Fc. Greenhalgh et al., CONTROL OF PHYTOPHTHORA ROOT-ROT OF IRRIGATED SUBTERRANEAN CLOVER WITH POTASSIUM PHOSPHONATE IN VICTORIA, AUSTRALIA, Plant Pathology, 43(6), 1994, pp. 1009-1019
Phosphonic acid was more effective in inhibiting the production of spo
rangia of Phytophthora clandestina in sterile pond water (ED(50) = 1.4
p.p.m) than it was in inhibiting the growth of mycelium of the fungus
on either corn meal agar (ED(50) = 13.8 p.p.m.) or lima bean agar (ED
(50) = 236 p.p.m.). Experiments under controlled environmental conditi
ons showed that better control of tap root rot of subterranean clover
caused by P. clandestina was achieved by application of potassium phos
phonate to a pasteurized soil mixture than by a spray on the foliage a
lone. However, in a soil from a pasture, foliar sprays were more effec
tive than soil treatments. Application of superphosphate at a rate of
250 kg/ha or higher to the soil reduced the effectiveness of sprays. I
n three experiments in irrigated pastures a spray of potassium phospho
nate 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.