26 September 1997

Survey to test brown rot risk to potato crop

MORE needs to be known about the latest outbreak of brown rot (News, Sept 19) in Beds tomato glasshouses before the risk to downstream potato crops can be assessed.

That is the message from industry specialists. In theory water from the same infected source that was used to irrigate the Beds glasshouse tomatoes could have spread the bacterial wilt to fenland potato fields. But no reports of the notifiable disease in the tuber crop have so far emerged this year.

Brown rot, a warm weather disease and the main limit to potato production in many parts of the world according to MAFF, first appeared in the UK in 1992 and again in 1995 in the Thames Valley. It was also found in a host weed, bittersweet, in the River Witham in Lincs, but infected plants were destroyed.

"Currently there is nothing we can do except be very vigilant," says Tim Berry, agronomist for MBM Produce based at March, Cambs. About 75% of the firms supplies come from irrigated crops, he notes.

Stuart Edwards of packer Fenmarc says it is too early to comment sensibly. "We really need some more authoritative guidelines." Sweeping advice not to irrigate next years crops is clearly premature until the extent of the problem is determined, he suggests.

Under a draft EU directive growers would be banned from irrigating crops with water known to be infected with brown rot bacteria.

Experience from the two previous incidences in UK crops is encouraging, says the ministrys Plant Health and Seeds Inspector Brian Ellham. After the first, symptoms were detected in groundkeepers the following summer. "But none have been found there since. It seems it can be eradicated from potato fields in our climate."

Central Science Laboratory experiments show that transferring the infective organism, is harder than first thought, says Dr David Stead. "We have failed to infect bittersweet by putting it in water known to be infected." That makes it hard to assess risks downstream of disease outbreaks, he says.

"I am concerned, but we dont want to over-react," says Suffolk-based ADAS consultant Colin Smith. "We have been here before with the Oxfordshire outbreaks."

One possibility is that the current infection arose from domestic waste water contaminated by peelings, says the BPCs Dr Mike Storey. But extra measures to tighten the already vigorous inspections on imports are unnecessary, he believes. "I am confident we have the science in place to deal with this."

Staffs-based microbiologist Tom Stones believes washings from plants processing imported ware could spread the disease in the UK. But all those bringing in potatoes from the main risk areas have been visited and nothing untoward has been found, maintains Mr Ellham. More resources would clearly help, he concedes. "But we have done what we think is reasonable."n

BROWNROT

&#8226 Beds glasshouse tomatoes hit.

&#8226 Origin of infection unknown.

&#8226 Ongoing official investigation.

&#8226 Downstream irrigation worries.

NFU VIEW

"We are obviously concerned about the latest outbreak," says NFU potato committee chairman Richard Watson Jones who farms in Shropshire.

With bacterial concentration apparently a key to infection, the results of a ministry survey of sewage outfalls, which might be a source of the disease, are keenly awaited, he notes.

The NFU, which is working closely with the ministry on the draft EU brown rot control directive, is concerned that infected imported ware remains a potential threat, he adds. "We need to ensure that the ministry satisfy themselves that there is no risk to UK production from that particular source."