A Look Back at Corn Diseases in 2016
This is a report from the K-State Plant Pathologist, Doug Jardine. It outlines the impacts of corn diseases on yield from across the state and a couple of these diseases impacted our area.
Significant rainfall amounts across most of the state alleviated drought conditions in 2016, but at the same time, the precipitation provided ideal conditions for many foliar diseases.
Gray leaf spot, while not present at the record levels seen in 2015, was still higher than the long term average. Unfortunately, because of low commodity prices, many producers chose not to apply a fungicide and this was a significant mistake where more susceptible hybrids were being grown. Yield losses could easily be more than 15 percent.
For the second consecutive year, southern corn rust made its first appearance in mid-June rather than the historical time period of late July to early August. The disease quickly spread across the entire state and certainly resulted in yield losses of 10 percent or more where corn was planted later and fungicides were not applied.
Goss's bacterial blight was present at near normal levels, with most of the reports coming from the western half of the state. A new bacterial disease, commonly referred to as corn bacterial leaf streak, was identified for the first time in Kansas. This disease has been present in Nebraska since at least 2014, and may have been in Kansas since at least last year, but 2016 was the first year that the causal bacterium, Xanthomonas vasicola pv vasculorum (Xvv) was positively identified as the cause. By year end, Xvv was officially diagnosed in 16 Kansas counties, most of which are in the western third of the state. The disease is most common and severe in fields that are in a continuous corn, no-till production system with overhead irrigation. At this time, it is not clear if this disease is associated with any yield loss.
Rainy weather at silking time also resulted in a record epidemic of Diplodia ear rot. This disease can cause entire ears to become moldy, shrinking and discoloring kernels. The disease can also penetrate the cob, causing "cob rot," which ultimately leads to large amounts of foreign material in the grain from infected fields and results in significant dockages at the point of sale.
Aspergillus ear rot, the cause of aflatoxin problems was present on a very localized basis. The most severe problem area was in southern Harper and Barber counties and into Oklahoma. While a few samples tested more than 1,000 ppm, most samples were well below the 20 ppm safe level established by the Food and Drug Administration.
Lastly, Fusarium, anthracnose and Diplodia stalk rots were present to varying degrees across a large part of the state. Stalk rots led to premature death of infected plants with the result being reduced yields from smaller ears and the additional threat of losses from lodging.