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Canola is not the best crop for going into freshly broken pasture because:
Competition. Pastures are primarily perennial plants and weeds, which will provide heavy competition all season long, even when using Roundup Ready canola and a glyphosate pre-seed burnoff. During pre-seed burnoff timing, flow within the perennial plant is up from the roots to the new growth. Glyphosate will provide fairly good top growth control, but the active ingredient will not move down into dormant buds on the roots — which are the key targets for effective perennial control. With in-crop glyphosate application, two one-half litre rates may not take care of perennial forage plants surviving initial management efforts.
Poor seedbed. Large chunks of sod still present in the field can impede good seed to soil contact — which is important for canola seed survival and emergence.
Low nutrient reserves. Pasture and hayland can be very nutrient deficient. What nutrition does remain will be tied up by microbes breaking down the large amounts of plant residue.
Low moisture reserves. Subsoil moisture tends to be lower in pasture and hayland, especially following a normal to dry year.
Wireworms. Wireworm populations tend to be high in pasture and hayland. Wireworms can wipe out a whole field of canola, and no seed treatment or spray is registered for wireworm control in canola. Growers will want to get down with a trowel and sifter and look for wireworms in these fields before making the final decision to seed canola. Bait balls are unlikely to work to scout for wireworms in these fields given the high volume of decomposing plant material. Gopher and cutworm numbers also tend to be high in pasture and hayland. Cutworms can be managed with surface applied insecticide.
Carryover herbicide. If the pasture was sprayed for weeds, what product was used? For example, Escort and Telar present a herbicide carryover risk for canola.
Generally poor land. Why that field was in pasture in the first place? It may not be highly productive land. In general, growers should lower their yield expectations for canola seeded into fields taken out of pasture and hayland. They should also evaluate each field to determine if canola is really the best crop choice. Click here for more tips on sod seeding.