Is your seed survival rate higher than 50-60%, which is typical for canola in western Canada? Start with a plant count, using one of the following methods:
By length of row. Use a metre stick and count the seedlings per metre of row. Take that number and multiply by 100 then divide by the seed row spacing in cm to get plants per square metre. For example, 25 plants per metre multiplied by 100 then divided by 25 cm (10” row spacing) is 100 plants per square metre. (Divide by 10 if you want plants per square foot.) Repeat.
Using hoops: To do counts, use a hoop with an inside diameter of 56 cm. This is equivalent to 0.25 of a square metre. Count the number of plants inside the hoop, and multiply by 4 to get plants per square metre. (Divide by 10 if you want plants per square foot.) Repeat.
If plant counts are lower than you expected based on your seeding rate, taking time now to figure out why will help fix the problem for next year. Use the Canola Diagnostic Tool to help. While scouting, look for the following, which will help with the diagnosis:
Differences row by row. Are some rows good and others thin? Or does it seems like strips of rows are poor while the rest are OK? These are likely the result of drill malfunction, or seeding too fast, with rear openers burying the front rows too deep. Openers may be worn or broken and no longer providing adequate isolation from fertilizer band. Check for seed depth and placement. Identifying these issues now will help to improve drill performance for next year.
Low emergence overall. If low emergence is fairly general throughout the field, seed may have been placed too deep, excessive fertilizer may have been placed near the seed, seeding rate may have been too low or seed quality was compromised. Large seed size combined with lower seeding rate and low seedling survival can result in thin stands. Consider this for next year.
Uneven growth staging. Large plants interspersed with late-emerging small plants can result from inconsistent seed depth from seed to seed. High fan speed on the drill may have caused seed bounce, which results in inconsistent seed placement. Worn openers and uneven residue cover are other possible factors.
Bald patches. Blank areas in the field can result from dry seedbeds, heavy winds, drowned plants, seed rots, cutworms and other insects, and from gophers.
Unthrifty, yellow or malformed plants. Unhealthy-looking plants can result from seedling diseases, herbicide carryover, herbicide burn, high rates of seed-placed fertilizer, fertilizer deficiency, low vigor and deep seeding, to name a few. Malformed plants can result from herbicide injury or disease, but possibly other factors.
Damaged plants. Environmental stress such as frost or hail are possible reasons. Look for insects, particularly flea beetles and cutworms, but also wireworms and early grasshoppers. Even if you don’t see obvious feeding on leaves, look under the leaves and on stems. If flea beetles have moved down the plant due to rain or wind, they can actually do more damage. Severing a stem is far worse than 25% damage on the leaf. Check leaves for blackleg lesions.
While doing the above ground scan, look at the weeds. What type, size and number do you see? This will help determine whether another spray is warranted and what tank mix and rate to use.
After the above-ground assessment, get a trowel and bucket and start digging around damaged plants. Look for cutworms and wireworms in the top 4” of soil. Look at the roots for signs of insect feeding or disease damage. Chomped roots are usually insect damage. Mushy or thin wiry roots and stems are often the result of seedling disease.
Thin stands need extra protection
The key with a thin stand is to do what it takes to protect those plants. A stand needs a minimum of 4-5 plants per square foot to reach its yield potential. For a canola field at or below that plant population, consider lowering the action thresholds for insect, weed and disease management all season long.
It helps to keep a scouting notebook and jot down all observations. Even if you see nothing of concern, early scouting gives you a baseline for crop emergence and condition of the stand. Then you’ll know for sure something is wrong if the crop doesn’t look as healthy the next time you scout.
Problems can escalate quickly this time of year and cause irreparable damage if not addressed early. Scouting alerts you to these problems. And while the cause and solution may not always be obvious, this insight motivates you to get help and make an informed decision on the most economic course of action.