Seasonal Fluctuations in Numbers of Larvae of the Cereal Cyst Nematode (Het'Erodera Avenae) and of Pratylenchus Minyus and T'Ylenchorhynchus Brevidens in Soil

Abstract

The seasonal emergence of H. avenae larvae in the field was studied for 3 consecutive years. Larval numbers were highest during late autumn and winter when levels of soil moisture and soil temperature were favourable for emergence. Low rainfall in the autumn may delay emergence. In a glasshouse experiment, soil from a field naturally infested with Heterodera avenae, Pratylenchus minyus and Tylenchorhynchus brevidens was exposed to five moisture regimes. In soil held at field capacity there was a low emergence of H. avenae larvae and few eggs were viable after 5 months. In autumn and winter, larval emergence was good in soil constantly maintained at 60% field capacity, and was further increased in soil subjected to wetting and drying cycles. Larvae were absent from the soil in late spring and summer. The patterns of hatching and emergence explain the increased severity of nematode disease following high autumn rainfall. Although the seasons in Australia and Northern Europe are opposite, larvae emerge during, approximately, the same months of the year. Emergence appeared to follow a lowering of temperature in autumn. In Australia, this may be as important for optimum emergence as adequate soil moisture, but there is no evidence for a very low temperature requirement prior to hatching. In the following autumn, hatch from eggs remaining in cysts demonstrated dormancy or diapause. In air-dry soil, eggs showed little loss of viability after thirteen months storage and good emergence followed soil wetting. This contrasts with European observations. P. minyus and, to a lesser extent, T. brevidens showed a good capacity to survive in dry soil and about 50% of the initial populations survived for fifteen and nine months respectively.