Still Time For a Crop Nutrition Top Up
Rainfall has renewed optimism in many key canola growing regions. Growers still have time to top up nitrogen and sulphur to take advantage of higher yield potential. Nitrogen should be applied before the 5-leaf stage to provide a strong economic benefit. Sulphur can be applied up to bolting. Click here for top up tips and photos of sulphur deficiency.
Apply whatever rate you feel is appropriate based on how much was applied earlier and the new yield potential of the crop. While there may be some leaf burn from high rates of nitrogen, the crop can usually grow through this damage without significant losses.
Efficacy can be very good for in crop applications. The key is to get a rain AFTER application to limit losses and move nutrient into the root zone. Uptake through leaves is minimal.
Rain that creates soil saturation can actually increase nitrogen losses due to denitrification, especially in fields with high residue. Crop residue, which provides a carbon-rich, nitrogen-poor food source for soil bacteria, will tie up (immobilize) fertilizer nitrogen stranded on the soil surface or in the shallow top layer. Whether using urea (dry) or UAN (liquid), Agrotain can limit losses while waiting for rain.
To minimize the effects of leaf burn, consider this tip: Apply liquid products when leaves are wet so the product runs off, but apply granular products in dry conditions since prills are less likely to stick to plant leaves.
Factors to consider before a top up:
-Nitrogen topdressing can extend the vegetative period and delay crop maturity. Consider the calendar date and the fall frost risk when making a nitrogen top up decision.
-As canola plants grow their roots will start to access sulphur reserves that moisture carried lower into the soil profile. Growers who have been applying recommended rates of sulphur may find that topdressing produces a smaller economic return than it does for those who have cut sulphur rates.
Disease update: Rain raises sclerotinia threat
Significant sclerotinia infections were reported in most regions last year, creating the potential for lots of spore production across the Prairies this year. If fields are moist at the time of flowering, and canola has good yield potential (e.g. 30 bu./ac. or more), then it will probably pay to spray a fungicide to limit sclerotinia losses.
The message this week is to consider the threat and budget for action. Spraying is not effective until the flowering stage, which is still a few days away for the earliest crops.
Areas that have been wet all spring will likely have apothecia emerging in any fields that were seeded to a susceptible crop like canola, lentils or sunflowers last year. Apothecia release the sclerotinia ascospores that are dispersed in the wind and land on canola petals.
Areas that had been dry but received rain this past week will likely see apothecia starting to emerge in a week or so. Apothecia need moisture to trigger their growth, and after a rain it takes 10-12 days for them grow to a point where they release spores. The Prairies could face a significant release of ascospores next week and if moist conditions continue, this release will continue throughout canola flowering.
With good canola prices, good yield potential and lots of moisture (so far), fungicide application could pay off for many growers this year.
Sclerotinia apothecia. Source: Faye Dokken-Bouchard, Saskatchewan Ministry of Agriculture
Sclerotinia apothecia are quite small. Source: Faye Dokken-Bouchard, Saskatchewan Ministry of Agriculture
Source: Faye Dokken-Bouchard, Saskatchewan Ministry of Agriculture
Blackleg: The application window for a fungicide to provide additional protection against early blackleg infection (which is the most damaging) is the 2- to 6-leaf stage. That window is closing quickly for most canola crops. (Link to blackleg article at www.canolawatch.org.)
Seedling diseases: Some fields in Manitoba have been completely wiped out by seedling diseases. Many of those fields were canola on canola, where the seedling disease complex load could have been very high. Slow crop establishment due to excess moisture and cool conditions made the situation worse. No foliar sprays are available for seedling diseases, but growers should still dig and look at roots and stems to identify whether disease is the cause for weak plants. Click here for more information on what to look for.
Source: Canola Council of Canada