Blackleg

When it comes to blackleg, the first step in management is being able to identify the disease. Right before swathing is an excellent time to assess blackleg prevalence in field. Look for areas that are lodged or have prematurely ripening plants. Look at the bottom to middle areas of the stems for lesions, which often have pycnidia (small black dots) within them (see photo on the left below). If blackleg infection is severe, canola plants will have woody cankers at the base of the stem. It is this type of canker that will cause yield loss. If you see plants exhibiting blackleg symptoms, use garden clippers and slice through the stem at the base of the plant (at soil level) to confirm the presence of blackleg (see photo on the right below). Making this confirmation will help determine if the blackleg pressure resulted in yield loss. Remember, canola crop residue that hasn’t yet decayed is a source for new blackleg infections in the field so be sure to keep accurate scouting records of blackleg infection ratings.

The longer length of time between canola crops allows the previous canola crop residue to degrade before another canola crop is planted in the field, limiting the source of new infection. The Canola Council recommends three years between canola crops for the decomposition of infected residue, to help with blackleg disease management.⁴

While good crop management practices such as crop rotation and active scouting are the most valuable tools to help reduce the spread of blackleg, planting blackleg resistant canola is another tool you can use. Planting blackleg resistant canola limits yield losses caused by the aggressive disease. Canola is considered to have a R-rated resistance if it is less than 30% susceptible to blackleg when compared to Westar which is a fully susceptible variety.

DEKALB canola hybrids are selected from an elite breeding program that focuses on developing blackleg resistant canola. The DEKALB canola line-up is comprised of canola hybrids with very strong resistance ratings for blackleg.

DEKALB® 74-44 BL is a broad-acre hybrid that is equipped with multi-genic blackleg resistance and offers outstanding yield potential. DEKALB® 74-44 BL also displayed a lower sclerotinia infection rating, on average, compared to Pioneer 45S54 in 2011-2016 Monsanto Field Scale Trials as well as higher yield.

In addition to its impressive disease package, DEKALB® 74-44 BL has consistent yield performance across all yield environments and has very good combining ease. These impressive features are why it has been the #1 selling Genuity® Roundup Ready® canola hybrid for four consecutive years.⁵

NEW DEKALB TruFlex canola hybrid, DKTF 92 SC and the first LibertyLink hybrid from the DEKALB brand, DKLL 81 BL both come equipped with multi-genic, R-rated blackleg resistance.

Field resistance to blackleg infection is based on both the non-specific background resistance to all blackleg, and the major resistance genes that provide very strong resistance to specific blackleg races.

There are at least 16 described virulent L. maculans races currently found on the Prairies.⁷ Growing the same hybrid repeatedly on the same field will select for races of blackleg that can overcome genetic resistance in that hybrid. Tight rotations of hybrids with the same blackleg resistance genes for more than two years will select for races of blackleg that can overcome genetic resistance in that hybrid and increase disease severity.⁶ Rotating varieties creates the opportunity to bring a mix of resistance genes to the field over time, which can reduce selection pressure and improve durability.⁷

Another option to consider is the use of a fungicide. In the right circumstances, fungicides can augment the blackleg protection offered in the canola hybrid under high blackleg pressure situations. However, the use of a fungicide will not replace the value offered inherently with blackleg resistant canola hybrids. As such, adopting this comprehensive approach to blackleg management is critical to preserving the genetic resistance tools which currently protect canola from blackleg and allow for high yielding and high-quality canola in Western Canada.