Story Posted: July 06, 2011

Canola Watch: Sclerotinia timing, Hail response

Issues of the week: Moist conditions increase the sclerotinia stem rot risk. High humidity (even if it doesn't rain) can promote apothecia to release higher levels of sclerotinia ascospores. Ideal timing for sclerotinia spraying is at 20% to 50% bloom.

Growers with hailed, late or thin poor looking crop are looking at fertilizer top up or other treatments to promote the crop. Fertilizer top up may help reduce stress on a hailed crop that is trying to recover, but remember that top up fertilizer can delay maturity.

We encourage growers to attend the Canola Council of Canada Combine Clinic in Westlock, Alta., July 18 or 19 to learn how to reduce losses, which can be 2-5 bu./ac.

Crop and weather update
Peace: Weather has been showery and cool, with temperatures rarely over 20 C. Wind is helping to dry out saturated fields. The north region has still not received meaningful precipitation. Most crops are at early bolt and bud stages.

Alberta: Crop is rapidly advancing with warm weather and good moisture. Spotty hail across the central region. Crop stage is anywhere from 2-leaf to 30% bloom across region. Alberta crop report.

Saskatchewan: Much needed heat has arrived. Scattered showers covered the province, with some flooding damage in western areas in addition to what had already occurred in the east. Canola staging ranges from 3-4 leaf to 40% flower. Saskatchewan crop report.

Manitoba: Rainfall this week as anywhere from zero to 1.5”, and hail hit some regions. Late seeded canola is at the cotyledon stage and the earliest is just flowering. The eastern side, in general, is further along than the west side. Manitoba crop report.

Canola can recover from hail at rosette and flowering stages
Hail damage in some regions this week ranged from a small smattering to 50-100% damage. Plants injured in the late vegetative or early flowering stages seldom die. A well established root system and the ability to develop secondary flower clusters help the plant recover. When buds and flowers are lost due to injury, the plant recovers rapidly by developing of flowers that normally would have been aborted. The plant also develops flowering branches from growth buds lower down on the plant, replacing to a degree, the lost buds, flowers and pods. Seed yield loss will depend on the per cent of leaves and branches lost. Click here and scroll down to Table 7 for details.

At the rosette stage, yield loss will be mainly related to lost leaf area. A general rule of thumb is that lost yield will equal about a quarter of the percentage of leaf area lost. Based on this, if 40% of petals are lost, the yield loss will be 10%.

Weed control in hailed canola. Hail that hits canola will hit the weeds, too, and if canola plants were ahead of the weeds before the hail, canola will likely be able to keep ahead of the weeds as it recovers from hail. Also remember that hailed canola is under stress and will be more susceptible to injury from the herbicide application. Finally, if canola is regrowing and immediately sending up buds, spraying herbicide could cause abortion of these buds. A plant that is already weakened and set back by hail may not be able to compensate for these losses.

New weeds that emerge after the hail are unlikely to impact crop yield. It might be better in this case to save your money until preharvest timing.

If recovering plants are still within the label staging restrictions (sending up new leaves not buds) and have yet to be treated then a statement regarding a negative impact on yield and therefore a recommendation to spray may have merit. Consider a grassy herbicide alone if weed pressure dictates.

Fertilizer top up for hailed canola? Fertilizer top dressing right after a hail has been shown in some anecdotal cases to improve canola recovery after a hail, but third party research into this practice is limited. As noted above, consider the stage of canola and its chance of recovery before investing in a fertilizer top up.

If your fertilizer rate was in line with yield potential before the hail, fertilizer top up after hail may not provide an economic yield benefit but it may provide a stress relief factor. Late fertilizer can also extend maturity, which increases the risk of fall frost reducing yield and quality. Remember, the yield response from a nitrogen application after the 5-leaf stage is reduced and any benefit may be offset by a delay in maturity.

Micronutrient or hormone treatments. Some growers are putting boron with herbicides and fungicides thinking it will boost yield for hailed, late or thin canola crops. Growers considering this treatment should leave a check strip to see whether any benefit shows up on the yield monitor. Note that the check strip should have the herbicide or fungicide treatment without boron. (The check strip should not be “no treatment” because if a benefit is observed in the treated strips, the grower won't know if it resulted from the micronutrient or from the herbicide or fungicide.)

