Biggest blight threat in years
INTENSE disease pressure and problems getting crops sprayed during wet weather mean blight poses the biggest threat to potato crops in two decades.
Stretched spray intervals and product wash-off left fast-growing haulm unprotected in many crops, warns national blight specialist Nick Bradshaw. "I have never seen blight pressure like this in 20 years with ADAS."
Although last weekends good weather let growers catch up with applications, extreme vigilance is still needed to prevent blight estab-lishing, Mr Bradshaw warns. "It is still very early in the development of maincrop yield – a lot of tubers are no bigger than marbles."
ADAS has confirmed widespread infection, particularly in Russet Burbank, Karlena and Saturna, untreated dumps and volunteer potatoes in sugar beet and vining peas. Check crops regularly, focusing upon sheltered areas of fields, areas around obstacles like pylons, urges Mr Bradshaw.
If blight is found spray out discrete patches with Reglone (diquat), and then use two tin-based sprays at 10-day intervals with Curzate M (cymoxanil + mancozeb), Invader (dimethomorph + mancozeb) or Shirlan (fluazinam) in between, ADAS advises. Curzate M is the only one of the three with no buffer zone restrictions, it adds.
Where no blight is yet apparent apply one of the last three fungicides as soon as travel is possible, even if it results in crop damage. Repeat with a different product five to seven days later and another different product five to seven days after that if blight conditions persist. *