Applying Fungicides Effectively

Timing and coverage is everything

Published in the May 2009 Issue Published online: May 03, 2009 Tyler J. Baum, Editor
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For some minor things in life, it doesn't matter which path you choose, only that you choose a path. For just about everything else, there's an effective and less-effective way of doing things.

Applying fungicides usually fits into the latter scenario. And the difference between effective and less-effective fungicide application may make the difference between an average yield and a higher one-or even no yield at all.

Eric Tedford, technical brand manager for fungicides at Syngenta, says that there are three things that need to happen to apply fungicides effectively: 1) you first need to know what kind of disease you want to control, 2) apply the product at the right time and at the right application intervals, and 3) you want a proper coverage of plant surface.

"It really comes down to timing and coverage," Eric says.


The first point is to know what kind of disease you want to control. A proper foreknowledge of the field's history and circumstances is a must to give you the best idea on what diseases to expect. However, as growers expand into new fields, that foreknowledge usually stays with the previous owners. And, as Eric says, "Sometimes Mother Nature throws curveballs." Sometimes diseases that you expect to come in, don't. "The key is knowing what disease you need to control. Knowing this will allow you to select the right product."

Eric admits that it's difficult for many growers to gaze into that crystal ball and prognosticate the kinds of diseases that will pop up in the field. The good news is that many fungicides have an arsenal of ingredients that treat a variety of diseases, such as Syngenta's Revus Top or Quadris Opti.

"The benefit is, if you put the application on, you have a good chance of controlling the disease you want to control, like Early Blight or Late Blight."

However, it's still really important to know the history of diseases in the field and in the area as well as properly identifying the diseases coming in so you can apply the right fungicide. Because most fungicides (with rare exception) are not curative, it's essential to apply the fungicide before the fungus becomes a problem-before the onset of disease.

"It's very difficult to control diseases once they're established," he says.

Fungicides applications are a lot like putting armor on the plant-an application provides a barrier to protect the plant when fungi launch their assault.

"Timing and coverage is everything," he says. "Protection is only as good as the coverage of the armor."

Eric urges growers to check and follow labels, and says that continual application will help fully protect the plants, for a couple of different reasons. First, most modern fungicides are not meant to persist over long periods of time for environmental concerns. Modern fungicides will degrade at the microbial level, wash off by rain and be affected by hot sun. Also, because the plant is still growing after you apply the fungicide, the new plant surface that emerges isn't covered by the previous application.

Eric says that some fungicides suggest 14-day intervals, but again suggests to read the label.

Finally, resistance management is something growers should be seriously considering. Applying fungicides using the same mode of action will help fungi build resistance, thus making it more difficult to fight them off the next time.


Leif Issaacson, an aerial applicator from Desert Air Ag, Inc., in Terreton, Idaho, says, "From our standpoint, every type of vehicle has its own advantages, [but] in airplanes, we have the advantage of speed."

Aerial applicators not only get across the field quickly, but the airflow from the plane pushes the fungicides onto plants for more complete coverage. Also, they'll use what they call piggy-back applications, mixing in fungicides with insecticides or other foliar applications so they only need to go over the field once-a cost-effective choice for growers.

Fungicides on potatoes are generally best applied first before potato row closure so that the fungicide gets down in the rows and underneath the plants. Once you have crop canopy cover, depending on the circumstances and what kinds of pressures are out there, applications may be required at intervals as short as 5-7 days.

"In wet years, we'll make applications a lot closer together than dry years. Then growers try to time [other types of] applications with fungicide applications, so we can piggyback applications to save them money," Leif says.