You might not think you can learn anything from very late-season scouting in the field or from the air. But then again, you might be wrong.

Dave Nanda scouted the Corn Watch ’17 field soon after both hybrids in the main part of the field had reached black layer. He was looking for signs of disease, differences in how plants dried down and how they stood up to late-season challenges. He found all those things. But he also found that some plants had put so much into producing a crop that nutrient deficiencies were showing up.

Nanda is an independent crops consultant. Corn Watch ’17 is sponsored by Seed Genetics-Direct, Washington Court House, Ohio.

When nitrogen deficiencies show up late, especially after black layer, it can mean several things. Perhaps the crop had enough nitrogen but didn’t have any left in the tank after grain fill. Maybe it did run short. If other nutrient deficiencies are showing up, but only here and there, it may be a minor issue. But it may be worth noting and reviewing soil test data, Nanda observes. For example, if you find signs of potassium deficiency, it would be prudent to check potassium levels in soil test results. If soil tests haven’t been done regularly, it might be an indication that regular soil testing would be worthwhile.

Single leaf
One leaf from the Corn Watch ’17 field showed signs of three possible deficiencies. Here is a closer look:

• Nitrogen deficiency. At this stage, N deficiency isn’t unexpected, especially on lower leaves, Nanda notes. Yield will be good in this field, and the plants used lots of N to produce grain. With N deficiency, yellowing starts at the tip and moves its way down the midrib. In older tissue, like this leaf, some of the tissue begins to die and turn brown.

This field was short of moisture for about three weeks in August. Drought stress can contribute to nitrogen shortages and symptoms, according to the Purdue University Extension Corn & Soybean Field Guide. 

• Potassium deficiency. Note the outer edges of this leaf have turned brown. The pattern goes all the way around the leaf. When plants begin to run short on potassium, according to the Purdue guide, the yellowing begins at the tip and runs down the outside margins of the leaves. Look for it in lower leaves first. As plants get older and if the deficiency persists, then tissue turns brown. Dry soils that limit rooting sometimes lead to K deficiency symptoms, even if there are still adequate potassium levels in the soil.

• Possible sulfur deficiency. Striping within the leaf, even though faint, suggests sulfur could be running short, even though the deficiency wasn’t confirmed, Nanda says. He advises corn growers to pay more attention to potential for sulfur deficiency today vs. 20 years ago. The amount emitted by utilities is much smaller today.