Goss's Wilt

Since its identification in Nebraska in 1969, Goss’s Wilt has spread through Colorado and Kansas in the Western United States Corn Belt, and now occurs in several Midwestern states and parts of Canada. Growers are advised to watch for this disease as they scout their fields.

Life Cycle

Goss’s Wilt is caused by the bacterium Clavibacter michiganensis subsp. nebraskensis, which overwinters in infected crop residue. Bacteria can enter plants through leaf injury wounds created by strong wind, blowing sand, or hail. Inoculum can be spread from field to field by wind physically moving crop residue. Infection can also occur when rain or irrigation water splashes bacteria from infected crop residue onto corn plants. Alternate hosts for this pathogen include green foxtail and shattercane.

Symptomology

Goss’s Wilt appears as either a vascular wilt or leaf blight. Systemic infections that occur early in the season result in vascular wilt. Symptoms of systemic infections include discolored vascular tissues containing orange bacterial exudates that may evolve into a brown rot of the lower stalk and roots. Wilt and death similar to what occurs under severe drought stress will likely take place.

Leaf blight symptoms usually appear mid-season and are long, gray-green to black water-soaked streaks with wavy margins. Smaller, darker water-soaked lesions, often referred to as freckles, are apparent inside the larger lesion. The lesions may ooze bacteria laden droplets in the morning. As the droplets dry, a crystalline sheen develops on the leaves. Eventually, the lesions will fade to a tan color and may blight large areas of leaves.

Seed Infection and Transmission

Goss’s Wilt can move from infected plants to seeds. Several studies have been conducted to determine whether these infected seeds could give rise to infected plants. A study at the University of Nebraska demonstrated that the transmission of Goss’s wilt bacteria from seed to plant occurred at a rate of less than 2.0%, when naturally infected seed was planted into sterilized soil². At Iowa State University, researchers showed that when seeds were artificially inoculated, the pathogen was transmitted to seedlings at rates of 0.1 - 0.4%³. They were unable to demonstrate transmission from naturally infected seed to seedlings. The discrepancy between these two studies may be due to different levels of bacteria present in the naturally infected seeds. These studies support the idea that Goss’s Wilt can be transmitted from seeds to seedlings, but usually at a low rate and high levels of bacteria are likely needed for transmission to occur.

Although the incidence of Goss’s wilt has increased over the past several years, the Iowa State University Seed Testing Laboratory has not seen an increase in seed samples testing positive for the bacteria causing the disease. Positive seed samples continue to be very rare (Gary Munkvold, personal communication).

Management Options

The primary tools to manage Goss’s Wilt include product selection, crop rotation, tillage, and weed management. For corn growers in Minnesota, any of the four practices for management of Goss’s wilt can typically be used.

One of the most important management options is product selection. Growers should evaluate product selection and placement on a field by field basis, matching yield, agronomic traits, and disease tolerance to their unique farming operation. Scout fields to note the location and severity of the disease to prepare for the following season. The best time to scout fields for Goss’s wilt is between VE and R6. Because injury from hail or high wind usually plays a direct role in initial infection, scouting after these events may be particularly helpful.

Rotations for two or more years out of corn can provide good control of Goss’s Wilt by allowing infected residue to degrade and bacterial populations to wane before corn is planted again. Non-host crops include alfalfa, oats, wheat, soybeans, and sugar beets.

Any tillage operation which buries infected crop residue, encouraging decomposition, can be effective in reducing bacterial populations and the rate of new infection. To help manage residue, growers may choose to harvest the infect plant material to reduce survival of the bacterium for the following year. Research conducted in 1975 found that pure cultures of the bacterium only survived less than two weeks when left in the soil.⁴ However, the bacterium survived longer in crop residue. When crop residue was buried in the soil (4 or 8 inches) the bacterium was detected in stalks after 10 months.⁴ No research has been conducted on the survival of Goss’s Wilt when ensiling corn; however, research has been conducted on similar bacterial diseases.⁵ When exposed to heat these similar bacteria populations were effectively reduced or eradicated. Therefore heat generated during ensiling may negatively impact the survivability of Goss’s Wilt bacterium.

Growers may choose to harvest and use corn residue for livestock bedding. There are no reports on the survivability of Goss’s Wilt when used for bedding. Depending on the condition of the bedding survivability of the bacterium may vary. The bacterium is less likely to spread if the bedding is dry; however, if the bedding is moist survival may increase. In moist bedding growth may still be low due to the bacterium’s specific nutrient requirements.⁶

Weeds such as green foxtail, barnyardgrass, and shattercane act as alternative hosts for this disease. Controlling weeds can help limit sources of inoculum.

Summary

Goss’s Wilt will probably continue to be a difficult disease to manage in areas where management options are limited. In years when favorable environmental conditions prevail, Goss’s Wilt has the potential to cause significant yield loss. Monsanto research scientists continue to develop new breeding methods to evaluate a broad range of germplasm from around the world to select hybrids with higher yield potential, improved geographical adaptation, improved agronomic traits, and enhanced tolerance to diseases such as Goss’s Wilt.