Story Posted: July 13, 2011

Canola Watch: Fungicide for thin crop, Insect update

Issues of the week: Growers with uneven, thin or late canola are struggling with the sclerotinia spray decision, especially if they've been without rain or high humidity the past week or so. Uneven crop presents a challenge for spray timing. A split application may be worthwhile if the later plants or late-flowering branches still present a significant yield potential and are likely to mature.

While scouting to assess the sclerotinia situation, take a few minutes to look at the field. Mark off areas that you expect will contribute the most to yield, then check those areas with the yield monitor at harvest to see if your mid season assessment proves true. If you see blank areas, try to figure out why these blanks occurred. These are good tests to train your eye and make adjustments for next year. Click here for more tips.

Did you deal with a lot of volunteer canola this year? Harvest losses are a key contributor to the volunteer canola seed bank. Learn how to reduce these costly losses at the Westlock combine clinic next week.

Crop and weather update
Peace: The whole region got rain the past week, including up to 6" in places that didn't need it. Some fields are underwater from corner to corner. On a positive note, the north region, which did need rain, got some. LaCrete area got 1.5" to 3". Most canola fields in that area are at 30-40% bloom, or less, so this rain will improve yield potential.

Alberta: The south received welcome but spotty rains the past couple days. Areas close to Calgary got a couple inches. Areas around Medicine Hat got next to nothing. Central Alberta received up to 4" in some areas and less than 1" in others. East central pockets could use a rain. Most canola crops range from early bolt to full flower in the south, and early to mid flowering in central regions. This is up to 10 days late, even though growing degree days are near where they were last year. Click here to find current and historic growing degree day maps. Alberta crop report.

Saskatchewan: Southwest could use a rain after a few dry days above 30 C last week. Southeast growers estimate that 20% of seeded crop has been lost to flooding. Crops in the north are looking better, although the northeast is hit and miss. Some areas have crops with yield potential above 50 bushels per acre. Other areas have yield potential of 5 bu/.ac. or less. Saskatchewan crop report.

Manitoba: Rain for the week was zero to 2". Growers in the east who floated on seed and top dressed fertilizer still need a good rain to move fertilizer into the root zone. Staging ranges from cotyledon to flowering, with canola in the east further along than in the west. Manitoba crop report.

Help for volunteer canola management
Volunteer canola is one of the more challenging weeds. It can provide a disease bridge for blackleg and clubroot in non-canola rotation crops, and it can create weed management and crop staging difficulties in following canola crops. Growers can significantly reduce their volunteer canola seedbank by reducing losses at harvest. Canola losses at harvest can be up to 5 bushels per acre, which is 50 times the typical seeding rate.

The Combine Clinic July 18 and 19 (pick one day) in Westlock, Alta., will explain how to reduce harvest losses, putting more yield in the combine tank and reducing the volunteer canola seed bank. Click here to register.

Here is what a few canola growers said about the Combine Clinic last year in Vegreville, Alta.:

Brad Lockhart of Viking, Alta: "I learned why correct placement of filler plates in the concave is important. We heard that no two combines are exactly the same so if you're running two or more machines, each needs to be set individually."

Tim Nerbas of Waseca, Sask: "I've been running the same machine for the past 15 years but I still came away from the clinic with some good information. It was good to tap into Les Hill's 35 years of experience and knowledge on every combine."

Nico Rookmaker of Ohaton, Alta: "It was helpful to see things pointed out while we walked around the machine." Rookmaker also met a technical representative from the manufacturer who pointed out updates on the Lexions that Rookmaker was not aware of.

Click here for an audio podcast describing the clinic.

Sclerotinia in an uneven crop: Consider a split application
Many growers with high yield potential are spraying fungicide to protect canola from sclerotinia stem rot. With $12 per bushel canola prices, high soil moisture, and high infection rates last year, it was an easy decision for many of them. The sclerotinia spray decision is more complicated for growers with canola stands that are thin, late or at multiple stages. Click here for an interview with CCC senior agronomy specialist Doug Moisey on this topic. Here are pointers for certain situations:

1. A multi-stage crop. With some plants flowering and others still bolting, do you protect the first plants or wait until the upcoming group starts to flower? If the stand is thin and has low yield potential, a spray may not be economical, especially if a lot of the yield potential is based on very late plants that may not mature.

