Ascochyta chickpea menace will thrive after rain events this winter

Ascochyta chickpea menace will thrive after rain events this winter

Cropping
The chickpea Ascochyta fungus growing from seed that had been stored on farm for more than three years is examined by Senior Plant Pathologist Kevin Moore, Tamworth. Photo. Toni Somes, GRDC.

The chickpea Ascochyta fungus growing from seed that had been stored on farm for more than three years is examined by Senior Plant Pathologist Kevin Moore, Tamworth. Photo. Toni Somes, GRDC.

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Hard to destroy or eliminate, chickpea Ascochyta will plague chickpea crops again this season.

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CHICKPEA emergence is beginning in the north while new plants will start emerging within the next two weeks in the Central West, and with new crops sprouting comes the potential widespread outbreak of Ascochyta blight which can set back yields and destroy seed for next year's plantings.

Estimated planting acreage may be a little lower than previous good seasons mainly due to the early autumn break from three years or more of drought, enabling farmers to get back to their cropping/grazing programs, and chickpea price returns being lower.

Current price at Darling Downs, Queensland, is just below $600 a tonne delivered.

As a wetter winter is materialising NSW Department of Primary Industries (NSWDPI) senior plant pathologist Kevin Moore, Tamworth, is urging growers to closely monitor their chickpea crops for Ascochyta blight.

Volunteer chickpea plants growing in a paddock that had chickpeas in 2019. Every volunteer plant inspected on May 7, 2020 had multiple Ascochyta lesions

Volunteer chickpea plants growing in a paddock that had chickpeas in 2019. Every volunteer plant inspected on May 7, 2020 had multiple Ascochyta lesions

"The disease is present in both seed and paddocks," Dr Moore said.

"In April we tested seed samples from a 2016 crop grown at Croppa Creek. That was a wet year with lots of Ascochyta and lots of pod infections," he said.

"The test revealed Ascochyta infections at the same percentage as tests done on (2016) samples in 2017. So not only has the disease survived for more than three years, it has also not declined in terms of the level of seed infection."

However, Dr Moore said that if seed had been treated properly before sowing, like most growers do, it would give 100 per cent control of seed transmitted Ascochyta.

High risk - low risk

"Most paddocks this year would be considered high risk," he said.

"Those paddocks could have had volunteer plants carrying Ascochyta, or paddocks next to last year's chickpea paddocks.

"The only low risk paddocks would be those that had no chickpeas growing in them or next to them in the past three years, and growers used good quality seed that had been treated with a registered seed treatment."

However, Dr Moore said there would be no cost benefit of applying foliar fungicide on low-risk crops until the disease was detected.

Post-emergence

In high-risk paddocks the first post emergence Ascochyta fungicide spray is the most important.

"This is because the spray is aimed at delaying or preventing the arrival of the fungus in the paddock," Dr Moore said.

"The first spray needs to be done just before the first post-emergence rainfall event, unless it is a low-risk paddock in which case you wait until you find the disease."

Preventative fungicides include active ingredients as chlorothalonil and mancozeb.

"There are other products registered but chemicals based on these two are the most used," Dr Moore said.

Blight pathogens survive and spread easily

The chickpea Ascochyta pathogen survives and spreads in infected seed, stubble and volunteer chickpea plants and according to NSW DPI senior plant pathologist, Keven More, under ideal conditions will go through a disease cycle in five to 10 days.

"It is readily spread by raindrop splash, wind, surface water flows, machinery and animals," Dr Moore said.

"Therefore it is critical for growers to determine the risk level of individual paddocks and implement appropriate management strategies."

Disease prevention is important during the reproductive stage as the disease on pods causes seed abortion, seed infection and seed defects rendering either unmarketable or unsuitable for planting the following season.

Dr Moore said fungicide products containing chlorothalonil and mancozeb need to be applied before rain.

"The beauty of mancozeb is it can be mixed with a Group A herbicide," he said.

Rainfall events spread the fungus and Ascochyta usually starts at the bottom of a plant.

"So there is some physical distance between where fungus is already on the plant (from the previous rainfall event) and new leaf growth," he said.

Dr Moore said while post-infection or salvage applications should not be considered part of a grower's standard Ascochyta management program.

"There were new chemical options with preventative and curative activity which could be useful in situations where a spray was missed," he said.

"Research at the NSWDPI Tamworth Agricultural Institute has shown the registered products, Aviator Xpro and Veritas, stop disease infection as long as they are applied within 48 hours of the rain starting."

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