Fungal disease risk looms after wet 2016
GroundCover™ Issue: 126 | 16 Jan 2017 | Author: Liz Wells
A sodden 2016 winter-cropping season has exacerbated disease risks for canola and chickpea crops in 2017 and growers are urged to stick to rotations and formulate management strategies to minimise the threat
Growers have been urged to adhere to proven crop practices and heed recommendations from researchers and advisers to minimise broadleaf disease risks in 2017 canola and chickpea crops.
The cautionary note comes in the wake of a sodden 2016 winter-cropping season across most of the GRDC’s southern and northern regions, which caused widespread outbreaks of blackleg in canola, ascochyta blight in pulses and sclerotinia in both.
Dr Kevin Moore, NSW Department of Primary Industries (DPI) pulse pathologist, and Dr Kurt Lindbeck, NSW DPI senior broadleaf crop pathologist, say appropriate paddock selection and disease management strategies are paramount in the lead-up to winter crop planting.
Dr Moore says eastern Australia’s record chickpea area in 2016 will challenge growers’ ability to select paddocks with a low risk of hosting a 2017 ascochyta blight outbreak. “Ascochyta inoculum from infected chickpea residue blown out the back of headers during the 2016 harvest will contaminate paddocks intended for chickpeas in 2017, so growers need to have a 2017 strategy for ascochyta management,” he says.
“Autumn burning of cereal stubble in paddocks intended for a 2017 chickpea crop is a management tool growers should consider.”
Dr Moore says seed treatment, seed testing, growing resistant varieties of known purity and wider row spacings are other management tools that will reduce the risk of chickpea disease.
Consideration of paddock history is crucial in control of sclerotinia and Dr Moore cautions growers against planting chickpeas into paddocks that have grown broadleaf crops, including canola and cotton, and broadleaf weeds in the past five years. “There was more sclerotinia in chickpeas in September 2016 than I have seen before and growers need to be aware that the sclerotinia fungus can survive in paddocks for many years.”
Dr Lindbeck says canola growers need to select paddocks and varieties carefully to minimise the risk of sclerotinia and blackleg, and factor in the cost of fungicide applications if they are growing canola more than one year in four.
“Growers are planting canola as often as every second year in rotation with wheat and sclerotinia will build up quickly in the soil, especially in wet seasons,” Dr Lindbeck says.
Sclerotinia develops in flowering canola when the canopy is wet for 48 to 72 hours. Most canola areas in South Australia, NSW and Victoria had at least one of those events in the 2016 growing season. The result could be sclerotinia-induced yield losses of up to 30 per cent – and up to 20 per cent due to blackleg – if preventive measures are not taken.
Dr Lindbeck says fungicides are effective management tools but should not be relied on as an alternative to prudent paddock selection, or to controlling outbreaks during prolonged flowering or wet weather. “We now have foliar fungicide options, but fungicides don’t provide the perfect answer.”
Due to an early planting strategy adopted by some growers, the flowering period for Australia’s canola crop now stretches from mid-July to October. “In eight weeks of flowering, one fungicide application will only give you a three-week window of protection. Growers need to be aware of that.”
Dr Lindbeck says blackleg is considered to be easier to control than sclerotinia because most damage caused by the disease occurs early in the growing season, up to the six-leaf stage.
However, blackleg can survive on canola stubble and can increase disease pressure on plants if conditions for an outbreak are favourable and inadequate crop monitoring or an inability to spray lets either disease take hold.
Dr Lindbeck is advising growers to have at least 500 metres between 2016 canola stubble and 2017 canola plantings to avoid the heaviest sclerotinia and blackleg ascospore showers.
He says burning canola stubble is not recommended as a sclerotinia or blackleg management strategy: “Burning stubble will reduce the risk of blackleg, but not eliminate it.”
Avoid market temptations
GRDC Northern Panel member and Lake Cargelligo-based consultant Andrew McFadyen says disease threats need to be acknowledged in the face of tempting commodity price outlooks, which have been encouraging growers to increase canola and chickpea areas at the expense of cereals.
“Pre-sowing commodity markets can at times lead growers into making emotional decisions about what to plant and where to plant based on the profit per hectare they hope to get for a crop. Sound agronomic practices are often forgotten with this approach to crop choice and rotation,” he says.
He warns against chasing profits at the expense of abandoning proven agronomic practices such as sticking to a sound rotation that minimises crop health risks.
“In the long run, stepping away from a good rotation will lead to diminished crop returns through areas like yield penalties and greater outlays to control disease.”
More information:Dr Kevin Moore,
0488 251 866,
Dr Kurt Lindbeck,
02 6938 1608,
GRDC Project Code DAN00147, DAN00176, UM00052-UG
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