Effect of cool season grazing on lucerne production and aphid populations.

In a P-year Wairau lucerne trial, plots were grazed on a 3or 6weekly rotation; Half of each plot was hard grazed in June to control overwintering aphids. In the second year a spring/autumn spraying was applied. June grazing reduced aphid populations in spring from 37 to 3 per stem, and gave no significant difference in dry matter yield. Three-weekly spelling, although reducing aphid numbers, halved plant populations and root weight and markedly decreased dry matter yield. In the second year, 6-weekly spelling yielded 13 120 kg/ha, and 3-weekly only 3 540 kg/ha. Spraying of aphids increased yields, but not significantly. The results show that cheap methods of controlling aphids in lucerne can be developed using grazing management.