17 July 1998

Early carrots hit by mystery virus

A NEW virus disease is causing havoc in early carrots this year and researchers are puzzled why it has suddenly flared up.

Trouble is common in Norfolk, Cambs, Lincs, Notts, Lancs and Yorks, but it is unclear if the disease is a new problem or an old one which has resurfaced due to the unusual season.

"We think it may be caused by the Poty virus in association with the motley dwarf virus complex, but we are not yet sure," says virologist Nicola Spence of HRI-Wellesbourne, Warks.

"We found the Poty virus on small-scale in field margins two years ago. Although it was known in the USA, it had not been reported in UK carrots before and we suspect it is at least partly responsible for this seasons trouble."

The current widespread and severe damage is being blamed on a non-persistent virus which is transmitted by migrant aphids. But it is also appearing where there were few aphids earlier in the season.

Symptoms, which are often clearer at row ends, include leaf distortion with a typical viral mottle. An infected plants youngest leaf is often dead and blackened while older ones appear unaffected.

"As well as affecting foliage of early carrots the virus also stunts roots, which become rubbery with dark staining of tissue," says Cambridge-based independent vegetable specialist David Martin of DMA crop consultants.

"In severe cases up to 40% of plants can be affected. In later maturing crops seedlings can be completely killed.

"The last time we saw similar trouble it was confined to fen early carrot crops along the Norfolk/ Cambs border, and was most common where phorate insecticide had been used. But I am very concerned that a lot of this seasons trouble is occurring where Temik was used," Mr Martin says. &#42