Population dynamics of cabbage aphid, Brevicoryne brassicae L. (Homoptera: Aphididae) in relation to weather factors on major brassica crops in central rift valley of Ethiopia: baseline studies for the management of the pest

Abstract

Cabbage aphid, Brevicoryne brassicae L. is a major pest of cruciferous crops all over the world. The population dynamics of the pest is highly influenced by weather factors. A field study was carried out in 2018/19 at Debre Zeit Agricultural Research Center (DZARC) to determine the role of weather factors on cabbage aphid population dynamics. Four brassica crops namely Ethiopian Kale, head Cabbage, Cauliflower and Broccoli were planted on two different dates at fifteen days interval. Results revealed that, maximum aphid population of 164.7 ± 2.93 and 70.2 ± 2.64 aphid/ inch2 leaf area were recorded on the date 15/12/2018, on late planted kale and head cabbage crops, respectively. The highest mean infestation for all tested crops (22.77aphids/inch2 leaf area) was observed on late planted crops as compared to 0.82 aphids/inch2 leaf area on early plantings. Accordingly, early planted crops were 96.4% safer than late planted crops for aphid infestations. Correlation analysis showed that, the maximum temperature had a significant influence on aphid population specifically on kale crop (r = 0.676, p = 0.032). Although, the relative humidity, minimum and average temperature, rainfall and wind speed has shown none significant correlation with aphid population growth. There was variation in aphid population, crop preference and infestation peak in relation to weather factors. In general, during the experiment higher aphid population was observed on kale crop when the maximum temperature and relative humidity were < 26.750C and 72%, respectively. This study provided information on time of initial infestation and also the peak activity of the particular insect in relation to temperature. Therefore, the population peak timing reported in this study (45th SMW) is useful as a critical infestation period for scheduling cabbage aphid management practices.