Potato growers could possibly achieve better long term control of blight if they made more use of product mixes and matched the strengths of different products to specific blight risk situations, according to Syngenta Potato Technical Manager, Michael Tait.

In a recent BPC survey around two-thirds of growers believed blight was increasingly difficult to control. More creative use of tank mixes to counter specific problems could counter the problem, advises Tait. "There has been regimented routine in the way many growers approach blight, when flexibility and pro-active agronomy decisions could have better results - both for reduced growing costs and more effective blight control. For years cereal growers have been tweaking tank-mixes to match disease pressure in a programme over the season; potato growers are only dealing with one pathogen in a more aggressive campaign, but could still utilise the beneficial techniques."

He believes that as growers move more towards smart decision support systems to make the best use of blight fungicides - extending intervals when blight risk is low and tightening spray intervals when the crop is at greatest risk - they will need to exploit the merits of different products.

Tait suggests that if growers can see a risk of blight coming into the crop, if prevailing weather conditions indicate high pressure or neighbouring crops or dumps are producing infective spores, for example, then it is imperative to get a protective application of Shirlan (fluazinam) onto the crop.

"But if a preventative application has been missed and a risk period occurs, don’t just continue with a straight Shirlan application regardless. Growers can now add Sipcam C50 (cymoxanil) to the Shirlan tank mix, to enhance kick-back activity. The inclusion rate of C50 can be tailored to the degree of blight risk and the time delay before an application can physically be made," he advises.

The individual strengths of specific products can also be fitted to growth stages of the crop, he advises. "Systemic products, such as Fubol Gold (mancozeb + metalaxyl-M), are essential during the rapid canopy development phase, to ensure the active ingredient (ai) is being transported into vulnerable new growth. It has consistently been shown that using Fubol Gold as the initial applications improves season-long blight control.

"Furthermore, as the canopy develops growers should look for an ai such as fluazinam that remains effective at low concentrations, so there is sufficient power available to control blight spores when stretched across the larger leaf surface and prolonged protection of isolated blight spores over an extended periods of time in low risk situations."

Tait also points out tank mixing will be essential for growers looking to recreate three-way mixes, that until the recent EU review, had been available as pre-formulated products such as Ripost (cymoxanil + mancozeb + oxadixyl). "Where growers face a high risk situation during rapid canopy development the tank mix of Fubol Gold and Sipcam C50 provides an effective three-way mix replacement. Some agronomists are also advocating this route as a ‘get out of jail card’, if there is a risk blight may have got into the crop and to clear up latent infection before it manifests as visible signs," he added.

With the range of new blight products available on the market, Tait advises growers to carefully assess the merits and strengths of each, and fully exploit their benefits at the most appropriate point in the programme. "Make sure you know what you want to achieve from every application, and chose the product or combination that will best meet it; don’t just switch from one to another for the sake of change.

"We believe that with Fubol Gold at the start of the season and then Shirlan as the core blight fungicide right through to harvest, growers can keep blight off the foliage to maximise yield, and out of the tubers to maintain the best quality."