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As13;10;corn approaches physiological maturity, leaf death or senescence 13;10;naturally occurs. Top dieback refers to when leaves begin to die earlier than normal, from the top down. Top dieback can result from drought, insect damage, or anthracnose. Regardless of the cause, the effect on yield is determined by the timing of dieback during the grain fill period.
Drought Stress. Excessive heat and moisture stress can result in early senescence13;10;of the leaves. Under severe conditions, the plants have a hard time maintaining13;10;leaf health, and stressed corn leaves may take on a gray-green color and wilt13;10;prior to death. Symptoms of drought can be observed in nearly all plants in13;10;drought-stressed areas of a field.13;10;Insect Damage. Tunneling insects, such as European corn borer or13;10;Southwestern corn borer, can also cause top dieback. These insects can damage13;10;the upper stalk or girdle leaf sheath attachments at the stalk nodes. Unlike symptoms13;10;of drought, top dieback that results from insect damage will be random13;10;throughout the field. Top dieback resulting from insect damage is less common13;10;today due to the widespread adoption of B.t.13;10;corn products targeting corn borers; however, top dieback can still be an issue13;10;in non-B.t. products.13;10;Anthracnose Top Dieback. The fungal disease, anthracnose, can also cause top dieback. The characteristic symptom of13;10;anthracnose top dieback are black lesions that are visible on the outer13;10;stalk tissue behind the leaf sheaths. Stalks can be split to closely examine the pith. Infected plants have rotted or discolored pith in the upper internodes. As the stalk rot progresses, water translocation to the13;10;top leaves is reduced, resulting in early senescence of the top leaves.13;10;13;10;Anthracnose13;10;can be especially damaging if it causes a shorter grain filling period due to13;10;premature black layer development. Top dieback due to anthracnose may appear as13;10;early as 1 to 3 weeks after tasseling. Anthracnose dieback usually occurs in a13;10;more random pattern across a field rather than affecting all plants within an area13;10;of a field.
13;10;13;10;Yield loss from top dieback may result due to reduced photosynthesis in the top leaves. Yield losses are greater the earlier13;10;symptoms appear. Once symptoms appear there are no treatment options;13;10;however, farmers can take preventative measures to reduce the likelihood of13;10;top dieback in future years. This includes good agronomic practices such as a13;10;sound fertility program, as well as selecting a corn product with less susceptibility13;10;to anthracnose.