Stage of Growth Counts, Not Plant Height

Labels tend to talk about stage of growth today.

Published on: Jul 8, 2010
Fungicide spraying is underway. I personally sighted a crop duster in an airplane spraying a field near power lines and Interstate 74 last week. Talk about guts! Then a helicopter with a wide boom sprayed a cornfield a quarter mile form me the other evening. Odds are you've seen them too. Maybe you've already contracted for spraying, or had spraying completed for either leaf diseases or insects that might affect pollination.

If your field hasn't been sprayed yet, you owe it to yourself to read the label about timing of application yourself. Don't read it near bedtime- it's not exactly juicy reading. But it's important reading in case a mistake is made, and your corn crop winds up damaged. The first question a company rep will likely ask is 'did you follow the label?' Most dealers are well versed in the products they sell. But ultimately it's your field, and you ought to know what the label says.

Some of you may still have smaller corn or soybeans to spray. Many labels once talked about plant height. Now most talk about stage of growth. That's because if conditions hold back growth, a plant may still move toward maturity. So it may be much shorter, but still near the same stage of growth. It's usually stage of growth that matters when it comes to applications and potential plant injury.

Working in the Farm Progress/Precision Planting plot at Throckmorton Research Center , a Purdue University farm, last week, we discovered two plants, both in the V-4 stage by the leaf collar method. One plant was twice as tall as the other. The shorter one was in a water-soaked area and running low on nitrogen.

Even where corn wasn't rain-soaked, there were differences in height of green plants that were both in the same stage of growth. In this case, the difference was due to differences in emergence, even though the plots were all planted the same day. Corn planted at one inch deep emerged more slowly, and some of those shallow-planted plots are still running behind, especially in plant height.

You can find instructions on how to determine the growth stage of corn plants in the Purdue University Corn and Soybean Field Pocket Guide, printed and distributed by the Purdue University Diagnostic Training Center. The Guide also discusses the droopy leaf method. Using the droopy leaf method, you usually estimate corn at about one leaf stage ahead of what you arrive at using the leaf collar method. Most agronomists prefer the leaf collar method. Check your label to see if it specifies which method it refers to when it talks about stage of growth of plants.