Flexibility is the key to blight control

UK - September 24, 2007

As the potato harvest progresses, many growers will look back on this year as being a very difficult season, with extreme blight pressure, difficult weather conditions, limited spray opportunities and some blight products in tight supply.  Those growers that kept their spray intervals tight and used robust fungicide programmes with tuber blight protection right through to harvest are the ones most likely to achieve a quality crop at a good price, according to Dow AgroSciences.

"According to the BPC's Fight Against Blight service, it has been a record year with over 300 blight incidences reported and confirmed as positive - more than twice the number of incidences recorded before.  This has also been the case for the Smith periods and near misses in the BlightWatch service, with double the average Smith periods recorded.  It was also the earliest year for blight, with the first confirmed outbreak being in late April in the West.  Growers have had to run the gauntlet of blight control from early on in the crop's life right through the season.  They have been applying at short intervals, juggling their blight treatments throughout the season and often mixing kick-back products such as cymoxanil with protectants such as Electis which offer tuber blight protection," says Andy Leader, Principal Biologist for Dow AgroSciences.

"Because of the unprecedented disease pressure, this has been a year where flexibility of label recommendations has been invaluable and why the protectant fungicide Electis has found an important place in many programmes."

Electis has approval for up to ten applications per season, one hour rainfastness, excellent blight protection, proven zoospore activity, compatibility with desiccants and a seven day harvest interval, offering more flexibility than many other blight fungicides, says Andy.

"Dithane NT (mancozeb), cymoxanil + mancozeb (Curzate M WG) and fluazinam (Shirlan) have no restrictions on the number of sprays and have been popular choices this year.  Other fungicides have limited number of applications or consecutive sprays and this has made product choice decisions much more difficult.  For example cyazofamid (Ranman) and benthiavalicarb-isopropyl + mancozeb (Valbon) can be used up to 6 times.  Fluopicolide + propamocarb (Infinito) can be applied up to 6.4 l/ha per crop, so at 1.6 l/ha has a maximum of 4 sprays."

"On top of this, growers also had to take into account label restrictions based on fungicides with the same mode of action.  For instance, mandipropamid (Revus), benthiavalicarb-isopropyl + mancozeb (Valbon) and dimethomorph + mancozeb (Invader) are all from the carboxylic acid amide (CAA) group.  Mandipropamid therefore has a maximum four sprays per crop, which can be applied up to a maximum of three applications in a block and should then be alternated with non CAA chemistry.  The planning process can be very complicated for some products - but not for Electis," says Mr. Leader.