Getting it right with potato blight control

There has been good progress with planting in the fine weather over the past four weeks and many crops are starting to emerge through the soil.  It is essential to stop blight now by preventing the initial source of inoculum from new growth on waste potato dumps.  This is particularly important this season when crops are already well advanced.  This is also the time to plan your blight control strategy for the season ahead.

The first incidence of potato blight in Northern Ireland this year has been detected on plants growing on waste potatoes in County Down.  Dumps are a major source of blight infection and their management must be incorporated into the blight control strategy.  The key to preventing the risk from blight on dumps is good hygiene and to adopt a zero tolerance approach to re-growth.

It is best to check dumps regularly, early in the season and prevent any re-growth occurring, this can be done by applying a single treatment of a residual herbicide containing dichlobenil (for example, Casoron G).  For best results dumps should be levelled and covered with a layer of soil prior to application before any sprouts begin to grow.  Dumps should then be covered with black plastic to stop light encouraging growth and checked regularly for re-growth.

On dumps where potatoes have started to grow diquat and paraquat (for example, PDQ) should be used to burn off any green foliage.  Relying on a late application of these herbicides is a high risk strategy as the foliage could already be infected with blight.

Start protecting your crop from blight whenever the first blight warning is issued or when plants meet within drills (whichever is earlier).

Blight warnings, based on weather conditions which favour infection will be issued by AFBI and CAFRE throughout the season via the radio, farming press, Blightline (02890 382372) and Blight-Net which can be accessed via the internet at www.ruralni.gov.uk/crops/potatoes.  Blightline and Blight-Net will be active from 5 June 2007.  Growers will also be alerted to the risk of blight by text messaging, contact Stephen Bell on 02894 426766 to register your number.

The first spray should be with a product with systemic activity (for example, Epok, Fubol Gold, Merlin, Tattoo) continue with a translaminar  (for example, Curzate, Infinito, Invader, Revus) or protectant (for example, Electis, Ranman, Shirlan), check the spray intervals on the label and ensure they are not exceeded.  Fungicide timing and good coverage are critical, angled jet nozzles with a medium spray quality give better canopy cover at all stages of growth but particularly up to and including full canopy cover at which point the crops become more open allowing better coverage.

The programme should be completed with at least three sprays of a product with tuber blight activity (Infinito, Ranman, Shirlan).  It is critical that the crop is protected until the haulm is dead, blight can attack green leaves when the crop is senescing or even after a desiccant has been applied.  To reduce the risk of tuber blight a blight spray should be applied with the desiccant and protected from blight until the haulm is dead.

Remember to check your buyer’s protocols for a list of approved chemicals.

Stephen Bell and Louise Cooke examining foliage blight from a recent outbreak on waste potatoes from County Down