Carrot virus strikes in Lancs
By Jeremy Hunt
PARSNIP yellow fleck virus, which was identified on many of last years carrot crops, may not be controllable by pesticides and could be the cause of violet root rot.
Symptoms include stunting, yellowing or reddening of the foliage, wilting and, in extreme cases, complete die-back of the foliage. A creamy-brown stain or rot is apparent when the crown of the carrot is cut.
PYFV differs from carrot motley dwarf virus, affecting plants at random rather than in patches. Recent observations suggest pesticide treatment had limited effect.
Most aphicides were too slow in taking effect and did not prevent the relatively short aphid feeding periods responsible for transmitting the virus. "PYFV is transmitted by the carrot willow aphid," says Lancs-based horticultural consultant Fred Tyler, who first noticed the disease last June on carrot crops in Northern Ireland.
"Eggs hatch in early spring and the aphid passes through 2-3 generations on its woody winter host plant – especially white willow and crack-willow – before developing into winged forms which migrate to other host plants including cow parsley and carrots when conditions are suitable.
"The main period of immigration on to carrots is late May until mid-June. It is essential growers check their pesticide programme will control carrot willow aphid and not just carrot root fly," says Mr Tyler.
Carrot roots affected by parsley yellow fleck virus may assume a cigar shape, show die-back symptoms on the primary root tip or some secondary root tips.
These plants have later developed symptoms identical to those associated with crown rot. Some scientists now believe parsnip yellow fleck virus may be the primary agent responsible for this disorder. Benefits from fungicide sprays for crown rot may have only limited the development of secondary pathogens on damaged tissues, they suggest.
lA proposed four-year MAFF LINK project hopes to develop advice to help growers combat carrot virus spread. *
PYFV threat across several counties
PYFV has been identified on crops in Yorkshire, Nottinghamshire and Lancashire this year.
Leading Lancashire grower Bob Travis says he first noticed the disease on carrots last year. Rejected carrots among loads bought-in to his washing plant near Ormskirk from the eastern counties in recent weeks have included some showing PYFV.
"The more I see of this disease and the more I talk to the virologists it would appear to me that crown rot is an extension of the PYFV," says Mr Travis. He advises growers to check crops closely this season, examining the underside of leaves closely to detect signs of attack. Migration of carrot willow aphid has just started and is likely to continue until mid-June, so several sprays will be required for effective control, he adds.