How much brassica should be used in the soil solarization with biofumigation technique?
P.L.CaliforniaAnswer: It is very important that you identify the pest, in this case nematodes, correctly, otherwise, any control measures may end up wasting time and money, not to mention being ineffective in controlling the pest. Have you positively identified the problem as nematodes? From the pictures you sent, it’s possible that you have root knot nematode (rkn), or a close relative to this pest. How did you positively identify the problem?If the problem is actually root knot nematode, then you must change your planting rotation. Use of poor or nonhost cover crops within the rotation sequence, may in some cases offer an effective approach to nematode control. Two leguminous cover crops adaptable for managing soil populations of sting or root-knot nematode include hairy indigo (Indigofena hirsuta) and American jointvetch (Aeschynomene americana). If Sorghum is also a popular cover crop restoring large amounts of soil organic matter, but is a good host for sting nematode but not root-knot. These strategies, if used in combination with the mustard fumigation, may provide some relief to the nematode damage. However, I should emphasize that if you continue to plant tomatoes, or other hosts to the rkn, then you will continue to have nematode problems. I talked with Rick Boydsten, USDA/ARS (Agricultural Research Service), Prosser Washington on Friday, September 10, 2010. He has been working in biofumigation research for several years. He suggested using a mix of two mustards, Brassica juncea (Indian mustard and other common names), and Sinapis alba (white mustard), which is the scientific name of the Idagold mustard cultivar that you’ll be planting. Seed blends of mustards can be had from High Performance Seeds (Dale Geis, Company Head, 509-750-4850), among other companies. Dr. Boydsten noted that most farmers will flail mow and then incorporate (disc) immediately to get the mustards incorporated, and some will irrigate to “cap” or seal the brassicas (and glucosinolates) in the soil. Your plan to use 1 lb of brassica plant reside per square foot sounds reasonable, but, as Dr. Boydsten noted, you may want to consider chopping it up into small pieces in order that the biofumigation effect occurs relatively quickly and intensely. Your rate comes out to 43,560 lbs/acre, or roughly 21 tons biomass per acre, which seems adequate. Dr. Boydsten mentioned that the researchers are studying the best mustard-seeding time for producing the most biomass, which is thought to be important for many of the crop’s biofumigation benefits?so the more mustard biomass, the greater the biofumigation benefit.Dr. Boydsten also noted that canola and camelina (both mustards) don’t have sufficient glucosinolates, which are the precursors to the chemical biofumigant, to be effective biofumigants.The use of the Solarguard film is likely to increase the effectiveness of any biofumigation. If the soil is slightly moist, that will also help.