Why the concern?
Neither of these serious bacterial diseases of potato occurs in Northern Ireland and everyone should strive to keep it that way. Both are quarantine diseases listed in the EC Plant Health Directive and are notifiable in the UK. The major yield loss caused by both is through rotting of tubers. In the USA annual losses from Ring Rot have been as high as 15%, while Brown Rot is the main limiting factor in potato production in many parts of the world. If either were to become established in Northern Ireland, not only would our potato industry suffer direct yield losses but the knock-on effect on exports from our seed-potato industry could be substantial. Once established, the costs of control, especially for Ring Rot, could be very high.
Control of these diseases requires vigilance by all sectors of the industry; from growers through to merchants, packers and retailers.
Brown Rot is caused by the bacterium Ralstonia solanacearum and is widely distributed in warm temperate areas of the world. In Europe there is a history of its presence in Portugal, Italy and Greece, plus an outbreak in Sweden in the 1970’s. More recently, outbreaks have occurred in Belgium and the Netherlands. A number of cases in ware crops have been recorded in England. Several waterways in England are currently contaminated with the Brown Rot bacterium and eradication measures on these waterways have been ongoing in recent years. The finding of Brown Rot in a seed crop in Wexford in 2007 was the first detection of the disease in the island of Ireland. Brown Rot is still not considered to be established in the EC.
The disease can cause wilting of the potato plant but the symptoms you are most likely to see is in the tubers. The initial symptom is brown staining of the vascular ring (hence the name "brown" rot) which later rots completely. A grey-white ooze may exude from the eyes and heel end of the potato.
The mostly likely sources of field infection are infected seed potatoes and contaminated waste material dumped either on fields or into water courses from which potato fields are irrigated. Spread within and between fields is possible via irrigation water, on equipment, or by insect or nematode transmission. In some northern European outbreaks, irrigation with contaminated water has been implicated as a key factor in disease spread. The bacterium itself is able to move through the soil and can survive in it for long periods when potato groundkeepers or solanaceous weeds, e.g. Bittersweet (Woody Nightshade) and Black Nightshade are present.
Ring Rot is caused by the bacterium Clavibacter michiganensis subsp. sepedonicus. Widespread in North America and the old USSR, it is also established in Northern and Eastern Europe and, within the EC, in Denmark, Germany, Finland and Greece. The first finding of Ring rot in GB was in November, 2003 in a Welsh seed potato crop planted with seed produced in the Netherlands. Ring rot could easily become established under our conditions because it is favoured by cool climates.
The disease can cause plants to wilt but, as with Brown Rot, you are more likely to come across symptoms in tubers. The initial symptom is a soft cheese-like rotting of the vascular ring,hence the name "ring" rot. In severe cases this rots completely and the skin of the potato may crack. Disease spread is largely by vascular infection of daughter tubers derived from infected seed. The bacterium is thought to be unable to overwinter in the soil but will do so in groundkeepers and debris from infected crops.
Infected groundkeepers lifted at the same time as an otherwise clean seed crop, can infect that crop. Bacteria can also survive and remain infectious on potato bags, barn walls, machinery and other equipment that have been contaminated by rotting ooze and, although this is not the main means of disease transmission, it can make eradication of the disease very difficult.
As with Brown Rot, the return of contaminated potato waste to fields is a possible source of infection. Unlike Brown Rot, though, the bacterium does not multiply in plants living in watercourses.
What is being done to help?
Under the terms of the EC Plant Health Directive and the Plant Health (Northern Ireland) Order 2006, importation of material carrying these diseases is prohibited. In addition, the EC Ring Rot Directive and Brown Rot Directive lays down control measures specifically aimed at eradicating these diseases.
The Department of Agriculture, Environment and Rural Affairs (DAERA) carries out an annual survey of potato stocks from seed producers and from a random selection of ware producers. Stocks grown from both local and imported seed are also surveyed annually to look for latent infection. These samples are tested for both Ring Rot and Brown Rot at Agri-Food and Biosciences Institute (AFBI) Potato Diseases Laboratory, Applied Plant Science Division. Water from rivers receiving discharges from premises washing or processing potatoes, especially imported potatoes, and roots of Solanum dulcamara plants in the river are tested for the presence of the bacterium causing Brown Rot.
Recent legislation requires growers and merchants to notify DAERA in advance of imports of seed potatoes from outside Northern Ireland. This includes imports from Scotland and the Republic of Ireland as well as imports of seed from England and mainland Europe. DAERA will try to sample all imported seed stocks which are from areas with a history of Brown Rot and Ring Rot outbreaks. A test in advance of planting could detect these diseases and prevent growers from planting infected stocks.
Consignments of imported ware potatoes are monitored by DAERA inspectors. Imports at processors premises are inspected and sampled with special attention given to stocks originating in areas known to have a history of these diseases.
What can you do?
Only plant classified seed
All classified seed potatoes produced in the EC are derived from material tested and found free from these diseases. Using home-saved seed does not provide the same guarantee of health.
Groundkeepers are a key factor in the long-term survival of both diseases. Their control removes an important source of disease inoculum.
Regularly clean and disinfect all machinery, equipment, containers, vehicles and storage facilities used during potato production. Dirty machinery spreads infection between stocks.
Keep potatoes for planting away from ware grading lines
Do not plant any potatoes that have passed over machinery handling imported ware potatoes. Bacteria from rotten potatoes can easily transfer to the next stock to be graded. Prepackers and processors should never return “seed” to growers
Don't dump waste on agricultural land Discarded potatoes and waste from potato processing could both harbour these diseases and should not be dumped back onto fields. If possible, dispose of all potato waste at an approved tip or by incineration.
Feeding potatoes to livestock
If feeding raw potatoes spread the slurry produced on fields for grazing rather than on ground to be planted with potatoes.
Keep a good look out
If you see any of the symptoms described above please contact Plant Health Inspection Branch - phone 0300 200 7847, email email@example.com - or your DAERA potato inspector.