Late September is a hectic time of year for grain and oilseed producers, and there aren’t many farmers who have the time or patience to fit another task into their already-busy harvest agendas.
But taking a few minutes to monitor canola fields for signs of blackleg is one of the most beneficial and least expensive investments a producer can make.
“Blackleg scouting hasn’t been a key priority for growers and agronomists in the past, but over the past couple of years, blackleg has been increasing,” said Errin Willenborg, research manager with SaskCanola.
“We’ve noticed that on our provincial disease survey results, and because of that, we’ve really been encouraging growers and agronomists to be out there, scouting and looking for blackleg at this time of year.”
The best time to scout canola fields for blackleg is just before swathing or immediately after.
For many growers, the opportunity to scout has already passed. But for others — particularly those in the northern grain belt — there is still time.
- At swathing time, pick five areas of each field and examine 10 to 20 plants in each area.
- Pull plants by the roots and examine the root structures for clubroot galls.
- After that, the stem of the plant can be cut with a pair of scissors or small garden shears.
- Make the first cut at the base of the stem, just above where the root begins.
- A clean cut will allow the vascular tissue inside the stem to be examined.
- Ideally, the tissue should be bright white.
- Any blackening or discoloration is a sign that blackleg infection may be affecting yield.
For example, if 10 percent of the plants have tissue discoloration that covers 25 to 50 percent of the stem’s cross section, this suggests that the blackleg phenotypes present in the soil may be immune to the blackleg resistance package contained in the canola variety being grown.
Determining yield loss can be difficult, but it is assumed that each plant showing discoloration on 25 to 50 percent of the stem’s cross section will have at least 40 percent yield loss.
Losses can be significantly higher in fields that have either a greater incidence of infection (more plants infected), or a greater severity of infection (discolouration on a greater proportion of the stem’s cross-section).
Assessing both the incidence and severity of blackleg infection is an inexpensive and reliable way to determine if growers should switch canola genetics to a variety that offers a different form of blackleg resistance.
Severe infection levels that go undetected can result in significant financial losses if the same variety of canola is planted in subsequent years.
For more information, visit www.saskcanola.com/quadrant/media/files/resource/pdfs/BLACKLEG-SP-Brochure.pdf.