The risk of foliar disease pressure in some fields may be higher this year due to the current wet, humid weather on top of extra disease inoculums from the cool, wet years of 2008 and 2009.
"Disease pressure varies greatly from field to field," says Brent Wilson, Pioneer technical services manager. "Foliar diseases — gray leaf spot, eye spot, northern leaf corn blight — are conducive to wet growing conditions.
"The window to see the greatest return from a fungicide application is rapidly closing as the corn crop and the disease cycle progresses. Fields with high disease pressure could still see a return on a fungicide investment."
The 2008 and 2009 growing seasons were cooler and wetter than normal. Those conditions allowed many disease inoculums to survive on field residue, specifically corn-on-corn fields, causing increased disease pressure in the wet 2010 growing season.
"Hybrids with a higher tolerance score will likely withstand any yield impact to foliar diseases," Wilson says.
Pioneer research shows yield response to a fungicide application is greater for hybrids with a low level of resistance compared to hybrids with a moderate level of resistance.
Foliar fungicide applications on corn have grown in popularity with many growers because of the limited amount of management options after planting. According to Wilson, Pioneer onfarm trials and research, applying a foliar fungicide to corn can lessen the effects of foliar disease outbreaks and boost yield up to 7 bushels per acre.
Fungicides potentially offer many positive effects, but the decision to apply a fungicide can be difficult for growers. Growers should assess disease situations on a field-by-field basis to decide if a fungicide is the best option, Wilson says.
Several factors negatively affect yield. Leaf disease susceptibility, continuous corn, excessive moisture, no-till or minimum tillage and late planting are all important factors that increase the chances of fungicide disease outbreaks. These factors play a big role in deciding if a fungicide is economically feasible.
Wilson says corn planted in mid-April is near the end of the application time frame. However, this is a good time to evaluate and take note of fields impacted by foliar diseases for the crop not only in the ground, but also to help assess hybrid performance for next year's seed-purchase decisions.
The correct timing of a fungicide application is imperative. During the time of tasseling is the best option for spraying. Foliar disease is not severe at this point, but is present and will start to cause damage. Wilson says growers should not spray prior to tasseling because fungicides can cause crop injury if sprayed too early.
"While the weather cannot be predicted a year in advance, these types of growing conditions offer up a great opportunity to reflect on seed choices on a field-by-field basis," Wilson says.