Story Posted: May 25, 2011

Canola Watch: Frost, Insect update, When is too late to seed?

Issues of the week: Frost hit many areas of the Prairies on repeated nights over the past week. Emerged crop is at risk, especially delicate cotyledons. Wait 3 or 4 days, then look for regrowth before making any management decisions. Find time each day to scout for insects, weeds and other stand establishment issues. And for growers facing continued rain delays, know your crop insurance seeding deadlines.

Crop and weather update
Peace (B.C. and Alberta): Canola seeding ranges from half to two thirds complete in the east, to 95% complete in the west. Most areas had some rain in the past week, except for the far north. Fairly regular showers are the reason for slower seeding progress in the east.

Alberta: Seeding is progressing well. Some areas are nearly complete. Others need up to a week to wrap up. Rains fell across most of southern and central Alberta in the past week, with over 2" in some areas. Frost was widespread in central Alberta, with some areas reporting as low as -6 C. Alberta crop report.

Saskatchewan: Canola seeding is near complete in west and northeast regions. Parts of the southeast have not started seeding due to excess moisture and continuing rains. Growers there are looking at new crop insurance deadlines, which are June 1 for some areas. Frost hit the north canola growing region, with lowest lows around -6 C. Rains fell across the south, which was welcome in the southwest but not at all in the southeast. Saskatchewan crop report.

Manitoba: Canola seeding progress ranges from nothing done in parts of the southwest to maybe half done in the south central region. The provincial average is probably 15-20% but this is hard to pin down since seeding is so sporadic. Only the northwest corner escaped rain in the past week. Many areas had light frost. Manitoba crop report.

After frost, give crops and weeds 3-4 days to recover
Many areas across the Prairies had frost in the past week. Some had fairly heavy frost, with -6 C reported in some locations. Other areas had just a light frost of -1 C or so. Two key questions arise after a frost: Did the crop survive? When can I resume weed control?

How to answer the questions:

Did the crop survive? It takes a few days before you can answer that question. With a light frost of 0 C to -2 C, the risk of crop damage is minimal. With a heavy frost that kills off the cotyledons, it takes a few days before new leaves will start emerging from the growing point between the cotyledons. (Top photo) If no growth occurs within this time, the plant is likely dead. Also, if the stem (hypocotyl) is pinched off or the plant flops over, the plant will likely die. The pinched off or broken stem cannot provide nutrients to the growing point. (Bottom photo)

	This cotyledon has a healthy stem (hypocotyl) and a new green growing point. It will likely survive.

	The stem is pinched off on this frost-damaged cotyledon. It will likely die.

Check the whole crop the day after a frost and 3-4 days after a frost to assess the situation. Click here and here for tips on how to check the field.

If many plants have been killed, the question is whether to reseed. If one or two plants per square foot have survived and if that stand is fairly consistent throughout the field, the best choice is probably to leave it alone. A thin stand is not optimal for yield but a thin stand at the end of May has better yield and quality potential than a reseeded field. If large parts of the field are lost, reseeding (or fallow) may be the only alternative for those areas.

When can I resume weed control? After a light frost, spraying could resume when the following conditions are met:

• a minimum of one night with minimum temperatures of 5 C (the minimum for biological activity to occur),
• a minimum of one day of good growing conditions (warm and sunny) have passed,
• good growing conditions (warm and sunny) are present at the time of spraying
• no evidence of frost damage (blackening and water soaked appearance) on the crop or the weeds. "Crop" is included here because even a herbicide tolerant canola crop requires that the metabolism of the plant be working at full capacity to enable it to effectively process the herbicide and prevent injury.

Always talk to your local product rep to see how they will support the use of their product following a frost or cool temperatures.

After a heavy frost, check for damaged tissues such as water soaked and darkened leaves that eventually lead to necrosis (dead, dry tissue). If tissue damage is greater than 40% of total leaf area, allow new leaves to grow before making herbicide applications.

