Effect of early spring seeding on diseases of canola
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Studies to determine the effect different seeding dates and fungicide application on incidence and severity of blackleg disease were established at Melfort and Scott, SK. A similar study to determine the effect of seeding date on incidence and severity of Sclerotinia stem rot was also conducted at Melfort. The Brassica napus cultivar Quest was seeded in late October 1998 (fall), mid to late April (early spring) and mid to late May (traditional). Following germination, seedling counts were taken. In the blackleg experiments at Melfort and Scott, azoxystrobin (125 g a.i./ha) was compared with a non-treated control. For the Sclerotinia experiment, vinclozolin (500 g a.i./ha) applied at 20–30% bloom was compared with a non-treated control. Evaluation of plants for disease incidence and severity and for plot yield was done at plant maturity. At all locations, seedling populations were reduced for the fall seeding date compared to the early spring and traditional seeding. Sclerotinia stem rot infection levels were higher in the fall and early spring seeded treatments compared to the traditional seeding date treatment. However yield from fall and early spring seeding dates was higher than yield from the traditional date. There were no differences in Sclerotinia levels with fungicide application within each seeding date. At Melfort, blackleg levels for fall and early spring treatments were lower than levels for the traditional seeding date. Fungicide reduced incidence and severity of blackleg infection for all seeding dates. Yield for all seeding dates were higher with fungicide application as opposed to yield from the non-treated control. However, significant yield differences were only observed with fall seeding date. Yields of the treated and non-treated early spring seeding date were at least 20 to 80% higher than both treatments for traditional seeding date. At Scott the fall seeding date had lower yields compared to the traditional and early spring seeding date treatments. At all seeding dates, fungicide application only reduced the blackleg incidence; disease severity was only reduced for the early spring and traditional seeding dates. Fungicide increased yield for the early spring and traditional seeding dates but not the fall seeded treatment. Variation in yield of canola over the seeding dates was small but yield was greatest for the traditional seeding date treatment. This study indicated that blackleg infection and subsequent yield loss differed with location. Under the conditions of the study, fungicide application on the fall or early spring seeded crop did not reduce Sclerotinia stem rot symptoms or increase yield in 1999.
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