Story Posted: June 30, 2010

Canola Watch 10: Insect threat builds

In This Issue: Insect threat mounts on many fronts, Lygus spraying starts in Peace, Good conditions for sclerotinia stem rot, Watch for blackleg on leaves, Recovering crop needs nutrients.

Issues of the week
June 30, 2010 - Lygus spraying starts in the Peace, cabbage seedpod weevil spraying starts in the southwestern Prairie, and we’re all on diamondback moth alert. Scout damage closely and spray only when necessary. With so many potential insect threats, multiple sprays are probably not economical. Oh, and don’t forget about sclerotinia.

Crop and weather update
Peace (B.C. and Alberta): Dry and hot conditions the past week add to drought stress. South and central Peace regions really need rain. Most canola fields are at bolting to first flower stages.

Alberta: Thunderstorms brought variable rain in the past week, ranging from 4" for some to less than a tenth for others. Hail flattened some fields in the east central region. Moisture overall is decent and with several nice warm days in the past week, "canola is going gangbusters," says John Mayko, CCC senior agronomy specialist (click to email John)for the west-central region. Earliest canola is flowering. Read the Alberta crop report.

Saskatchewan: Thunderstorms bring patchy rain. Melfort, St. Brieux and Birch Hills, for example, got "incredible amounts of moisture" again this week, says Jim Bessel, CCC senior agronomy specialist (click to email Jim)for the northeast region. Baldwinton and Cut Knife in the west got 4" in one day. Crop staging across the province varies widely from cotyledon to 30% flower. Read the Saskatchewan crop report.

Manitoba: As in Alberta and Saskatchewan, thunderstorms bring variable rain from 4" in some spots to under half an inch in others. Earliest canola is in full bloom, and many fields with good yield potential have been sprayed with fungicide already. Read the Manitoba crop report.

Coming Events
Southern Applied Research Association at Lethbridge offers its one-day Diagnostic Field School July 6, 7 and 8. The agenda includes CCC senior agronomy specialist Jim Bessel explaining how to minimize combine losses. For more information, call 403-381-5118 or email sara.research@connectcomm.ca.

The Crop Diagnostic School in Carman, Manitoba will run July 6 to 9 and July 12 to 16. Canola topics include seedling diseases, sclerotinia, blackleg and insects. Click here for more information and to register.

BCGPA will hold its Annual Field Crop Tour and BBQ July 14 starting 4:00 p.m. at the Fort St. John Research Farm. CCC agronomy specialist Erin Brock is speaking. Visit the BCGPA website for contact information.

Combine Performance Clinic: CCC and Alberta Canola Producers Commission present the one-day workshop July 27 or 28 in Vegreville, Alta. Learn tips to cut combine losses, which can be 3-5 bushels per acre. Click here for more information or to register online. Space is limited to 250 per day.

Insect threat mounts on many fronts
Hold off on cabbage seedpod weevil spray. Some growers in southern Alberta and southwestern Saskatchewan are tempted to spray at this early stage. Weevil numbers will continue to build until early flower and they will reinvade if sprayed now. If the crop is not stressed, hold off until early flower.

Diamondback moths came in early and could be a threat across the Prairies. Feeding damage at flowering and early pod stages may warrant control. For more information, click here for a factsheet or click here to read the Prairie Pest Monitoring Network’s monitoring and control tips.

Cutworms like mud? Cutworm feeding continues, particularly in Saskatchewan. Although they usually prefer drier soils, they have been seen feeding in low wet areas. With rain and warm conditions, canola should grow quickly through the threat, but sprays may still be warranted on some later fields.

Root maggots may alter your plans for 2011. One field south of Edmonton has "root maggots like I’ve never seen before," says Lloyd Dosdall, entomologist with the University of Alberta. Erin Brock, CCC agronomy specialist (click to email Erin) for the Peace region, also reports "heavy" root maggot feeding on a field near Eaglesham. Nothing can be done except recognize the problem and rotate out of canola for a couple years and increase seeding rate next time. "Tight rotations play into root maggots’ hands," Dosdall says.