Weeds stressed by frost are not more susceptible to herbicide. In fact, they are more likely to be less susceptible.

Because of the above concerns, chemical companies may not be able to guarantee their products' performance if applied too soon after a frost. And for some products, performance may be reduced if applied at temperatures below (or above) a certain temperature. Check the performance restrictions on a product before using it. Talk to the retailer or check the guide to crop production. Click your province for your guide: Alberta Saskatchewan Manitoba.

Just want to get seeding. Growers who want to do a preseed burnoff and then get seeding may not want to wait 3-4 days for the weeds to recover from a frost. In this situation, growers should recognize that if they go ahead and spray right away, efficacy may be reduced. However, even with the lower efficacy, doing the burnoff and then seeding may provide a higher return than seeding without the preseed burn and letting all the weeds compete until an early in-crop application. Consult with your supplier for information on product performance in these conditions to determine the best approach.

In all cases, it helps to know the weed spectrum and weed sizes before deciding the best course of action. Weigh the pros and cons of each option, and set expectations accordingly.

Spray early in crop
Early weed control is the most economical and often the most successful. It reduces weed competition for nutrients and moisture, improving the yield potential for canola. Younger weeds are also easier to control and that control may be achieved with lower rates. Later emerging weeds have less impact on yield than those emerging with or ahead of the crop. For these reasons, in-crop weed control should occur as early as possible.

A possible strategy to control early weeds to maximize yield while also catching later germinating seedlings is split applications. This is an option with glyphosate on Roundup Ready canola varieties and Liberty on Liberty Link varieties. The first application of the split is best timed just as the crop is emerging. The second application, if necessary, can go on before the maximum crop stages for each herbicide system and at the optimum stage for control of the emerged weeds.

Here are the staging options for each herbicide tolerance system:

Roundup Ready: The window is from seeding to the 6-leaf stage. Two applications are an option, but the maximum application rate per season is the equivalent of 1.0 litre per acre of the original 356/360 g/L formulation in RR canola.

Liberty Link: The window is from cotyledon to early bolting. Set the rate based on weed pressure. Split application is an option, but the maximum allowable rate per season is 2.97 litres per acre.

Clearfield: The window is from the 2-leaf to the 6-leaf stages. Odyssey, Odyssey DLX or Absolute can be applied only once per season (no split applications) but have some residual activity.

Scout fields to see what weeds are present and at what size and plant density before choosing an appropriate rate and/or tank mix option. For example, Canada thistle is 3 to 4 times more competitive than wild oats and may require a special approach for effective control. Research from AAFC in Lacombe, Alta., shows it only takes 10 Canada thistle shoots per square metre to cause a 10% yield loss in canola. For more on this, read the Canola Council of Canada factsheet, "How many weeds are too many?"

Consult with your company representative to determine the appropriate rates and tank mix combinations for your situation and weed population, or click your province for a link to your guide to crop protection: Alberta Saskatchewan Manitoba.

Insect update
Take a few extra minutes each day to scout emerged crop for insect damage. Rain delays provide time to give each field a close inspection.

Flea beetles
High levels of flea beetles have been observed in the Peace River region, but right now they're feeding on volunteer canola because not a lot of crop has emerged. For crop that is emerged, scout and assess the threat before spraying.

When 25% of leaf area is lost, on average, and flea beetles are still present and feeding, then a foliar spray will often pay off. But look closely at the damage, including on the underside of cotyledons and stems. If damage on first leaves is less than on cotyledons, this may indicate flea beetle pressure is waning. A spray may not be warranted in that case, but keep scouting - especially if this is an early crop and the overall flea beetle threat continues. With higher temperatures, flea beetle pressure can change in a hurry. Keep scouting until the threat is known to be over.

Spot or perimeter spraying may be enough in some cases, if populations are moderate and cool conditions keep them less mobile. Flea beetles overwinter in forage areas, shelterbelts and grass areas along field borders. Start looking for damage in parts of the field that border these areas. Spot spraying may be all that's required.

