Diseases on Corn, Grain Sorghum, and Soybeans in Kansas in 2014

By Doug Jardine, Extension Plant Pathology

Corn diseases

Above-average rainfall in many areas of the state was responsible for corn yields well above average. These same rains however, provided conditions favorable to several diseases. Continuing a recent pattern, Goss’s bacterial wilt and leaf blight continued to spread across the state. In 2014, Goss’s leaf blight was found in 16 Kansas counties for the first time ever, most of which were in south central and the eastern one-third of the state. Goss’s blight has now been reported in 55 different counties since its reemergence in the last decade.

Gray leaf spot, historically the most common foliar disease in the state, was active again in 2014.  Irrigated fields that are in continuous no-till corn or which received rain in mid- to late-June were the most affected, especially if moderately susceptible hybrids were planted. Northern corn leaf blight, a less common disease in Kansas, was present in many areas. However, this disease, which likes cooler weather, rarely reaches levels requiring fungicide treatment. Anthracnose leaf blight and southern rust, the other common foliar diseases, were also present in 2014, but there were no reports of fields that required spraying because of their presence.

Late in the season, stalk rots became an issue in many fields. All four of the common stalk rots that occur in Kansas were identified somewhere in the state. These include Fusarium stalk rot, charcoal rot, anthracnose stalk rot, and Diplodia stalk rot. Charcoal rot was present in areas that were droughty during grain fill. The other three are associated with higher levels of moisture starting as tasseling on through the later stages of kernel development.

Rain also helped significantly reduce the presence of Aspergillus ear mold, the cause of aflatoxin. Surveys in the areas of the state where the disease is most common indicated that the incidence of the disease was very low.

Sorghum diseases

The 2014 Kansas sorghum crop may have been one of the healthiest in years. Some problems were reported throughout the growing season, but most were minor in severity. There were fields around the state that suffered from Fusarium seedling blight and some replanting was necessary. Sorghum downy mildew was reported in southeast and central Kansas. This disease is associated with soils that remain saturated for extended periods of time, especially early in the season. Yield losses from downy mildew are generally minimal. 

At the higher altitudes of western Kansas, summer rains caused bacterial leaf diseases to develop. While giving leaves a distinctive purple striped appearance, there typically is no yield loss associated with bacterial infections. Numerous reports of physiological problems occurred throughout the reproductive stages of sorghum growth. These are non-pathogenic problems caused by an interaction of hybrid genetics with specific environmental conditions. These problems often mimic diseases, but they do not spread and usually do not result in yield loss. If you looked hard enough, sooty stripe and northern corn leaf blight could be found, but it is doubtful there were any fields where economic yield loss occurred.

Late in the season, a number of reports of grain mold and Fusarium stalk rot were received, but these were few in number compared to some previous years. There were no observations or reports of stalk rot associated lodging in the state. There were also no reports of sorghum ergot in 2014.

Soybean diseases

The disease loss estimate for soybeans in Kansas in 2014 was 10.4%, compared to the long-term average of 12.5%. More than half of the total loss came from a single disease, charcoal rot, which was responsible for slightly more than half of the statewide disease loss. Charcoal rot was most severe in southeast Kansas, where many areas received less than two inches of rainfall in the two-month period of July and August. Charcoal rot is favored by hot, droughty conditions. Areas of central and north central Kansas also had fields with considerable charcoal rot loss.

Another disease of note was sudden death syndrome. The disease was present in all of its normal areas in 2014.

Figure 1. Areas where soybean sudden death syndrome is most commonly found in Kansas.

In 2014, it was by far the most severe in northeast Kansas where frequent August rains provided ideal conditions for disease development. In Atchison and Doniphan counties, it was reported that yield losses reached 50% in the most severely affected portions of fields. Sudden death syndrome also appeared in many upland fields that have not previously shown symptoms of the disease.

A disease that has not been observed in Kansas for a number of years made a big comeback in 2014. Heavy June rainfall in many parts of the eastern half of the state created the opportunity for Phytophthora root rot to develop. Fields with significant losses were identified in east central, south central, and north central Kansas. Fields planted to susceptible varieties were particularly hard hit.

On a positive note, good planting-time conditions significantly reduced losses to the seedling disease complex that includes Pythium, Rhizoctonia, and Fusarium. Losses were estimated at 1% statewide compared to the long-term average of 3.3% and the 2013 average of 5%. Also, no new counties were added to the list of those infested with soybean cyst nematode. 

Other diseases that were observed but with minimal yield loss include anthracnose, brown spot, frogeye leaf spot and purple seed stain, and stem canker.

Source:ksu.edu