Insects
Aphids and a seedpod weevil have the greatest potential for concern in southern canola production. Other insects including several caterpillar species, plant bugs, stink bugs and flea beetles may be common in the crop but are rarely cause for concern. Aphids colonize the crop in the fall and continue feeding during the winter and spring.
While these insects may not commonly reduce yield, producers should prevent stand loss from early aphid infestations through careful scouting.
Start scouting the entire field 40 to 60 days after planting and treat if you find 5 aphids per leaf (up to 4-leaf stage) or 10+ per plant (4- to 8-leaf stage). Insecticide spray products labeled for canola are listed in Table 1.
Diseases
Canola is susceptible to a number of diseases but usually only after the crop has been grown in an area for a number of years, allowing pathogens to build up.
A major concern in new canola areas is blackleg, caused by a Leptosphaeria fungus. The fungus is seedborne so all planting seed should be certified as “blackleg-free,” if possible, and all seed treated with an effective fungicide to minimize the risk of introducing blackleg into an area. Once canola is established in an area, crop rotation and the destruction of crop residue and wild mustard plants become important, since the blackleg fungus survives on both.
Blackleg causes a dark lesion at the base of affected plants, causing death or lodging.
Varieties resistant to blackleg are known and should be used if the disease becomes a problem.
Another important disease is Sclerotinia stem rot – or simply stem rot – caused by the fungus Sclerotinia sclerotiorum. Again, this disease becomes more troublesome over time as canola production in an area increases, giving the fungus a chance to build up. Stem rot is mostly a springtime disease, favored by wet conditions during flowering. Symptoms include light tan to grey lesions on the lower stem that may be more than a foot long (Figure 1).
If split open, the affected stems contain “sclerotia” of the fungus that are black, 1/4 inch or more in length and irregular in shape (Figure 2).
Plants infected early during flowering will produce fewer and shrunken seed, while if infected later, they may lodge and break over (Figure 3).
The primary fungicide used to prevent stem rot is azoxystrobin (Quadris) and it must be applied prior to infection (first flowering) for best control.
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