Nodes or leaves? Clearing up confusion on pulse crop staging and herbicide timing

As we enter into post-emergent herbicide timing in parts of the Prairies, crop staging becomes key in deciding when to spray or not to spray. Particularly with pulse crop staging, it can be confusing to compare what’s on an in-crop product label with staging guides from Alberta Pulse Growers, Saskatchewan Pulse Growers, or the Manitoba Pulse and Soybean Growers Associations.

The critical weed-free period for pulse crops is anywhere from the two to six leaf stage, depending on which species it is and on growing conditions. Pulse crop yield can be lost to weed competition as early as the two to three leaf stages.

Check out this RealAgriculture Pulse School episode on the critical weed-free period!

If early weed control and crop safety is so important, why do crop protection guides, product labels, and staging guides all have to use different terminology?

I can understand why certain pulse crop species may be grouped together for staging due to the type of germination — peas, lentils, chickpeas, and faba beans all have hypogeal germination, where cotyledons and growing points remain below ground. Soybeans and dry beans have epigeal germination, where cotyledons and growing points are above-ground. But why can’t we just use nodes or just use leaves?

Let’s use field pea as an example, since they are commonly grown in all three Prairie Provinces (sorry Eastern Canada, but I’m leaving you out of this discussion for now).

First, we have to make sure the crop is within the application staging of a product. For an agronomist this is easy, as the staging has been drilled into their head through any crop physiology class and from practice.

Generally, the staging is quite similar for those species of pulses with hypogeal germination. Start from the bottom and move up the stem: first node (first scale leaf), second node (second scale leaf), third node (first true leaf). After that, you continue counting nodes. Each node also counts as a leaf stage.

Now, reach for the crop protection guide. The product lists an application stage range from one to six true leaves. Ok, that one’s easy to figure out.

Then, if you grow more than one pulse crop, you move on to staging let’s say, lentils. Count nodes, look at book, and scratch your head. The first product’s application staging range says “two to nine nodes” and under the same active ingredient the next product says “two to six leaf stage.”

Either the amount of active ingredient isn’t quite the same in the generic product versus the name-brand and the application stage range truly is different, or this is a legal thing, where the two products can’t use the same terminology.

For those pulse crops with hypogeal germination and emergence, the first two nodes are below-ground. So which is it? Nodes or leaves? Are we talking about the total number of nodes, or only above-ground nodes? When true leaves are listed, application recommendations become a lot clearer.

A quick call to your chemical representative or agronomist may be the easiest way to clear up any confusion, but there must be a way to standardize the terminology surrounding pulse crop growth on product labels, at least for the two groups of pulse crops. Perhaps there’s a standard used in the pulse crop chemical development sector that is not being adhered to.

The point of this story is that you may have to cross-reference your provincial pulse crop staging guides with the herbicide label. Ensure your crop’s stage matches what the label says, whether it’s listed in leaves, total number of nodes, or above-ground nodes. It may take some deciphering, but always follow the label directions and get clarification if you need it.

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