Questions of the Week

Whether to spray for sclerotinia at the end of the fungicide window?

Fungicide is still a high priority given elevated sclerotinia risk in fields with high humidity, especially where there is a dense crop canopy. Fungicide spraying is optimal at 20-30% bloom, before significant petal drop. Though early infection causes the most yield loss, fungicide application late in the 20-50% bloom application window can provide valuable protection if flowering is extended from heat stress or other factors, or if conditions support disease development. Fungicide applied after 50% bloom usually provides little benefit. (Factors in the sclerotinia spray decision) (Fungicides available for sclerotinia stem rot)

What can be done to support canola through heat?

This summer’s heat is not doing canola any favours. Yield will be impacted when daytime temperatures exceed 28-30°C, especially during flowering, and even more so if nights don’t cool enough to allow some recovery. Flowers with shortened stamens that don’t protrude above the petals – a sure sign of heat damage – likely won’t produce pods. Heat has long-lasting consequences as it can take a week or more for canola’s hormones to rebalance once temperatures fall. We don’t have research to show reliable results from any product claiming to combat heat stress in canola. If trying something, consider strip trials to see how they work. (Heat at flowering)

Why are pods missing?

There are many reasons for flower abortion and missing pods. Heat blast can have a severe effect on the fertility of flowers and pod formation. Consider if missing pods could also or instead be due to drought/excessive moisture stress, late off-label herbicide / drift / tank residue, male sterility, nutrient deficiency (especially sulphur and boron), and/or insect feeding. As canola plants produce far more flowers than pods, canola can compensate for early flower loss. (Many reasons for missing pods)

What’s eating my crop this week?

Gophers continue to cause significant damage in southern regions of Saskatchewan and Alberta. Adult gophers are only active for about 100 days a year and are now beginning their summer hibernation. Juveniles will continue activity through mid-September (females) and into October (males). Preliminary testing indicates that bait stations are effective within about a 50(ish)-foot radius, but reduce population less in summer than in the spring before green-up. Support predators, especially badgers and birds of prey. Saskatchewan’s gopher control program ends July 31. 

Clover cutworm damage has been reported in the north Peace around Fort Vermillion. They are similar in size and appearance to bertha armyworm; however, major damage is not common and spraying whole fields is not usually economical. Read more in AAFC’s Cutworm Pests on the Canadian Prairies – Identification and Management Field Guide.

The new threshold of lygus bugs is 20-30 per 10 sweeps. Use the lower value for stressed crops. In Alberta’s black soil zone when good soil moisture exists, agronomists have in the past used a threshold of 50-80 lygus bugs per 10 sweeps or higher. More heat in the forecast could support peak emergence of bertha armyworms. Nothing can be done for late-season flea beetles. 

Manitoba Crop Pest Update: Trap results: diamondback moth, bertha armyworm 
Saskatchewan survey updates: bertha armyworm, diamondback moth
Alberta live maps: bertha armyworm, cabbage seedpod weevil, cutworms, diamondback moth