Control of some mistletoe species on eucalyptus by herbicide injection.  G. Minko and P. C. Fagg.  May 1988.  24pp. (unpubl.)

SUMMARY

Control of mistletoe, a cause of tree decline and death, was investigated in the North-East Region because of reports that mistletoe infestations had increased in recent years.

A study was designed to evaluate the potential of four herbicides to control mistletoe (Amyema spp.) by injection of the trunks of host eucalypts. Eleven eucalypt species were injected in different months in 1984 and 1985 with solutions of the translocatable herbicides GARLON, LONTREL, ROUNDUP and VELPAR.

Evaluation and analysis of mistletoe control in conjunction with host health at 12 and 24 months after injection showed that mistletoes could be partially controlled on most species with certain herbicides. The best results were given by ROUNDUP (diluted 1:3 in water) or GARLON (1:4) injected at the rate of 1 mL per cut, with cuts spaced at 10 cm intervals around the lower trunk of the host tree. LONTREL and VELPAR gave unsatisfactory results, though they received only limited testing.

The particular herbicide and month of injection that gave the greatest percentage control of mistletoes with no or limited host mortality varied according to the eucalypt species, although the most effective months were commonly January and June. Site factors were probably important influences on the results.

Only low levels of mistletoe control were achieved on red ironbark (20%) and river red gum (40%), and further trials with other herbicides would be desirable with these species.

Smaller host trees (<30 cm diameter) were significantly more susceptible to death following injection than larger trees. For mistletoe control on such trees, reduction of herbicide dosage rate or physical removal of infested branches could be attempted.

This study has established that host injection with certain herbicides is a feasible and effective technique for reducing Amyema spp. populations on many eucalypt species. The results should be applicable to the 11 studied host eucalypt species infested with Amyema spp. growing elsewhere under similar conditions, but extrapolation to other species or genera (of host or mistletoe) would be inadvisable without further trials.