Protection of direct-sown eucalypt seed from destructive organisms.  F. G. Neumann, F. Y. Kassaby and J. A. Harris.  May 1978.  34 pp. (unpubl.)

SUMMARY

The results are reported of a study during 1977 on the phototoxicity of several pesticidal seed coat treatments and on the effectiveness of these as protectants of Eucalyptus regnans seed on an ash bed site near Powelltown. Early results of the types of fungal pathogens and of insects that may cause seed loss a given, as well as a review of thiram - a fungicide that has been incorporated in seed coat treatments of eucalypts since the late 1960’s.

Thiram either alone or in mixture with other pesticides, and at various concentrations, was found to be severely phytotoxic to both seed and cotyledon-stage germinants, the symptoms being reduced germinative capacity and stunted tap roots and/or secondary roots. This is the first report of adverse effects of thiram on eucalypts. Other severely phytotoxic pesticides were: capthion (fungicides 8.5% w/w captan and 19% w/w sulphur + insecticides 6% w/w maldison insecticide and 7% w/w DDT); a 1:1 mixture by volume of 4% w/w carbaryl insecticide + 70% w/w dexon fungicide; and a 1:1 mixture by volume of pyrethrum insecticide (0.22% w/w pyrethrins + 1.25% piperonyl butoxide) + 80% w/w mancozeb fungicide.

Six of seven fungi isolated from diseased seedlings raised on ash bed soil caused significant reductions in germination, particularly species of Fusarium and Monocillium. There was also evidence that insects, probably species of the ant genera Iridomyrmex and Pheidole, are responsible for substantial seed loss.

Coatings with commercial R and T Special Seed Bed Dust (5% w/w mancozeb fungicide + insecticides 2% w/w DDT and 0.5% w/w lindane) diluted with mucilage and kaolin in the ratio of 1:1:2 by weight increased laboratory germination on field soil, compared to coatings with kaolin, 14 fold when it occurred following 1 month field exposure, and five and three fold when it occurred following 2 and 3 months exposure respectively.

As a result of the study, special Seed Bed Dust is to be used as a protectant of E. regnans seed, and thiram is to be excluded from seed coats of all other eucalypts in the Commission’s 1978 seed coating program.