Questions of the month

Who tests stem pieces for verticillium stripe? 

We are all learning about verticillium stripe. This is a good time of year to send in samples for disease testing and confirm your visual diagnosis. The general protocol for verticillium stripe is to collect 10-12 stem pieces with disease symptoms. Include about 12” of stem, starting from around 1” below ground level. Put stem pieces in a paper bag, label them with the farm name and field location, and ship them to the lab in a box or padded envelope, as shown in this video and this video.

The labs: 

• Pest Surveillance Initiative (PSI) Lab, Winnipeg, MB Verticillium test details
• Discovery Seed Labs, Saskatoon, SK Verticillium test details
• 20/20 Seed Labs, Nisku, AB Test details

Free disease testing programs for canola growers in Manitoba and Saskatchewan. More on verticillium stripe identification.

What is the best time to apply fall fertilizer? 

Apply fall fertilizer as close to freeze up as possible to reduce losses due to high microbial activity in warm soils. The goal with fall application is to keep nitrogen in ammonium form over the winter. Urea and anhydrous ammonia are both ammonium-based fertilizers. When soil microbes convert ammonium to nitrate it becomes vulnerable to losses. To keep nitrogen in ammonium form: 

• Apply when soils are below 10°C.  

• Place N fertilizer in narrow bands ideally 4” deep. 

• Use an enhanced efficiency fertilizer, especially if the first two steps are not achievable. Urease inhibitors, nitrification inhibitors and controlled-release nitrogen all have possible benefits for fall application of nitrogen, especially in higher risk scenarios (warm soil, broadcast, moist soils.)

For fall applications of sulphur: Elemental sulphur is best left on the soil surface to oxidize. Ammonium sulphate is less prone to volatilization losses than other forms such as urea, and can have flexibility in “right place.” Application timed as close as possible to plant uptake is always preferred, but fall can be a good time to apply for many logistical reasons. 

Jason Casselman talks soil sampling on Canola School on soil sampling. More tips on fall soil sampling.

Can I spray weeds after a fall frost? 

Yes, but check on recovery and wait for a warm day. Many weeds – Canada thistle, for example – are fairly frost tolerant, so a light frost will barely slow them down. Effective control of any weed is possible after a frost if most of the leaf tissue is still healthy and growing, and if the forecast includes a few warm sunny spray days. For glyphosate to be effective after a frost, weeds need at least 48 hours with temperatures above 4°C at night and 13°C daytime minimums. Read our new Fundamentals article on fall weed control.

How many canola cultivars should each farm grow? 

At least two. If trying a new cultivar for 2025, consider seeding a block with the new cultivar through the middle of a field of the farm’s current favourite cultivar. That way the two cultivars get a head-to-head test in the same field with the same soil type, weather and field history. This works best in a big field where each cultivar can be managed separately, if required. This helpful article walks you through cultivar decisions. Current cultivars and their blackleg, clubroot, shatter resistance and herbicide tolerance traits. The September 2024 Canola Digest features a few new cultivars.