Questions of the Week

How to manage stem feeding from flea beetles?

Wind and rain make leaf-feeding more difficult for flea beetles and can push them to chew on stems as well. A relatively small bite into a seedling’s stem can kill the entire plant, especially when hot and dry conditions follow feeding and cause the plant to desiccate at the wound. When flea beetles are doing excessive stem feeding, the spray decision may not align with the recommended 25% leaf area action threshold. Since there is no threshold specific to stem feeding, use this rule of thumb: if the crop is looking better every second day that you scout it, the crop is probably outgrowing flea beetle feeding and spraying is generally not necessary. Spray may be warranted in fields with active flea beetle feeding, plant density below five plants per square foot and slow growth (where seed treatment is running out). (How to assess leaf area loss from flea beetles) (Stand up to flea beetles) (Canola seed treatments: understanding protection options and efficacy) 

Aim for one herbicide pass or two?

Ongoing wet, windy conditions have made herbicide application difficult, but weed growth continues. The good news is that dust-free, rapidly growing weeds are easiest to kill. Attack weeds as soon as possible — time is of the essence as early weeds rob the most yield. While a two-pass herbicide application can best control a late flush of weeds that might be missed in a single pass, aim for success in a first pass in case it ends up being the one and only: tank mix, ensure appropriate product rates, use adequate water volume, check water quality and spray when canola is at the one to two-leaf stage. As the spray window may be short and delays long, keep sprayer clean-outs in mind between products: racing from field to field is when errors are most common. (Spraying tips for tough conditions) (Weed control strategies for each HT system)

Is there more yield potential than available nutrition?

Good soil moisture means better germination and higher yield potential, but a bigger-than-anticipated crop can only meet its potential if it has adequate nutrition available.

  • Step 1) Assess yield potential. When canola reaches the two- to four-leaf stage (10-15 days post-seeding), start evaluating the available moisture and the plant stand using these counting tips.
  • Step 2) Match nutrition to yield potential. If the nitrogen rate determined last fall or at seeding won’t feed this year’s yield potential, there is a short in-season window available to top-dress. To ensure the crop isn’t short-changed at any point in the growing season, apply nitrogen in-crop prior to the six-leaf stage. Sulphur can be applied as late as early flowering to still offer full yield benefit. Very little phosphorus is plant available in the year it is applied when top-dressed. Potassium fertilizer broadcast applications can help improve soil K levels for subsequent crops. Read this for more tips on in-crop nutrient application. (Canola Encyclopedia – nitrogen) (Volatilization losses from surface-applied nitrogen)

Is fungicide to counter blackleg worthwhile?

The best management options for blackleg happen before seeding. Choosing resistant cultivars and either Saltro or Lumiscend seed treatment offers much more protection than anything that can be done in-crop. Fields that suffer high rates of infection almost always have an obvious prior history with the disease. Scout canola residue for blackleg’s spore-producing fruiting structures, which appear in old stems as a black ‘dirt’ that doesn’t rub off. These will release spores that can infect this year’s crop, causing lesions in cotyledons and young leaves. Mist/gentle precipitation can help spread the disease within and sometimes between fields. 

If a field is planted to a cultivar with no R-gene label, the field hasn’t been scouted previously for disease, the seed was not treated with Saltro or Lumiscend, and the rotation is every second year or less, consider a foliar fungicide to reduce risk. DO NOT WAIT to apply a blackleg fungicide. The window for in-crop spraying is incredibly small: application should occur around the 2-leaf stage. Fungicide can generally be added to herbicide but watch to ensure adequate water volume. Always leave a check strip (or three) to test the impact and ROI of a fungicide application. (Six basics of blackleg management in canola) (Blackleg scouting, identification and next steps)