Abstract
The effects of climate on both host and parasite have been studied for two serious crop diseases of west Scotland.
First‐early Epicure potato crops in the coastal belt of Ayrshire and Wigtownshire make appreciable tuber growth before the soil temperature rises to 43°F, which is the minimum temperature of activity of the potato‐root eelworm, Heterodera rostochiensis. By the time the earliest crop is lifted early in June, cysts of the eelworm are white or yellow in colour. It is shown that such cysts make little contribution to the permanent soil infestation, thus explaining the low infestations of land consistently devoted to the growth of first‐early crops. Later lifting allows the cysts to become brown, and such cysts add considerably to the permanent soil infestation. The initial period of eelworm‐free growth on first‐earlies limits the loss in yield to 30 to 40 per cent, as compared with 80 to 100 per cent loss if the variety Epicure were planted later, at the time for a maincrop variety.
Correlation coefficients have been calculated for comparisons over eight years between the percentage of club‐root disease on swede turnips and monthly means of air and soil temperatures, bright sunshine and rainfall, for the separate months from May to October. Significant and near‐significant correlations show that a low incidence of the disease is associated with a relatively high soil temperature in July, relatively high amounts of bright sunshine in June, July and September, relatively low rainfall in September and relatively high rainfall in October.
The differential effect of soil temperature on host and parasite with potato‐root eelworm is a ‘disease‐escape’ mechanism but the effects of bright sunshine on the amount of club‐root disease are considered to be, in the present setting, an effect upon disease involving growth of the host.