As farmers make post-herbicide applications, Field Agronomist Nicole Stecklein says one simple habit may separate clean, healthy fields from those that suffer preventable herbicide injury: counting collars, not leaves.
In a year marked by what she calls “weather whiplash” — one of the wettest Aprils on record in Iowa followed by one of the driest Mays — corn is racing through the early vegetative stages. That puts timing pressure on farmers who want to clean up their fields with a post herbicide while being mindful of product label restrictions.
For Stecklein, the starting point for determining application timing is basic crop staging. “When we stage a corn plant, we want to make sure we are counting collars, not counting leaves,” she says.
In a YouTube video, available here, Stecklein walks growers through the visual cues that help define each stage of corn growth. In the video, she demonstrates how she identifies the plant as being at the V4 growth stage.
That distinction is more than academic for farmers, as herbicide labels are written to crop physiological stages.
The Critical Window Of V2 To V5
Across much of her area, Stecklein says corn is in that V2 to “just coming on” to V5, right as most post passes are being lined up. Development inside the plant is changing fast.
“The importance of actually staging this crop correctly is that developmentally there’s [a variety of] things happening at different physiological stages,” she says. “If we put the wrong herbicide on at the wrong time, we could end up hurting [the crop] at a very important physiological time.”
The potential for damage increases as corn moves through the “ugly corn” stage — roughly V2 to V3.5 — when the plant is shifting from dependence on its seed root to its permanent root system, the nodal roots.
By the end of V4 and into V5, the nodal roots “really get well developed,” she adds, and finally start doing the heavy lifting for water and nutrient uptake – a time that is a vulnerable moment in corn development.
That’s why Stecklein warns against relying on calendar days or planting logs to time herbicide post passes and encourages corn growers to count collars.
The process provides a consistent, plant-based benchmark that travels from field to field and hybrid to hybrid. Herbicide labels typically specify a maximum growth stage — commonly V4, V5 or V6 — for safe application. Miscounting leaves can lead growers to underestimate how far the crop has advanced.
Staging And stress: When The Plant Is Least Forgiving
The same hot, dry conditions that have limited rain to activate residual herbicides also increase the risk of crop stress if post applications go on at the wrong time.
As nodal roots push into dry, compacted or partially open seed furrows, Stecklein notes they can struggle to establish — setting up problems like rootless corn and “floppy” plants. Layering herbicide stress on top of that, especially during the V2–V4 transition, can magnify injury.
While her video update centers on several in-field challenges — sidewall compaction, fertilizer burn risk on low-organic-matter soils and uneven planting depth — she repeatedly comes back to staging accuracy as the piece growers can control before pulling into the field with their sprayer.
Her message: collars are the common language between farmers, product labels and the corn itself.
In summary, here are Stecklein’s three key guidelines for farmers heading into the heart of post-emerge herbicide application season:
- Stage plants by collars at the field edge before spraying. Count fully visible collars, not leaves, to determine crop growth stage and cross-check against the herbicide label for application timing.
- Pay special attention in the V2 to V4 window. This is the “ugly duckling” transition when the plant shifts from seed roots to nodal roots and is especially sensitive to stacked stress.
- Use collars, not the calendar, to manage risk in each field. Variable emergence, soil type and weather mean two fields planted the same day may be at different growth stages when you’re ready to spray.
