One of the biggest reasons pulse and soybean growers need to understand the growth stages of their plants is to determine the correct timing of in-season herbicides and fungicides, which varies by crop and growth stage. The application of chemicals in field peas, for example, is typically determined by what node stage the crop is at.
“Specifically, second- and third-node stage is where pea growers would be applying a product like Odyssey,” says Dennis Lange, Manitoba provincial pulse specialist. “Because peas sometimes grow very rapidly, in some cases, growers could be at three or four nodes while the crop still looks fairly short. If they try to judge the crop based on the height of the plant, they may be getting out of the [ideal] stage [for application]. Odyssey, for example, is not recommended to be sprayed after the sixth node.”
If growers delay weed control when the plants are already at the fourth-node stage, and then get a period of rain that prevents travel on the field for a week or so, they could miss the opportunity to spray altogether.
“If growers spray that product (Odyssey) after the sixth node, they can have stunting issues in the crop, delayed maturity and possibly some yield loss,” says Lange.
Stages for rolling and chemical applications
In soybean, growers may need to know early crop stages when they plan to roll the emerging crop. “The first trifoliate is the ideal stage for rolling because then growers know the majority of the crop is past the hook stage, where it’s just poking through the ground,” says Lange. “Growers also want to know if it’s too late to roll because even at second or third trifoliate, it’s probably a little late for rolling and they could do damage to the crop.”
During soybean’s later growth stages, it’s crucial to know when the plants are past the stage where products can safely be sprayed. For a product like glyphosate, the recommendation is to apply up until flowering only, and it’s important not to go beyond those stages for a number of reasons, including potential yield reduction.
Typically, says Lange, farmers have a lot of experience with their crops and growing conditions and know when they need to apply products, so it’s just a matter of taking careful note of crop stages as they do their regular field scouting.
“I know some farmers that rely totally on their agronomist to regularly scout their fields, and there are other farmers that like to take the quad, drive across the field and do it themselves,” says Lange.
“It’s especially important to do that pre-scouting before they actually do any herbicide application, and to do post-scouting afterwards because they want to see what kind of weed control they got. If there are any problem weeds that didn’t get controlled, was it a missed strip, or potentially some resistance issues? Could it be a problem with things like spraying at the wrong time of the day? It’s important to go out once a week when the crop is first out of the ground to see what growth stage they are at, and as they get closer to the timing for spraying, at least a couple of times a week.”
Growth stages at maturity and harvest
At the other end of the growing season, crop staging is important to determine crop maturity and harvest timing. “Growers who are considering using some kind of desiccant on a crop need to make sure they are at the right stage,” says Lange.
In crops like dry beans and peas, the rule of thumb for a desiccant application is when the crop is at 80 to 90 per cent leaf-drop stage, but if the crop isn’t maturing evenly, it can be a challenge to get the timing right.
“Sometimes growers have to be aware of what their field looks like and know if there are areas of the field that could be sprayed or harvested separately,” says Lange. “I know sometimes that’s not always an easy call to make, but if it is a crop that has some maximum residue limit (MRL) issues with certain products they spray on it, growers need to pay attention to that and make those adjustments.”
Lange emphasizes it’s vitally important to follow the label guidelines for each product to avoid exceeding MRLs. “Whether it’s pre-harvest or spring-applied herbicides and fungicides, growers need to check what the pre-harvest interval is to make sure the product they are spraying isn’t interfering with that,” says Lange. “Some products have a very short pre-harvest interval like two weeks and some have a 60-day pre-harvest interval.”
Sometimes weather is the determining factor on whether a grower could or should use a desiccant or not, as last year’s fall season demonstrated very well. Because of the hot, dry conditions in August, some pea crops were slow to dry down because there wasn’t enough moisture to help finish off the crop and let it mature evenly.
“Growers could consider desiccating in that situation, but need to ask if it will give them the same benefit as if they just waited a little bit for the seed to mature if they don’t have weed challenges,” says Lange. “Last year was a very unique year because of how hot and dry it was during harvest.”
To assist growers in making some of these staging decisions, Lange points to the Keep it Clean guidelines released every year at https://keepingitclean.ca/, which provide information for different crop types on MRLs, and the Manitoba Field Crop Protection Guide for pre-harvest interval information.
Resources for determining pulse and soybean growth stages
Find information online for determining growth stages of soybean, field pea, dry bean, faba bean and lentil.
Pulse and soybean plant growth stages are classified as V (vegetative) and R (reproductive). The Manitoba Pulse and Soybean Growers and Saskatchewan Pulse Growers have detailed fact sheets on their websites with growth and maturity stages for a number of pulse and soybean crops.