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Come walk the crops with us – Crops and weed staging

By Isabelle Piche, Crops Summer Student

One of this month’s #SKCropWalk topics was the staging of both crops and weeds, during which the importance of proper staging was discussed. Ensuring the proper timing for pesticide application is important to avoid stressing the crop more than it already has been in this spring’s dry conditions.

In the first video, Crops Extension Specialists discussed how to properly stage cereal and pulse crops. To begin staging a cereal, orient the plant with the first leaf on the left side. Begin at the base of the plant, counting each leaf until the top. One of the most important things about staging cereals is differentiating the main shoot and the tillers. The main shoot will often be the largest stem with the most leaves. For a leaf to be counted, it must be at least half the length of the leaf before it. As the crop matures, it begins to produce tillers, which are counted in addition to the number of leaves. There are two types of tillers to be aware of: the coleoptile tiller and the primary tillers on the stems. The coleoptile tiller emerges from the root of the plant, below the soil, and may be mistaken for another plant when viewing from above the soil surface. The primary tillers originate from the crown of the plant, appearing as shoots emerging from within the leaves of the primary shoot. The last leaf before the head emerges, known as the flag leaf, is extremely important for yield, and the second-last leaf is called the penultimate leaf. Staging grassy weeds is very similar to staging cereal crops.

When staging peas, focus on counting nodes rather than leaves. The first node or two on the plant are found below the soil surface and followed by a small node just above the soil. These first nodes will have reduced leaves called scale leaves, which are not considered to be true leaves. True leaves are compound leaves with several leaflets attached to a central vein and tipped with one or more tendrils, or modified leaflets. Leaflets will begin to form on true leaves produced at the third node, and tendrils will begin to emerge on the fourth node. Nodes can vary in length depending on environmental conditions. In dry conditions, nodes will be more compressed. Correct staging of pulse crops is very important when applying herbicide, particularly when the crop is already stressed. Late application timing of Group 2 herbicides may cause more stress to the plant and result in temporary yellowing or “flashing” of the crop.

Staging canola begins with the cotyledons (paired kidney-shaped leaves), which are the first leaves to emerge on a broadleaf plant but are not counted as true leaves. The first true leaves are those that emerge after the cotyledons. Staging of canola seedlings up to the bolting stage depends on counting the number of unfolded true leaves. When spraying, especially with glyphosate or glufosinate, it is important to apply the herbicide within the application window listed on the label. Application outside of this staging is considered off-label and may stress the plant, and could lead to flower abortion in some varieties.

Cleavers seedling
Cleaver seedling with whorled leaf
Broadleaf plants can have various leaf attachments, which are staged differently:
  • Alternate leaf arrangement patterns means the leaves emerge one after the other, one per node, proceeding up the stem, and each individual leaf is counted (e.g.: lambs quarters and canola).
  • With opposite leaf arrangement there are two leaves per node with each pair of leaves rotated from 45 to 90 degrees from the previous leaves. For this type of leaf arrangement, each pair of leaves is counted as two leaves (e.g.: hemp nettle). Note: some plants with opposite leaves may occasionally produce a third leaf at a node, but are still considered opposite leaves.
  • Whorled leaf arrangements have three or more leaves emerging from the same node (e.g.: cleavers). The number of leaves in each whorl may vary. Most herbicide labels will stage whorled plants by the number of nodes. However, if the label does not, be careful to count each individual leaf.

For a number of plants, staging by counting the number of leaves becomes more challenging after the fourth leaf stage. As a result, many herbicide labels will then have the stage of the weed listed by height. The 2019 Guide to Crop Protection is a good resource for information on staging weeds and crops, herbicide mode of action (Herbicide Resistance Groups), and weed control strategies.

Overall, this #SKCropWalk provided a good overview of crop and weed staging that can be used to optimize herbicide application timing and minimize crop damage.  

For additional resources for staging, visit the Guide to Crop Protection or the Saskatchewan Pulse Growers staging guide for pulse plants, and check out the Crop Walk videos on the Ministry of Agriculture’s Facebook page.

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