July 30, 2014 – Issue 17
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Four the week
Lygus schmygus. Sweep net counts approaching thresholds have been reported in many areas across the Prairies, but high counts may not require a spray if canola is growing vigorously and has good moisture conditions.
Low bertha. Trap counts for bertha armyworm adults are fairly low across the Prairies, except for a few hotspots in central Alberta. This suggests a minimal threat of heavy worm damage overall, but don’t let your guard down completely.
Diamond backtrack. Beneficials seem to be doing a good job on diamondback moth larvae. Unless you see significant pod feeding and counts exceed 20-30 per square foot at a few random sites in the field, spraying will not likely provide an economic return.Why the miSing podS? Six leading factors can cause blanks up the stem. Sulphur deficiency is one of them, and could be a leading contender this year.
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Map of the week
This map from StatsCan’s Crop Condition Assessment Program uses NDVI satellite imagery to show crop growth. This map compares growth to July 21 this year with the same period last year. Yellow indicates that growth is about the same as last year. Light brown is behind. As you can see, crop growth for most of the western Prairies is around the same pace as last year while most of the eastern Prairies is behind.
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July 30 Quiz
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Lygus thresholds — Economics
Threshold tables for lygus suggest, for example, that if canola is $12 per bushel and spray costs $8 per acre, the threshold at the early pod stage is 5 lygus adults or late instar nymphs per 10 sweeps.
Current thinking is that 5 lygus per 10 sweeps (0.5 per sweep) is too few to warrant a spray, and that the economic threshold is likely quite a bit higher.
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Bertha armyworm thresholds
Bertha armyworm is one pest that can do a lot of damage in a short time. They’re large and eat a lot. Even within an area showing low risk on provincial maps, hot spots can flare up. (Photo credit: Roy Ellis)
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Diamondback moth larvae — Thresholds
Thresholds are 100-150 larvae per square metre in immature to flowering plants and 200-300 larvae per square metre (20-30 per square foot) in plants with flowers and pods. While these nominal thresholds are based on dense stands of 150-200 plants per square metre, plant population is not a major factor. Fewer plants will have more branching and more pods, so the number of pods per square foot probably won’t change much regardless of plant population.
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New swede midge locations
A swede midge infestation has been confirmed near Meota, Saskatchewan, well outside the Nipawin-Carrot River epicentre. Higher numbers have also been reported near Hudson Bay, Saskatchewan, indicating an eastward migration as well. But while the insect seems to be spreading in distribution, overall numbers and levels of damage are down this year across the province.
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Leave required time between spraying and cutting
Pre-harvest interval (PHI) refers to the amount of time that must lapse (in days) after a pesticide application before the crop is cut. Cutting refers to swathing or straight combining. Each crop protection product has its own PHI, and the PHI for a specific product often vary by crop.
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6 causes for missing pods
Seeing stems with lots of blanks where pods should be is often cause for alarm. There are many possible factors. Here are the top 6:
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Disease diagnostics
Seeing signs of canola disease but you don’t know what it is?
Read this article: Disease to look for while harvest scouting.
Watch this video: CCC pre-swath disease scouting video.
Use the Canola Diagnostic Tool
