Winter Wheat Allelopathic Impacts on Establishment of Winter Canola.

Winter canola (Brassica napus L.) is growing in importance as a rotational crop for no-till winter wheat (Triticum aestivumL.) in Oklahoma. However, stand establishment has been a problem over the last 5 years. It has been theorized that some wheat varieties inhibit winter canola germination and survival by exuding allelopathic compounds, particularly into no-till systems where crop residue is left in place.

Straw samples were collected from two wheat variety trials in Oklahoma at Chickasha and Lahoma. A complete 2 x 42 factorial experiment was established, factor one: canola variety; factor two: wheat variety. Forty eight hour water extractions were made from each wheat straw sample equivalent to the residue following harvest of a 2360 kg/ha crop and 2.5 cm of rainfall from harvest to canola planting. Three mLs of each extraction was used to treat 10 canola seed in individual petri dishes. Subsequent to treatment, canola seed were watered with distilled water until germination. Fresh and dry weights were taken 7DAT. Data were subject to ANOVA and means separated by Fisher’s protected LSD (p=0.05).

Approximately 30% of varieties tested significantly decreased winter canola biomass 7DAT.  Several wheat varieties decreased canola germination and biomass accumulation, regardless of location, by 50% or greater including: Endurance, Pete, Armour, OK Rising, WB-Grainfield, and Doublestop CL+.

The wheat varieties identified in the lab as severely impacting canola germination were selected for field testing. Wheat straw samples from 17 varieties from the 2 locations were secured inside permeable bags and bags were secured in place in a conventionally tilled field from June to September 2015.  Canola was seeded into the field after residue bag removal. Trials were taken to yield.  Seven wheat residues contributed to a 675 kg/ha or greater yield reduction for canola. These were Doublestop CL+, CJ, LCS Mint, OK Bullet, OK Rising, Pete and WB Grainfield.  It is not recommended that canola be seeded into wheat stubble of these varieties as canola planted will suffer a yield loss.