If conditions are moist and humid all through flowering and the crop has good yield potential, two sprays 7-10 days apart may be warranted to protect this multi-stage crop. You may decide the second application isn't necessary if conditions turn dry or if the later flowering plants are simply too late and too high risk to be worth protecting. Plants that have not started to flower by next week will be well into September before the seeds are ready for swathing. This raises the risk for frost damage and high green seed counts. Lance, Rovral and Serenade are the only fungicides approved for a split application.

2. Thin healthy crops. Thin crops with large plants will also flower longer. The plants themselves may be at the same growth stage, but they will have multiple branches that flower later than the main stem. If the stand is thin as a result of low seeding rates or low seedling survival but existing plants are now healthy and the crop has decent yield potential, this field may benefit from a split application.

Also, the perception is that a more open canopy will allow a drier microenvironment leading to reduced sclerotinia risk. This may be true under dry conditions, but if conditions remain wet and humid throughout flowering, the additional branching and longer flowering period create more opportunities for infected petals to be caught on leaves or stems, leading to more potential points of infection.

Note: In a field with large heavily branched canola plants, infection of the main stem tends to produce much higher yield loss than infection of side branches. When conditions remain conducive to sclerotinia infection, spraying late to hit flowering side branches will not provide the same economic return as an earlier spray to target petals are more likely to drop onto lower leaves and stems leading to main stem infections.

3. Thin weak crops. If the stand is thin and bolting prematurely because of saturated soils or some other stress, these plants may not provide an economic response to fungicide because disease is unlikely to be the major factor limiting seed production.

Other questionable situations for sclerotinia spraying

Low yield potential. The lower the yield potential, the larger the percentage yield loss from sclerotinia needed to cover control costs. For example, if control costs $24 per acre and yield potential is only 20 bu./ac., at $12 per bushel the breakeven yield loss is 2 bu./ac. (or 10%). Using the rule of thumb that yield loss is typically about half the disease incidence, that means you need about 20% or more of the plants infected before a fungicide would pay.

No recent history of sclerotinia. Growers in a region that hasn't had much sclerotinia for the past four years (the Peace region, for example) may not see many apothecia emerge to distribute spores. But with all the moisture in the Peace this summer, skipping a fungicide spray may not be worth the risk. Under optimal conditions, it may not take many spores to cause an economic level of infection. This may be a good year for a petal test to see if spores have in fact landed on the petals. Submit a sample at early flowering if possible. That will provide enough time to get test results and still be within the spray window if action is required.

Sclerotinia spraying: Ground vs. aerial
All sclerotinia control products are registered for both ground and aerial application. Both methods have their positive and negative aspects. If a fungicide is needed, getting it applied at the right stage will be the most important consideration.

High clearance ground sprayer. In moist conditions, which are conducive to sclerotinia infection, the ground may be soft and sprayers will leave ruts. These ruts can slow the harvest process and be present in the field for years afterward. But if the aerial applicators are busy and can't get to your field in a timely fashion, ruts may be tolerable if it means getting the fungicide applied on time. Ground sprayers will also trample crop, but a 100-foot boom with 12" tires (times 2) equals only 2% trampling, or possibly less if the sprayer has crop dividers. Yield loss is not usually as high as the level of trampling. Yield loss from sprayer trampling should be less than 1 bu./ac. on a 50-bushel crop, which would be tolerable if the ground sprayer does the job on time and effectively.

Airplane: Spraying fungicide by air can be faster and more timely if the sprayer can't make it through the field because of soft conditions. If everyone is in the same situation, booking a plane to do the job at the correct stage may be a challenge. If you can get a plane booked, then a plane has its advantages: It doesn't leave ruts or trample crop, and it can do the job in conditions when a ground sprayer can't. Ensure the applicator uses the higher end of the range of water volumes recommended for aerial application to allow maximum coverage, especially for denser crop canopies.

