At some point in July, your corn plants have all the leaves they will have. They also will produce tassels and ear shoots, and then form ears and kernels. A large part of how the plant looks is determined by genetics. You can learn a lot about how a plant will mature by dissecting it and looking inside when it’s still young. The other major factor that impacts how a plant looks by this point in the season is its environment — primarily weather conditions.

Dave Nanda decided to prove this point by carefully examining a young plant at the V7 growth stage in early June in the Corn Watch ’18 field. Nanda is an independent crop consultant based in Indianapolis. Corn Watch ’18 is sponsored by Seed Genetics-Direct, Washington Court House, Ohio.

Dissect the plant
Here is a closer look at what Nanda found when he looked at a single, healthy plant:

• Growth stage. First, Nanda determined the plant’s growth stage. “Sometimes, the first rounded leaf, and even the next leaf or two, are gone by the time you look at a plant this size,” he explains. “In this case, they were still there. Counting the rounded leaf, there were seven leaves with collars. That means the plant was at the V7, or seven-leaf, stage.”

• Growing point. The growing point typically emerges above ground between the fifth and sixth leaf stage. When Nanda inspected the field two weeks earlier, most plants were at the V5 stage, and the growing point in a plant he dissected was at ground level.

“The growing point in this plant today was several inches above ground level,” Nanda says. “If hail or some other calamity occurred at this stage and destroyed the growing point, you would not expect the plant to recover.”

• More leaves forming. When Nanda dissected the plant and inspected the whorl above the growing point, he was able to unroll 13 leaves that were already forming inside the plant. The leaves grow up and around the growing point.

“The tassel wasn’t yet visible inside the stalk above the growing point, but it would have been in another leaf stage or two,” Nanda says. “All the parts the plant will have are formed inside the stalk when it’s relatively young.

“Leaf number is largely genetic. That is also determined early.”

TRACK THE PARTS: Everything but the tassel was already formed when Dave Nanda checked a plant in the seventh-collar stage in the first week of June in the Corn Watch ’18 field. The tip of the knife points to the growing point. At least 13 leaves are already forming in the plant. They are at the left side of the photo and have already grown up and around the growing point.

• Early decisions. Other features, such as number of kernel rows per ear, are also determined early in the plant’s life cycle. While this is also a decision based largely on genetics, environment can affect it.

“These plants had plenty of moisture and heat early, so I would expect they made favorable decisions,” Nanda says. “They were tattered by hail with the growing point still underground. It’s hard to say for sure, but that likely will have little effect on yield.”

• Later impacts. Where weather can play a bigger role is in determining the length of the ear and what happens during pollination and grain fill, Nanda says. That’s why it’s important to scout in late July and early August.

“Even if kernels form to the tip, if it turns off dry or plants are stressed for other reasons, those tip kernels which form last may abort,” he notes.