Foliar Fungicides in Corn

As we reach full tassel stage in corn, we are receiving some last-minute questions regarding fungicide applications.

One of the questions that we regularly receive is: "Which PRIDE hybrids are more likely to have a positive response to a foliar fungicide application?"

This interest in hybrid specific response is also spurred on by preliminary research done out of University of Guelph - Ridgetown Campus which has indicated that some hybrids respond more than others.

First of all, most would agree that we would not expect all hybrids to react the same to a fungicide. We know that corn hybrids vary in how they are affected by different diseases and so it would make sense that we would see different responses.

Second, we know that each year brings different environmental conditions and different diseases and plant stresses. It would then make sense that hybrids might respond differently from one year to the next. This varying response in different years was highlighted by the U of G research where a repeat of the 2008 trial showed different hybrid response results in 2009.

Third, there is evidence that some fungicides may provide more than just disease control and have some 'plant-health' effects and improved standability. These reasons make it difficult to say with certainty if a hybrid will respond to a fungicide with a net profit benefit.

We have witnessed some rather phenomenal responses of 20+ bu/ac so we know in certain situations the payback can be very substantial.

There are other reasons to consider use of a fungicide than just hybrid. These include:

· yield potential
· type and level of disease infection
· weather outlook - moisture and temperatures conducive to disease development
· previous crop and tillage type
· crop stress - shallow roots, drought concerns, hail damage, etc.
· standability concerns
· expected selling price of corn

Various Approaches to Foliar Fungicide Application in Corn

1. Spray every acre every year.

This approach still represents a small portion of the corn growers in Ontario but is increasing as growers have positive yield results with foliar fungicides. Growers using this approach believe that they can increase yields and maximize returns in the long run. The target may not necessarily be spraying for disease control but rather for yield benefits that may occur even in the absence of visual leaf disease.
Key Advantages: Plan for application every year - have product and application in place and best situated to apply at correct timing.
Challenges: Investing substantial costs in some situations where benefits are not realized.

2. Spray some years.

Growers in this category would base their decision to apply a fungicide based on the given conditions in a year. Presumably this decision is based on disease pressure or anticipated disease pressure that could develop in the reproductive stages of corn development (post-flowering).
Key advantages: Increase likelihood of economic benefit from disease control.
Challenges: Lining up application and product on short notice.

3. Spray some fields each year.

There are a number of factors that could be involved in spraying some, but not all, fields each year. Crop rotation might influence a grower to spray corn following corn, but not spray corn following soybeans for example. Tillage method could also influence if a grower uses different tillage methods - this is not all that common, but a grower could decide to spray no-till corn fields but not conventional tilled corn fields.
Key advantages: More targeted approach to utilizing technology. Decision-making can be done in advance when laying out field by field cropping plans.
Challenges: Ensuring accurate information and predicting the upcoming year's disease potential to base decisions on.

4. Spray based on scouting findings.

Scouting for leaf disease is one approach that certainly has merit in terms of using foliar fungicides. It is important to evaluate disease infection and development regularly, particularly where intent is to use a preventative type fungicide. Where disease has already become established the use of a curative or curative + preventative fungicide may provide greater benefit than a preventative type fungicide. One of the goals with a preventative fungicide applied at full tassel stage is to help keep upper leaves on the plant with low levels of disease in the early and mid-reproductive stages prior to disease infection occurring.

For this reason, the scouting approach has tremendous challenges and is more likely to be a combination of scouting as well
as evaluating the year's climate for determining disease development.
Key advantages: Increase likelihood of economic benefit and can make decisions based on the most available information at the time.
Challenges: Procuring product and application services on very short notice or when it is too late for maximum benefit.

One of the conclusions that can be made is that response to foliar fungicides is somewhat complex. Multiple factors are likely at play including: fungicide product and rate, application method and timing, overall leaf disease development, fungal species involved, corn hybrid, field history (previous crop, tillage method, etc), and climate prior to and following application. As
more experience is gained in use of fungicides on corn there will be growers who change from one approach to another as they determine where economic benefits from increased yields can be realized.