The weather, an unpredictable entity, is the number-one factor in determining how significant blight will be to this season’s crops. Now with the advent of more aggressive blight strains dominating the composition of the UK’s blight population, growers are faced with a more difficult blight threat than ever before.
According to Michael Dempsey, an agronomist with Matthews Agricultural Services in North East Ireland, the arrival of more virulent blight strains, which have been evident in fields, presents a greater challenge to blight control and the programmes chosen.
“These newer strains are much more aggressive and once established are much more difficult to control, bearing this in mind prevention is the best approach. We simply cannot let it establish in crops without dire consequence,” he believes.
Despite this, Michael who advises growers across the counties of Louth, Meath and Dublin, believes growers are well equipped for the season ahead, even in Ireland, where the wetter climate and high rainfall is extremely conducive to blight development and spread.
“Given the range of products available today, and by cleverly placing them in selected programmes it is possible to keep crops free of blight.
Each variety has its own strengths regarding leaf, stem and tuber blight. “These strengths should form the core of your product selection when adopting a programme.
“It is when you don’t have a programmed approach when you are most likely to run into problems with blight establishing in the crop. Once this happens then you are chasing it for the remainder of the season.
“Blight forecasts and the use of Smith Periods while useful, in no way eliminate the necessity for a programme of treatments.
“Adopting a programmed approach, alternating actives, is what’s needed to respond to the evolving, tougher, blight threat. It is a must,” urges Michael.
“Those not in a programme and where blight establishes can find themselves having to go out at two or three day intervals in order to get on top of blight. Very often the cost involved in this emergency situation is greater than if a programme had been adopted in the first place. Worst still the problem continues right up to desiccation.”
With a very good range of fungicides now available in the marketplace, such as Infinito (fluopicolide + propamocarb), Ranman (cyazofamid), Revus (mandipropamid), Shirlan (fluazinam) and Valbon (benthiavalicarb-isopropyl + mancozeb) plus ZinZan amongst others the challenge is their placement in the programme to get a blight free crop or as near as possible to one.
He advises against devising a strict inflexible plan in advance. “Blight is unpredictable. Last year blight pressure in relative terms, was low, it was a dry year in comparison which helped suppress disease development.
“Conversely two years ago, pressure was extremely high and intense. And in such a bad year we can be putting on as many as 13 to 17 treatments in a season.
“Programmes should first be tailored on a field-by-field basis to suit the variety of the potato and address any weaknesses it may have.”
“Then being responsive and adaptive to the season as it develops is vital.” Different conditions and timing makes different demands on chemistry. “We have to be equipped and respond to these with a range of different modes of actions. That way we shouldn’t run into any problems.”
An awareness of product characteristics and attributes – be it contact, systemic or translaminar, is important to inform product choice and placement.
Growers should be looking to inhibit the pathogen before it has any chance of penetrating the leaf or stem. Fungicides with attributes such as ‘Kick-back,’ offered by Valbon, is very important. If caught by the weather between treatment timings, having a product in place with ‘kick-back’ gives fantastic comfort that you have control / protection for an additional two or three days against incoming infection,” he explains.
“Products with systemic activity are important during rapid growth, enabling uptake and redistribution of the fungicide active through the plant to protect newly emerging green foliage.
“Rainfastness is another critical formulation attribute to have throughout the entire programme,” believes Michael. “With capabilities to spray huge hectarages in a short time, rainfastness within an hour or two is a big plus.”
The inherent blight risk also means keeping spray intervals tight is critical, “adopting a standard seven day spray interval if high pressure is present.” Alternatively some flexibility can be introduced in the programme if you hit a spell of prolong dry weather.
Michael believes a prompt start to the programme is a necessity.” In practice this now means we are recommending growers kick off blight control programmes really very early, at 50-60% emergence, to ensure crop remains free of blight.
“If we get blight into crops at an early stage we can have significant problems trying to then control it. We need to be ahead.”