purple corn

Look for patterns to help determine causes of the purple corn. 

COLUMBIA, Mo. — Ugly corn is better than no corn this year, says University of Missouri Extension corn and small grains specialist Greg Luce.

“There are some good corn stands in Missouri this year, but there are a lot of ugly ducklings also,” says Luce. Those ugly duckling stands have struggled in the aftermath of historic May rains.

Corn often looks ragged in early growth stages, he says, but this year more fields appear exceptionally ragged.

Extended wet conditions and cold periods left corn uneven, pale, yellow and even purple.

“Don’t despair,” Luce says. “The corn will be improving soon.”

Warmer weather in June will boost corn’s appearance. As corn reaches the V5 stage and beyond, the root system grows rapidly. Strong roots support healthy growth above ground.

Some cornfields are showing their royal colors. Corn can become purple-tinted when temperatures drop at nighttime and sunny days follow. This causes early season stress and restricted root growth. When growth slows, sugars produced by photosynthesis accumulate in leaves. This triggers anthocyanin pigment colorization and results in purple corn.

Corn usually outgrows the “purpling” condition by V6 stage (12 inches).

Phosphorus deficiency, root injury from insects, fertilizer burn, compaction and herbicides also can cause purple corn. Purpling usually appears in an application pattern or certain soil types.

Purple corn uniformly across the field usually results from the anthocyanin and varies by genetics.

Do nitrogen problems cause pale yellow corn?

Absolutely! Soils lose nitrogen during warm, wet periods. The cooler weather earlier slowed corn root development. Corn yellows as a result. The pale yellow appearance also shows when the root zone lacks oxygen. This can happen even when the soil contains enough nitrogen.

How do I know if I have enough nitrogen?

As soil dries, oxygen returns and growth rates pick up. Plants green up if there is enough nitrogen. However, too much rain and warm soil create the right conditions for denitrification. This happens most often on poorly drained soils.

“This type of loss only affects nitrate, but all nitrogen fertilizer eventually converts to nitrate in soil,” Luce says. “As we get later in the season, most of the nitrogen has been converted to nitrate.”

If there is a silver lining this year, it’s that farmers were unable to apply nitrogen at the usual time due to wet fields, so the nitrogen not applied has not been lost. Where nitrogen was applied, Luce says, it is important to remember that anhydrous converts to nitrate more slowly than other fertilizers. In neighboring fields applied with anhydrous or urea at the same date in mid-April, the fields fertilized with urea lose more nitrogen.

“The good news is that corn can recover from a lack of early season nitrogen more than we once thought,” he says.

Many tests are slow and difficult to do well, or they may not reveal patchy nitrogen-deficient areas that are common.

MU Extension nutrient management specialist Peter Scharf says a “bird’s-eye view” remains the best way to assess nitrogen need. Satellite images show yellow corn and affected areas.

“If 5% of a field is yellow-green, it’s not worth fixing,” Scharf says. “But if 50% of the plants are yellow-green, it pays to apply more nitrogen.”

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