Thinking about an Early-season Fungicide Application in Wheat?

There are a number of great resources and articles by experts in other areas of Canada and the United States. Here are two articles by Andrew Friskop, Extension Plant Pathologist with North Dakota State University, on the factors producers should consider when evaluating an early-season fungicide application in wheat (i.e. herbicide timing or T1).

The first article appeared in the NDSU Crop & Pest Report – May 19, 2016 edition.  The complete article is available here: Early-season fungicide application in wheat.

An updated article was recently posted in the NDSU Crop & Pest Report – May 18, 2017 edition: Early-Season Fungicide Application for Wheat (5/18/17)

There are several factors that will influence the value of an early-season fungicide and Andrew Friskop reviews some of those, including crop rotation, tillage, weather, variety selection, scouting & fungicide selection. The 2016 article reads “What to expect from an early-season fungicide application? – Studies conducted by NDSU over the last 20 years have shown that a 2 to 6 bushel response occurs when an early-season fungicide was used in a wheat-on-wheat production system with minimum tillage when favorable weather was present. The incorporation of other management tools such as crop rotation and tillage will reduce the risk of tan spot development and reduce the expectant yield response. Also, remember an early-season fungicide will protect the leaves available at the time of application, but as the wheat crop matures, newly developed leaves will be left vulnerable to leaf spot and rust pathogens.”

One factor not discussed in the articles was disease resistance management – it must be another consideration. When a fungicide is used multiple times, the risk that pathogens can develop resistance to the fungicide can increase. Where fungicide application is required, producers should rotate between fungicide groups.

 

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Should I spray a fungicide in my soybeans?

As with any fungicide application the first question you need to ask yourself is, “What disease am I targeting and is there disease pressure present?” Fungicides should not be sprayed in the absence of disease pressure.

While there are common foliar diseases that we see in soybeans it is very rare that these diseases cause any yield loss. Here’s a list of some of the more common foliar diseases in soybeans, some of which are included on fungicide labels:

1)      Septoria brown spot – often shows up on the lower leaves, identified as small necrotic flecks, may be quite numerous in lower canopy; rarely causes yield loss

2)      Bacterial blight – may look similar to Septoria brown spot, but with chlorotic halo surrounding lesions; cool, wet weather favours development of this disease; it’s caused by a bacterium, so a fungicide wouldn’t help anyway; more often seen in the spring when the temperatures are cooler; rarely causes yield loss

3)      Downy mildew – similar symptoms to what we see in other crops, chlorotic spots visible on the upper leaf surface and cottony growth on the lower surface of the leaves; rarely causes yield loss

4)      White mould AKA Sclerotinia stem rot – same causal agent as sclerotinia in canola, sunflower, dry beans, etc.; conducive conditions include wet, cool weather when the crop is flowering; soybeans are not as susceptible to sclerotinia as canola or sunflowers, so we don’t generally see the same losses from this disease in soybeans

Of all these foliar diseases, the main one with potential to cause loss in Manitoba is white mould. However, even in years where we see loss in canola or sunflowers due to sclerotinia we have not seen widespread loss in soybeans.

Another thing to consider when spraying fungicides is the potential development of fungicide resistance. There are more cases of pathogens developing fungicide resistance each year around the world and one of the candidates for this in Manitoba is Sclerotinia sclerotiorum, the causal agent of sclerotinia stem rot/white mould. Since fungicide applications is one of the main ways we control this disease in other crops, such as canola, it is important that we don’t overuse this technology to a point where it is no longer effective.

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