So should Manitoba producers consider penciling in a fungicide application in their cost of production for 2009? There are two ways to look at it: from a pathology perspective and the plant health perspective. First the pathology view. It is generally agreed upon that producers can expect economic yield responses from fungicides when diseases are present over economic thresholds. In Canada, Headline is registered to control the fungal leaf diseases Gray leaf spot and Rust (common). In the United States, the list of fungal diseases Headline is registered to control includes the above fungal diseases plus Anthracnose, Northern corn leaf blight, Northern corn leaf spot, Southern corn leaf blight and Yellow leaf blight. Many of these leaf diseases have been found in Manitoba, with the exception of Gray leaf spot. Although these disease are present, to my knowledge there has only been one suspected case where leaf disease caused economic loss. So using Headline in Manitoba where disease pressure is generally low most likely won’t result in yield or economic benefit.

 

So what about the plant health benefits and supposed resulting increases in yield we’ve heard so much about, especially in situations where there is a lack of disease pressure? Much of the data available is still inconsistent when it comes to plant health claims. Plus the question now becomes a discussion of plant physiology and not plant pathology. Some fungicide classes (such as strobilurin fungicides - Headline) can have other impacts on plants besides disease control. One of the most visual results that can occur is a "greening effect." If the corn plant stays green longer, grain fill period may be extended allowing for increased kernel weight, therefore increasing yield potential. However, staying green longer does not automatically add yield. Basically, if other benefits occur because of a fungicide application, that is a bonus, but application for plant health reasons should not be the primary reason.

 

In 2008, the Manitoba Corn Growers Association conducted a Headline fungicide trial at Carman, MB. Results from the one trial indicated there was no significant difference in yield between the unsprayed treatment and Headline applied at either the low or high rate. Of course this is only one site year of data. If there is interest, research may continue on the use of Headline under Manitoba growing conditions. The challenge will be to apply fungicides to fields where the odds of getting a real return on investment are better than 50%. Initial suggestions for fields to target include: evidence of leaf diseases, higher levels of crop residue, corn after corn, hybrids that have poorer disease ratings or hybrids that have higher yield potential. The bottom line is pathology issues should be the main reason in deciding to apply a fungicide to realize economic benefit rather than plant health benefits.