Lentil and chickpea growers should be monitoring their fields for ascochyta blight before the crops flower.
During the past few years, ascochyta blight has been the most damaging disease of these crops, especially chickpeas.
High humidity and frequent rainfall help the disease become established, but the susceptibility of the host and the aggressiveness of the disease pathogen can determine its severity, said Penny Pearse, a plant disease specialist with Saskatchewan Agriculture.
Susceptible host crops are plentiful this year.
Saskatchewan farmers intend to grow 1.6 millions of lentils and one million acres of chickpeas.
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While many lentil varieties have good resistance to ascochyta blight, chickpeas have only partial resistance.
“This partial resistance is greatest for the first four to six weeks after planting,” Pearse said.
“When conditions that favor disease spread are present, such as frequent showers and high humidity, even partially resistant varieties can suffer severe losses in seed yield and quality.”
Ascochyta was a problem in chickpea crops last year, which means the pathogen is present in residue and infected seed.
As well, seed-testing laboratories have reported high levels of ascochyta on this year’ s chickpea seed samples.
A little rain may be all that is needed to start development of the disease.
“Still, growers should not assume that the disease will reach the same high levels as they did last season,” she said.
“Some well-planned scouting can help determine whether or not to spend money on fungicide and, second, how to get the most efficient use out of a fungicide application. Early identification is critical, as it allows time for a decision before ascochyta blight gets a foothold in the crop.”
Pearse reminds growers that the disease is caused by microscopic organisms, so walking the field is recommended.
By the time large-scale symptoms can be seen during a quick drive-by, damage has been done and it may be too late for action.
Farmers should start scouting in high-risk crops, including those planted with ascochyta-infected seed, even if a seed treatment was used; those with the same type of pulse crop in the rotation during the previous two years; and those next to infested residue from the previous year.
“Within these high-risk fields, first scout in problem areas such as in hollows where moisture is common, the field edge closest to last year’ s residue, and those patches where the seeding rate was a little heavy,” Pearse said.
“If hot spots are identified, fungicide application initially can be limited to these areas.”
Field monitoring should start at the pre-bloom stage.
Last year, ascochyta blight was first observed in chickpeas in early June, and fully developed stem lesions were present by mid-June.
Although the pathogens causing ascochyta blight in chickpeas and lentils are different, the resulting symptoms are similar.
Plant tissue attacked by the pathogen will develop round or oval discolored spots called lesions.
Lesions occur on stems, leaves and pods, and are typically light brown with a darker brown margin. The centres of the lesions are often speckled with tiny, black fruiting bodies that contain fungal spores.
Bravo 500 should be applied at the first sign of ascochyta blight lesions on the stem, or at early flower if lesions are present on leaves.
Bravo 500, the only foliar fungicide registered for control of ascochyta blight in chickpeas and lentils, is a protectant fungicide. It coats the plant’ s surface to provide a barrier against spores.
It therefore needs to be applied before disease becomes widespread.
To confirm the presence of ascochyta blight, contact an extension agrologist, or send a sample to the Crop Protection Laboratory, 346 MacDonald St., Regina, S4N 6P6 or telephone 306-787-8130.
More information about pulse diseases can be found on Saskatchewan Agriculture’ s website or at www:paridss.usask.ca/special
crop/pulse_diseases/index.html.
