Searching for clover root weevil (Sitona lepidus) resistance/tolerance - A progress report

Abstract

The decimation of white clover in Waikato and Bay of Plenty pastures owing to the invasion clover root weevil (CRW) initiated an extensive screening of legume germplasm to identify plant material that could survive and remain productive under high CRW pressure. A total of 50 000 plants from 275 lines and six species, were planted on seven commercial farms and evaluated for tolerance/ resistance to CRW under conventional farming practices. Plant productivity and level of CRW damage were both highest on white clover. Significant CRW damage was also observed on red clover and caucasian clover, but not on birdsfoot trefoil, lotus major or lucerne. However, the productivity under stock grazing of the latter three species was not sufficient to consider them suitable alternatives to white clover. Within the white clover lines there was encouraging variability in the level of CRW damage, and in the ratio of damage to shoot production. While root damage is of greater importance than shoot damage, the latter reflects CRW activity and egg deposition and is a good indicator of likely larval development and root damage. Factors such as farm type (dairy farms versus dry stock farms) had some influence on shoot production, but very little influence on CRW damage. Climatic conditions appeared to have strong influences on clover shoot production and CRW damage, with dry conditions from late spring to early autumn having a particularly suppressive effect on CRW damage and CRW population growth. Top performing lines have been selected from this screening and are currently being evaluated in more detail under high CRW pressure. Keywords: clover, clover root weevil, plant screening, Sitona lepidus, tolerance, Trifolium repens