Blight Control Strategy 2010

Dumps are a major source of blight infection and good hygiene is crucial - adopt a zero tolerance approach to re-growth.

With the loss of dichlobenil (Casoron G), the only option for preventing re-growth on dumps is by covering with black plastic to stop light encouraging growth.  They should be checked regularly to ensure that the covering remains intact and any re-growth 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 will also be alerted to the risk of blight by text messaging, contact Stephen Bell on 02894 426766 to register your number.

Due to changes in the blight population, control programmes need to be revised.  The Blue 13 blight genotype is now present at over 50 percent of the population in Northern Ireland.  This strain is phenylamide-resistant, so it is advisable to reduce reliance on products containing phenylamides (for example, Epok, Fubol Gold, Intro Plus).  If you have any of these products in store, apply them early season, no more than two applications and keep intervals tight.

Where new product is required for early season use, the only other spray containing a systemic (propamocarb) is Consento, since the other products containing this active (Merlin and Tattoo) are no longer available.  In the past, we have emphasised the importance of using systemics for early sprays to protect new developing foliage.  However, recent trials at Newforge have shown that translaminar Revus is very effective in controlling foliage infection early season, probably because it is re-distributed into the new leaves as they expand.  A tank-mix of Revus + Shirlan is the best option as it combines foliage and tuber blight protection.

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 protected from blight until the haulm is dead.

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