Dr. Dan Talks Agronomy


By Dan Davidson
DTN Contributing Agronomist

Whenever commodity prices drop, or even when they remain up, growers question whether a fungicide application will pay for itself, either by protecting yield, bumping it, or a combination.

Fungicides are typically applied to defend against a perceived threat. Some of those threats are already showing up: Plant pathologists from both the University of Wisconsin-Madison and Iowa State University reported northern corn leaf blight outbreaks early the week of June 12. More information on those areas can be found here: http://fyi.uwex.edu/…

If diseases don't come, the follow-up question farmers ponder is: Do the secondary benefits -- improved plant health, physiological enhancement, reduced lodging and better standability in corn -- give enough yield boost to at least break even on application costs?

Last winter, when just nominal inputs and land costs put many fields below breakeven, I would have said no. Since then we have seen an uptick in commodity prices. That puts the fungicide decision back in play.

Fungicide use has become a routine production practice. University scientists cringe at this practice because it is not following the principles of integrated pest management (IPM) when pesticides are applied only when the threat of a disease or insect outbreak is real. They also worry that continual and routine use of fungicides could lead to pathogens developing resistance to that active ingredient. We know that a strain of frogeye leaf spot is now resistant to Group 11 (QoI-strobilurins) fungicide.

Fungicide use has continued to grow. The systems growers have adopted over the past decade during the boom years taught them that investing in inputs, season long, paid a dividend in bushels at the end of the season. That lesson is difficult to reverse even when prices are down because bushels are still the goal.

One thing to remember about fungicides is that they all work some of the time on some of the acres but not necessarily all, and they work better in some years but not in others. In a year of high disease pressure or stress, there is a great yield benefit, but in a year with no stress or disease pressure, returns are less. However, it is hard to predict in advance the impact of weather and disease.

Yet growers can predict high-risk fields based on rotation, tillage, variety characteristics and soil type. For example, growing continuous corn under no-till, planting racehorse varieties with weaker defensive packages and growing during a warm and humid summer is probably a field at risk to disease and will benefit from a fungicide application.

Pulling the trigger on the fungicide decision should be easier today than six or eight years ago. Many of you now have experience using fungicides in boom times and have a good idea when and where it works and how to get a return. Use that knowledge today to make a prudent decision where to apply fungicides in 2016.

Dan Davidson can be reached at AskDrDan@dtn.com

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