The effect of inter-planted wattles on the establishment of eucalypts planted on forest sites affected by Phytophthora cinnamomi.  I. W. Smith, G. C. Marks, G. R. Featherston and P. W. Geary.  September 1988.  14pp. (unpubl.)

SUMMARY

The feasibility of using wattles as a nurse crop to reduce the impacts of Phytophthora cinnamomi on planted eucalypts was examined in two field experiments established on forest sites in South and East Gippsland severely affected by 'dieback'.

In the Mullungdung State Forest, South Gippsland, Silvertop, a disease-sensitive eucalypt species, was planted alone and in a mixture with each of four wattle species. On a similar site in the Waygara State Forest, East Gippsland, Silvertop and two tolerant species of eucalypt (Southern Mahogany and Red Ironbark) were inter-planted with and without Sallow Wattle.

The results showed that, within three years of planting, about 50 and 60 percent of the disease-sensitive Silvertop had died at Mullungdung and Waygara respectively, with most losses being recorded within the first six months. At Waygara, subsequent mortality was associated with periods of heavy rain during spring and summer. Losses among the disease-tolerant species were low.

For each eucalypt species at each site, mean height growth was significantly greater when inter-planted with wattles. This response was also reflected in diameter growth at Mullungdung.

Spot measurements of soil moisture after heavy rain at the Mullungdung site showed that the soils were considerably drier under the wattle canopy. At Waygara, a delay in the wetting cycle of the soil was also recorded in plots containing wattle.

The nurse crops of wattles were unable to protect Phytophthora-susceptible eucalypts on disease-prone sites due to high early mortality. However, on the basis of the observed growth responses, inter-planting of wattles when establishing eucalypts on infertile sites is worthy of further examination.

Also published:

Smith, I.W., Marks, G.C., Featherston, G.R. and Geary, P.W. (1989)  Effect of interplanted wattles on establishment of eucalypts planted on forest sites affected by Phytophthora cinnamomi.  Aust. For. 52: 74-81.