A sudden loss of disease resistance in the expected bumper chickpea crop in South Australia this year is raising concerns.

South Australian Research and Development Institute (SARDI) pathologist Dr Jenny Davidson said she was concerned about the level of infection in varieties thought to be resistant to the disease.

Authorities have approved minor use permits for farmers to use chemicals to spray their crops to limit the spread of ascochyta blight.

Ascochyta blight has been detected in several cropping regions over the past few weeks — including the Mid North, Lower North and Yorke Peninsula.

Dr Davidson said not only was the extent of the disease concerning, but so too the pace of the outbreak had been unexpected.

"Suddenly this year, which we assume is to do with the rain in winter, the disease is creating some really severe problems.

"This sudden loss of resistance is something that is a little bit surprising, [given] the speed with which it has happened."

"We were aware that something was changing and we gave information out to industry last year to monitor their crops because something was changing.

"But suddenly we've got a dramatic shift in the whole spectrum of what's going on."

Scientists are urging farmers to get on top of the outbreak as soon as possible, and by doing this farmers can help reduce its severity.

"If they get out there and spray their fungicides, and continue to put out sprays, they should be able to get those crops through.

Dr Davidson said to use protectant fungicides ahead of rain fronts, starting at the next rain front.

"They need to get a fungicide spray out, then during podding. They really need to be very diligent about getting those sprays on the crops," Dr Davidson said.