Northern corn leaf blight, eyespot and anthracnose leaf blight are the three plant diseases likely to strike corn this year; white mold is the main threat for soybeans; and fusarium head blight (scab) has infected a number of winter wheat fields now being harvested.
That synopsis was presented by University of Wisconsin-Extension Service field crops pathologist Damon Smith during the 2014 summer twilight meeting of the Fond du Lac and Dodge County Corn Growers Association on July 24.
The cool and wet conditions of the early part of the growing season set the stage for the possible outbreak of northern corn leaf blight, Smith said. He reported that the disease has been detected in corn in Iowa and advised Wisconsin growers to check for it.
No-till fields, continuous crops of corn, the presence of residue that contains the pathogen and corn hybrids with low resistance to the blight are the top candidates for disease outbreaks, Smith said.
As corn starts to tassel, the time is right to begin scouting for corn leaf blight, eyespot and anthracnose. He said so far he hasn't seen much disease in Wisconsin's corn fields this summer.
To the question of applying a fungicide to prevent an outbreak or provide control on the spread of any of those diseases, Smith is cautious. That's because extensive multi-year research shows average yield gains of 3.5 bushels per year with a fungicide application — an increase that would not come close to covering the cost of the application, especially with the prices for this year's corn at well below $4 per bushel, he said.
With soybeans, white mold is the major disease for which a fungicide application can often be justified, but this needs to be done at the onset of the flowering stage up to early pod development, Smith advised. Those outbreaks are most likely in fields with a history of white mold.
Too often the reaction of soybean growers to plant diseases is "when should I spray?" Smith said. What's really important, he explained, is to identify the disease and then react accordingly.
When approached in that way, Smith said the research in Wisconsin indicates that white mold is the only disease in soybean for which a fungicide application (Aproach, Endura and Proline have provided the best results) is likely to pay off.
With the winter wheat harvest well underway, growers need to be aware of the possibility of fusarium head blight infestations in their fields and take the proper precautions, Smith said. One is to adjust the combine in order to blow out the infected (light) kernels and thereby reduce the impact on test weights, he noted.
Another major concern is the possible presence of mycotoxins that would affect the safety of the wheat as livestock feed and human food; the marketability of the grain; and their crop insurance coverage, Smith said. For crop insurance, they should be checking with their agent at the start or harvest so eligibility for a claim is not lost.
Although it is likely grain elevators will be testing for the presence of toxins before accepting delivery, growers who will be storing their wheat were advised to get a mycotoxin test. Federal regulations indicate wheat is not acceptable for cattle and poultry feed if the concentration of the vomitoxin DON is above 10 parts per million or for swine and all other animals if it is above 5 parts per million.
Because corn also acts as a host for the fusarium head blight, Smith suggested that winter wheat be planted after soybeans rather than after a corn crop, especially if corn residue is left on the field. As verified this year in the Extension Service's wheat trial plots where the blight struck, he pointed out that wheat varieties also vary greatly in their susceptibility to the disease.