Cutworms
In a canola field near Vermilion, Alta., 3 out of 10 plants per row were found clipped off this week. Digging uncovered 2 to 3 pale western cutworms per foot of row. Over on a field near Westlock, Alta., dingy cutworms were found feeding at 2:00 in the afternoon, which is uncharacteristic of cutworms. Cutworms are usually nocturnal. Cutworms will be a pest to watch again this year. Click here for more on cutworm identification, scouting, thresholds and control measures.

Wireworms
Wireworms are another below-ground feeder, like some cutworms, and can cause bare patches or wilting plants to appear in canola fields. (Note that there are other potential causes for these symptoms, including wet conditions.) Wireworm numbers tend to be higher in pasture or hayland put into annual crop production. Nothing is registered or effective for wireworm control in canola. If wireworms are found, this gives us an opportunity to identify what species are present in an area and find out more about the insects. It also helps to develop control strategies for the future. You can send samples to Bob Vernon at Agriculture and Agri-Food Canada's Pacific Agri-Food Research Centre. The address is 6947 Highway 7, PO Box 1000, Agassiz, B. C. V0M 1A0.

When is too late to seed canola?
Manitoba crop insurance data show that canola seeded the first week of June yields about 85% of canola seeded mid May, on average. (See the table below.) Trends are similar for other provinces. Growers in rain-delayed Manitoba, eastern Saskatchewan and southern Alberta are wondering when is too late to seed canola? Factors in this decision are maturity of the variety, average date of first fall frost, crop insurance deadlines and profit potential of alternative crops.

Maturity of the variety. Ask for the days to maturity of the variety you plan to seed. Consider regional differences. Growers could try to find an earlier maturity variety, but that is often easier said than done - especially in a year when canola acres are predicted to rise and seed availability is limited. Click here for tips on how to get canola to mature earlier.

Average date of first fall frost. This will tell you how much growing season you have left - on average. Click your province for a map showing average dates for first fall frost: Alberta Saskatchewan Manitoba. (Click here for frost probabilities for each station on Alberta's AgroClimatic Information Service (ACIS) website.) Most fall frosts occur within two weeks either side of the average date for your area. For example, if the first fall frost is between August 31 and September 6, on average, then a variety with 100 days to maturity should be seeded this week to be on the lower risk side for fall frost losses.

Profit potential of other crops. Yield potential for all crops drops with late seeding. Will a lower yielding canola crop provide a better return than a lower yielding wheat or barley crop? Take time to pencil out the economics.

Crop insurance deadlines. Manitoba has an earlier crop insurance seeding deadline for 2011. In Manitoba, crop risk area 2 has a deadline of June 10 for canola, and crop risk area 1 has a deadline of June 15 for full coverage. In Saskatchewan, the deadlines vary by R.M. Call the SCIC toll free customer service line at 1-888-935-0000 or visit the local SCIC office for specifics. For Alberta deadlines, click here to find contact information for the local AFSC office.

Aerial seeding a last resort
Some growers in Manitoba and southeastern Saskatchewan are considering seeding by plane or helicopter. There are no studies on aerial seeding of canola. It has been done in very wet springs, but if growers have to seed by plane because the field is too wet for a broadcast floater, that means it's probably also too wet for weed control, fertilizing and harrowing - each important to a profitable broadcast canola crop.

Fields too wet for ground equipment have probably been wet for a month or more. That means most of the nitrogen reserves have been lost. Since fertilizer is too heavy to apply efficiently by plane, the canola seeded by plane will not get a nutrient top up until the ground is firm enough for ground equipment. Canola needs fertilizer early, and ideally at the time of seeding, to reach its full yield potential.

Canola emerging in wet soil will also be oxygen deprived. This is not a hospitable environment for seedlings. Seeds may germinate, but the roots will likely die.

