Identifying the leaf collar and first true leaf are critical to accurately stage corn, according to Dr. Jourdan Bell. (Texas A&M AgriLife photos by Kay Ledbetter)
Amarillo, TX (June 6, 2018) - Weed control in corn is important to profitability, but producers need to be aware of herbicide application timing, says Dr. Jourdan Bell, Texas A&M AgriLife Extension Service agronomist in Amarillo.
“We know post-emergent herbicide applications are necessary for season-long weed control,” Bell says. “However, it is important to follow post-emergent corn herbicide labels, which define the latest growth stage for which herbicide applications can be made without causing crop injury.”
She says herbicide applications past the recommended growth stages can result in significant crop injury, so it is important producers understand and recognize each of the stages.
“Some herbicide labels also provide a recommended height for the last herbicide application as plant height often corresponds with a particular vegetative stage.”
The first round-tipped leaf. (Texas A&M AgriLife photo by Kay Ledbetter)
However, Bell says, in high-input environments with abundant irrigation and/or precipitation and fertility, internode distances can expand at a greater rate than new leaves.
“Consequently, plant height does not always correspond to the correct vegetative stage,” she says. “So, it is important to accurately stage the corn crop before making post-emergent herbicide applications.”
Bell also warns stressful production environments with limited water or cool temperatures can slow corn growth, which can result in magnified crop injury because the plant does not metabolize the herbicide quickly enough to avoid injury.
For labels that provide both plant height and growth stage, the applicator should follow the more conservative recommendation, she says.
The vegetative stages are described using the leaf collar method. Leaves are counted from the lowermost first rounded-tip leaf to the uppermost leaf with a leaf collar, which is the connection between the leaf blade and the leaf sheath, she explains.
“The key features to identify are the leaf collar and the first round tipped leaf,” Bell says. “While the individual stages are important, it is key to be able to identify the leaf collar and first true leaf to accurately stage corn.”
The leaves in the whorl that are not fully expanded are not counted, she says.
Leaf stages are labeled as “V” stages. Some of the more important V stages include:
Another consideration, Bell says, are non-labeled spray adjuvants. Spray adjuvants are to enhance herbicide performance, but under certain conditions, non-labeled spray adjuvants can increase herbicide injury from a poorly timed post-emergent application. Consequently, it is always recommended to check the label for appropriate adjuvants.
“In addition to the crop stage and condition, knowledge of the weed species and weed size are also important for effective post-emergent herbicide applications,” Bell says.
A complete list of post-emergent corn herbicides evaluated in the AgriLife corn herbicide trials at Bushland is available at: https://tinyurl.com/cornherbicidepub.