Factors that stress corn throughout the growing season can lead to stalk rots, which can lead to yield loss due to premature plant death or lodging. Understanding stalk rots risk factors and management practices are critical.

Traditionally a problem disease in the western Corn Belt, Goss’s wilt is now prevalent across the Corn Belt and spreading into Canada. Once corn plants are infected, yield potential can be reduced by up to 50 percent. There are no effective chemical control measures for Goss’s wilt. The best way to limit spread of the disease is by selecting hybrids with strong Goss’s wilt tolerance.

This bulletin provides information about Goss’s wilt and tolerance ratings for Mycogen® brand corn hybrid families. The ratings are the result of 2011-14 field trials conducted in Illinois, Iowa, Minnesota, Nebraska, South Dakota and Wyoming.


DISEASE INFORMATION
Goss’s wilt is caused by the bacterium Clavibacter michiganensis subsp. nebraskensis. It overwinters in infected corn residue, primarily found on or near the soil surface. Inoculum in the infected residue primarily spreads by wind and splashing rain. To a minor degree, Goss’s wilt also can survive in seed.

To infect a corn plant, the bacterium needs an entry point or wound, which is generally caused by heavy rain storms, hail, wind, blowing sand or mechanical damage. Humid, wet weather is another risk factor because moist or wet leaves are conducive to the spread of disease.


IDENTIFYING GOSS’S WILT
Scouting is important because infection can occur at any point during the growing season. Infested seedlings show systemic wilting, stunting and a variety of leaf symptoms.

More-mature plants demonstrate the foliar leaf blight version of the disease. The first signs of infection are dark green to black, oblong spots that are water-soaked with a greasy look that appear parallel to leaf veins. Streaks of freckles within the lesions are a distinctive feature of Goss’s wilt. Droplets of bacterial exudate ooze from the freckles, leaving a crystalline substance that glistens in direct sunlight. The spots coalesce as they enlarge, forming long lesions with wavy edges. As the lesions age, they turn tan and can blight much of the leaf. Systematically infected plants have discolored (orange) vascular tissue and likely slimy stalk rot.

Key Symptoms:
• Freckles in lesions
• Crystalline deposits
• Droplets of exudate

Commonly confused with:
• Drought damage
• Heat stress or sun scalding
• Other leaf blights


CONTROLLING GOSS'S WILT
Because Goss’s wilt is a bacterial disease, it cannot be treated with fungicides. The best method of control is planting hybrids with strong Goss’s wilt tolerance. Tables 1 through 4 demonstrate the wide range of tolerance in hybrids.

Growers can limit the spread of Goss’s wilt to uninfected fields by selecting tolerant hybrids, harvesting infected fields last and thoroughly cleaning harvest equipment. Destroying infected crop residue will lower the amount of bacteria present. This is most effective when done immediately after harvest. In most situations, rotating to a nonhost crop, such as soybeans, dry beans, sugarbeets or alfalfa, is a more viable option. Last, manage irrigation to reduce humidity in the field during the growing season.

Talk to your Mycogen Seeds sales representative or customer agronomist to learn more about managing Goss’s wilt on your corn acres.

Early season seedling damage can significantly reduce yield. Scout cornfields regularly and diagnose problems before economic losses occur.

Flooding affects fields differently based on a variety of factors. Manage flooded corn to minimize damage and ensure optimum plant health and yields.

Wet and/or humid conditions can lead to black, sooty molds in cornfields at harvest. Sooty molds are species of secondary saprophytic fungi — microorganisms that feed on dead plant material. The presence of these molds can create excessive amounts of black dust when harvesting affected cornfields.

Dry summers and relentless pests increase your corn crop’s susceptibility to aflatoxins, which are harmful to livestock. Reduce your exposure with effective management.

A bacterial disease that has been prevalent in areas of the western Corn Belt for decades, Goss’s wilt has expanded to additional areas of the central and eastern Corn Belt in recent years. If infections occur early in the season, during key crop development times, yield potential can be reduced by up to 50 percent.

Warm, moist conditions from July to September can cause increased disease incidence in corn. Recent studies have show potential economic benefits from foliar fungicide applications. Fungicide treatments can give protective or curative benefits for corn diseases such as: gray leaf spot, common rust, eyespot and antracnose. These diseases can limit photosynthesis due to tissue death. Loss of leaf tissue also may result in grain production loss or harvest loss due to weakened stalk strength and harvestability issues.

Increased use of reduced tillage and no-till production practices has increased gray leaf spot occurrence. Caused by a fungus, the disease leads to leaf tissue loss, resulting in a decrease in plant sugars and decreased grain production. Potential yield losses range from 5 percent to 40 percent.

Southern rust is a common threat to corn crops across the southern United States. The disease damages crops in the Corn Belt only about once every five years, but when it does yields may be cut by more than 40 percent.

Nutrient deficiency symptoms are not always caused by a lack of nutrients in the soil. Other factors can be to blame, such as poor root development, unfavorable soil conditions or weather. Plant tissue sampling helps identify the problem and determine corrective action.