Agronomy Talk

PHYSODERMA BROWN SPOT

AGRONOMY BRIEF

Published on Tuesday, August 23, 2022

 

Many growers experience Physoderma Brown Spot in their corn crops each year. Disease pressure has increased over the past decade due to higher yield conditions and excess water. The disease is caused by Physoderma maydis, a fungus that overwinters in the residue of previous crops.

Spores are wind dispersed or splashed into the whorls of developing corn plants. The disease is seen more when the whorls are filled with water for an extended period (excessive rains or irrigation). A corn plant is most susceptible to infection between the V5 to V9 growth stages, but physical symptoms usually do not show up until later in the year (tassel time).

Disease Appearance

Infected leaves will have tiny oval to round spots. These lesions will be yellow to brown in color on the leaves (Figure 1). Dark purple to black lesions can also appear on the leaf midrib, stalk, leaf sheath, and husks (Figure 2). Infection of the stalk near node six can also cause stalk rots and standability concerns.

Do not mistake this disease with Southern Rust. Southern Rust will wipe off and usually is NOT present on the bottom side of the leaf.
(Remember purple/black lesions grouped along the midrib - Physoderma Brown Spot)

Disease Control

Physoderma Brown Spot rarely has any yield impact. Extreme cases can cause stalk integrity issues. Infection near nodes 6 and 7 can cause the stalk to break easily. Often, symptoms are not always visible on the leaves of plants infected with stalk rot. Many times, affected plants can be healthy and still have good yield potential.

Although the disease has historically been of little importance, there are a few ways to control Physoderma Brown Spot:

  1. Rotate to a non-host crop.
  2. Reduce corn residue on the soil surface to help eliminate opportunities for infection.
  3. Plant tolerant hybrids. Some fungicides are labeled for Physoderma Brown Stem, but little data is available to provide proper application timing or show a positive ROI. 
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Author: Travis Coleman

Categories: Agronomy, Agronomy Talk

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