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Poor-looking canola | Sclerotinia | Root rots
Diagnosis: Ugly. A lot of canola crops are looking pretty sad, with small plants, low counts and a wide range of stages. This makes for difficult management decisions, including when to spray for sclerotinia stem rot — or whether to spray at all.
Late fungicide. The application window for fungicide to manage sclerotinia stem rot closes at 50% flower (or earlier for some fungicides). Early applications usually provide the highest return, but not always. Sprays late in the window can be effective.
Roots? Where? Discoloured splindly plants may be severed from their roots as a result of brown girdling root rot, foot rot and root maggots — which are at higher than usual levels this year, or so it seems. Rotation and brassica weed control are the best management steps.
Behold thresholds. You can find lots of insects in canola, but only a few are actual pests and canola can tolerate a reasonable number of them before spraying pays off. Consider the risk window and economic thresholds for each insect before making a decision to spray.
How well can you identify the causes of canola root damage? We have six photos for you, including the one above.
This zoomed in section of the Alberta bertha armyworm map shows the only location across the Prairies, to date, showing a “severe” level of adult moths. That location is at Lacombe.
Growers in many regions are reporting canola fields that just don’t look as good as usual. Many are thin stands with weak plants and variable stages of maturity. Here are 10 most likely reasons.
Foot rot and brown girdling root rot (BGRR) seem to be more common this year. If you see dying plants or plants with lower leaves dying off while other plants remain green, this may indicate abnormal root function. Dig them up and check the roots for rots and girdling.
Hot days (28-30°C and up) and warm nights (16°C and up) from bud to mid-flowering stages can have a devastating effect on canola yield.
Hot, dry conditions the past number of days and variable field staging have made the decision to spray fungicide to manage sclerotinia stem rot even more difficult this year.
Moisture is the key risk factor for sclerotinia stem rot. Without moisture before, during and after flowering, disease severity and the return on investment from fungicide will be lower than if moisture is present all through these periods. Moisture can come as rain, dew and/or humidity above 80%.
Canola’s need for water is highest during the flowering growth stage, which means growers using irrigation have to provide more water during this stage. However, moisture at this stage also increases the risk of sclerotinia stem rot infection.
Alberta’s irrigation scheduling strategy recommends less frequent and larger irrigation volumes during the flowering growth stage. This will provide the water the crop needs, but by increasing the time between irrigations, the canola canopy has a chance to dry out to discourage sclerotinia stem rot.
While insects are not a major threat in most fields at this point in 2014, diamondback moth larvae are around, cabbage seedpod weevil are still laying eggs, and bertha armyworm larvae have been found in some locations — although at very low levels for the most part. (See the Map of the Week.) Here is a review of thresholds for the four major insects found in canola at this stage of the season…
The goal when spraying cabbage seedpod weevil (CSPW) is to stop adults from laying eggs in newly formed pods. CSPW don’t do their damage until pods are at least 1” long — so aim to spray just prior to that stage, at about 20% bloom. By late July, adults have been around for two months and are coming to the end of their lifespan. As they get old, they won’t lay as many eggs.
Swede midge females lay their eggs in canola apical meristems (growing points). Larvae hatching from those eggs feed within the meristems. Plant damage depends on the canola growth stage at which feeding occurs. The younger the canola plant, the greater the damage.
Damage typically includes one or more of the following….
We have reports of an “alarmingly high” rate of canola spoilage across the Prairies. Have you checked bins lately? Hot conditions increase the storage risk, even if canola is dry. Take a look, and turn the bin or turn on the fans if necessary.
Click here for an update on PAMI’s summer storage research. This research will help us determine whether canola is best left alone (although checked regularly), turned or aerated for safe summer storage.
Read more for summer tours and other canola-related events across the Prairies.
Let us help you get the most relevant info by telling us where you're from and what you do.
If you have general questions about the Canola Watch Email Newsletter, direct them to Jay Whetter.
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