Think about your agronomic plan before considering aerial seeding. Will you be able to get across the field in a timely fashion?

Top up nitrogen before 5-leaf stage
Growers may have good reasons for a post emergence top up of nitrogen this year. For example, maybe they couldn't get the supply they wanted at seeding time. Or maybe they cut back rates at seeding because of wet soil conditions with a plan to top up later if conditions improve and a good stand emerges.

If planning a top up fertilizer application, nitrogen must be available before the 5-leaf stage of the crop to provide the largest yield benefit.

With very nitrogen deficient soils, growers will want to apply earlier than the 5-leaf stage to make first stems and flower clusters more productive. This is especially important when seeding is delayed. Later applications will stimulate more branching, which will delay maturity.

Click here for more top up tips.

Early blackleg infection causes yield loss
Early blackleg infection - from the cotyledon to 3-4 leaf stages - leads to the greatest yield loss. If growers see blackleg lesions on cotyledons or leaves early in the season (see the top photos, below), this may indicate a greater risk of potential blackleg problems.

These tiny lesions may be tricky to spot, and you probably won't see many of them. When scouting, also look for blackleg pseudothecia (black spots) on old canola residue, which may still be present on fields with a tight rotation. (See the bottom photos, below)

Even if you can't spot lesions on new plants or old stubble, the field could be at risk of serious blackleg infection. Here are factors that increase the blackleg risk:

1. Tight canola rotation

2. Using the same variety many times in the rotation

3. Yield loss to blackleg in previous years

4. Using untreated non-certified seed

5. Poor brassica weed control in previous years. These weeds can host blackleg in non-canola years

6. Moist soils and warm humid conditions

Using R rated varieties and rotating varieties, especially out of varieties that showed blackleg damage in previous years, can reduce the blackleg risk. But those measures alone may not be enough in areas where blackleg risk is highest.

If the above factors and your crop scouting suggest high risk for blackleg, consider a fungicide as an additional tool to limit infection and yield loss. Check the guide to crop protection for fungicides registered to control blackleg. Click your province for a link to your guide: Alberta Saskatchewan Manitoba. It is always good to leave a check strip and compare yields of treated to untreated areas.

	Blackleg lesions on young plants are more likely to cause significant yield loss than infection later in the season.

	Blackleg lesion on cotyledon.

	Blackleg lesion on early true leaf.

	Blackleg pseudothecia (reproductive organs) on old canola stubble. These pseudothecia release the spores that infect new plants.

	Another view of pseudothecia on old canola stubble. Source: Ralph Lange, Alberta Innovates.

For more information, contact a Canola Council of Canada agronomy specialist in your region:

• Kristen Phillips, agronomy specialist, Manitoba, phillipsk@canolacouncil.org, 204-761-2143
• Jim Bessel, senior agronomy specialist, Central Saskatchewan, besselj@canolacouncil.org, 306-373-6771
• Shawn Senko, agronomy specialist, Eastern Saskatchewan, senkos@canolacouncil.org, 306-270-9307
• Clint Jurke, agronomy specialist, Western Saskatchewan, jurkec@canolacouncil.org, 306-821-2935
• Dan Orchard, agronomy specialist, Central Alberta, orchardd@canolacouncil.org, 780-777-9923
• Troy Prosofsky, agronomy specialist, Southern Alberta, prosofskyt@canolacouncil.org, 403-332-1412
• Doug Moisey, senior agronomy specialist, North Central Alberta, moiseyd@canolacouncil.org, 780-645-9205
• Greg Sekulic, agronomy specialist, Peace Region, sekulicg@canolacouncil.org, 780-832-2382

This media release is supported regionally by: Alberta Canola Producers Commission; SaskCanola; Manitoba Canola Growers Association; Canola Council of Canada; Peace River Agriculture Development Fund; B.C. Ministry of Agriculture & Lands.

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