Aerial weed control | Cabbage seedpod weevil | Sulphur deficiency
Cutworms continue feeding, flea beetles may still be a threat for late-seeded canola, and cabbage seedpod weevils have arrived on early-seeded canola in the southwestern Prairies.
Earliest crops are starting to flower, which means sclerotinia prediction time. Wet weather and a dense canopy at flowering should encourage higher rates of sclerotinia stem rot infection in regions where the disease has been present in the past. However, if the weather changes from late flowering through ripening it could inhibit infection and/or development of the fungus, reducing this potential for high rates of disease, as it did in some fields last year.
Wet conditions have prevented timely weed control for many growers. If weeds are plentiful and getting ahead of the crop, an aerial application may pay off if fields are too wet for a ground rig.
Remember to return unused unopened seed. Seed companies encourage growers to return all unused, unopened, undamaged bags to the retailer for a refund. The return-by date is soon for most seed suppliers. Seed carried over on the farm will lose germination if not kept cool and dry all year long, including through the summer.
Finally, we remind growers not to use malathion in bins planned for canola. Bin prep is one of many jobs done in the weeks between spraying and harvest. If bin treatment is necessary to remove storage insects, apply approved products (like diatomaceous earth) to bin surfaces prior to storing canola.
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If weeds and crop are advancing toward the end of the application window and the ground is too soft and wet to support a sprayer, then aerial spraying may be the best economic response. Here are the options for aerial herbicide application in canola:
—Roundup WeatherMax is the only glyphosate registered for aerial application at this crop stage, but use is subject to certain conditions which are outlined in detail on the label. (Many others are registered for pre-harvest.)
—Liberty (glufosinate) is registered for aerial application at this stage. Remember, Liberty works best at higher water volumes. Centurion and Select are also registered for aerial application.
—None of the Clearfield herbicide system products is registered for aerial application on Clearfield canola.
—Assure II, Equinox and Poast have aerial labels.
Benefits of aerial application: If weeds are plentiful, at the same stage or ahead of the crop, and canola canopy closure is unlikely to effectively limit their growth, then it will probably pay to control these weeds by air if you have no other option. Aerial spraying also avoids wear and tear on sprayers and on the field when conditions are wet. Under these very wet conditions, ground sprayers can leave deeps ruts to contend with in subsequent spray applications and at harvest, while destroying the crop in those tracks. And getting a sprayer unstuck can be a long, messy job.
Downsides to aerial application: Buffer zone requirements for aerial application are substantially further from sensitive habitats than buffers for ground application. For Liberty, for example, the buffer zone for aerial application is 30 metres from non-target plants and animals compared to a 1 metre buffer for ground application. Aerial application also represents another cost. On that note, in very wet conditions, growers should make sure the crop has recovered before stacking on the extra expense of aerial weed control.
Canola hit with light hail at up to 20% flower may recover with only minimal to moderate yield loss. Plants will flower longer and compensate.
However, canola that flowers longer in response to hail may be at increased risk of sclerotinia. Hail damage also allows a point of entry for diseases such as alternaria black spot and blackleg. Fungicides may help reduce the development of diseases but make sure the remaining yield potential warrants protection and conditions remain conducive to disease development. Also consider the possible impact of delayed maturity, as fall frost damage could negate the potential benefits of the fungicide application.
If applying crop enhancement products such as fertilizer and micronutrient blends on hail-damaged crops, keep in mind that there is very little research available on the efficacy of such products under these extreme conditions. Leave appropriate check strips in order to make an accurate yield comparison at harvest.
An in crop application of sulphur can make financial sense for canola if:
—Growers could not put the desired rate on at seeding.
—Yield potential improved and growers want to add sulphur to their nitrogen top up. If field conditions have been excessively moist, sulphur may have moved lower in the soil profile. As canola plants grow, their roots will extend into these reserves. For that reason, growers who have been applying recommended rates of sulphur may not see as much economic return from a sulphur top up compared to a grower who has cut sulphur rates in recent years.