In the case of boron, for example, do soil tests show low boron levels? Does canola show signs of deficiency? Leaf symptoms from boron deficiency include leaf convex cupping, yellow chlorosis, red coloration or brownish or even whitish interveinal coloration. Root symptoms also are evident (small, thick roots). Boron symptoms would be worse in high pH soils.

Hail can increase sclerotinia risk
Regrowth after hail may extend the flowering period, which also increases the sclerotinia stem rot risk. When hail hits at late flowering, broken stems and leaves along with lodging can further increase the sclerotinia risk due to the fungus growing from plant to plant directly. But should a grower automatically spray fungicide on a hailed crop? That depends. If yield potential is still high and if conditions favorable to sclerotinia stem rot persist, then a fungicide spray may pay off.

Hail and other diseases: Hail wounds on the plant can provide points of entry for alternaria black spot or blackleg if environmental conditions have been conducive to spore production and disease development.

Sclerotinia checklist: What does your score mean?
Even if it doesn't rain during flowering, high humidity can promote apothecia to release sclerotinia ascospores. Consider that when using the checklist below to calculate your sclerotinia stem rot risk. Don't forget that the risk of sclerotinia infection doesn't only come from your fields but also your neighbors' fields. Check fields that were in canola last year for apothecia development. Click here and scroll down for photos of apothecia.

Assessing your score. This checklist developed in Sweden can be useful in helping to assess disease risk in fields. Growers should fill out the checklist for each field shortly after first flower (when 75% of the canola plants have at least 3 open flowers). The greater the risk score for a field the higher the probability of a positive economic return. Results in Sweden have suggested that fields scoring 40 or higher will likely benefit from a fungicide, but this may vary a bit depending on fungicide cost and commodity price. Using this checklist effectively requires scouting for apothecia, usually in nearby cereal crops following canola or other host crops (e.g. beans, sunflowers) in the rotation. The same moist soil conditions conducive to apothecia production can also favor the development of many other types of mushrooms or fruiting bodies.

Fertilizer top up to rescue late thin crop
What is the risk with investing more inputs in a late thin crop that already faces a high risk of yield and grade losses due to fall frost? As a rough guide, a crop needs 40 to 60 frost free days after the start of flowering to reach maturity. That takes us to late August or early September if the crop is flowering today. If a late crop is still two or three weeks from flowering, it is already at high risk of fall frost damage which could negate any economic benefit from added nutrient. Increasing the nitrogen rate will delay maturity as the plant tries to make use of this nutrient.

Insect update
Cabbage seedpod weevil
Adults have arrived and are feeding on volunteer canola at the bloom stage in southern Alberta and southwest Saskatchewan. Weevils move to canola fields at the bud to early flower stages. Growers should start scouting.

The proper way to scout for cabbage seedpod weevil adults is with a sweep net. Begin sampling when the crop first enters the bud stage and continue through the flowering period. Select 10 locations within each field and at each location, count the number of weevils from ten 180° sweeps. Sample both the perimeter and interior of the field to obtain an accurate estimate of weevil numbers throughout the field. Click here for more detailed information on proper sampling techniques.

The economic threshold for the weevil is 20 to 30 in 10 sweeps, depending on crop price.

It is important not to spray too soon, as the weevil will typically continue to invade for at least a week to 10 days after the first flowers open. The optimum time to spray for cabbage seedpod weevil is early flowering (10% flower if possible). Spraying at 10% flower will allow the weevils more time to move into the field, while at the same time it is still early enough to keep them from laying any significant number of eggs in the newly forming pods. Spraying after 10% flower when populations are at or above threshold may not only result in yield loss, but will also impact beneficial insects including pollinators who have moved into the field. It is important to keep in mind canola's ability to compensate for weevil feeding on buds and stems where moisture is not limiting. Where moisture constraints are present, the ability to compensate may be reduced, and using the lower end of the threshold range may be appropriate. The Prairie Pest Monitoring Network provides identification and more monitoring tips: 2010_CSPW protocol

Scott Meers of Alberta Agriculture & Rural Development is recruiting scouts and crop consultants to enter cabbage seedpod weevil data into an online survey. This data will populate a google map that will show weevil hotspots in real time. Call 310-2777 (only in Alberta) and provide name, sample date, location (LLD or GPS), total number of sweeps, and total number of weevils in those sweeps.

