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Canola Watch #33

Topics for the month

Our theme this month is scouting. It’s not scouting season, obviously, but the variety of different stresses and pests in different regions that affected the crop in 2012 reminds us why it is so important to properly monitor canola throughout the year. We have articles this week on what to keep in a scouting kit and on how to find an agronomist that can effectively assist with your scouting efforts or give advice on management options. Growers want an agronomist who understands their farming philosophy, understands the growing region, and has access to a network and resources to help provide the support they need. The January farm shows give growers a chance to scope out a few agronomy service providers, and re-stock their scouting tool kit.

The scouting toolkit

The standard sweep net has a 15" (38 cm) diameter. Source: Shelley Barkley, AARD

Professional entomologists, plant pathologists and agronomists use many of these tools. Growers may want to keep some or all of them handy as well.

Smart phone

Various growers and agronomists who answered a Twitter query about scouting tools said their smart phone was a key tool for collaborating with others, keeping records, and taking photos. It can sometimes be difficult to identify an insect by photo alone. To help entomologists with insect identification by photo, include various angles of the insect (top, side, front), photos of the damage the insect is causing, and photos that show where the insect is feeding on the plant. Keep these four basic pieces of information for each photo: What crop is the insect in (and where on the plant was it found), location of the field (legal location or GPS if possible), name of the person who collected the sample or took the photo, and the date.

Seed depth tool

Growers can use the tool to make sure every run of the drill places canola at the recommended half inch to one inch depth. Click here for tips on where and how to check seed depth.

Hand trowel

Hand trowels are handy for wireworm and cutworm scouting, and trowels with depth markings on them can also be used to determine the depth from which seedlings are emerging while evaluating health of hypocotyls and roots. When scouting for underground cutworms, look aboveground for bare patches, holes or notches in foliage, and clipped plants. Start digging where you find damaged or missing plants. In moist soils, cutworms will stay close to the surface. In dry soils, they may go down 8-10 cm (up to 4”). Dig up soil from a one square foot area to a depth of 10 cm and put it into a basin. Loosen the soil and shake it up to activate cutworms. Repeat a few times throughout the field. A sieve can help separate insects from dry soil. Find a sieve or strainer with holes big enough for your soil type.

Sweep net. Source AARD

Standard sweep net

Lygus bug and cabbage seedpod weevil economic thresholds are based on sweep net counts, and proper counts depend on using the standard sweep net and technique. The standard size has a 35” long handle and 15” (38 cm) diameter net. Lygus can show up in all areas of the Prairies, but even if you don’t typically have lygus or cabbage seedpod weevil, a sweep net can be useful to identify the presence of beneficial insects, of diamondback moth larvae and other insect pests. Alberta and Manitoba government sites have more on where to buy them.

Large Ziploc bags, especially the breathable ones, are a handy companion for the sweep net. Flying insects can pop out of the net quickly, making it harder to do an accurate count. Carefully dump all contents into a Ziploc bag, then count insects through the perforated bag.

Note: Sweep net sampling is notoriously variable. Making a spray decision based on one set of 10 sweeps means a high chance of making the wrong decision. Extension entomologists recommend a minimum of 5 sampling sites, in a W or X pattern throughout the field, with 10 sweeps at each site. With lygus in particular, time of day, temperature and wind speed can make a difference in counts. You may want to scout two days in a row, unless average numbers are well above threshold.

Magnifying glass/hand lens

A magnifying glass can be used to identify different insect species based on specific markings, to identify very small insects, such as thrips, to spot pycnidia in blackleg lesions, and to look at the growing points of frosted canola to see if they’re regrowing.

Three sided or two sided “square”

Some insect thresholds are based on counts per square foot or square metre, so use a two or three sided “square” to slip more easily into a heavy canopy and help you more accurately estimate the area of your counts. A home-made two-sided square, with a grid on each length showing one foot, half metre and full metre lengths will serve multiple purposes. With open sides, the square slips into the canopy more easily than a full square. For bertha armyworm, for example, lay down the square with the half metre length on each side, give canola plants a shake and count the berthas that fall into that half metre by half metre square. Multiply by four to get the count per square metre.

Hoop or metre stick

Plant counts can help you assess whether the stand has reached the minimum 40-50 per square metre, and whether these stands are uniform throughout the field. This can help with reseeding decisions and seeding rate assessment, and in future decisions about pest threats and whether thresholds should be lowered if plant stands are at critical low levels. Click here for more on how to do counts with a metre stick or hoop.


Clipping stems just before swathing and looking at their cross sections is how to check fields for incidence and severity of blackleg. Clippers provide a nice clean cross section, better than a jack-knife. Splitting stems by hand is too difficult and destructive to provide a good cross section. Spend the money on a good set that can cut through a large canola stem cleanly.

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Source: Alberta Canola Producers Commission