Written question asked by Duke of Montrose (Conservative), in the House of Lords. It was answered by Lord Henley (Conservative) on Wednesday, 16 February 2011.

Trees: Phytophthora

Question: To ask Her Majesty’s Government whether they expect the recent cold weather to have had any beneficial effect on the Phytophthora infections.

Answer: There are two Phytophthora species causing the current disease outbreaks on rhododendron, ornamentals, trees and heathland plants. Research at the Food and Environment Research Agency is showing that the two species, P. ramorum and P. kernoviae, are very different in their sensitivity to environmental conditions and that growth and sporulation of P. kernoviae is limited by extremes of heat and cold, whereas P. ramorum is more tolerant. These results may indicate that the recent extreme cold weather might have adversely affected the survival and spread of P. kernoviae, but they also indicate that P. ramorum may have been relatively unaffected by such conditions. It is not possible to state with confidence that the cold weather will have reduced levels of inoculum or restricted further spread of the pathogens in the natural environment, as there are many other factors involved in the epidemiology of these organisms. The relative rates of epidemic spread in relation to weather factors will continue to be closely monitored over the next 12 months.

Secondary information