Canola Watch Report No. 15
Western Canada August 14, 2008
In This Issue
Swathing under way, but just barely
Lygus bugs sticking around
Grasshopper hot spots
Keep scouting for bertha and diamondback larvae
Revised insect thresholds
Start watching for late season diseases
Swath timing a big challenge
Thinking about straight cutting?
What about chemicals to assist dry-down?
Watch preharvest interval and keep bins insecticide-free
Next year’s weed control? Already?
Finding any flea beetles?
Questions & Contacts
The Alberta Canola Producers Commission (ACPC) has developed an Alberta focused version of this report. Visit the ACPC website at: http://www.canola.ab.ca and click the Alberta Canola Watch button.
Lygus bugs sticking around
Growers in areas of eastern Manitoba, southern Alberta and the Peace region continue to report lygus bugs at levels above economic thresholds in some cases. However, a large proportion of the population are young nymphs that will do very little damage until they mature to later instars or adults. Consider crop stage when deciding whether or not to spray. Later maturing fields may still be at significant risk, but fields nearing maturity may reach the swathing stage before younger lygus bugs can do economical damage. Fields nearing maturity will also be less vulnerable as the pods mature and become tougher for lygus bugs to pierce. For this reason it may be reasonable to exclude from sweep net counts early instar nymphs without visible wing buds as the crop gets closer to maturity.
Remember that the preharvest intervals for insecticides registered for control of lygus are all at least seven days. Preharvest interval is the time between application and cutting of the crop. For more info on lygus and thresholds go to: http://www.industrymailout.com/Industry/Redirect.aspx?u=115753&q=83695522&lm=11426940&r=107325&qz=55793b49cf144fffe0aa0c0923df1b52
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Grasshopper hot spots
High grasshopper populations in southwestern Manitoba and northwestern and southeastern Saskatchewan continue. Canola is not a preferred food source for grasshoppers, but they will cause damage to the crop in some instances. Often there will be an edge effect as grasshoppers move into canola from other preferred host crops, so it is important to scout throughout the field to determine the extent of the infestation. The recommended threshold for control in canola is about 7-12 per square metre, but do confirm that the species present are pest species. For more information regarding grasshoppers check the following link: http://www.industrymailout.com/Industry/Redirect.aspx?u=124026&q=83695522&lm=11426940&r=107325&qz=5de0ea3d5d511d393a7af47beb3ff4d4
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Keep scouting for bertha and diamondback larvae
Bertha armyworm moth trapping is now wrapped up, with a number of locations in Saskatchewan, including areas north of Tisdale, northeast of Saskatoon and several spots north and east of Regina, remaining areas of concern. Because young larvae are emerging in some of these areas, continue scouting fields. When determining the number per square metre, make the assessment in various parts of the field and be sure to beat the plants together to dislodge all the larvae. Thoroughly inspect the soil surface, including areas beneath leaf litter, to get an accurate count. Check the revised insect threshold link below for more information on appropriate economic thresholds. For further information, go to the bertha armyworm section at the following link: http://www.industrymailout.com/Industry/Redirect.aspx?u=124027&q=83695522&lm=11426940&r=107325&qz=dccedd83bd6c9a95be5aac4d2a6ffdd3
In some instances diamondback moth larvae are also showing up in fields. For more information on diamondback moths refer to: http://www.industrymailout.com/Industry/Redirect.aspx?u=125344&q=83695522&lm=11426940&r=107325&qz=73856dd497e1028733d64d4d4d0df459. Also keep in mind that a general rule of thumb is to decrease thresholds by 25% when more than one type of insect is contributing to the same type of feeding damage.
Prairie-wide bertha armyworm moth maps are in development, and web links for Manitoba, Saskatchewan and Alberta are:
MAFRI:
http://www.industrymailout.com/Industry/Redirect.aspx?u=121112&q=83695522&lm=11426940&r=107325&qz=3f9e0950f58294191291e10904bdbaf9
SAFRR:
http://www.industrymailout.com/Industry/Redirect.aspx?u=122474&q=83695522&lm=11426940&r=107325&qz=e93c71c2c861617e4bbd67c7194a1b7b
AARD:
http://www.industrymailout.com/Industry/Redirect.aspx?u=121114&q=83695522&lm=11426940&r=107325&qz=193e77f8d8d35745980f3e7727073da6
Moth numbers in the above maps are cumulative, which means the total moth count to date is reported. Trap counts are still being collected and added to the maps. Keep checking for updates, even in areas showing low risk because these numbers may still increase to higher risk levels.
Remember these maps are an indication of risk in a region. Field scouting is still required to ensure economic damage does not occur in individual fields.
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Start watching for late season diseases
In addition to the blackleg symptoms noted in previous Canola Watch reports, other late season diseases are starting to affect canola. These diseases may cause premature ripening, which makes plants much more susceptible to pod shatter. Knowing how prevalent they are will be important for making harvest management decisions.
