NEBRASKA CROPWATCH/UNL EXTENSION

As plants approach or are beyond the 6-leaf stage, the lower leaves begin to slough off, making it more difficult to accurately determine corn development stage. The same challenge can occur in fields where plants have been damaged by early-season hail or frost. This raises a common question: How do I determine corn growth stage when I can no longer count leaves? To answer that, it is critical to understand leaf staging corn by the leaf collar method, leaf method, and plant height method.

It is important to accurately growth stage corn particularly if you are planning to apply a post-emergence herbicide because each herbicide has restriction based on corn growth stage or plant height (Table 1). Herbicide applications made past the recommended application stages can result in significant crop injury. Some herbicides can be applied later according to the label using drop nozzles which prevent the herbicide being sprayed into the whorl.

The leaf collar and split stalk methods are the most accurate in using the plant to properly growth staging corn. The Corn GDD tool can aid in predicting when a specific growth stage will occur. Using proper growth staging methods are especially important to avoid crop damage as one makes post-herbicide and other post-pesticide applications.

Post-emergence herbicides are an important tool in the overall weed management plan. Here are some considerations to assure a successful weed management plan using a post-emergence herbicide: Always pay attention to the growth stage or height noted on the label prior to application. Application beyond that point may result in crop injury.

Absorption of post-emergence herbicide and potential crop injury are influenced by environmental conditions. Avoid herbicide applications when the crop and weeds are under stress.

Do NOT apply post-emergence herbicides with foliar fungicides or nitrogen fertilizer.