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Troubleshooting emergence and assessing plant stand densities in flax or canola

Crop Production News 2018 - Issue 2

By Matthew Bernard AAg, Provincial Specialist, Oilseed Crops

June 2018

It is important to regularly monitor emergence and plant stands once your seed is in the ground. Understanding the cause of poor stands will help determine best management practices for the current crop and help optimize stands in future years.

Take plant counts after emergence is complete, which is about 10 days after seeding canola or seven to 14 days after seeding flax, under average conditions. Count plants in a square foot (ft2) or square metre (m2), and do counts in several locations (and away from the headlands) in each field to get a better idea of what is happening across the field. Yield potential is significantly reduced once plant stand densities fall below 30 plants/ft2 (300 plants/m2) in flax, or four to five plants/ft2 (40 to 50 plants/m2) in canola. But, remember to compare the counts in the field with the expected targeted stand densities that you decided on when seeding that field. If the average plant stand densities are lower than expected, there are several causes to consider when troubleshooting.

Insects

The lower the plant stand density, the more severe the impact of insect feeding. A population of insects will have fewer plants available for feeding, therefore the damage will be relatively higher than in a field with higher plant stand densities. Emergence might be patchy. Fields expected to have higher insect populations can be seeded at a higher rate, but crops with lower stand densities should be scouted more frequently and intensively to ensure action thresholds for control are caught at the right time. Insect scouting charts and other information can be found on the Prairie Pest Monitoring Network Blog.

Disease

Fusarium wilt can cause yellowing/browning on flax seedlings and ashy-grey roots. Blight will cause seedlings to turn yellow, wilt and die; this might be seen in individual plants, rows or entire patches. If the disease is unknown, send a plant sample to the Crop Protection Lab for diagnosis. Yellow plants may also be caused by fertility or herbicide residue issues, so consider the pattern of damage and review past fertilizer and herbicide application records, as well.

Appropriate rotations are important considerations when troubleshooting or planning future years.

Moisture

Flax is relatively sensitive to moisture due to its shallow root system; poorly drained soils can therefore reduce emergence. However, lack of moisture can appear as low or patchy germination. Rain in the middle of a dry period can result in crusting, also reducing emergence. Maintaining a firm seedbed, reducing tillage and on-row packing can help maximize soil-to-seed contact. Dry conditions can increase the risk of carryover of herbicides from previous applications; be sure to check your field records and product labels for restrictions for exceptionally dry conditions.

Hail

Damage resulting from hail will likely be patchy throughout the field. Seedlings that do not survive are those with both cotyledons broken off, or where the stems have been snapped. Damage at the growing point will be exceptionally damaging.

Seed

Seed quality will impact emergence. Information obtained from a germination test prior to seeding is a useful tool for troubleshooting later in the season. Weathered, cracked or diseased seed, as well as seed with residual herbicides, can reduce germination rates. Send a sample of seed you used during seeding to a lab to test germination rate, seedling vigor, or presence of pathogens or residual herbicides to be able to rule this out as a cause of low emergence. Use certified seed or hybrid seed that is already germ-tested.

Weeds

Poor weed control in the spring will stunt the crop. Poor sprayer tank clean out, or incorrect order of mixing products, can negatively affect their efficacies. Improper timing of broadleaf herbicides will also damage the crop; be sure to check product labels. Information on timing and the weeds controlled by a herbicides can also be found in the 2018 Guide to Crop Protection.

Wind

Strong winds can move seeds and even seedlings out of the ground; symptoms can also appear as sandblasting damage and can tip or break the plant. Damage will be more evident on hill slopes facing the wind, or hill tops, and may be patchy. Consider the entire field before making reseeding decisions. Adopting zero-tillage can alleviate concerns of soil erosion by wind under most conditions.

Temperature

Seeding early into cooler soils can delay or reduce emergence. Check your soil temperature records from seeding (which is more meaningful than date of seeding) when troubleshooting. Frost-damaged seedlings may have browning at the stem, darkening of the growing point, pinching on the stem or below the growing point, or cause the plant to collapse in severe cases; light frosts causing wilting might cause yellowing or whitening. Damage at the growing points will be most destructive. It is important to wait several days before assessing the actual severity of the frost damage, as visible signs of recovery may take a week or more to appear. Shallow roots make flax relatively susceptible to extreme soil temperature changes; however, temperatures as low as -3 C (for cotyledons) or -8 C (two leaf) are tolerable in flax, if they have hardened off. Canola seedlings may show damage after temperatures around -3 C to -4 C, but environment, growth stage and rate of growth can all influence frost susceptibility in both crops.

Agronomy

Poor emergence of canola seedlings due to deep
seeding in dry conditions. Photo credit to Nicole
Philp, Canola Council of Canada.

Seeding too deep, especially with flax, can reduce emergence rates, as well as delay emergence; even if germination is normal. Dry or cool soils at seeding could have reduced emergence. Check your records to be sure there was not an error in seeding rate or depth. Excessive fertilizer placed with the seed, particularly in dry conditions, could have a negative effect on emergence; flax is particularly sensitive to seed-placed fertilizer. It is important to have had a soil test done previously for troubleshooting purposes, as this will be informative to rule out potential nutrient deficiencies.

Should you reseed?

Reseeding will not necessarily improve the yield potential or profitability; aside from the added cost of seed, late-seeded crops typically have lower yield potential and could push maturity late enough to put the crop at risk of first fall frost. Due to the “plastic” physiology of canola and flax, they can be forgiving crops, as they will increase branching to take advantage of lower competition from fewer neighbouring plants of a reduced stand and offer some compensation. This can differ between varieties, however. In cases where an insurance claim is submitted with Saskatchewan Crop Insurance Corporation, make sure to know their deadlines.

Poor emergence could be due to many causes. It is important to know the numbers in the field, to consider the net profitability of taking a hit with the current crop, or accepting the risks and costs of re-seeding.

For additional information, visit the Canola Watch website or the Flax Council of Canada’s website, see the “Growing Flax Profitably” booklet or contact the Crop Protection Lab at 306-787-8130.


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