Impact of defoliation by Essigella californica on the growth of mature Pinus radiata and response to N, P and S fertilizer

Abstract

A study of responses of radiata pine (Pinus radiata D. Don) to fertilizer applied after thinning and the impact of repeated infestations of the Monterey pine aphid (Essigella californica Essig.) over 12years showed that the defoliation of upper crowns was exacerbated by nutrient deficiencies of P and S. Remedial treatment with NPS fertilizers in 1997 and 2003 improved average retention of foliage especially during the second 6-year period of the study when damage from annual infestations of aphids was relatively consistent. In 2003 treatment with N, NP and NPS raised N and P in foliage to satisfactory levels while the sulfur status of trees ranged from severe deficiency to satisfactory. This increased average foliage retention by 6%, 12% and 20% compared with unfertilized trees. Corresponding volume responses to N, NP and NPS over 6years were estimated at 12, 45, and 88m3ha−1 at Warrenbayne and 19, 31 and 48m3ha−1 at Stanley indicating a significant response to the remedial treatment of sulfur deficiency.There was considerable variation in aphid damage between trees irrespective of fertilizer treatment reflecting strong genetic variation in susceptibility of radiata pine to defoliation by aphids. This had a substantial impact on tree growth showing a three to fourfold difference in basal area increment over 6years across a wide range of aphid damage classes. The reduction in basal area increment was strongly correlated with average retention of upper crown foliage. Although remedial treatment with NPS increased average foliage retention from 50% to 70% therefore reducing aphid damage by 20%, a significant proportion of trees (around 25%) continued to be severely defoliated by aphids and did not respond to fertilizer. The reduction in basal area growth due to defoliation of trees treated with NPS fertilizer was estimated at approximately 30% over 6years. Selective removal of susceptible trees at thinning was shown to be a feasible management strategy without any unacceptable changes in stand structure and reduced potential defoliation by aphids by 15%. This together with remedial fertilizer treatment provides a viable option for the management of radiata pine plantations to reduce aphid damage and improve stand productivity.