A relatively new UK sugar beet disease, widespread elsewhere in Europe and the US, could threaten northern crops.

In 2003, 60% of samples from the York factory contained Beet chlorosis virus (BChV), one of the three virus yellows species, says Broom’s Barn virologist Mark Stevens.

“It has really exploded, though we don’t know why, and even this year well over 50% of Yorkshire leaf samples that showed yellowing again tested positive for this virus.”

That is twice the level in the rest of the UK, where Gaucho (imidacloprid) seed treatment is widely used.

“The biggest problem we saw was on a farm near Goole where 70% of the plants were infected even though they had been sprayed with aphicide twice in the summer.”

BChV has a much bigger potential impact later in the season than beet mild yellowing virus (BMYV), warns Dr Stevens.

The yield penalty, at about 15% from early July infection, is almost twice that from BMYV, he says.

Where northern growers relied solely on aphicide sprays this season (ie no seed treatment) BChV levels in some fields are up to 20-25%, he estimates.

Part of the problem is that some growers still insist on applying broad-spectrum insecticides, such as pyrethroid-based products, rather than the preferred pirimicarb, colleague Mike May believes.

“They kill or repel aphid predators, which just makes matters worse and crops suffer as a result.”

BChV infects only sugar beet and related species and cannot be transmitted by the potato aphid (Macrosiphum euphorbiae), notes Dr Stevens.

So, in theory, it should be less of a problem than BMYV, which is harboured by several weeds, notably shepherd’s purse, chickweed and groundsel.

While sugar beet volunteers in set-aside may be acting as a source of infection, he suspects undelivered sugar beet and fodder beet retained to feed livestock could be the main culprits.

andrew.blake@rbi.co.uk