Control of Phytophthora root rot of irrigated subterranean clover with potassium phosphonate in Victoria, Australia |
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Authors: | F. C. GREENHALGH,R. F. de, BOER ,P. R. MERRIMAN,G. HEPWORTH,P. J. KEANE&dagger |
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Affiliation: | Institute for Horticultural Development, 621 Burwood Highway, Knoxfield, Victoria 3181;LaTrobe University, Bundoora, Victoria, 3083, Australia |
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Abstract: | Phosphonic acid was more effective in inhibiting the production of sporangia of Phytophthora clandestina in sterile pond water (ED50= 1·4 p.p.m.) than it was in inhibiting the growth of mycelium of the fungus on either corn meal agar (ED50= 13·8p.p.m.) or lima bean agar (ED50= 236 p.p.m.). Experiments under controlled environmental conditions showed that better control of tap root rot of subterranean clover caused by P. clandestina was achieved by application of potassium phosphonate to a pasteurized soil mixture than by a spray on the foliage alone. However, in a soil from a pasture, foliar sprays were more effective than soil treatments. Application of superphosphate at a rate of 250 kg/ha or higher to the soil reduced the effectiveness of sprays. In three experiments in irrigated pastures a spray of potassium phosphonate at 300 or 313 ml/ha, applied to cotyledons of subterranean clover and to soil, reduced severity of Phytophthora root rot and increased the annual production of dry matter of the legume by 1·96 to 5·11 t/ha in comparison with untreated controls. |
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