Bulletin of Entomological Research

Table of Contents - 1976 - Volume 66, Issue 01  

Original Articles

Effects of groundnut sowing date and plant spacing on rosette virus disease in Malawi

J. A. K. Farrella1 p1

a1 Agricultural Research Council of Malawi, Chitedze Agricultural Research Station, P.O. Box Lilongwe, Malawi

Abstract

In a series of field trials at Chitedze, Malawi, groundnuts were sown at spacings of 30 cm, 7·5 cm and 2·5 cm within rows 90 cm apart. Contrasting sowing dates were approximately 1 December and 1 January. Immigration of alatae of Aphis craccivora Koch, monitored on observation plots, commenced 5–6 weeks after the emergence of early-sown groundnuts. Numbers of immigrant alatae were significantly greater on late-sown or open-spaced than on early-sown or close-spaced groundnuts, and were correlated with numbers of randomly distributed primary rosette virus infections. During observations, more alatae landed on 56–60-day-old plants than on 85–112-day-old plants. Similar numbers landed on 11–26-day-old plants at 30-cm and 2·5-cm spacing, but significantly more aphids settled on 30-cm spacing. The incubation period of rosette virus was consistently longer in 2·5-cm than in 30-cm spacing, and increased with plant age at inoculation. The virus was transmitted from a low proportion of infected plants before the appearance of rosette symptoms, and from a high proportion of plants snowing symptoms. The rate of spread of virus transmissions from inoculated sources within the crop varied significantly with spacing as 30 cm > 7·5 cm > 2·5 cm. Secondary spread of rosette varied, approximately, with the numbers of aphids per infected plant.

(Received September 02 1975)

Correspondence:

p1 Present address: Entomology Division, Department of Scientific and Industrial Research, Private Bag, Christchurch, New Zealand.