Improvement in a foxglove aphid density assessment in soybean [Glycine max] field
2005
Sakakibara, M.(National Agricultural Research Center for Tohoku Region, Morioka (Japan)) | Sakai, J.
To improve the method of assessing foxglove aphid (Aulacorthum solani) population density, the effect of sample units on the number of aphids was evaluated in the summer of 2004 in two soybean fields in Morioka City, Japan. There were some disparities in the number of aphids among sample leaves, and there are some indications of the improvement regarding the assessment method. First, more aphids were observed on the middle leaflet than on the right and left leaflets of a fully expanded trifoliate leaf: therefore, a trifoliate leaf should be appropriate as a sample unit. Second, more aphids were observed under the leaves that show many yellow spots on the upper side than under those with few yellow spots caused by aphid feeding; therefore, sample leaves should be chosen without predetermining the number of yellow spots. Third, many aphids were observed at the middle part of the plant in late summer and at the upper part in early autumn; therefore, sample leaves from each part should not be mixed. Fourth, significant differences in aphid population density between fields that differed in insecticide treatment were observed when 30 trifoliate leaves were sampled; therefore, 30 trifoliate leaves are likely to be sufficient for the detection of aphid population density differences among fields. Last, there were no significant relationships between adult number and nymph number on the same leaf when aphid population density was not very high, suggesting that adult aphids move frequently among soybean leaves, plants and fields; therefore, adults and nymphs should be counted separately.
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