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Measuring corn growth

What are the critical stages in the life of a corn plant? Actually, corn needs a lot of tender loving care throughout the growing season. The growth of corn is pretty consistent and is driven by heat units or Growing Degree Days (GDDs).

• How do you calculate GDDs? Calculate average daily temperatures by adding the highest and lowest temperatures of each day and divide by 2. Subtract 50 from the average daily temperature to get the GDDs for each day with the limitation that if the low falls below 50 degrees F, we use 50 as low and if the temperature goes above 86 degrees F, we use 86 as the high for that day. This allows us to make some adjustments in the formula.

• If we add the GDDs of each day from emergence to physiologic maturity (Black layer), we will have the total GDDs needed for the hybrid to mature. We need 2400 to 2800 GDDs from emergence to physiologic maturity of 105 to 115 day relative maturity hybrids.

• According to Bob Nielsen, Purdue Extension Corn Specialist, after seedling emergence, with moisture, nutrients and normal sunlight availability, corn growth is pretty consistent. From emergence to V10 leaf stage, about waist-high corn; it takes an average of 82 GDDs for each leaf added. After V10 stage, corn picks up speed and adds a new leaf every 50 GDDs. Now you can almost see the corn plants grow!

• At V6-V8 stage, be sure to side-dress with nitrogen before the plants are too tall, if you are going to apply additional nitrogen. Check for deficiency of nutrients like sulfur, zinc, magnesium and other micronutrients.

• Pollination is the next most critical stage. Make sure that insects like Japanese beetles, western corn rootworm beetles are not clipping the silks. Use insecticides if needed to control these pests.

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