Insect update
Lygus. Some Alberta fields have had 6-8 adults per 10 sweeps in the past week. Any field getting 0.5 to 1 lygus per sweep at early flowering should be monitored closely as it comes out of flower. Those numbers at early flower mean the next generation of lygus that comes out at the podding stage is more likely to be at damaging numbers - as long as weather conditions (warm and fairly dry) favor buildup. At the pod stage, counts of 8 or more per 10 sweeps can be enough to trigger a spray at today's prices. If we continue to get bands of showers, lygus populations will likely decline.

Diamondback moth. Adult counts in traps are generally low - except in eastern Manitoba. As fields come out of flower and are podding, growers in areas with high counts need to scout aggressively to assess the threat of damage from larvae.

Slugs. Slugs are feeding on canola plants in a few fields in Alberta. The situation is not widespread but causes anxiety for those few growers. There is no registered product to control slugs in canola. Metaldehyde is a molluscicide registered for slugs in vegetable gardens and ornamentals. However, even in high value vegetable crops, control is considered too expensive on a large field scale. Aside from drier conditions, one long-term management consideration for fields with high slug counts could be tillage, but that is not proven and does not provide a remedy for this year's canola crop.

Cabbage seedpod weevil. The weevil is at thresholds in pockets of southern Alberta, but numbers are down from previous years. In southwest Saskatchewan, counts are not near economic threshold. The highest recorded count in Saskatchewan is 12 adults in 10 sweeps (or 1.2 per sweep, on average.) At prices over $8 per bushel, an average of 2 to 3 weevils or more per sweep is the recommended economic threshold.

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. Adult moth counts were elevated in some areas in northwest Saskatchwan. Entomologists do not anticipate a big issue with bertha this year. Generally the peak emergence of the moths is about the middle of July so it will take a couple more weeks of monitoring to completely rule out the threat.

Root maggots. Plants are toppling over in some fields in central Alberta. Growers think disease is the cause, but when they pull up a plant they find the roots full of maggots. There are no effective control options in crop, but growers should note these fields as they plan cultural control strategies for next year.

Aphids. Thirty to 40 per plant have been spotted in a canola field near Elie, Manitoba. This is a rare event. Aphids, if they do appear in canola, tend to cluster on a few plants here and there within a small pocket of the field. Turnip aphid is the one species that will feed on canola bud clusters. (See the top photo, below.) Those are the ones you have to be concerned about. If 10% to 20% of stems have aphid clusters around the flower buds and if this is spread over a large enough area, then a spot spray of that area may be warranted. Dimethoate (Cygon and Lagon) are registered for aphid control in canola. Look for lady bug larvae and adults before spraying. (Bottom photo, below.) Lady bugs eat a lot of aphids and can keep populations from escalating, but keep watching. Aphid numbers can explode quickly.

	Aphids can cluster on canola but rarely reach levels that require a spray. Source: Scott Hartley, Saskatchewan Ministry of Agriculture

	Lady bug larvae and adults can eat a lot of aphids. Look for them before spraying. Source: Scott Hartley, Saskatchewan Ministry of Agriculture

Blackleg in eastern Manitoba
Canola fields in eastern Manitoba are showing signs of blackleg infection. The photos below show typical damage. There is no effective fungicide for canola at this growth stage (protective sprays had to be applied early in the season) but growers are encouraged to scout and assess the level of damage before they harvest the crop. This will help in blackleg management decisions for future years.

	Blackleg lesion on leaf in eastern Manitoba canola field. Source: Anastasia Kubinec, Manitoba Agriculture, Food and Rural Initiatives

	Blackleg damage on canola leaves, Manitoba July 2011. Source: Anastasia Kubinec, Manitoba Agriculture, Food and Rural Initiatives

	Blackleg damage on canola leaves, Manitoba July 2011. Source: Anastasia Kubinec, Manitoba Agriculture, Food and Rural Initiatives

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 run daily through to the end of this week. Click here for more information. To register call 204-745-5663.

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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