Proper disease management is critical to preserving corn yields. If not properly managed, diseases can be a major yield-limiting factor.
The first line of defense for managing corn diseases is genetic resistance. DuPont Pioneer rates its hybrids for resistance relative to known susceptible and resistant hybrids using a 1 to 9 rating system (1 = susceptible, 9 = resistant). These scores are made available to customers to aid in hybrid selection.
Figure 1. Northern corn leaf blight lesions on leaves of 2 hybrids with differing levels of genetic resistance in Johnston, Iowa, 2010.
Foliar fungicides are an important management option for fungal diseases. Over the course of 5 years, DuPont Pioneer researchers conducted 587 on-farm fungicide trials comparing yield of untreated corn to corn treated with a foliar fungicide between tasseling and brown silk. Across these trials, the average yield response to fungicide application was an increase of 6.7 bu/acre (Figure 2).
Figure 2. Corn yield response to foliar fungicide application in 587 DuPont Pioneer on-farm trials 2007 to 2012.
One of the most important factors in determining the value of a foliar fungicide application is disease pressure. For example, in a 2009 Pioneer research trial, yield response to a fungicide application was impacted by common rust. Across locations where common rust was prevalent, yield response averaged 11.4 bu/acre whereas at locations where common rust was less prevalent yield response averaged 3.9 bu/acre (Figure 3).
Figure 3. Average fungicide yield response of hybrids with low resistance (3 rating) and moderate resistance (4-6 rating) to common rust in DuPont Pioneer small-plot trials.
Disease pressure is generally lower under drought conditions because common foliar diseases favor moisture and humidity to develop and spread.
When comparing foliar fungicide trials conducted in Iowa and Missouri in 2011 and 2012 (both abnormally dry years) to trials done in prior years, drought conditions were shown to reduce the average yield response to foliar fungicide application (Figure 4).
Figure 4. Comparison of average corn yield responses to foliar fungicides in on-farm trials conducted in Iowa and Missouri from 2007-2010 and 2011-2012.