In particular, the sclerotinia symptoms of premature ripening and bleaching of infected plants continues to occur in untreated fields in parts of Manitoba, central Alberta and the Peace region. Alternaria is also beginning to show up in irrigated fields around southern Alberta, and this can affect seed quality as well as contribute to pod shatter.
Check the roots of crops as clubroot has begun to show up in some of the counties around Edmonton where it has been prevalent the last couple of years. Damage to roots from fairly widespread root maggot feeding also has the potential to provide a point of entry for root rots. For more information on these diseases, check the appropriate section of the Canola Growers’ Manual at the following link: http://www.industrymailout.com/Industry/Redirect.aspx?u=124029&q=83695522&lm=11426940&r=107325&qz=f869a9bf537c3d8429f879e2cad07766
For pictures of symptoms of blackleg (and other canola diseases) check out our image library: http://www.industrymailout.com/Industry/Redirect.aspx?u=124030&q=83695522&lm=11426940&r=107325&qz=69c9e83dd3366f302180d16816d688e6
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Swath timing a big challenge
Growers continue to question when to swath canola fields because they’re at various stages of maturity. While this makes it difficult to stick to traditional swathing stage recommendations, growers still need to ensure that seed colour change is occurring when assessing the proper time to swath. The colour of plants and pods will vary among varieties as they mature. Do not use plant colour to gauge proper timing as some pods will appear ripe on the outside before the seeds are mature. Open up pods on the main stem and look at the colour of the seeds to accurately assess swathing timing.
Canola Watch had more questions this week regarding situations where canola is re-flowering following hail damage or due to rain following drought stress. Any pods forming from new flowers at this point in the season are unlikely to produce mature seed prior to fall frost. You would have to wait until currently formed pods were at high risk for shattering to allow these new pods to mature. In most cases they should be ignored when assessing seed colour change for swathing, as they will likely contribute little to the overall yield.
Research indicates that the optimum stage to swath for both yield and quality is up to an average of 60% seed colour change (SCC) within the field. Unfortunately, this year an average of 60% SCC may mean that a large portion of the plants are at 80+% SCC and very prone to shattering. However, swathing earlier may be premature, increasing the potential for green seed issues and yield loss from shrinkage of immature seed. In these situations the best approach is likely to swath when the most mature plants are at about 60% SCC, provided that the least mature plants are showing some seed colour change at the base of the main stem and that the seeds in the upper pods (and branches) are dark green and firm inside. That will minimize yield loss from seed shrinkage and improve the odds that the seed will cure, although it will likely take longer and may require more moisture.
If maturity varies more, determine which plants represent the majority of the yield to determine whether it is better to delay swathing and sacrifice a bit of yield to shattering, or swath a little early and sacrifice some of the translucent seed in the least mature plants. Either way, avoid swathing during the hottest part of the day to minimize shattering of mature plants and slow dry down of less mature ones. This reduces the chance of green seed. This strategy will also help in situations where hail or insect damage is present or diseases such as alternaria black spot have predisposed the plants to shattering. If damage from these factors is fairly severe and shattering risk is high, consider swathing earlier. But try to wait for 20-25% average seed colour change if possible. To learn more about proper harvest field assessment, refer to the revised Canola Council publication Canola Time of Swathing Guide or the following link: http://www.industrymailout.com/Industry/Redirect.aspx?u=124032&q=83695522&lm=11426940&r=107325&qz=5cb72b12c0d3e0098a97ea54eb4e682c
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Thinking about straight cutting?
Many growers are looking at straight cutting their canola this year. To improve the odds of success, consider the following factors:
Crop Canopy – The crop should be well knitted and slightly lodged to reduce the chance of pod shelling and pod drop. Remember pod integrity (including petiole strength which influences pod drop) can be affected by frost, drought and insect damage (e.g. exit holes from cabbage seedpod weevil, pod feeding by diamondback moth or bertha armyworm larvae).
Disease – The crop should be relatively free from diseases including blackleg, fusarium wilt, sclerotinia and alternaria. These diseases can cause premature ripening, which can in turn cause pod shattering.
Hail - Crops affected by hail are poor candidates for straight cutting due to the probability of greater disease infection through damaged tissue and reduced pod integrity from physical damage. Also, any late season hail often causes greater levels of damage to standing crops than swathed crops.
Frost Risk – Canola seed in the pods is at significant risk for fall frost damage until seed moisture drops below 20%. This will take much longer in a standing crop than in the swath, making late maturing, standing crops much more vulnerable to yield loss and downgrading from frost damage. Late maturing crops are not good candidates for straight combining.
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What about chemicals to assist dry-down?
Growers who have decided to straight combine some of their canola may also be considering preharvest weed control or desiccation, particularly in fields with uneven maturity. It is important to recognize that these products do not hasten the maturity of less mature canola plants, they simply kill those plants. It is also important to understand that these products are not designed to seal the pods against pod shattering, and may in some cases make the crop more vulnerable to shattering if harvest is delayed. Be prepared to harvest as soon as the crop is ready, as rapid dry down will leave the crop vulnerable to shattering much sooner than if it is left to mature on its own. For applying preharvest chemicals prior to harvest with ground rig sprayers, the use of crop dividers can reduce crop loss due to trampling and shattering. Traveling back and forth in the direction of prevailing crop lean also will further reduce losses.
