July 17, 2013 – Issue 16

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  • Issues of the week

    Diamondback moth larvae feeding on pods.

    The pod stage is the critical time to watch for insect feeding in canola. When flowering is done, the crop cannot produce more flowers to compensate for insect losses. Thresholds for insects such as bertha armyworm, diamondback moth larvae (shown in the photo above) and lygus bugs are based on losses at pod feeding.

    However, take care with timing. Jumping the gun with early insecticide applications on flowering canola can create a whole lot of trouble for beneficials, have limited benefit in terms of insect management, and be a step back in sustainability. With a healthy beneficial population, insect outbreaks are never as severe as they will be without the beneficials to keep populations in check. Adding insecticide to a fungicide mix may “only” cost $5 per acre, but the timing is not right for insect management — other than for cabbage seedpod weevil if at thresholds. There are likely many other better ways to spend that money — including waiting until early pod stages to spray. If finding time to scout is an issue, consider spending part of the $5 per acre to hire someone to scout for you.

    Tweet of the week, from the July 17 #ABbugchat on Twitter:

    Tweet of the week July 17

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  • Canola Watch quiz

    Quiz July 17

    What is this worm?

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  • Grasshopper thresholds

    grasshopper feeding small

    Grasshopper numbers are at or near thresholds in some regions of the Prairies. The nominal threshold for grasshoppers in canola is 8-12 per metre square. How you go about counting them is the challenge. As soon as you walk into an area, grasshoppers take off and do not cooperate with your attempts to count them. So entomologists have come up with a more practical scouting technique. It involves three steps…

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  • Insect update: bertha counts video

    Bertha armyworm moth counts continue to accumulate across the Prairies. Many areas are now at moderate to high risk, and adult numbers will continue to build this week. Adult counts can hint at the potential level of feeding by the larvae — the actual armyworms — starting about two weeks after the first wave of adults showed up in traps.

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  • Bertha armyworm scouting tips

    These are all bertha armyworms, showing the variation in color that can make idenfication a challenge.

    —Go out in early morning or late evening when larvae are mostly active.
    —Mark out an area a quarter-metre square (50 cm by 50 cm) and beat the plants growing within that area to dislodge the larvae. Count the larvae that have fallen to the ground and multiply by 4 to get the number per metre square. Larvae will hide under leaf litter and in cracks, so check closely.
    —Sample at least 5 locations (10-15 is recommended) a minimum of 50 metres apart. Do not sample headlands and areas within the crop that are not representative of the field. Use the average number of larvae at the sites surveyed to determine if the economic threshold has been exceeded.
    —Scout each field. Adjacent fields may have very different larval densities, depending on how attractive the crop was when the moths were laying their eggs. Adjacent fields may also have different-sized larvae, depending on when the eggs were laid.
    —For best results, apply an insecticide as soon as economic thresholds are reached. A single well-timed application of any registered insecticide is usually effective. Check provincial crop protection guides for registered insecticides.
    —Apply insecticides early in the morning or late evening when the larvae are actively feeding. Do not apply during warm afternoons.

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  • How to ID 50% flower

    Fungicide applied late in the window can provide valuable protection from sclerotinia stem rot if flowering is extended or if conditions become more conducive to disease.

    The fungicide window to manage sclerotinia stem rot closes at 50% flower. 50% flowering is when:
    —The crop is at its “most yellow.”
    —There are more than 20 open flowers on the main stem. In this case, include aborted flowers and developing pods as “open flowers.”
    
—You may notice signs of sclerotinia infection down in the canopy around rotting petals.
    
—Side branches are starting to flower.


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  • Options for canola wiped out by hail

    Canola at late flowering flattened by hail. Source: Leeann Minogue

    Canola destroyed by hail could be harvested as forage, replaced with a short-season barley silage crop, or turned under for green manure.

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