Why Are My Corn Stalks Purple?

Cold Weather

• Corn plants that are suddenly exposed to cold temperatures often start to display purple discoloration of stalks. The plants are healthy except for the purple color, gradually assuming the natural green once temperatures have stabilized. A pigment called anthocyanin, found naturally in corn foliage along with chlorophyll, leads to the purple color. Under cold-weather conditions, the plants produce less than the amount of chlorophyll required to maintain their green color, leading to a more pronounced purple shade in the stalk and leaves. Once chlorophyll levels are normalized, the purple disappears.(Reference 5)

Phosphorus Deficiency

• The deficiency of phosphorus in corn is a major cause of the plants turning purple. This deficiency is commonly caused in plants growing in acidic soils, where the low soil pH makes plants unable to process phosphorus. A pH of less than 5.5 lowers the phosphorus availability by nearly 30 percent, states eXtension, a partnership of American universities. The root growth of corn growing in acidic soils is also gradually stunted, making plants unable to process phosphorus.

Correcting Deficiency

• To help relieve the symptoms related to phosphorus deficiency, an injectable side-dressing of phosphorus is recommended. Applying phosphorus in the form of fertilizer to the soil surface will only make the nutrient available to the top couple of inches of root zone. However, when the nutrient is injected into the roots in the form of side dressing, it is available to the entire root area. Once the plant absorbs the nutrients effectively, the green color gradually returns.

Favorable Conditions

• Corn plants that are rotated with rice are especially prone to purpling due to phosphorus deficiency. Corn rotated with soybeans or cotton is also prone to the discoloration, as the phosphorus requirement of corn is twice that of soybeans or cotton. Plants that are suddenly exposed to optimal growth conditions following wet or cooler weather also start to display symptoms. A consistent deficiency of phosphorus leads to delayed maturity and stunted plant growth.