WINNIPEG – While some northern areas of the Prairies were still waiting for rain in the last week of May, others had more moisture than they wanted. Nearly all areas have been hit by some combination of snow, excessive rain or cold temperatures this spring.
Wet, cold soil conditions lead to diseases, root rot and crusting over of the seed rows. Some crops compensate well by tillering, branching or increasing head size. Other crops suffer badly and require replanting.
In mid-May, Manitoba Agriculture compiled a set of recommendations dealing with these spring conditions. Full details can be found on the Manitoba Agriculture website.
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Cereals – Wheat, oats and barley typically have a stand of 18-25 plants per sq. foot in a normal year. The minimum viable plant count after spring trauma would be eight plants per sq. foot. Oats and barley with as few as 12 plants can still produce a near normal yield because of their tillering ability.
The early development of the growing point in cereals is below the soil surface, making these crops more tolerant to frost. In a healthy cereal plant, the growing point should be white or cream coloured. If it’s dark or soft, the plant will likely die.
Canola – A normal spring count in canola is seven to 11 plants per sq. foot with the minimum stand for salvaging the crop at three or four plants.
The minimum temperature for canola growth is 5 C. The optimum soil temperature for seeding canola is 10 C for both species, while the optimum temperature for growth is 20 C.
Canola seed that has been sitting in cool soil for any period is vulnerable to attack by soil-borne organisms, affecting both water and nutrient absorption by the seedling roots. This increases the vulnerability to insect and disease damage once the plant is up and growing.
A canola seedling will usually recover from a light spring frost as long as the growing point is not damaged. If the leaves are wilted, but not brown, the plant should be in good shape. It will recover if there is green at the growing point in the centre of the frozen leaf rosette. New growth from the growing point will take place in five to 10 days.
Sunflower – Because sunflowers require a longer growing season, they are usually planted in early May, making them vulnerable to spring weather trauma. The normal count is 16,000-20,000 plants per acre. A minimum threshold is 10,000-12,000 plants per acre. Sunflower seeds are large with thick hulls, so they require a higher germination temperature. It is uncertain whether May weather was wet enough to cause seeds in the ground to rot. As for frost, sunflowers that are up are tolerant up to the four-leaf stage.
Peas – Field peas typically run only five to eight plants per sq. foot. If the count is still three to five plants per sq. foot, the crop should be left alone. Because it is a cool-season crop, most pea fields were probably seeded before the May snow arrived. Peas don’t like excessive moisture in the spring. They require oxygen in the soil and are susceptible to rotting in the soil. If the soil dried quickly, the plant count could be high enough to stick with the crop. If a field is saturated for too many days, the peas may not reach the minimum plant count.
Flax – Unlike cereals, where the growing point is below the surface, the delicate part of the flax plant is fully exposed above ground and susceptible to frost damage. Once the plant is past the two-leaf stage, it’s generally cold hardened and can tolerate temperatures down to Ð8 C.
Flax stands are typically 37-56 plants per sq. foot. A minimum stand after a bad spring would be 20-25 plants. Research shows that compared to early May seeding, a June 1 reseeding date reduces yields seven percent, a June 10 reseeding date reduces yields 29 percent and a June 20 reseeding date reduces yields 52 percent.
Corn and beans – Corn stands are typically 24,000- 28,000 plants per acre. A stand is worth saving when in the range of 18,000-20,000.
Soybeans and edible beans are warm-season crops and likely had not been planted by the time the snow and cold arrived.
Fertility -Manitoba Agriculture says normal fertilizer rates should be appropriate for a cool, wet spring.
Potassium and soil-derived phosphorus are less available to the young seedlings in cool conditions, due to slower diffusion, lower solubility and slower root development.
On the other hand, lower soil temperatures have a favourable effect on applied phosphorus and potassium fertilizers. Low temperatures slow the transformation of these fertilizers into the less soluble forms that the roots have trouble accessing. Also, low temperatures cause the roots to proliferate in the fertilizer bands.
As far as nutrient losses due to runoff, most of the fields hit by the spring snowfall were dry enough that the moisture soaked in without significant amounts of runoff. It’s also unlikely that any leaching occurred because rainfall equivalent amounts were below 50 millimetres in most areas. Surface broadcast urea was likely moved into the soil as the snow melted, thus preventing volatilization losses.
In areas where seedbeds were dry and there was concern about damage from seed-placed fertilizer, the snow melt will dilute the impact of salts and ammonia close to the seed.
Weed control – Most herbicides should continue to work under cool conditions, as long as the target weed wasn’t injured by the cold. Most herbicides require an actively growing plant to work effectively. The exception would be contact herbicides, which will not be as effective in cool weather, regardless of the condition of the target plant.
However, products of all types will not work as quickly when the temperature is low. Under good growing conditions, glyphosate activity should be visible on annual weeds within four days. Under cool conditions, that same degree of activity may not be visible for 10 days or longer.
Crop injury to young seedlings may become more pronounced in cool conditions because the lower temperature reduces the herbicide metabolism, thus keeping the chemical in contact with the crop for a longer time.
Dry conditions last year may cause greater herbicide carryover in Group 2 and 3 products. Although the moisture received in some areas will help promote herbicide breakdown, generally low temperatures across the Prairies will prevent this herbicide breakdown from happening at the usual speed.
The efficacy of Group 3 herbicides may be reduced on flooded fields. Unfortunately, weed seeds are not harmed by flooded fields.
When making spray decisions, keep in mind that cool conditions always favour C3 weed species such as wild oats, wild buckwheat, quack grass, dandelion, thistles, stinkweed, flixweed, shepherds purse, volunteer canola, volunteer cereals and wild mustard. The C4 species such as green foxtail and barnyard grass do not thrive in these cool conditions.
Rainfast information for each herbicide is found on the product label.
Forages – In the spring, the growing point for grasses is at or below the soil surface and generally protected from injury. In many cases, the stand may actually benefit from the additional moisture provided by snowfall.
Legumes, however, elevate their growing point with each increase in growth, making that point more susceptible to frost injury. As long as the crown is not damaged, the plant can recover and send out new growing points. Even if the top 10 centimetres are wilted or discoloured, the plant will eventually put out new shoots from the branches on the main stem or from the crown. Yield potential should not be affected.
In seedling fields, it’s a somewhat different story. New alfalfa plants may be killed if the temperature drops to -5 C for only four hours. If the seedling is frozen so that all trifoliate leaves are discoloured, that plant will not recover.
Flooding can hurt grasses and legumes. Plant roots require oxygen to remain healthy. The flood tolerance of various forage crops is well documented. Alfalfa can take two weeks of water cover. Alsike clover and smooth brome grass can tolerate three weeks of flooding. Meadow foxtail can take six weeks. The winner in this category is timothy with a flood tolerance of up to seven weeks.
