Potato growers should keep up fungicide programmes to protect against the spread of resistant late blight strains as rain returns, says Ed Maule, Agrii’s lead technical advisor for potatoes. 

 “We learned last year that even in a dry year it can still turn wet late in the season and then, all of a sudden, EU_43 or EU_46 appears,” he cautions.

Fortunately, Fight Against Blight monitoring has not detected EU_43 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 supported by sponsors across the potato industry.

“Now we have had some rain, it’s good to put some focus back onto blight programmes,” says Dr Cooke. “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, these outbreaks have been controlled by good programmes, alternating chemistry, and a bit of luck because of the weather becoming so dry,” says Dr Cooke. 

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 and fluazinam) and Privest (ametoctradin and 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 notes.

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.

“Even though this season will largely be known for very low pressure, we knew at the start that it would still need a flexible approach,” says Ed.

To report a blight outbreak to Fight Against Blight, visit their website.