Wilt moves in on UKpotatoes
VERTICILLIUM wilt, a well-known scourge of strawberries, could be hitting potato yields.
Although a common problem in North America, Israel and Southern Europe, it was not considered a threat here. But ADAS work shows the disease can halve UK yields too.
Occasional cases of verticillium wilt have been identified in diagnostic laboratories. But Tom Locke, plant pathologist at ADAS Rosemaund believes the typical patchy, early senescence is too often blamed on nematodes or drought stress.
"I suspect the importance of verticillium wilt is seriously underrated. We know the disease is quite widespread in UK soils. Strawberry growers know potatoes can increase pathogen levels. But no one knew if it affected the potato crop itself or how different varieties might be affected."
MAFF-funded work, started in 1993, showed the disease was a common cause of premature crop death. It was found in 20 out of 21 fields where crops had died early. Of those, nine were the variety Record. Other trials in the same year showed Estima was more susceptible than Piper.
Yield trials in the following two years showed losses were as high as 50% in Record, Estima and Saturna. Pipers output is typically cut by a quarter.
This year a trial investigating crisping varieties was established on an infected site near Newport, Shrops, with PMB funding.
"Record was not as badly affected on that site. That may indicate a variation within the verticillium population," says Dr Locke. "But Saturna was hit hard, suffering 38% yield loss."
A soil test is available at £170 a sample to confirm disease presence once patches are seen.
The fungus increases in the presence of its many host plants, particularly linseed. Pulses and other broad-leaved crops can maintain levels. No chemical control exists, apart from with soil fumigants such as methyl bromide.
Early Canadian work has shown that adding organic matter such as soya bean meal or blood and fishmeal may help. "It needs 1-2% by weight of soil to a depth of several inches. But we may be able to refine that," says Dr Locke.
Under-rated threat – verticillium wilt can cause high yield losses.
• 50% yield loss possible.
• Main crisping varieties hit.
• Early dieback easily confused with nematode or drought stress.
• Soil test to identify.