Growers advised to protect against resistant blight strains

Potato growers are being advised to keep up fungicide programmes to protect against the spread of resistant late blight strains as rain returns.

That is the advice from Agrii’s lead technical adviser for potatoes, Ed Maule, who points to last year, which was also dry before turning wet late in the season. “Then, all of a sudden, resistant strains like EU_43 or EU_46 appeared,” he cautions.

See also: Why genetics must be central to late blight management

Fortunately, Fight Against Blight monitoring has not detected the EU_43 blight strain this season, although the other new resistant strain, EU_46, has been detected in two separate outbreaks, says Dr David Cooke, senior research development scientist at the James Hutton Institute. Fight Against Blight is run by the James Hutton Institute and is supported by sponsors across the potato industry.

“Now we have had rain, it’s good to put some focus back onto blight programmes,” says David. “It can still infect low levels of green leaf late in the season, and volunteers will need managing.”

The fact that EU_43 was first detected on a volunteer last autumn highlights this risk, he adds.

“We found EU_46 at two sites this season, just before it got really dry. One in Shropshire and one in Lancashire. We aren’t entirely sure of the origins, but the evidence points to ingress from airborne spores because, in one case, the infection spread across the field.”

Fortunately, David says these outbreaks have been controlled by good programmes, alternating chemistry and a bit of luck because of the weather becoming so dry. 

Alternaria

So far this season, the main focus in the East has been on alternaria and keeping crops green, says Ed.

“We have some varieties, like Nectar, that can produce big yields, but we have really had to focus on canopy retention if we are going to hit that potential with late-season bulking,” he adds.

Because of this, his programmes have leaned toward anything with an elicitation or plant-stimulus effect.

Products like Voyager (valifenalate + fluazinam) and Privest (ametoctradin + potassium phosphonates) have featured heavily. Ed has also used a lot of Innocul8, which is a peptide-based plant defence elicitor.

“Innocul8 also provides the plant with zinc and manganese. Foliar feeds have been another important part of spray programmes this year to maintain a healthy canopy,” he says.

Late blight

However, with attention once again turning to late blight for the final few weeks of the season, programmes will need tweaking towards late blight and tuber blight. Intervals may also reduce.

“Where there is still green leaf that needs protecting from blight, Lieto [cymoxanil + zoxamide] will form the backbone of programmes from now on. We will alternate with Ranman Top [cyazofamid], Shinkon [amisulbrom] or Infinito [fluopicolide + propamocarb] for tuber blight protection.”