Potato yield suffers due to pink rot
• Tai Packer of Branxholm and backpackers Ciara McCormack and Oisin Harper harvesting potatoes at Telita.
• Eelworm causes raised bumps on the potatoes and a glassy texture under the surface.
By Daisy Baker
June 26, 2019
The potato harvest is drawing to a close, after what has been a tough season for many local growers with higher incidents of pink rot and eelworms than usual.
Roberts state agronomy manager Stuart Millwood said pink rot is an increasingly growing problem state-wide with potatoes due to continuous potato rotations.
“It’s not necessarily worse than last year state wide, but the North-East has probably experienced a higher-pressure season. Last season the Midlands experienced a higher than normal pressure season,” he said.
“It is a serious issue that we’re facing in the potato industry.
“One of the issues we had this season in the North East was quite a big rainfall event in February where we saw about 100ml around Branxholm and 80ml at Scottsdale, which provided perfect conditions for pink rot infection following a hot spell.”
Pink rot (Phytophthora erythroseptica) can be a devastating disease, especially in hot dry years however wet soil is required for infection.
“Pink rot is an organism predominantly associated with ground where potatoes have been cropped previously,” Mr Millwood said.
“It’s soil-borne and can also be transferred paddock-to-paddock by soil on machinery or stock coming in.
“Pink rot often raises its head in paddocks where tubers have been left behind by previous crops providing a source of infection.”
Legerwood harvesting contractor and farmer Mark McDougall said pink rot is a serious problem for the industry.
“Pink rot started to become a big issue in the last 10 years, and it’s definitely the biggest issue facing the potato industry – it can wipe you out,” Mr McDougall said.
“What we’ve seen in the field is people losing up to 50-80 per cent of their crop to pink rot.
“We harvested a crop this year of 30 tonnes and lost 10 tonnes to the acre to pink rot.”
There is a preventative chemical program for pink rot, with active ingredient Metalaxyl.
“Like anything, it’s certainly effective but you will still get some pink rot, although you won’t get the yield loss you might see otherwise,” Mr Millwood said.
“It protects the tubers up to around 100 days from planting, but for the last 50-80 days they’re in ground they are prone to infection.”
Pink rot often becomes evident once the crop gets to around 100 days and it makes the crop unsuitable for storage.
It only attacks the underground plant, sometimes causing crop yellowing late in the growing season.
Mr Millwood said tubers may appear sound at loading but breakdown quickly within a matter of minutes.
Local farmer Trevor Hall said while pink rot wasn’t much of an issue for him this year, he has experienced it previously.
“We harvested 1400 tonnes this year and we didn’t have any real problems with pink rot because we grew in paddocks that hadn’t had potatoes in them for a long time,” he said.
“Last year we had a paddock that was a real disaster – we probably lost 10 tonne to the acre or 30 tonne per hectare.”
Once pink rot is found in a paddock, it becomes a processing paddock and farmers are put on a processing schedule.
“If potatoes are not suitable quality for storage, the harvesting needs to be scheduled for direct factory delivery, therefore harvesting is delayed, exacerbating the issue,” Mr Millwood said.
Eelworm is a separate issue which can affect potatoes and other crops, and has been present in several crops throughout the North-East this year.
Mr Millwood said eelworm will express itself more in a hot year like we’ve just experienced.
“It lays its eggs under the surface of the potato skin. The potatoes end up with raised bumps and under the surface they have a glassy texture,” he said.
“There could be 3-4mm of glassy texture, leaving less processable material.”
Mr Hall said this year was the first time in a long time he’s see eelworm in his crop.
“The nights have been a lot warmer the last few years and it hasn’t probably got under 15-16 degrees so that could be part of the reason.”
Mr McDougall said this year was one of the worst years he recalls for eelworm.
“With eelworm, the skin comes up very bumpy and Simplot have to turn the peelers up – where they might normally take two slices off the skin they end up having to make much more to get rid of it meaning they don’t pay us as much.”
Mr Millwood said working the ground the autumn before planting to get rid of surplus organic matter and turf can help prevent eelworm.
Negotiations are currently taking place for the potato price for the 2020 season, which is expected to be released in the coming weeks.