Accumulated Temperature and Rainfall as Measures of Nematode Development and Activity

Abstract

Because the females of sedentary root endoparasitic nematodes are able to obtain an uninterrupted supply of food and water, temperature is the factor determining their rate of development in a country like the British Isles where climatic extremes are not experienced. When accumulated temperature above an assumed basal development temperature of 4.4° C is plotted against time, the curves produced closely resemble the curves for the development of Heterodera schachtii on sugar beet. The activity of root ectoparasitic nematodes is influenced by temperature and rainfall. The time during which nematodes are active following rainfall is proportional to the amount that has fallen. An index of activity was derived from accumulated temperature and rainfall and tested against the area of sugar beet reported as stunted by Trichodorus and Longidorus from 1963 to 1974. A significant correlation was obtained between log area stunted and the index calculated over a 5 week period embracing the month of May, but not between log area or accumulated rainfall alone. Temperature and rainfall data used in studying the development of H. schachtii and the activity of Longidorus and Trichodorus were from single weather stations distant from the infested fields. In both studies diurnal temperature fluctuations were disregarded because they are usually small 5 to 10 cm below the soil surface. For nematodes active in the soil surface where diurnal fluctuations are sometimes large, the mean temperature would underestimate the rate of activity or of development because of the Qio relationship between temperature and rate.