/3 rate treatments. We also detected nematode survival at a depth of 150 cm in the following treatments: full rate under PE tarp and carbonated 2/3 rate. Four pathogensspecies were investigated: fusarium, phytophthora, pythium, and verticillium. Efficacy varied significantly among the species. Untarped full rate of Telone C35, and 1/3 rates showed no differences in pathogen control as compared to unfumigated treatment. The full rate under TIF had the lowest survival rate and was most similar to MeBr. Weed counts taken after fumigation trial identified 13 weed species. In general, bare soils resulted in increased weed densities relative to tarped (PE or TIF) treatments. Higher rates of Telone C35 (i.e. Full vs. 2/3 and 2/3 vs. 1/3) generally resulted in significantly reduced weed densities. There were no differences in weed density observed between the PE and TIF tarps.


Last Modified: 10/31/2014
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