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Sponsored: Scout for Foliar Disease

Your first line of defense is to plant corn hybrids with a well-rounded disease resistance package. However, if you are faced with a disease outbreak, there are steps you can take to prevent stalk rot and improve overall stalk integrity.

In addition to the potential to greatly reduce yield, foliar diseases can negatively affect corn plants’ stalk strength. Herbicide injury may also mimic disease symptoms and affect stalk integrity.

Among the diseases that can quickly cover foliage and decrease stalk strength are southern rust, gray leaf spot and northern corn leaf blight.

Gray Leaf Spot

The development of gray leaf spot, which can reduce yield by as much as 40 percent, is influenced by hybrid susceptibility, environmental conditions and the use of reduced tillage and no-till production practices. Caused by a fungus, the disease leads to loss of photosynthetic leaf surface area, resulting in a decrease in plant sugars and reduced grain production.

Scout for gray leaf spot after tasseling. Look for orange-red lesions surrounded by narrow yellow halos. As lesions mature, they appear tan or brown in color and are rectangular in shape. Lesions are one-half inch to four inches long and interveinal, giving them a straight-edge appearance.

Northern Corn Leaf Blight

Northern corn leaf blight, which can cause substantial yield losses, is most detrimental to a corn crop’s potential when development begins before or during tasseling and silking.

The disease can be identified by tan-colored lesions that reach up to 6 inches in length. As the disease progresses, the lesions become tan or gray in color and are more oblong in space. Fungal spores produced by the disease may make the lesions appear darker.

Southern Rust

While the fungus that causes southern rust does not overwinter in the continental United States, it can develop quickly and cause substantial yield losses, especially in later-planted corn. In general, the fungus that causes southern rust blows into the corn production area annually. Therefore, southern rust may not always be an annual occurrence.

The disease prefers warm, moist conditions, and its symptoms are sometimes incorrectly identified as common rust or other diseases. Identifying characteristics include large, densely packed areas of small, round pustules that are orange to light brown and are often observed on upper leaf surfaces.

Taking Action

In addition to scouting and controlling foliar disease outbreaks, Mississippi State University Plant Pathologist Tom Allen offers the following stalk strength management tips:

  • Choose hybrids that best fit your location and environmental conditions. Some hybrids are more susceptible to stalk rot, and hybrids can have varying levels of inherent stalk strength.
  • Tailor your fertility program to your geographical location, field history, the plant population present in each specific field and the hybrid planted.
  • Drought conditions can exacerbate stalk rot. When possible, irrigate to avoid drought stress and improve stalk strength.
  • Scout for stalk rot, and if greater than 15 percent of plants in a field exhibit symptoms of compromised stalk integrity, harvest that field as early as is economically feasible.
  • The longer corn remains in the field, the more susceptible it is to further damage. Harvest those fields first that experienced early season stress or stresses that affect root and stalk health.

Mycogen Seeds offers several hybrids that are time-tested through extensive research and in-field testing to ensure disease tolerance. Using tolerant hybrids provides an earlier, more extensive source of inoculums for disease development.

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