“The worst thing you can do is to say, ‘Yeah, I have this thin stand. I’m not going to put any more money into it.’ That’s a real recipe for disaster.”
– MURRAY HARTMAN, AARD
Sometimes they die, sometimes they don’t.
If half the tiny canola seeds that farmers put in the ground in spring survived, then getting a good stand established would be easy. They would just use more seed to make up for the losses.
“But the problem is that it’s not always 50 per cent. Some years it’s 20 per cent, some years it’s 80 per cent. It’s that inconsistency, that wide range, that makes it so difficult to get a good canola stand,” said Murray Hartman, an oilseed specialist with Alberta Agriculture and Rural Development at Lacombe, speaking at the Canola College workshop here last week.
Getting a good stand is critical to making a profit with canola. That’s because a poor start inevitably leads to more management headaches throughout the growing season. Weeds sprout up to fill in the gaps. With fewer plants per square foot, the economic threshold for insect damage is much lower. At harvest time, poor uniformity in the stand makes it hard to know when to swath.
Even researchers are not immune to the vagaries of canola, Hartman noted. At AAFC Lacombe, a recent three-year study saw wide variations in mortality with both hybrid and open-pollinated varieties, even under the meticulous eyes of the scientists, he said.
“So this is not about the farm or the farmer, it’s related to the crop itself as much as anything,” he said.
Farmers often hear that under “average” conditions, half the canola seed will die at some point between seeding and emergence.
There’s a lot of talk about the causes for that, but generally there’s not one single factor behind this phenomenon. Instead, it’s more often the result of a “tangle” of several issues at play, he said.
As with all crops, weather is the biggest factor, with soil moisture right at the top. Dry soil during seeding or the week after – even when it’s not a drought – can bump up the seedling mortality rate well over 50 per cent.
Seedlings short on water are vulnerable as they push their way up through the soil, because they need it to maintain turgor pressure in the hypocotyl, or stem. Too little water, and they won’t make it to sunlight. Knoll tops, which tend to be drier, are particularly susceptible.
In this case, it’s easy to diagnose. If emergence is poor everywhere but in the tire tracks, that’s a sure sign that seed-to-soil contact due to dry conditions or poor packing is to blame.
“Sometimes in a wet year, you see the reverse,” he said.
Low seedbed moisture often magnifies other factors, such as herbicide residue, fertilizer in the seed row, seedling blight, or poor seed vigor.
Once it becomes obvious that the stand is a writeoff, a canola grower must decide what to do next.
“Are you going to want to reseed back into dry soil? As it gets later into the season, you have less and less options,” he said.
If it’s still early in May, a farmer could opt to wait for rain. But if the clock is ticking later in the season, and it still hasn’t rained, then reseeding the field to barley or oats at sufficient depth to hit moisture might be the best solution.
Once those options are gone, then it’s time to look at just how thin the stand actually is. Optimum is seven to 10 plants per square foot, but as few as four plants or even less can still turn into a decent crop.
“At the end of May, I know that I’ve already lost 20-30 per cent yield,” said Hartman. “In fact, I’ll live with one plant per square foot as long as it’s at least somewhat uniform.”
In such cases, keeping up with careful management is key. Two applications of herbicide might be needed to beat the weeds back. Swathing can be problematic with low-density stands because the plants are branchier, and growth may be uneven, so harvest may need to be delayed by a week or two.
“The worst thing you can do is to say, ‘Yeah, I have this thin stand. I’m not going to put any more money into it,’” he said. “That’s a real recipe for disaster.”
The trend toward earlier seeding dates is often another cause for poor stand establishment. Soil temperatures of less than 5C can slow emergence and increase mortality by 10-20 per cent.
In such cases, shallower seeding in the warmest part of the soil can pay dividends, as can the use of starter phosphorus to give the germinating seedlings a “pop-up” boost. Earlier planters may also choose to compensate simply by increasing their seeding rates.
If only low-lying areas, or parts of a field that are covered in residue or shaded by shelter belts, show reduced emergence, then low soil temperature is the likely cause. The solution is not to panic, but instead wait for the slowpokes to catch up as warmer weather arrives, he said.
Diagnosing frost mortality in canola can be a nightmare, he added, but only if you don’t know where to look. The best indicator is the neck, or top of the white hypocotyl. Constriction, or a choke point there, is a bad sign.
“If that has withered or turned brown, that seedling is done,” he said.
On the other hand, purpling on the stem only indicates stress of some sort. Even when frost turns the leaves brown or black, the plant can still make a comeback. A good rule of thumb, he added, is to wait at least five days before making a decision.
Hartman said he once convinced a farmer near Red Deer to take a chance on a frost-damaged field that was left with just one to four plants per square foot. Eventually, the crop came back and yielded 38 bushels to the acre, better than a nearby field that was reseeded.
“For the most part, reseeding is a mistake,” he said. “Part of the reason that it did so well is that it was a herbicide-tolerant type. That allows us such better weed control because it gives us the ability to manage a thin stand.” [email protected]