Seasonal Fluctuations in Population Densities of Pratylenchus Penetrans Under a Rye-Tobacco Rotation in Ontario 1)

Abstract

Seasonal changes in soil and root population densities of Pratylenchus penetrans (Cobb), and changes in soil moisture and temperature, were studied at weekly intervals for 28½ months under a rye-tobacco rotation in Ontario, Canada. In general, population densities tended to be low in the summer and high in the fall, but the seasonal changes were not consistent from year to year. The results indicate that it is very difficult to predict population densities much in advance of the tobacco crop and that density determinations should, therefore, be made in the fall or spring rye crop prior to tobacco planting. Winter mortality of P. penetrans in both soil and roots ranged from 40-65%. Fall and winter fallow in place of the normal rye cover crop reduced the number of P. penetrans and increased the growth of the ensuing tobacco at mid season.