Helicoverpa armigera egg counts made in 1973 and 1975 from cotton fields within four blocks of the Sudan Gezira were compared with rainfall information from a network of rain gauges. Aspects of rainfall in the 6 days before an egg count were analyzed in conjunction with the count. In the 1973 season there was a significant rise in the frequency of egg counts above spray threshold, following many days with rain and high total rainfall. Counts recently preceded by rainfall were also more likely to be above threshold. In 1975, only the number of rain-days was significant. Over the 2 years studied, the mean probability of an egg count being above threshold was 0.28. Given details of recent rainfall however, the probability could be estimated more accurately, and was found to range from 0.11 where no rain had fallen, to 0.48 in those areas where rain fell on 3 days out of the previous 6.
Madden, A.D.; Haggis, M.J.; Holt, J. Helicoverpa armigera oviposition on cotton in the Sudan Gezira associated with rainfall. Crop Protection (1993) 12 (1) 51-54. [DOI: 10.1016/0261-2194(93)90019-F]