Bertha armyworm
Adults showing up in traps across the Prairies. Numbers are on the rise, so start watching fields for larvae as fields are coming out of flower.

Diamondback moth
Eastern Manitoba has high counts of adult moths and numbers are on the rise in other locations. Now is the time to start scouting and watching your fields on a regular basis so you can watch for economic thresholds of larva if required.

Root maggot
High counts are reported in some parts of western Saskatchewan and the sandier land in Manitoba. If you see sick-looking canola plants starting to wilt, pull up a few and look at the root. Look for tunneling along the root. There is nothing that can be done to control maggots now, but canola on canola can increase the risk. Fields with high maggot populations may benefit from an extended break from canola. Higher seeding rates should be considered to reduce the overall feeding damage on a per root basis.

Volunteer canola control in an unseeded field
Growers with unseeded acres are finally able to do some spraying. They need to control volunteer canola that is now done flowering. Canola that is done flowering will have already produced a large amount of viable seed. Unfortunately, controlling plants at this stage of growth will do little to reduce the viability of those seeds.

If controlling volunteer canola is desirable for other reasons (i.e. moisture conservation), apply glyphosate at 420 grams per acre to non-Roundup Ready volunteers. For Roundup Ready volunteers, growers have a variety of herbicide options that can be used on unseeded fields. Before spraying these products, ask the retailer or company rep for recommended rates for volunteer canola at this size, and check the product's recropping restrictions. Some have residual periods that may affect cropping options for next year.

Growing a cereal on that field in 2012 will give the field a canola break and provide another opportunity to control any volunteers that set seed. Mowing and tillage are other options.

Coming events
Combine Clinic. The Canola Council of Canada and Alberta Canola Producers Commission will host a Combine Clinic in Westlock, Alta., July 18 and 19. Click here to register. Click here to hear a podcast for more information.

Crop Diagnostic School in Carman, Manitoba runs this week and July 11-15. Click here for more information. To register call 204-745-5663.

Farming Smarter diagnostic field school ends July 7 in Lethbridge, Alta. Click here for more information and a registration form.

Conservation Learning Centre tour, July 12 at Prince Albert, Sask. For more information, call Curtis Braaten at 306-960-1834 .

Wheatland Conservation Area and AAFC tour, July 12 at Swift Current, Sask. For more information, call Shannon Chant at 306-778-8291

AAFC and Western Applied Research Corporation's Scott Field Day in Scott, Sask., is July 13. The morning tour is from 9:00 to 12:30 and the optional afternoon tour is 1:30 to 3:00. Canola topics include inputs to target high yield, seeding speed and its impact on emergence, and canola variety shatter resistance. For more information, contact Sherrilyn Phelps at 306-446-7475.

CCC Webinar: Sclerotinia Management in 2011 with Faye Dokken Bouchard, plant pathologist with Saskatchewan Ministry of Agriculture. July 14 at 10:00 a.m. CDT. Click here to register.

Canada-Saskatchewan Irrigation Diversification Centre tour, July 14 in Outlook, Sask. For more information, call Gerry Gross at 306-867-5523

AAFC and Indian Head Agricultural Research Foundation tour, July 19 in Indian Head, Sask. For more information, call 306-695-4200

Southeast Research Farm tour, July 20 in Redvers, Sask. For more information, call Elaine Moats at 306-848-2856

Crop Protection Field Day (University of Saskatchewan and AAFC), July 20 at Kernen Research Farm, Saskatoon. To pre-register, call at 306-966-5857

AAFC and Northeast Agriculture Research Foundation tour, July 21 at Melfort, Sask. For more information, call Kim Stonehouse at 306-878-8807 .

East Central Research Foundation tour, July 21 at Canora, Sask. For more information, call 306-788-1508.

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