When you shift from spraying weeds to spraying disease, you have to make adjustments in the way you set the sprayer. You need to anticipate diseases you can’t yet see, and your sprays have to penetrate dense canopy

You know where to look for weeds. You can see them and you can usually tell when they’ve been controlled. But disease control is a totally different cat. Crop disease management takes some thinking ahead. In many cases you have to make a spray decision based on the risk of disease development because by the time you see a disease it is too late to control. Then how do you know your spray did any good? Effectiveness of control measures may not be completely obvious until you start the combine.

Disease, fungicide, and application specialists from across Western Canada have several important tips for you to assess the risk of disease and then decide how and when to control it.


Timing of fungicide application in different crops is one of the most important factors to provide effective disease control, says Kelly Turkington, a plant pathologist with Agriculture Canada in Lacombe, Alta. In cereal crops, for example, he says it is most important to protect the top two leaves in wheat or the top three leaves in barley to achieve optimum grain fill and yield.

“As farmers are out checking fields for weeds in late May and early June, they should also be looking for signs of disease,” he says. “In early June if they are seeing some evidence of disease then they know they need to be monitoring their fields closely.”

Generally a “single well-timed treatment” of fungicide at or just before flag leaf emergence should be sufficient to protect leaves in the top part of the plant, Turkington says.

How do you know if a treatment is necessary? Again, as a general guideline if there is less than one to two per cent of disease evident on the third leaf a treatment may not be warranted. (Count down from the top — you have the flag leaf, then the second, and then the third leaf.) “So if there is less than two per cent infection of diseases such as scald and net blotch on this third leaf, then a treatment may not be needed,” he says. “But if you are seeing more than two per cent of disease infection on this third leaf you may need to treat. You certainly want to be monitoring the crop closely, especially if the weather changes, to see if the disease is building.”

Timely treatment is important for all diseases, but some are more volatile than others, says Turkington. “Timely treatment of rust in cereals is a good example,” he says. “The disease is so explosive if conditions are right, so you need to be monitoring fields. If you see signs of the disease and conditions are favourable you may need to be treating fields even before the flag leaf stage.”

Aschocyta in chickpeas is another “explosive” disease that needs to be monitored carefully. The disease needs to treated early and will probably require multiple treatments during the growing season.

Farmers also need to get a jump on sclerotinia in canola. Producers need to assess the disease risk, and monitor growing conditions and treat crops before there is visible signs of the disease on the plant. It is unlikely

Credit: Syngenta


that a fungicide will do much good if a producer discovers signs of the disease on leaf tissue in late bloom or after bloom, says Turkington.


Turkington says usually a fungicide only helps to protect the plant tissue that is present at the time of application. So if the treatment is made too early, it won’t protect leaves that emerge later. And fungicides generally aren’t designed to eradicate a disease that is fairly well established. A fungicide won’t be able to eradicate a disease that has been on the crop for 10 days or more.


In crops that receive multiple fungicide applications to control a disease, in season, Turkington warns of the risk of developing fungicide resistance. He urges producers to consult provincial crop protection guides, or a certified crop advisor for advice on fungicide options.

“Probably the worst-case scenario is the farmer growing continuous wheat or has wheat in rotation every two years,” says Turkington. “They may go in early and apply a fungicide and then if they see disease at the flag leaf stage they make a second application. And then next year they repeat the same process. They are running a real risk of developing pathogens that are resistant to fungicide. They need to be changing fungicide groups. Maybe in one application they can use a product like Tilt, and then later a product like Headline. But they need to know the disease pathogen they are dealing with and of course use the proper registered products.”


For a fungicide to work properly, apply the proper amount of product where it is needed, says Tom Wolf, an Agriculture Canada research scientist specializing in crop protection.

“The biggest difference between applying a herbicide and a fungicide is the amount of crop canopy you have to deal with,” says Wolf, who is based in Saskatoon. “In most cases, with herbicides you are dealing with a single plane; a horizontal crop surface and if you get the product through to the ground you’ve controlled the weed.

“When applying fungicides, whether it be in canola, peas or a cereal crop, you could have a crop that is two, three or four feet high, and then you have to know where the disease is and find a way to get it there. Is it in the top of the canopy, is it midway down the plant on the stem, or it is near the ground?”

