Dr Steve Marcroft works on canola disease experiments at his base at Grains Innovation Park, Horsham, Victoria.
Despite anecdotal evidence of lower plantings in 2015, growers and advisers across south-east Australia are encouraged to be on the lookout for a range of diseases in canola crops this year.
In the lead-up to and during seeding, much of the focus has been on blackleg. In a small survey held last year Dr Steve Marcroft, Marcroft Grains Pathology, identified blackleg isolates with tolerance to the fungicide fluquinconazole – or seed treatment Jockey®. Blackleg is a sexually reproducing disease with enormous genetic diversity, meaning plant breeders are in a constant battle to maintain canola’s disease resistance. Dr Marcroft says in recent years blackleg has not been too severe in southern Australia, but 2014 was a “variable” year for the disease.
“Blackleg is most severe when canola is sown late at the start of winter and can cause considerable yield loss,” he said.
“The last few years we have had good early rain and the canola has grown quickly through the seedling stage. Last year we saw blackleg lesions form on the flower because the plants developed too early.”
With four million hectares of canola planted across Australia last year, Dr Marcroft says the risk of blackleg will be on-par with recent years. However, he is advising growers to have a fungicide management plan in place to avoid resistance.
He says canola-wheat rotations are very reliant on fungicides to control blackleg.
“If the fungicides don’t work growers will have to change their whole farming system,” Dr Marcroft said. “Therefore, we want growers to have a fungicide management plan in place for when new actives come onto the market and we are also encouraging growers to change varieties based on resistance groups.
Watch a video with Steve Marcroft
“From a fungicide perspective, it is very difficult to find a crop that hasn’t been treated with fungicides so we’re not sure if they are working, and secondly, we don’t want to lose that fungicide control option.”
Fungicides applied as seed treatments work against blackleg from seed through to the three-leaf stage, while fungicides such as Prosaro® are applied at 4-6 leaf stage. If lesions develop at three-leaf stage they may not be affected by the fungicide.
Dr Marcroft says at the end of the season, growers should pull some canola plants out of the ground and cut the stem open to see if they have blackleg symptoms. If more than half of the cross-section of the stem is discoloured, yield loss will occur.
Dr Marcroft is currently running a Grains Research and Development Corporation (GRDC)-funded survey in which he aims to screen 2014 canola stubbles from 200 different paddocks. He says it does not matter if the stubble has had a new crop sown into it, he is chasing 20 pieces of stubble from that paddock (see More Information for details on sending in stubble samples).
Sclerotinia stem rot
Like blackleg spores, sclerotinia spores are present each year and are produced from small mushrooms that germinate from sclerotia. Dr Marcroft says if weather conditions are warm and wet at petal fall then sclerotinia is likely. It is difficult to control because it cannot be monitored prior to stem rot developing.
“Generally the rule is that if you have had sclerotinia in the past then it is a risk and if you receive rain during flowering then it is important to use fungicides as a control measure,” he said.
Best practice disease control is applying a fungicide before rain at flowering to act as a protectant.
The GRDC is funding a sclerotinia modelling project with the aim that growers can receive a disease warning and spray before rain.
White leaf spot and downy mildew
While white leaf spot and downy mildew are often not as prevalent as blackleg and sclerotinia, they have can cause yield losses under specific circumstances.
“They can be very prevalent during winter, but at this stage there is no current management,” Dr Marcroft said.
Dr Steve Marcroft
03 5381 2294
For more information on how to send a stubble sample in for blackleg screening, email Dr Marcroft via BlacklegMGP@gmail.com who will then provide a sampling protocol via email.
GRDC Project Code
UM00051, MGP0003, DAN00177