Key practice: Recommended fertilizer rates and seeding rates that provide for a competitive stand will make canola more resilient against weeds, insect damage and disease.
Key research: Brandt, S.A., Agriculture and Agri-Food Canada (AAFC), et al. “Seeding Rate, Fertilizer Level and Disease Management Effects on Hybrid Versus Open Pollinated Canola (Brassica napus L.).”
Effective pest management uses all the tools available in a method that reduces the severity and economic impact of the pest problem. All inputs must work together to establish a plant stand and crop canopy that are resilient against weeds, insect damage and disease and to maintain this protection through to harvest.
“Seeding Rate, Fertilizer Level and Disease Management Effects on Hybrid Versus Open Pollinated Canola (Brassica napus L.),” published by Stu Brandt of AAFC et al discusses studies conducted to investigate the influence of seeding rates, fertilizer level and fungicide application on canola variables, including growth and seed yield.
The objective of Brandt’s study was to determine if recent high-yielding canola cultivars require different seeding and fertilizer rates from past recommendations. The study also analyzed the benefit of fungicide across various soil-climatic zones.
The three-year study involved two high-yielding canola cultivars, one hybrid and one open pollinated, seeded at rates of approximately 2.5, 5 and 7.5 lb./ac. at three sites in the Canadian Parkland region. Fertilizer was applied to supply 67 percent, 100 percent and 133 percent of the commercially recommended level of nitrogen (N), with phosphorus, potassium and sulphur proportionally varied for each level.
Vinclozolin fungicide was applied at the 20 to 30 percent bloom stage to control sclerotinia stem rot, which was observed at very low levels at all but one site-year, where it was moderate. Both chosen cultivars were highly resistant to blackleg which was therefore observed at very low severity. At only one site-year, azoxystrobin fungicide was applied at the two- to four-leaf stage to further inhibit blackleg development.
In terms of overall growth, seeding rate had more of an impact on time to flowering or plant maturity than the cultivar or fertilizer rate. Fungicide had no notable impact.
Averaged over all site years, the incidence of sclerotinia was higher in the hybrid cultivar compared to the open-pollinated, and also higher when no fungicide was applied. Seeding rate and fertilizer level had no significant impact on sclerotinia.
Blackleg incidence was low and also not affected by any of the treatments in this study.
There was a significant interaction across all site-years between seeding rate and fertilizer level, indicating that seed yield response to one input was dependent upon the rate of the other.
In general, the high fertilizer level increased yield by zero to six percent over low-level fertilizer when plant densities were less than 45 plants per square metre. When plant densities were 65 plants or more per square metre, the high fertilizer level resulted in 12 to 18 percent higher yield than the low level.
At the low fertilizer level, yield increased with an increase from the low to mid rate of seeding, but with no further yield increase at a high seeding rate. However, at the high fertilizer rate, there was a notable further increase in yield when the seeding rate was increased from mid to high. This would indicate that the full yield potential of a higher seeding rate is only realized with a higher rate of fertilizer application, and vice versa.
Brandt reports, “Overall, the hybrid performed better than the open-pollinated, and the full economic value of high-yielding canola cultivars was only realized when fertilizer and seeding rates were at or above the current recommended rates.”