Figure 1. Corn yield from fungicide treatments applied to two hybrids at tasseling in 2006 prior to severe southern rust and gray leaf spot development. (Image links to larger version.)

Figure 2. Corn yield from fungicide treatments applied to hybrid in 2005 prior to gray leaf spot development. (Image links to larger version.)

Figure 3. Corn yield from six hybrids (rated either susceptible or tolerant to gray leaf spot) treated with Headline 6 oz/ac at tasseling prior to severe southern rust and gray leaf spot development.(Image links to larger version.)

Figure 4. Corn yield from Headline treatments applied at 2-4 feet, 5-6 feet tall, and tasseling with either 3, 6, or 9 oz/ac. (Image links to larger version.)

July 13, 2007

As corn prices have increased so has the aggressiveness of disease management strategies for corn. Fungicides are being widely used in corn right now, but may not always be necessary. Yield data from corn fungicide trials at the UNL South Central Agricultural Lab near Clay Center during 2005 and 2006 are summarized here. As in all research, data from only a single year is not sufficient for drawing long-term conclusions and this research is being repeated.

Comparison of Foliar Fungicides

Multiple foliar fungicides applied at recommended rates were compared simultaneously in this study. Products with single and mixed active ingredients are included: Quadris®, Tilt®, Quilt®, Headline® and Stratego®. In 2005, fungicides were only applied to a single hybrid, Asgrow RX 752 YG. In 2006 (shown below), fungicides were applied to hybrids that were listed as susceptible (blue bars) and tolerant (purple bars). This trial is being repeated for the third year in 2007.

All applications in these trials were made at tasseling (VT), unless otherwise noted, regardless of disease development. In 2005, gray leaf spot was mild/moderate in severity and common rust was negligible; however, in 2006 moderate/severe southern rust and gray leaf spot developed during August with substantial disease pressure in the plots. In 2005 and 2006 the greatest yield increase was obtained by Headline applied at tasseling at 6 and 9 oz/ac, respectively.

Yield Effects of Headline on Multiple Corn Hybrids

The effects of Headline (pyraclostrobin) on yield was tested across different hybrids. Six corn hybrids were selected from six different seed companies that were reportedly tolerant (three) and susceptible (three) to gray leaf spot. Headline was applied at 6 oz/ac at tasseling (prior to disease development in 2006) via backpack sprayer. In 2006 yield was increased on five of six hybrids under heavy disease pressure (southern rust and gray leaf spot).

Yield Effects of Headline on Corn Applied at Three rates and Timings

Headline applications were made at three rates (3, 6, and 9 oz/ac) to corn at three stages of development (2-4 feet tall, 5-6 feet tall and tasseling). Yield increases did not occur in every treatment. In this study the greatest increase was observed with the 9 oz/ac rate applied at tasseling.

Effects of Different Rates and Application Timings of Headline

Fungicides in all of the trials described here were applied with a CO₂-pressurized backpack sprayer and a 10-foot wide hand-held boom. Spray volume was 15 gal/ac at 38 psi. to mimic the conditions of a ground applicator as closely as possible. All treatments were arranged in a randomized complete block with six replications of 30-foot long plots of four rows each. Grain was mechanically harvested from the middle two rows of the plots. (Beginning in summer 2007, most applications are being made with a high clearance small plot mechanical sprayer to better simulate producer conditions. )

Factors Affecting Economic Returns with Foliar Fungicide Applications

Yield effects of fungicides can be highly variable and dependent upon many conditions. The conditions listed below (adapted from P. Vincelli, University of Kentucky) are important considerations when making application decisions. The applicability of more of these factors increases the likelihood that a foliar fungicide application will provide an economic return in corn.

• Susceptible hybrid
• Continuous corn
• No-till
• Late planting
• High yield potential
• Irrigation
• Early disease activity
• Field history of severe disease
• Favorable weather conditions for disease development

Risks Associated with Fungicide Use

Widespread and frequent application of any pesticide, including fungicides, has the potential for undesirable consequences. Fungi, like weeds and insects, can develop resistance to pesticides with repeated applications. Certain fungicides, namely those in the class of strobilurins (QoI  Quinone outside Inhibitors), are particularly high risk for the selection of resistant fungi. Caution should be taken when considering fungicide use to minimize these risks and we encourage good IPM practices when choosing to make applications. For example, alternating modes of action and minimizing the number of applications per season will help avoid the selection of resistant populations of fungi.

Safety should always be a consideration when applying a pesticide, including fungicides, because of the potential for health risks. The toxicity of fungicides vary by product, application method, etc., so you should always read and follow all label instructions when using them.

Disclaimer

Reference to commercial products or trade names is made with the understanding that no discrimination is intended of those not mentioned and no endorsement by the University of Nebraska-Lincoln Extension is implied for those mentioned.

Tamra Jackson
Extension Plant Pathologist, LIncoln