Montana chickpea growers – who produce a third of the U.S. chickpea crop – face a serious foliar crop disease known as Ascochyta blight.
It’s caused by a poorly understood pathogen- Ascochyta rabiei that requires growers to make multiple fungicide applications each season. That’s not only expensive, it’s a recipe for fungicide resistance development.
“Some fungicides are already losing their sensitivity towards Ascochyta,” explained Vishal Monga, a PhD student at Montana State University. “And because of the large number of fungicide applications needed, Ascochyta blight is the primary limiting factor to farmers integrating chickpeas into their rotations.”
In Montana chickpea is often rotated with wheat. The fungus can be present both in chickpea seeds and crop residue. It survives Montana winters, and the fungus spores emerge and spread by wind in the spring, travelling up to 10 miles from the original source.
What growers need to know – and Monga is researching with funding from a Western SARE Graduate Student grant – is exactly what conditions lead to spore dispersal, when growers should make the first fungicide application, and how often they will need to make repeated applications of different fungicides to effectively manage the disease. In his study, Monga is rotating between fungicides with different modes of actions to discourage resistance development in the pathogen.
“We are interested when the spores are released,” Monga explained. “We have placed chickpea residue from the previous year in eight locations around the state, so that the residue can overwinter and we can assess if our Montana climate is favorable to spore production.”
Surrounding the chickpea residue will be spore traps and chickpea seedlings grown from certified disease-free seed of varieties known to be susceptible to Ascochyta blight. Monga will record detailed weather data and look to pinpoint the conditions that lead to spore release.
“The next objective for this study is to determine the best timing of fungicide application for the growers,” he said. “We are testing four timings of fungicide application with two different frequencies of applications.”
The four fungicide application timings are early application, first appearance of symptoms, flowering and late flowering. Each of those timings will also be tested with an every-two-week reapplication timing and an every-four-week timing.
With the data from all those applications and timings, Monga hopes to be able to provide growers with a clear recommendation of when to begin treating the disease, and how frequently.
And even then, it’ll only be an element of an overall control strategy for the pathogen.
“Ascochyta is a disease and you can’t rely solely on fungicides,” he said. “You have to use integrated control. You need to get the certified seed. You need to get it treated. You need to get the best available varieties in the market. In a growing season, you should do a protective application, at least. But if there is a high pressure, it is highly recommended you should rotate your crops away from chickpea for two to three years to break the disease cycle.”