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small corn plant with roots exposed Tom J. Bechman
DETERMINE CAUSE: This seed produced a plant, but it was much smaller than those around it, meaning it emerged late. Why not dig it up to determine if disease or some other factor was the cause?

5 reasons corn plants look less than perfect

Corn Illustrated: Scout and evaluate corn stand establishment. Watch for these five problems.

Once corn emerges and you get sunny days when the temperature hits 80 degrees F, plus a shower when needed, your cornfields should look great. But in case you don’t live in this dream world where everything always works like it should, here’s advice from Bob Nielsen, Purdue University Extension corn specialist.

“The next phase of the growing season after planting is stand establishment,” he says. “Take time to evaluate your stands in each field, and look for potential issues that might develop if environmental conditions are less than perfect.”

A key to top yields is even emergence. Nielsen recommends evaluating stands to see if you obtained uniform emergence in each field. If you didn’t, this is the best time to determine why some plants emerged later — while the signs and symptoms are still fresh. You likely won’t be able to help this year’s crop, but you could learn valuable information to plug into decision-making in the future.

Possible problems

Here are five factors that could contribute to uneven emergence:

1. Seedling diseases. If it turns cool and wet, be on the lookout for disease symptoms. Seed is treated with fungicides, but they begin to lose effectiveness two to three weeks after planting, Nielsen says.

Brownish or discolored seedling roots, kernel tissue or mesocotyls are symptoms of seedling disease. A disease can devastate young plants if it takes hold before nodal roots from the crown area develop successfully.

2. Frost injury. Early-planted fields can be subject to nipping by light frost if temperatures dip just as seedlings emerge from the soil. The coleoptile, which is the first part of the plant to poke through the soil, normally splits to allow emergence of true leaves. If frost nips the coleoptile at the wrong time, you may see a “laddered” or “knotting” appearance. This is caused as true leaves rupture through the sides of discolored, injured coleoptiles.

3. Saturated soils and crusts. Where corn didn’t emerge after planting before heavy rains hit, there could be an impact on emergence. Waterlogged soils are deficient in oxygen, which can interfere with normal germination and early seedling development. If temperatures also drop after such a storm event, germination and emergence will likely slow down.

In extreme cases, sweet corn seeds, being less hardy, may rot under these conditions. Conventional corn is less prone to rot, but staying in the soil longer aggravates susceptibility to diseases and insects. If a hard crust develops once soils begin drying out, you may need to dig out the rotary hoe, Nielsen says.

4. Seeds that didn’t germinate. Remember that germination is usually around 95%. That means up to 5 seeds out of 100 may not germinate, even under ideal conditions, Nielsen says. So, don’t assume a skip in the row means the planter didn’t drop a seed. Dig and see if a seed is there that simply failed to germinate.

5. Purplish plants. Especially if soils are cool and wet after emergence, you may see purplish discoloration in some plants, Nielsen says. Purpling can indicate a phosphorus deficiency. However, there may be plenty of P in the soil — plants just aren’t accessing it due to cool, wet conditions. If this is the case, plants normally green up once conditions improve. Some hybrids naturally show more purpling than others.

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