The Prairie Giants Crop Report

Field observations at your fingertips

June 6, 2021

Taylor Kurtenbach

Welcome to the Prairie Giants Crop Report! We’ll be breaking down our observations from the field into a concise, semi-regular report.

Blackleg in Canola
Seeding is almost wrapped up with lots of canola up and growing! Seeding depths varied, with many looking for moisture in the dry spring conditions. Thankfully, the rain we got at the end of May has helped with germination and stands are looking good! Flea beetles are actively feeding, with some reaching threshold to spray. First pass Liberty and Roundup are also starting to be sprayed. Now is the time to start thinking about protecting your canola against blackleg. Blackleg is a serious disease in canola that can cause yield losses as high as 50%2. There are two species of fungus that cause blackleg, L. maculans and L. biglobosa[1]. L. maculans is an aggressive, highly virulent strain; L. biglobosa is a weakly aggressive, weakly virulent strain that infects plants near maturity causing little damage[1][2]. The fungus overwinters in seed and crop residue, releasing airborne spores in the spring which are then dispersed by wind and rain. These spores can travel as far as 10 km2!!

Once infected, greyish-white lesions form with black pepper-like spore bodies. In wet conditions, secondary infection can occur from these sites. Once the fungus infects the leaves of the canola it can spread to the stem. In severe cases, stem cankering can occur restricting moisture and nutrient uptake causing premature ripening, shriveled seed, and shattering[1][2]. For a more in depth look at the disease cycle and symptoms, check out this link!
Canola Cotyledons

Weather plays a big role in disease development and spread. The most severe cases occur in warm, humid conditions with frequent rain, where as warm, dry conditions slow development. Blackleg can still be an issue in dry years if there was sufficient moisture early to disperse spores[2]. It is also common to see blackleg infections in plants affected by hail damage as the wounds provide an entrance for spores.

This past fall, we noticed blackleg in majority of the fields that we scouted. Although severity was low (majority of fields rated a 1 on the blackleg disease severity rating scale), it was very prevalent. It was the most severe in fields where the same, older variety was repeatedly grown in rotation. In a webinar hosted by the Government of Saskatchewan back in February, they reported that 81% of crops surveyed had at least trace levels with an average incidence (plants with symptoms) of 15%. Incidence increased from 2019, but overall severity was low. The East-Central region had approximately 70% prevalence and 10% incidence.

The following are the recommended practices to help control the disease.
  • Practice a crop rotation of canola 1 in 4 years.
  • Grow “R” rated hybrids.
  • Rotate resistance genetics – growing the same variety multiple times on the same field selects for races of L. maculans that can overcome resistance[2]. The more you grow the variety, the higher the risk.
  • Scout – clip stems, where the stem meets the soil, at swath timing to assess for blackleg. Plants are rated on a scale from 0 – 5; for each point increase in severity, yield declines approximately 17%[3]. Infected plants can be sent away for testing to confirm the presence of blackleg and identify the races present in the field. This is done through Pest Surveillance Initiative and is free for MCGA members.
  • Use seed treatment fungicides – Prosper Evergol and Helix Vibrance control seed-borne blackleg only. Syngenta has a new seed treatment, Saltro, that suppresses both seed and air-borne blackleg. Available for the 2022 season.
  • Control weeds that are also hosts such as volunteer canola and wild mustard.
  • Apply a foliar fungicide.
Foliar fungicide applications should be made between the 2 – 6 leaf stage[3], before symptoms are present[2]. Early infections, those that occur before the 6 leaf stage, often have the largest impact on yield[2]. There are many products registered for control of blackleg including Bumper (propiconazole), Nexicor (fluxapyroxad/pyraclostrobin/propiconazole) and Quilt (azoxystrobin/propiconazole). Not sure which product is the best fit for your farm? We are here to help! Talk to Doug, Braden or Taylor to discuss.

Sources
[1] Bailey, K.L., ed., Gossen, B.D., ed., Gugel, R.K., ed. And Morrall, R.A.A., ed. 2003. Diseases of Field Crops in Canada, 3rd Edition. The Canadian Phytopathological Society. 
[2] Canola Council of Canada. Blackleg. Canola Encyclopedia. [Online] Available: https://www.canolacouncil.org/canola-encyclopedia/diseases/blackleg/
[3] Bayer Crop Science. Crop Disease Guide: Canola. Bayer Crop Science.

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