Potato blight control 2011

Dumps are an important source of blight infection and good hygiene is crucial.  To prevent re-growth cover dumps with black plastic to promote rotting and stop light encouraging growth.  Check dumps regularly to ensure that the covering remains intact.  Any growth should be sprayed off with glyphosate and covered.

Fungicide timing and coverage are critical.  No matter how good the product, nothing can make up for a late start, stretched intervals or areas left unprotected, which allow blight to get a foot-hold in the crop.  Angled jet nozzles with a medium spray quality give better canopy cover at all stages of growth.

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 are issued by AFBI and CAFRE throughout the season via the radio, farming press, Blightline (02890 382372) and Blight-Net.  Blightline and Blight-Net will be active from the first week in June.  Growers can be alerted to the risk of blight by text messaging, contact Iain Johnston on 028 94426770 to register your number.

Formulations including the novel fungicide ametoctradin (Initium) are now approved.  This non-systemic fungicide absorbs into the wax layer on the leaf surface is reported to provide good rainfastness and long-term protection.  It is marketed as Resplend (formulated with the translaminar dimethomorph) and Decabane (with mancozeb).  Resplend is recommended for both early season application during rapid canopy growth and late season use, while Decabane is intended to be used mid-season.  These formulations were trialled for the first time at AFBI Newforge in 2010 and performed well, but further evaluation under more testing conditions is planned.  Other new options this year include Morph, a straight dimethomorph formulation, to be used as a tank-mix with fluazinam (or mancozeb), and a higher approved rate of 2.4 kg/ha for Invader (dimethomorph + mancozeb).

The phenylamide-resistant A2 blight genotype Blue 13 was present in over 50 percent of outbreaks sampled last year so it remains advisable to avoid relying on products containing phenylamides (for example, Epok, Fubol Gold, Intro Plus).  For early season use during rapid growth, the only non-phenylamide systemic is propamocarb, in Consento and other formulations.  Consento has proved an effective option for this stage in trials at AFBI Newforge.  The translaminar mandipropamid (in Revus) has also performed well in controlling foliage infection early season in our trials, probably because it is re-distributed into the new leaves as they expand.  If using Revus, a tank-mix of Revus + Shirlan is the best option as it combines foliage and tuber blight protection. ‘Resplend’ is also an option at the early season stage.

Continue the programme with a translaminar (for example, Curzate, Infinito, Invader, Revus) or protectant (for example,  Electis, Ranman, Shirlan).  Note that both Revus and Invader contain ingredients which have the same mode of action (CAA fungicides); to reduce the risk of resistance, no more than three consecutive applications of these products may be applied and the total number of applications is also restricted to no more than half of the intended spray programme (for further advice see product labels and consult www.pesticides.gov.uk ).

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 and this can lead to tuber infection.   To reduce the risk, a fungicide should be applied with the desiccant (check product labels for approved tank-mixes) and if necessary further fungicide applications made until the haulm is dead.

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

If you have any queries, please contact your local crops adviser.

Londonderry/Antrim: Robin Bolton 028 77721823

Tyrone, Fermanagh, Armagh: James Knox 028 94426786

Down: David Crawford 028 44618075