Late blight, the fungal disease responsible for the Irish potato famine, has been found in the Carberry area for the first time this year.
Commercial potato growers should apply fungicides to protect uninfected fields and treat infected ones, but it’s home gardeners Vikram Bisht wants to get a warning to. Potatoes infected with late blight this fall and planted next spring in a garden could be a source of the disease, said Manitoba Agriculture, Foods and Rural Development’s potato and horticultural crops plant pathologist.
“I would emphasize that the tomato home gardeners should look for late blight, especially in those areas (around Carberry),” Bisht said, noting that tomatoes also get the disease. “If they have any suspicions and see funny, large spots and their potatoes might also be getting something, they should report suspicious things to us so we can ensure that it is controlled.
“It’s best to buy new (potato) seed (each spring) that way they don’t risk starting an infection.”
Although Manitoba’s processing potatoes are close to harvest, many plants are still vulnerable, he said. To maximize yield processing potatoes tend not to get desiccated.
“Growers need to spray (a fungicide) if they are planning to hold the crop for a couple more weeks,” Bisht said.
The first case of late blight this season was confirmed in a sample received Sept. 11. The following day infection was found mostly on the top foliage and fine branches of some potato plants, Bisht said in the Sept. 14 Potato Disease Report.
“The sample was confirmed positive for sporangial production,” he wrote.
A second case was found in another field about a mile away.
“Scouting is critical now, mainly in wind sheltered areas and the dips in field where the foliage is greener compared to the senescing crop around,” Bisht wrote. “Especially for fields which have a few more weeks to harvest, fungicide application to protect the crops is very important. Systemic (translaminar) fungicides could be considered. Dew and rains could take the (disease) spores to tubers close to the surface. There is a forecast of precipitation in the mid-week.”
Potatoes infected with late blight now could rot in storage, Bisht said. Late blight doesn’t rot potatoes, but the damage it causes allows other infections to develop resulting in rot.
Treating potatoes with phosphorus acid (Phostrol, Rampart and Confine) as they are placed in storage can protect them from rot, Bisht said.
“The better the coverage, the better security you have for good storage,” he added.
Late blight doesn’t normally overwinter in Manitoba. Bisht suspects the latest infection was delivered by a thunderstorm that hit the area Sept. 4.
“I can say that because the infection is mostly the top of the leaves scattered in a field rather than a big circle or patch within the field,” he said. “If it’s a big patch of disease then you can speculate that it started in that area, but when it’s a few spots here and there then it’s an indication that it came from outside.
“People in that corridor east and west of Carberry probably need to scout their fields to ensure they don’t have late blight,” Bisht said.