Timing and Coverage Are Important Factors in Fungicide Application

Tips to mitigate disease in your pulses

Keeping crops healthy and disease free is a priority for producers and one practice that can help achieve these goals is applying fungicide. That said, producers need to consider both disease risk and economics when deciding whether to apply a fungicide.

Disease risk will be influenced by the field history, including crop rotation and levels of disease the last time a susceptible crop was grown, the environmental conditions such as temperature and precipitation levels, and the level of variety resistance to the disease in question. Barb Ziesman, the 
Provincial Plant Disease Specialist with the Saskatchewan Ministry of Agriculture, says this requires some basic understanding of the disease, including what other crops are susceptible, as well as the environmental conditions that favour disease development.

On the economic side of the coin, she adds that a fungicide should only be applied if the risk of disease is high and an economic return is expected. There are a number of factors farmers should keep in mind once they decide the disease risk and economics make fungicide application necessary. The two most important are timing and coverage.

Timing

Tom Wolf with Agrimetrix Research and Training in Saskatchewan says in the summer months, plant growth and disease progress can be very rapid so it is essential for producers to be ready to apply when the fungicide is needed. That means having sprayers equipped with the correct nozzles and fungicides on hand.

He says using a low-drift spray can be useful since it allows the application to be safely made even when winds may be a bit higher. “Contrary to common belief, it is not usually necessary to apply fungicides in a fine spray except in some special cases,” says Wolf. “Fine sprays create a lot of drift potential that limits the weather conditions in which they can be safely used. In practice, that means not being able to spray on time.”

The most common mistakes producers make with fungicide application tend to be related to the producer’s need for productivity. “Applying lots of water or driving slower to get the spray further into the canopy are unpopular when the forecast is bad and there is lots of area to cover,” says Wolf. “Missing the ideal window of opportunity is very costly and a fungicide applied at the wrong time can lose much of its effectiveness. It is a balancing act and we look for ways to spray properly and get it done on time.”

Coverage

Good coverage is also critical for a fungicide to be effective. To achieve this during application, target the plant part that needs protection, be it the leaves, stems, or leafstalks, and do so with adequate droplet density. This is because most fungicides do not move from one part of the plant to another very well. That is why it is important to understand the disease, including which plant parts must be covered by spray and where – top, middle, or bottom – they are in the canopy. Then assess how easy it will be for a spray to reach the target zone.

“The further down in the canopy, the more challenging it is for the spray to reach further,” says Wolf, adding there are a limited number of tools to use in this case. “The most effective is water volume. The more dense the canopy, and the further down it needs protection, the more water should be used. For many pulse canopies, volumes should be no less than 15 U.S. gallons per acre, and reaching 20 gallons per acre or more in some cases.”

To get the best coverage, fungicides should be applied prior to canopy closure. Ziesman says one of the biggest mistakes producers make is using inadequate water volumes. “This will limit the ability to get the fungicide where it needs to be.” Droplet size is also important for some canopies, such as the very dense canopies of lentils or chickpeas, which are not usually penetrated by larger droplets.

Is One Application Enough?

Often a single, well-timed fungicide application is effective enough to manage disease and maintain yield potential. However, if the environment remains favourable for a prolonged period of time, producers may want to consider subsequent fungicide applications. “This should be assessed by scouting,” says Ziesman. If more than one application is used within a growing season, she adds that producers need to make sure they rotate fungicide groups and do not use a single mode of action more than once. They should also consult the product’s label for the preharvest interval when they consider later applications.