Pulse growers in northwestern North Dakota have been warned that ascochyta has developed a strong tolerance to the strobilurin family of fungicides, especially in chickpeas.
The affected areas are situated a few miles south of Estevan, Sask. The United States Department of Agriculture said that lentils, peas and chickpeas are severely affected in some areas.
“We’re seeing a lot more ascochyta in chickpeas this year, and now it’s appearing in lentils and peas, which had previously been resistant to ascochyta,” said Chet Hill, agronomist at the N.D. State University extension centre in Williston.
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“In chickpeas, ascochyta adapted to the disease resistant traits, which has been bred into genetics,” said Hill.
“The other problem is that ascochyta has built up a tolerance to the strobilurin fungicides. Farmers haven’t rotated the modes of action in their fungicides. They stayed with strobilurin and now strobilurin doesn’t work.”
North Dakota seems to be a hotbed for mutations. Four years ago, Roundup tolerant weeds were found in a number of fields. Hill said pesticide rotation is essential in preventing these situations.
“The strobilurin situation is the same as our Roundup situation. If growers don’t rotate the mode of action and continuously use one group of products, mutations reproduce and flourish.
Hill said some growers are on a short lentil/wheat rotation. As a consequence, he’s starting to see a buildup of ascochyta in those fields, along with root rot. Other producers are growing peas every other year.
Chickpeas are in a three or four year cycle because that’s what crop insurance rules require. The current ascochyta outbreak is most severe in chickpeas because the ascochyta pathogen no longer responds to strobilurin fungicides.
Strobilurin tolerance is widespread in North Dakota and growers are cautioned against using these products in case the fungicide tolerance strengthens and spreads.
“Ascochyta in peas and lentils is at
risk for the development of fungicide resistance if sequential applications of the same fungicide are made,” said the USDA.
Hill said that Headline and Proline are two fungicides that are working well in North Dakota. Other fungicides that are not as effective are also recommended because they help stretch out the fungicide rotation.
