Methyl Bromide Alternatives and Improvements

This report culminates a 5-year multi-commodity study to find the best field-testable methods for using methyl bromide with reduced volatilization and/or identifying alternatives to its use as a pre-plant soil treatment. No systemic herbicides or treatment methods could be found that would kill old roots prior to vine removal. The best treatment was Garlon painted to cut trunks which only provided kill to 18 inch soil depth. Root kill in the surface 4 to 6 ft of soil is common following 350 lb/acre methyl bromide. Root kill in the surface 4 to 5 ft of soil is common following 350 lb/acre Telone when applied to dried soil. A drench of Vapam at 325 lb MITC in 6 acre inches water (100 gal/acre) can kill roots to 2XA to 3 ft depth. Doubling the Vapam rate provides kill to 4 ft depth but plants do not grow well after such doses unless there is a one year waiting after the drenching. Non-tarped methyl iodide at 325 lb/acre performs as well as methyl bromide but with Prunus spp. we have observed phytotoxicity so a range of grape rootstocks would have to be screened after various treatment rates to determine its feasibility. Enzone at 300 gal/acre drenched in 6 acre inches water will not kill remnant roots. Clorox solutions, urea, extracts of marigolds or safflower or walnut hulls drenched in 6 acre inches water will not kill old roots nor the nematodes within. Eighteen months of cover cropping involving Sudan grass, vetch or barley will not kill old roots or the nematodes within although they can reduce nematode populations within soil. Forty days of flooding during winter time will not kill old roots. The delivery of Vapam via an existing drip line at 250 ppm MITC in enough water to uniformly spread product 4 ft deep and 4 ft wide will kill old roots within that zone but provide no more than one year of nematode protection. This treatment in combination with rootstocks having broad resistance to soil pests is a tactic in need of field testing. Telone shanked at 35 gal/acre followed in one to two days with a drenching of 250 ppm MITC will produce vine growth and nematode control comparable to methyl bromide while reducing Telone volatilization. Chloropicrin is a mediocre nematicide at 350 lb/acre but promotes plant growth when present at 125 lb/acre or more. There needs to be field testing of Telone C-35 at 50 gal/acre. The use of composts, manures and soil amendments can improve vine growth but do not solve the replant problem nor nematode problems. Portions of the replant problem can be solved by killing old roots and waiting 18 mo. before replanting.