Soybean and corn disease update
Some products are being marketed for Goss's wilt control; however, Byamukama said there is insufficient data in the region on the efficacies of these products.
Holcus spot, another bacterial disease was seen in one corn field in Brown County, the same field also had Goss's wilt. Holcus spot is caused by a different bacteria, Psedomonus syringae pv. sringae. Holcus spot is a rare disease and even when it occurs, seldom will it cause yield loss. Byamukama explained that the pathogen also survives on residues and is favored by rainy and windy weather early in the season.
Common smut and rust
Common smut on corn leaves was seen in a few fields that had hail damage in the northeast counties. The fungal pathogen infects young, actively growing parts usually through wounds and forms galls. The fungus survives on crop debris or soil and can remain viable for several years. If the spores land on the silk, the fungus will infect the developing kernels resulting in galls on ears.
"Most corn hybrids have good resistance to common smut, however, corn on corn, no-till, and hail damage conditions may increase the risk for common smut infection on leaves," Byamukama said.
Another disease beginning to develop on corn is common rust. Several fields scouted had trace levels of this rust developing.
"This disease rarely develops to high levels to cause yield loss because most hybrids have good tolerance to this pathogen. The common rust pathogen does not survive in South Dakota; the spores are blown in from the southern states in spring. . Therefore residue management or crop rotation will not affect common rust or any other rust disease, for that matter", he said
If growers plan to apply fungicide, Byamukama said a general note on fungicide application on corn is that several research reports show that increase in yield from fungicide application happens when disease severity on flag leaf at R5 is greater than 5 percent. He encourages growers to review a publication published by Iowa State University, at see: http://www.extension.iastate.edu/CropNews/2010/0706muellerandrobertson.htm
"Most of the corn scouted across the state looked very clean with no disease developing. Corn following corn or corn on no-till may have an elevated risk for significant disease to develop, depending upon the cultivar planted and weather conditions," he said. "Applying a fungicide at tasseling in this case may be beneficial."
The corn plant pathology working group published a list of fungicides that are effective for several fungal pathogens on corn. This table can be found here: http://www.uky.edu/Ag/GrainCrops/Briefs/CDWGCornFungicideEfficacy_Table_2013_FINAL.pdf
Byamukama said fungicide application should be done when all corn has fully tasseled to avoid arrested ear syndrome, a physiological disorder that is caused by nonionic surfactant (NIS) fungicide additives when applied before tasseling. To learn more about this visit, www.extension.purdue.edu/extmedia/BP/BP-85-W.pdf.
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