—Canola shows signs of sulphur deficiency. With sulphur deficiency, yellowing and leaf cupping tend to occur on new leaves first. Purpling of leaf edges can show up when deficiency is fairly severe. In fields short of sulphur, crops can usually find enough to get past the early rosette stage without visible symptoms. Deficiency symptoms often show up at flowering.
Post-emergence sulphur can be applied up to early flowering and still provide a yield benefit. When doing an in-crop application, growers could target only those areas — such as hill tops — that tend to be sulphur deficient.
Source and rate: Ammonium sulphate (dry) or ammonium thiosulphate (liquid) provides sulphur that is immediately available to the crop. It also provides a nitrogen top up at the same time. As few as 10 to 20 pounds of actual sulphur may be enough to provide an economic benefit, but higher levels may also provide a good return on investment if the soil is very deficient.
Application technique: Application just prior to rainfall is best. Surface applied ammonium sulphate requires rain to move it into the root zone. Sulphur is not volatile like nitrogen fertilizer, so while dry conditions may delay availability to the crop, losses will be minimal if rain is not immediately forecast. Avoid spreading granular product when the leaves are moist from dew to limit sticking of the prills and leaf burn as a result.
If dribble banding liquid ammonium sulphate (8-0-0-9) or ammonium thiosulphate (12-0-0-26), keep in mind that damage from leaf burn tends to be more severe when canola is smaller than the 5-leaf stage. Applying when leaf surfaces are wet can allow liquid to run off and limit this damage.
Applying sulphate fertilizer in a tank mix with herbicide/fungicide may not provide enough sulphur to provide a benefit to the crop. Also, flat fan sprays that cover the leaf are far more toxic to the crop than fertilizer dribbled on the soil surface. Plus, the crop can’t take up much fertilizer through the leaves.
**Links** Include link to Resource article on top dress http://www.canolawatch.org/2011/05/18/top-up-tips-for-nitrogen-and-sulphur/ and to last week’s article about moisture and N loss http://www.canolawatch.org/2012/06/13/n-and-s-lost-with-heavy-rains/
Cabbage seedpod weevils move to canola fields at the bud to early-flower stages. The recommended crop stage to spray for seedpod weevils is around 20% flower (which is about a week after you see the first flower in the field). Many weevils may be present at the bud-rosette stage but one cannot sweep at that stage and spraying is not recommended at that time because it is too early.
On days above 12 C with low to moderate wind, weevils will be concentrated in the top area of the crop. In these conditions, they are easy to pick up with a sweep net.
Cabbage seedpod weevil nominal thresholds are based on sweep net numbers, which requires proper sweep net technique. 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.
The nominal economic threshold for weevil was set at 30-40 in 10 sweeps (3-4 per sweep) in 2001, and has been lowered to 2-3 per sweep based on higher canola prices. Anything below that and canola plants will generally compensate for seedpod weevil damage to the buds and flowers.
Don’t spray too soon. Products registered for cabbage seedpod weevil can be sprayed only once per year, so correct timing is important. Also note that if a product has already been used on flea beetles, it may not be available for use again in that crop if the label permits only one use per crop per season.
If you have the earliest crops in the area:
Healthy crops with good plant counts are going to compensate well from weevil feeding on buds. CSPW do their most costly damage at the podding stage by laying eggs in the pods. (Larvae emerging from these eggs can eat the seeds in a pod.) Growers may choose to hold off on weevil spraying at the flowering stage and save that spray for when early pods are about an inch long — which is when the majority of the egg laying begins.
Crops that are under stress (low plant counts, drought, heat, flooding) are more likely to set back by bud feeding. In that case, spraying at 10% to 30% flowering may pay off if fields have even fewer than 2-3 weevils per sweep. But beware there still may be another invasion, and you may want to save your spray. The Prairie Pest Monitoring Network provides more identification and monitoring tips: 2010_CSPW protocol
Growers spraying to control adult weevils at the flowering stage could leave a check strip to see how well the product worked. At harvest, compare plants in the check strip and in the sprayed field to see what percentage of pods have exit damage from weevil larvae feeding inside the pod and then exiting.
