There are various reasons that corn seedlings could turn purple soon after emerging. You may be able to do something about some of them, but perhaps not all of them, at least not this year. And some of the causes may be no big deal. It may only be a temporary situation. It only becomes a big deal if the purple conditions persist.
This information was prepared with the help of the Purdue University Corn & Soybean Field Guide.
1. The soil is truly deficient in phosphorus.
Reddish plants is the number one symptom of a phosphorus deficiency. If plants are turning purple, and you check and find soil test levels in that part of the field are low for phosphorus, then it may be a true deficiency. It would need correcting by an addition of phosphorus before you could expect the condition to go away. Even if the corn recovers, if the soil is truly deficient in phosphorus, expect yield to be reduced. Applying phosphorus in starter fertilizer may actually pay a return in this situation. If phosphorus levels are adequate or high, then nitrogen is often the nutrient recommended to aid in starter fertilizer.
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2. Cool, wet soil conditions may produce purpling
The purpling develops because the plant isn’t taking up enough phosphorus. The plant is deficient in phosphorus, but the soil may not be deficient. It’s just harder for the plant to take up phosphorus when conditions in the soil are cool and wet. Once the weather improves, especially if the temperatures warm up, the purpling may disappear. Whether or not there is yield impact may depend upon the longevity and severity of the cold outbreak.
3. Different genetics may show signs of purpling
Some genetic families will cause a certain amount of purpling in younger corn. In this case the purpling normally disappears later. It should not be a factor in yield. Instead, in this case, it is just a trait of the hybrid.
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4. Soil compaction or saturated soils may cause purpling of corn plants
Purpling results form a buildup of sugars in the leaf, the Purdue guide says. That can result from soil compaction or saturated soils. Not working soils to wet, and installing tile drainage in advance when possible, would lessen the effects of this effect.