16 February 1996

Cold comfort for brown rot

BROWN rot can no longer be viewed as a disease of warmer climates, delegates at the ADAS Arable Centre/DowElanco conference in Peterborough heard.

Trials with Race3/Biovar2 have shown 34% infection in daughter tubers at a soil temperature of 15C. The original race gave no infection at such a low temperature, commented Denis Buckley, potato agronomist at ADAS Wolverhampton.

The bacterial infection has no chemical control, making early detection vital, he stressed. Typical symptoms are brown vascular rings when a tuber is cut, "goo" oozing from the vascular bundles and soil sticking to potato eyes.

The disease can be carried without showing visual tuber symptoms, so plant health laboratories at Harpenden are checking 640 samples from imported Dutch seed, he explained.

Up to last week 414 samples had been tested, with just one sample of Minerva testing positive. Testing is continuing at the rate of 100 samples a week, with a turn round time of about three weeks.

Mr Buckley urged growers receiving Dutch seed to label each tray of chitting seed with the relevant Dutch batch number and also to stack each batch separately. If one batch tests positive and others are not clearly segregated, all seed may have to be disposed of, he warned.