Diseases on corn, grain sorghum, and soybeans in Kansas in 2013
Rain finally returned to Kansas in 2013. Delayed planting due to wet soils allowed soil temperatures to increase to the point that there were relatively few stand establishment problems due to seedling diseases in the corn crop.
It was anticipated that gray leaf spot would be a problem in 2013 due to the generally increased precipitation compared to the previous two years. That however, was not the case. Only scattered fields reached disease levels that required a fungicide application. Lack of inoculum from the previous two years is partially responsible, as well as a lack of June rainfall in some areas of the state traditionally plagued by gray leaf spot.
Northern corn leaf blight, which is normally uncommon in Kansas, was present in a number of fields in the north central and northeast part of the state. Cooler temperatures are usually associated with the outbreak of this disease. Incidences and severity were generally low however, and no fungicide applications were needed.
Goss’s bacterial wilt incidences continued to increase. The disease was reported in 22 different counties across the state in 2013. Severity varied with time of infection, with early infected fields having the most yield reduction. Incidence and severity of the disease continues to be correlated with no-till, continuously cropped corn fields planted to moderately susceptible hybrids.
Common rust was found throughout the state, but there are no indications that any yield loss was suffered from it. Southern rust was identified in McPherson County on August 1. This is just about the average time of appearance in Kansas. Because of delayed plantings in many areas, it was anticipated that many acres of corn might have required a fungicide application. Cooler than normal temperatures in early- to mid-August however, greatly slowed the progress of the disease and few if any fields required spraying.
Incidence of Aspergillus ear mold decreased greatly over the previous two years. For instance, in fields near Fredonia that had incidences of 50% molded ears in 2012, those fields had incidences of only 15% in 2013. Reports from grain handlers indicate that aflatoxin was only a problem in some early harvested fields in southeast Kansas. Over one-half of the early submitted samples tested above 100 ppb with many over 400 ppb. As later harvested corn came off, levels fell to under 20 ppb for approximately 65% of the samples, with only a few over 100 ppb. In northern production areas, little aflatoxin could be detected.
The 2013 growing season was a good one for stalk rots in corn. Depending on your location in the state, all four major stalk rots were identified; those being Fusarium stalk rot, charcoal rot, anthracnose stalk rot and Diplodia stalk rot. Fusarium stalk rot was the most common and severe of the four. The weather pattern of wet early, dry mid-season and wet near seasons end is always a good combination for the development of Fusarium stalk rot.
Grain Sorghum Diseases
With the exception of stalk rots, disease pressure in the 2013 Kansas grain sorghum crop was minimal. Pythium seedling blight was identified in a few early planted fields.
Sooty stripe was present in some fields that received frequent rainfalls and that were planted to susceptible hybrids using no-till, continuous cropping practices. No fungicides are registered for control of this disease.
As in 2012, stalk rots were significant with many fields lodging late in the season. Unlike 2012 when charcoal rot was prevalent, Fusarium stalk rot was most common in 2013. As with the corn, Fusarium was favored by the dry mid-season followed by an increase in rainfall during the grain fill period on through maturity. The increased lodging due to stalk rot can offer producers the opportunity to truly evaluate the standability of hybrids and allow them to adjust their hybrid portfolio choices for the upcoming year.
The soybean season started out with plenty of seedling blight pressure caused by Pythium. In some instances, even fields planted with fungicide treated seed had stand establishment problems. State wide, yield losses were estimated at 5%. While wet soils after planting can cause seedling diseases, they also allow the initial infection of both sudden death syndrome (SDS) and charcoal rot to occur, even though these diseases typically do not become visible until the reproductive growth stages.
Foliar diseases were generally light. A dry June reduced infection by brown spot and frogeye leaf spot, the two most common foliar diseases in Kansas. A scattering of pod and stem blight and Cercospora blight (purple seed stain) occurred in some fields, but damage was minimal.
The late summer of 2013 turned out to be a banner year for SDS. It occurred at record levels in the Missouri, Kansas, Republican and Arkansas River valleys. The disease was brought on by the combination of the early season wetness and the cooler, wetter weather in early August. The cooler, wetter weather probably also helped to mask some of the damage from soybean cyst nematode, which continues to spread into new areas. In some areas that had lengthy dry periods in late August and September such as southeast Kansas, charcoal rot was a problem, although overall, yield losses were about average.
The other disease of note was soybean vein necrosis virus. This disease was first identified in Kansas in 2011 and continues to spread, being found mostly in the eastern half of the state. The disease is transmitted by thrips. Yield loss potential of the disease is still being studied.
Doug Jardine, Extension Plant Pathology