It might be that several issues are being encountered or more than one may compound damage in pulse crop
A plant health issue in Saskatchewan’s chickpea crop has agricultural researchers perplexed.
The problem first surfaced in 2019 with Gravelbourg, Assiniboia and Coronach in southwestern Saskatchewan among the worst hit areas.
In 2020, a wider area of the province was affected by the mystery ailment, and chickpeas again had a lot of chlorosis, wilting and some plant die-off.
Michelle Hubbard from Agriculture Canada led a webinar available on the Sask. Pulse Growers website. She and other scientists are working to figure out the new issue.
She said in 2019, the plant health issue seemed to affect CDC Orion more than CDC Leader and so it was thought that the problem might be ascochyta blight, which can evolve quickly to break down varietal resistance.
Hubbard and her team set up growth chambers and grew Orion and Leader and inoculated them with ascochyta blight from samples from the affected regions, but they saw no differences in terms of resistance to the pathogen.
Also, Orion and Leader share a parent from which they draw their resistance, which means the genetic source of their resistance overlaps.
“So all of that argues against the ascochyta blight overcoming resistance in Orion but not Leader as being a major cause,” Hubbard said.
Researchers tested samples for a wide range of diseases and although many diseases were found including root rots, none stood out as the causal agent for this new health issue.
Scientists then pooled all the diseases together to look for trends.
“My thinking in doing this was just maybe it’s not one particular pathogen but the pathogen load in unhealthy samples, but that really doesn’t seem to be the case,” Hubbard said.
She said it’s still possible the cases are being caused by a disease or a consortium of microbes they didn’t test for.
Researchers also failed to find any viruses that stood out as possible causal agents.
To help track down the cause, the Saskatchewan Pulse Growers contacted agronomists in southern Saskatchewan and received 27 samples from 15 different fields, as well as the field histories, and then tested for a range of different pathogens, performed nutrient analysis and herbicide residue testing.
Residual herbicide damage came to light as a possible cause, partly from anecdotal evidence from farmers and from environmental conditions.
In much of the affected areas in 2019 and 2020, there were early dry conditions followed by a big dump of rain.
Some previously applied Group 14 herbicides could have been still active in the soil and taken up by the chickpea plants when the large rain event occurred.
However, typical plant damage caused by Group 14 herbicides were not observed in areas affected by the plant health issue, and some of the affected fields did not have a preceding application of a Group 14.
Shaun Sharpe at Agriculture Canada in Saskatoon, investigated whether herbicides could be to blame.
“We were looking at herbicides that were being applied in chickpea production and we didn’t really see anything. There is no clear trend that this herbicide or that herbicide influenced the injury that we’re seeing,” Sharpe said in the Sask. Pulse Growers webinar.
He also examined other herbicides that were applied prior to the chickpeas because chickpeas do not have a high metribuzin tolerance and its possible Group 14 herbicides weren’t broken down in the soils, particularly when wheat preceded the chickpea crop.
“Auxin carryover, in particularly fluroxypyr, clopyralid I’m concerned about. These herbicides are very stable compared to 2-4D or Dicamba. They are absorbed in treated vegetation and then it’s actually persistent, so when that vegetation breaks down, it’s released back into the soil,” Sharpe said.
He said when there is a heavy rain these substances may be washed from crop residue into the soil, which can be exacerbated when dry conditions prevent the molecules from breaking down and if the crop is stressed from lack of moisture before the rain.
“Pest management is often times many little hammers and I believe with the range of symptoms that we’re seeing here is kind of the opposite issue; where we’re having many little cuts that are causing stress to the chickpea,” Sharpe said.
But no definitive conclusion was reached and more investigations must be conducted in 2021 if the issue returns.
Nematodes were found in two samples but analyses on these pests were not performed.
James Tansey, an insect and pest specialist for the Saskatchewan government, led an analysis of pests found on affected chickpea fields.
No definitive culprit was found so the role pests played in the plant health issue is still outstanding.
Fertility concerns, including possible toxicity from excess nutrients and plant stress from inadequate nutrients, were investigated but found no obvious cause.
Hubbard said further nutrient analysis, including using electrical conductivity and PH analysis will be conducted.
Dr. Mario Tenuta of the University of Manitoba will also look at the samples for nematodes, and Agriculture Canada staff in Saskatoon plan to sequence and broadly scan the soil samples this winter.