For more on insect issues around Alberta, click here to hear Scott Meers’s interview on the ACPC website.

Lygus spraying starts in Peace
Some Peace fields have 4-5 adults per sweep, prompting many farmers to spray at the bud stage. This is earlier than normally recommended, but with drought stress, canola may not be able to compensate for bud losses.

Scout for signs of damage. Look for penetration marks at the base of the bud where adult lygus bugs are present.

If damage is evident, use the sweep net to take a count. Lloyd Dosdall, entomologist at the University of Alberta, provides these guidelines:

• Sample when the temperature is above 20°C using a standard insect sweep net with a 38 cm diameter.
• Take 10, 180-degree sweeps through the bud area.
• Count adult lygus numbers per 10 sweeps.
• If the count is 15 adults and higher at 5 locations within the field, if canola is stressed by drought ,and if lygus are actively feeding on buds, spraying may help under the current hot and dry growing conditions.

Other factors to consider in the decision are:

• Is the profit potential of the crop sufficient given the moisture situation?
• The potential that other insects will be a concern later in the season. Multiple sprays in one season may not be economical.

Click here for an Alberta Agriculture factsheet on lygus bugs. Click here for a more detailed version of this article.

Good conditions for sclerotinia stem rot
Spraying to prevent sclerotinia stem rot has started in Manitoba and many canola fields across the Prairies are coming into the spray window - 20% to 50% bloom. With good moisture and high humidity, growers with canola at early flower should use the checklist below to assess their sclerotinia stem rot risk. Fields scoring 40 or higher could benefit from fungicide, depending on canola price, yield outlook and fungicide cost.

When scouting for apothecia, the tiny mushroom-like structures that release infectious ascospores, keep two things in mind:

1. Make sure what you see are apothecia. They are tan or honey-coloured, 5 to 15 mm across, and tops are cupped like a golf tee. They will be growing from sclerotia in the soil or decaying canola. See the photo at the top.

2. When scouting for apothecia, check low spots in cereals that were in canola the previous year. If low spots are still water-logged, look in areas that have been wet but not saturated.

While flooded areas may kill sclerotia, many areas of the field will have prime conditions for sclerotinia stem rot infection. For more information on sclerotinia scouting, download our Canola Disease Scouting & Risk Assessment Card.

Watch for blackleg on leaves
Blackleg presence is higher than usual on canola in Manitoba and southeastern Saskatchewan. If you see grey lesions with black picnidia (peppery spots) on leaves, monitor the field. The variety may have adult resistance, so early infection on the leaves may not result in severe stem damage.

Spraying is not likely economical. Blackleg can infect canola all season long, so fungicide application timing can be challenging and expensive as applications may need to be repeated to control this disease.

If blackleg is serious at harvest and yield loss is likely, avoid planting canola on that field for a few years and next time consider a different variety with different resistance genes.

Recovering crop needs nutrients
Canola fields are recovering with the past week of warm weather. Crops recovering well from excess rains, which leached away nitrogen and sulphur reserves, may benefit from a fertilizer topdress. Applying 20 to 30 pounds of actual N and S in the form of ammonium sulphate can help, especially where canola shows signs of nutrient deficiency.

When canola reaches complete ground cover, keep these tips in mind before fertilizing:

• Apply dry fertilizer when plants are dry so prills roll off leaves for minimum leaf burn.
• Dribble band liquid fertilizer when plants are wet so the fertilizer washes off plants and into the root zone.

Topdressing with a sprayer nozzle when canola is at complete ground cover is not recommended as leaf burn will occur, further stressing the crop.

Applying C3 as a fix for poor rooting? There is very little published research on this practice. For anyone trying a product like this, leave a check strip — and monitor the check strip through to harvest. "The crop may green up and look better right away, but that doesn’t always carry through to final yield," says Derwyn Hammond, CCC senior agronomy specialist for Manitoba (click to email Derwyn).

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