Diseases on corn and soybeans in Kansas
The 2012 growing season was unusually hot and dry for Kansas corn growers, so much so that even irrigated corn was affected. Gray leaf spot, the most common foliar disease in most years, was almost nonexistent in 2012. Only a few irrigated fields and possibly some dryland fields that caught some timely rains were even considered for fungicide applications.
Goss’s bacterial wilt, while less common than in 2011, was still severe in some fields that received hail damage early in the season. Goss’s wilt is typically more severe in fields that are in continuous, no-till corn and that have received injury due to hail or sandblasting. The disease has spread rapidly across the Corn Belt in recent years and scientists are trying to determine the reasons for the rapid increase.
Aspergillus ear rot, the producer of aflatoxin, was as severe as or possibly even a little worse than in 2011. Fields with significant levels of Aspergillus were found as far northwest as Rooks County, an area that rarely has to deal with aflatoxin problems. Fortunately, aflatoxin amounts were generally at levels where the elevators would accept the grain without penalty, but some loads were docked for excessive levels, and a few loads were simply rejected. Because of the dry conditions, charcoal rot was also prevalent in many non-irrigated fields.
On a positive note, because of the drought in Texas and Oklahoma, southern rust was again at very low levels. That, combined with the early maturity of the crop, greatly reduced the threat of yield loss from the disease. The only other disease of concern was common smut. Poor pollination leaves ears more susceptible to this disease and the high heat at pollination resulted in many fields with poorly filled ears and increased levels of common smut.
The hot dry conditions also reduced the incidence of soybean diseases in 2012. Common foliar diseases such as brown spot and frogeye leaf spot were absent from most fields. The hot, dry weather proved to be highly favorable for the development of charcoal rot, bringing statewide losses to even higher levels than 2011.
One interesting development in 2012 was that in an effort to keep up with water demand, some fields were actually overwatered and sudden death syndrome (SDS) developed at levels higher than expected. Overall however, levels of SDS were well below average.
A statewide survey for soybean cyst nematode (SCN) was completed in 2012. Approximately 20% of Kansas soybean fields were found to be infected. The majority of these fields have SCN levels in the range where only low to moderate losses are likely occurring. In some counties, such as Cherokee County in southeast Kansas, however, the percentage of fields infested was approaching 100% -- with a few having nematode levels that are likely causing significant yield loss.
Other diseases identified in 2012 include bean pod mottle virus, stem canker, bacterial blight, and iron deficiency chlorosis.