In dealing with fusarium head blight, for example, hitting the top of the crop canopy with a

Leaf diseases typically begin low on the plant and move up, so if you scout at tillering and again at flag leaf emergence, you’ll be prepared to spray on time if necessary. If you see mild infections on middle leaves (third or fourth leaf), a fungicide application will prevent the disease from climbing any further and infecting the flag leaf.

fungicide is usually sufficient. But if it is a pathogen that attacks the stem of the plant, or a soil-borne disease, deeper penetration into the crop is canopy is needed.


Adequate coverage usually requires higher water volumes. Generally with herbicides water volumes are between five and 10 U. S. gallons per acre. For proper coverage with fungicides the range is 10 to 15 gallons of water per acre, Wolf says.

Travel speed and boom height are also important factors to consider. Again, if the disease affects the top of the crop canopy speed may not be an issue, but if it is further inside the canopy, then a slower travel speed may be needed.


The newer-style low-drift, flat-fan nozzles will work effectively in most fungicide applications. And the industry has developed a standard droplet sizing system that describes spray sizes as either fine, medium, coarse or very coarse. Directional nozzles that direct spray forward and backward can be beneficial, but again it depends what and where the disease is in that canopy.

Wolf agrees with long-time field sprayer marketer Tim Criddle that air boom or air assist sprayer systems can be effective. Criddle is marketing manager for Miller sprayers, which feature the Spray-Air air boom technology. Wolf says using some type of air system to apply crop protection products may not be needed in all situations, but they are beneficial when it is important to get coverage inside a crop canopy.

Criddle says Spray-Air technology which was developed by SAT Industries at Carseland, Alberta doesn’t just blow droplets from conventional flat fan nozzles into the crop. Spray-Air uses a specially designed nozzle that atomizes the droplet size and with an air boom that can deliver a range of droplet sizes into the crop canopy with up to a 100-mph wind force.

“The feature of Spray Airtechnology is that you can deliver whatever droplet size you require deep into the crop canopy to apply fungicide where it is needed,” says Criddle. The droplet size can be adjusted on-the-go from inside the spayer or tractor cab as spraying conditions change. More details on Spray-Air technology can be found online at www.millerstn.com.


Your weed control techniques might not work for fungicides. You need to switch your thinking from how to control weeds to how to control a different type of pest under different conditions, says Richard Marsh, technical sales manager for Syngenta for the eastern Prairie region.

He urges producers to follow label recommendations when applying any crop protection product, and especially fungicides. “If a label says to apply 15 gallons of water with this product or 18 gallons of water with that product, those recommendations are there for a reason,” says Marsh.

“In many cases producers have just gone from spraying for weeds and now they are into a potential 60-bushel wheat crop or a 100-bushelbarley crop and they are trying to protect the flag leaf and the top two or three leaves against disease. That is a lot of leaf area to cover. So water volumes as recommended on the label are important. If you are cutting water volumes you are cutting your control.”

For example, products such as Tilt and Stratego, which are registered for control of septoria, tan spot, and rust in cereals, has a recommendation of nine to 18 gallons of water. The lower rate is intended for fungicide application early in the growing season (about the same time as weed control treatments) while the 18 gallons is recommended for later in the season when the product is being applied at the flag leaf stage. Crop conditions have changed, so water volumes need to change.


Wolf’s fungicide recommendations include a sprayer checkup. Evaluate nozzles, spray booms, pressure gauges and other parts to make sure everything is operating as it should. Marsh also promotes this recommendation.

“I know people are pushed for time at this time of year, but it would be well worth their while to take a couple of hours to check sprayer operation in the field,” Marsh says. He recommends producers place water-sensitive paper at different levels of the crop canopy and then run the sprayer, with water, over the test area.

“It might take two or three hours to run this test, but then you can see how the sprayer is working, see where water is being applied, and you’ll know if you are reaching the target area at the rate that is intended,” he says. “If you have 3,000 or 5,000 acres to spray, those couple hours could be a very worthwhile investment.”

Water-sensitive paper is available from many dealers who carry sprayer supplies. You can also order it online from companies such as Rittenhouse at www.rittenhouse.ca.

Lee Hart is a field editor for Grainews in Calgary, Contact him at 403-592-1964 or by email at [email protected]

About the author

Field Editor

Lee Hart

Lee Hart is editor of Cattleman’s Corner based in Calgary.



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