Field pea producers in Western Canada must meet stringent quality levels to ensure their product is fit for human consumption.
Bleaching is the most common quality problem with green peas while in yellow peas it is the presence of green. To manage these issues, farmers can choose to apply either Reglone as a desiccant or glyphosate as a pre-harvest weed control option.
“Working with the Alberta Pulse Growers, it was determined that it was a priority to look at not only what you applied but when you applied, with Reglone desiccation or pre-harvest glyphosate application,” said Ken Lopetinsky, pulse research agronomist with Alberta Agriculture’s Crop Diversification Centre North in Barrhead.
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“At that time, producers had their own perception of which one worked better and why. People were spraying with one product and finding out it didn’t do what (they thought) it would do. Our attempt was to look at the two products and determine what effect they had on field peas at different application timings.”
One concern was that application of these products at the wrong time could result in more bleaching in green pea, plus more immature seeds. It was also believed that desiccants were more effective when there was a long flowering period, which resulted in a range of pod maturities on one plant.
A three-year study was set up to compare pre-harvest glyphosate and Reglone applications at three different maturity stages. The intent was to identify production techniques that would consistently produce high quality field peas. It would also determine maturity characteristics of field peas that can be visually identified and used to monitor crops to attain high quality, plus assess the final quality of desiccated products compared to natural dry down systems.
Three growth stages were selected:
- Early, when there were green to yellow pods, with no orange peel texture on the upper pods, with seed still soft and wet in the upper pods.
- Mid, with the beginning of the orange peel texture on upper pods, with the seed still easy to dent.
- Late, with orange peel texture on upper pods and firm seed that’s harder to dent in the upper pods.
The study indicated the early stage was too soon for green and yellow pea application, that the mid stage was the proper one for green pea applications and late stage was best for yellow pea application.
Lopetinsky said glyphosate takes longer to dry down than a desiccant like Reglone. The difference is seven to 14 days longer for glyphosate, applied at the same stage.
“Most farmers would like as rapid a dry down as possible. Applying later, in regards to yellow pea quality, there wouldn’t be an issue. It’s naturally going to be yellow, so that’s OK. It’s just not drying down the more immature patches that may occur in the lower spots of the field if the field’s not uniform,” Lopetinsky said.
“The normal thing on yellow pea is that you’re applying glyphosate primarily for perennial weed control before you combine. In regards to Reglone application, it’s to get the highest quality possible because it is a big difference in days to combining by applying Reglone versus applying glyphosate.”
He said producers have to understand what their crop maturity is, then understand why they are using which product.
“If you apply either of them too early, we have shown you may lose yield. Some of that would be through a reduction in size of the seed and you’d probably lose quality.”
Lopetinsky said if either product is applied too early, it can also lock in the greenness in a yellow pea, resulting in lower than a #2 yellow grade.
“There should be a colour change in the seeds of the uppermost pods. The colour change does not mean that they’re yellow. It means that parts of the seed have become yellow,” said Lopetinsky.
“In field conditions, it’s a lot more difficult. Reasons why producers may have the trouble they do is that they don’t do enough scouting, or there may not be a high clearance sprayer or aerial applicator available when the opportune time is there.”
Lopetinsky said rainfall on green peas doesn’t necessarily mean they will bleach.
“If you have rainfall, you don’t have sunlight and it’s the intensity of sunlight that causes bleaching. It depends on the intensity of sunlight between the rainfall and the time that we harvest. We know it’s dry, so to re-dry shouldn’t take that long.”
It’s important to understand that yellows and greens are different.
“Greens don’t have to change colour. They’re green right from when the pod starts filling. The biggest thing is the quality and possible yield loss from going too early on yellows,” he said.
“Quality can be a big issue. Where you’ve gone too early with either product and you don’t make the grade, now you have feed peas, which may be worth $1 lower per bushel. In regards to the green pea, applying Reglone versus glyphosate, there is less bleach of the peas through Reglone application because your harvest is earlier, if everything goes good.”
Lopetinsky said that for producers, it’s a matter of looking at their situation to decide how one or both products may fit.
“The value of the crop has to come into the equation of whether to use one or the other product. (Farmers) that know their quality will be feed may not see the economics of using either product, regardless of the price. But if you have a good crop coming and you’re shooting for human consumption, green or yellow, there may be an economic advantage to use Reglone on part of the field. If it’s a weedy situation, then perennial weed control may be your first criteria. Therefore, your choice may be the use of a glyphosate product.”
He said yellow peas are forgiving with respect to deterioration of quality.
“On the other hand, green quality can be lost within 24 or 48 hours. Excess bleach is excess bleach and you’re in a feed grade. If the products don’t fit into a farm program, then the better criteria would be to grow yellow peas ….”
In summary, three years of data from the study suggest that a pre-harvest glyphosate or Reglone application applied too early can reduce seed size and yield, while proper timing can result in a high quality product. Both products can reduce the risk of reduced seed quality associated with late harvest and bad weather, which results in a prolonged dry down.
Temperatures above 28 C during the flowering period can cause substantial flower blast. If this happens, the result can be a similar maturity of upper and lower pods. This situation would minimize the benefits of dry down products.
The study concluded that the economics of product and application costs must be compared to the value associated with ease of earlier harvest, better quality and long-term price advantage for human consumption quality versus a feed pea.
One last concern was that producers must remember that glyphosate-treated field pea seed cannot be used for planting the next year.
