The lack of dry weather that occurred this fall has created mold and fungus problems that corn and soybeans growers have not seen on such a widespread scale.
Dr. Alison Robertson, Iowa State Extension agronomist, is a crop disease management specialist. She presented information last week on problems with the moldy corn harvested this fall and the white mold that significantly reduced soybean yields to corn and soybean growers at meetings held in Worth and Cerro Gordo counties.
Hollow soybean stems with sclerotia. The disease is the black area where it can remain for several years.
White mold in soybeans has happened before, Robertson noted, but not to such a degree as seen during this harvest. White mold thrives with moist, low light conditions that occur when soybeans are canopying.
The sclerotia fungus over-winters in soil and plant debris. The sclerotia germinate as mushrooms releasing ascospores that migrate up to 50 feet. The infection site is at the flower as it is dying with a 90 percent infection rate. The result is hollow stems with sclerotia inside where it can remain for several years.
Management of white mold can be attempted through fungicides, herbicides, cultural control and genetic control, according to Robertson.
Fungicides that can be used include Topsin and Domark. These are applied at flowering and a second application may be needed. Thorough coverage of blooms and foliage is required.
Herbicides for white mold are Cobra and Phoenix. These are applied just before bloom and will suppress white mold. These cannot be applied after the occurrence of the infection.
Cultural practices for white mold include crop rotation with row spacing and reduced population to eliminate shading.
Genetic control can de done through selecting varieties that are resistant to lodging and have less branching narrowing the canopy size.
Research is being done using Contans WG as a biological control. Contans WG is applied on the soil for disintegrating the sclerotia. It needs to be incorporated in the soil three months ahead of when white mold will occur. Once applied, no other tillage can be done to prevent any sclerotia from being brought to the surface.
Contans WG is applied at one to two pounds per acre and costs $18 a pound.
In corn, the problem resulted in ear rot diseases, which were influenced by genetics, weather conditions of hot/cool or dry/wet, plus damage from hail, insects, and birds.
The mold seen on the corn crop can be of several varieties. These include aspergillus, diplodia, fusarium, gibberella, nigrospora and cladosporium.
Of these, it is the cladosporium, which is of least concern.
The other molds can produce mycotoxins, Robertson said. Aspergillus can result in aflatoxin. Gibberella can produce vomitoxin, zearalenone, or T-2 toxin. Fusarium can lead to fumonisins.
With 65 percent of the Iowa's corn crop going to ethanol production, there is a problem in the concentration of toxins in the distiller's dried grains after the ethanol process is completed.
Robertson recommends to scout for ear rot and if more than 10 ears show signs of rot, harvest must be done as soon as possible.
Contact Clayton Rye by e-mail at email@example.com.