Ascochyta blight goes hand in hand with chickpeas, says a chickpea grower. To control the disease, farmers need to time fungicide applications well, rotate fungicide groups, and make sure they’re getting enough coverage.
The ascochyta blight pathogen overwinters on chickpea residue, and can also spread through infected seed. Spores can travel several miles on the wind, infecting new fields. Rain splash also spreads disease to neighbouring plants. Crop rotation, variety selection, seed treatments, and using seed with very low infection levels are all important management practices. But even with the best management practices, farmers will need to spray several times if the weather favours the blight.
Dan Flynn farms near Lucky Lake, Saskatchewan. He started growing chickpeas with his dad in 1999, and has been growing them off and on since then.
“I remember, we thought we could spray it once with Bravo with an airplane and get away with it. Fungicide was such a foreign term back then,” says Flynn.
Now Flynn pencils out four fungicide applications for B90s, and five for kabulis.
“If my numbers don’t work penciling out that many applications, then I just can’t afford to risk growing them.”
Rotate fungicide groups
Rotating fungicide groups can prolong the life of the fungicides.
Dr. Bruce Gossen is an Agriculture and Agri-Food Canada research scientist based in Saskatoon. Gossen and his colleagues looked at the pathogen’s response to strobilurin fungicides over time. The strobilurins are extremely effective, but are prone to breakdown, Gossen says.
In 2003, there were trace levels of ascochyta blight pathogens insensitive, or resistant, to the strobilurins in some fields. But the level of pathogens insensitive to strobilurins kept climbing.
“And then by 2007, a large part of the population was no longer sensitive to that particular group of fungicides,” says Gossen.
Gossen says the breakdown occurred across the whole production area. Applying the same fungicide group several times within the same season selected for pathogens immune to strobilurins.
“It forced the pathogen to adapt or die. And it adapted.”
Farmers now have a new generation of fungicides to choose from. Gossen says farmers should rotate fungicide groups through the growing season to extend the fungicide’s life.
Flynn does rotate fungicide groups during the growing season. “If a guy doesn’t do that, I think we’re just shooting ourselves in the foot.”
Application timing and coverage important
Flynn applies fungicide proactively with his chickpeas.
“I think once the disease is there, the damage is there. You’re just trying to contain it at that point,” says Flynn.
Gossen says he initially thought farmers could wait for symptoms before applying fungicides. But spraying before symptoms appear is often more effective.
“And the (fungicides) you can use to protect the plant are often cheaper, and less subject to breakdown, than the ones that you apply once there’s already a bit of an epidemic going,” Gossen says.
Flynn keeps an eye on the weather when deciding when to spray. In 2012, he was spraying by the second week of June. July’s humidity led him to spray as much as he could economically. Even with the fungicide applications, the chickpeas yielded $100 more per acre net profit than the second most profitable crop on the farm, says Flynn.
Gossen says chickpea growers have developed expertise in controlling ascochyta blight, even when weather conditions favour the disease, as was the case in 2012.
“There were low levels of disease spread right through the fields. But the timely application of the right fungicides kept everything under control.”
Ascochyta blight needs moisture to germinate, making the stems and lower canopy more prone to the disease. Some farmers adjust their nozzles to spray coarse droplets that fall through the canopy, while others use double nozzles to get a fine mist. Angling nozzles forward can also get more fungicide into the canopy. Gossen says these modifications can improve coverage by up to 10 per cent.
Flynn uses an AIM Command spray system from Case, which gives him the same droplet size no matter his speed. He prefers a fine spray. But he says water volume and coverage is everything with a fungicide. He uses 10 to 12 gallons, depending on the crop size and canopy.
“Everyone likes to cheat on water, if they can. That’s probably the last thing you want to do with a fungicide. It’s one of the more expensive chemicals you can spray. When it comes to chickpeas, it’s probably the most important chemical you will spray.”
“When the crop is worth as much as it is, it’s just foolhardy to go ahead and try to cut water to save 45 minutes of filling.” †