Check throughout the field. Cabbage seedpod weevils enter a field from the side and work their way to the middle. Scouting borders of fields twice a week may allow you to catch their first arrival, possibly allowing adequate control with a perimeter spray of the outside edges of the field. Shelterbelts and fence lines are a good clue as to which side might be first, but check all four to be safe. Also, continue to scout after application if relying on perimeter sprays (keeping in mind safe field re-entry times), in case re-invasion occurs.
Leaf roller. Leaf rollers were found in some canola fields in northeast Saskatchewan in the past week. The little green worm that dances around when you touch it can be confused with diamondback moth larvae. They are typically a pest of leaves on trees, so their potential for causing economic damage to canola at this stage is uncertain, but is probably low unless defoliation is extensive.
Wireworm. Surveys by AAFC found that two species are most prevalent and likely cause most of the wireworm damage to Prairie crops. They are Hypnoides bicolor and Ctenicera destructor. C. destructor grows to an inch long, and can live 4 years in the larval stage. H. bicolor grows to about half an inch, but are more numerous than destructor. Their lifecycle is about two years. In late spring and early summer, the adults — click beetles — move into cereal fields or pasture, and lay eggs throughout the field. Three weeks later eggs hatch. These first instars will feed on cereal roots, overwinter and continue feeding in following years. Wireworms feed on a variety of plants, but their preferred food is cereal and grass roots. In the absence of these, wireworms will feed on canola plants, but the volume of root tissue in the soil might satisfy them without taking out a large proportion of the crop. Feeding tends to look like holes in the roots. Wireworms spit out an enzyme that will break down root tissue, then they slurp it up, leaving a hole.
Nothing is registered to control wireworms in canola. Scouting is still important to distinguish wireworm feeding from cutworm feeding, which can be stopped with insecticide. If wireworms are the cause, growers can manage the threat with wireworm seed treatments on cereals. Bob Vernon and Wim Van Herk with AAFC continues their survey of Prairie wireworms. Collected wireworms can be put into sealed containers with soil and shipped to his address. When submitting worms, in addition to precise location and grower information, please add additional information on the crop involved during the collection, and whether wireworms were suspected or confirmed alongside any damage, and the severity (% loss) of damage in the field. Click Bob’s name above to contact him for more information. This is very important in determining the damage potential of these species in canola to guide the need for future research.
Bertha armyworm. Bertha armyworm monitoring programs are underway and counts are coming in. The first maps of the season will soon be available. Bertha armyworm trap cooperators please remember to forward your land locations and weekly counts. In Saskatchewan, contact Sean Miller at 1-888-323-7842 or firstname.lastname@example.org. In Manitoba, contact John Gavloski at (204) 745-5668 or email@example.com
Flea beetles. Canola at the cotyledon stage is still at risk. Although flea beetle populations have been dropping significantly over the last couple of weeks, adults will feed from April to July. After the 4-leaf stage, canola is growing fast enough that flea beetle feeding is no longer a threat — even though the insects may still be present in the field.
Earliest canola is starting to flower this week, which means the sclerotinia spray decision looms. Spray timing, if a grower decides to go for it, should be within the window from 20% to 50% bloom. (Some products are registered for only 20% to 30% bloom.) At 20% bloom, no petals have dropped and no pods are forming. At 30% bloom, petal drop has just begun and side branches are just starting to bloom. Canola can reach 20% flower in 4-5 days after first flower, so prepare to assess the sclerotinia stem rot risk as soon as flowering starts.
Boron. We have limited research on the benefits of a boron application at flowering. Ontario research is inconclusive on the benefits of boron, which is often applied in southern Ontario to help reduce flower abortion during summer heat waves. Tank mixing boron with a fungicide in the sclerotinia window will reduce boron application costs, but check with fungicide companies about compatibility. Some boron products may increase pH in the spray tank, which can degrade fungicides. For example, Rovral is known to degrade quickly in alkaline (high pH) spray solutions. Also, pesticides in PVC packets that dissolve in the spray tank are not compatible with boron.
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