If a Roundup Ready canola variety has been grown, a pre-harvest glyphosate application will assist in some dry-down of green weeds and offer perennial weed control, but it will not dry down the crop. For other types of canola, it will be even more critical not to apply the product too early. Apply when the crop has 30% or less seed moisture content. At this stage, which is past the typical swathing timing, the pods are green to yellow and most seeds have turned from green to yellow or brown. For a faster acting desiccant like Reglone, it is even more important to delay application to allow seeds to reach physiological maturity. The recommended stage is when an average 60-75% of seed (on the whole plant) has turned brown. Keep in mind that this will be well past 75% seed colour change on the main stem.
Finally, there have been many reports of short crop heights and lodging resulting from the stresses of the season. This means it will require cutting close to the ground to capture all of the pods on the plants, leaving less stubble to anchor swaths. This will make it even more critical to reduce the odds of wind damage to swaths by swathing parallel to the typical direction of prevailing winds in the area, and by utilizing a properly adjusted swath roller to anchor swaths as much as possible.
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Next year’s weed control? Already?
With swathing and harvest getting under way, consider a valuable weed control tool to set up for next year's canola crop – preharvest glyphosate. The challenging conditions this spring have resulted in less than ideal control of perennial and winter annual weeds in some fields. Fall may be an opportune time to control them for next year. It's the most consistent and effective timing for many perennial weeds, providing an effective and economical alternative to in-crop applications. In early fall, perennial weeds are moving nutrients down into roots and rhizomes to prepare for winter. This is when they are most vulnerable to herbicide translocation to the roots, and better control is possible. Wait three full days (72 hours) after application before cutting to allow thorough translocation of the herbicide to ensure extended long-term weed control. If using this to control weeds in canola crops prior to swathing, keep in mind that three days typically translates to a 10-15% increase in seed colour change. In fields with uniform maturity you should be able to spray at up to 40% seed colour change and still swath prior to 60%. In less uniform fields you may not be able to wait for an average of 60% seed colour change to swath, but try to keep herbicide application as close to whatever swathing stage is appropriate as possible (three days) to avoid yield loss from premature death of less mature plants. Keep in mind that the use of preharvest glyphosate on crops grown for seed should be avoided.
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Finding any flea beetles?
During swathing is a good time to assess the population of emerging adult flea beetles. These will make up the overwintering population that you may have to deal with next spring. If you find high numbers in any fields this fall, Agriculture and Agri-Food Canada would like to know. They are hoping to collect some flea beetles for their research. Please contact Dr. Julie Soroka at:
107 SCIENCE PLACE
SASKATOON, SASKATCHEWAN S7N 0X2
Telephone: (306) 956-7294
Fax: (306) 956-7247
Email: sorokaj@agr.gc.ca
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Questions & Contacts
Direct questions regarding this report to Derwyn Hammond, Agronomy Specialist, Manitoba with the Canola Council of Canada at hammondd@canolacouncil.org, 204-729-9011.
Direct specific questions regarding regional issues to one of the following Canola Council of Canada regional agronomists or provincial oilseed specialists:
Ingrid Kristjanson, Manitoba Agriculture, Food and Rural Initiatives, Ingrid.Kristjanson@gov.mb.ca,
204-746-7504
David Vanthuyne, Agronomy Specialist, Eastern Saskatchewan, vanthuyned@canolacouncil.org,
306-946-3588
Venkata Vakulabharanam, Saskatchewan Agriculture, Venkata.Vakulabharanam@gov.sk.ca
306-787-2594
John Mayko, Senior Agronomy Specialist, Parkland West (West Central AB), maykoj@canolacouncil.org ph/fax:
780-764-2593
Doug Moisey, Agronomy Specialist, Parkland East (East Central AB & NW SK), moiseyd@canolacouncil.org,
780-645-3624
Matthew Stanford, Agronomy Specialist, Chinook (Southern AB & SW SK), stanfordm@canolacouncil.org,
403-327-4832
Erin Brock, Agronomy Specialist, Peace Region, brocke@canolacouncil.org,
780-568-3326
Murray Hartman, Alberta Agriculture and Rural Development, murray.hartman@gov.ab.ca,
403-782-8024
Kerry Clark, BC Ministry of Agriculture and Lands, Kerry.Clark@gov.bc.ca,
250-784-2559
The Canola Watch Report provides just-in-time information on canola production to growers and industry. Contributors to the Canola Agronomy Network are:
Manitoba Agriculture Food and Rural Initiatives; Manitoba Canola Growers Association; United Farmers of Alberta; Viterra; Saskatchewan Ministry of Agriculture; Saskatchewan Canola Growers Association; Saskatchewan Canola Development Commission; Alberta Agriculture and Rural Development; Alberta Canola Producers Commission; BC Ministry of Agriculture and Lands; Agriculture and Agri-Food Canada, and the Canola Council of Canada