EFFECT OF FUNGICIDES APPLIED AS FOLIAR SPRAYS AND TRUNK INJECTIONS ONNUT ROT OF CHESTNUTS CAUSED BY PHOMOPSIS-CASTANEA IN VICTORIA

Fungicides applied in vitro, as foliar sprays and trunk injections wer e evaluated for the control of phomopsis nut rot, an important storage disease of chestnuts in Australia caused by Phomopsis castanea. Benom yl, imazalil, prochloraz and propiconazole were most effective in vitr o against mycelial growth, with EC50 values <0.1 mu g/mL. Iprodione wa s less effective with an EC50 Value between 1 and 10 mu g/mL, while ch lorothalonil and phosphorous acid were ineffective with EC,, values >1 00 mu g/mL. Up to 4 foliar sprays of benomyl, or phosphorous acid, app lied to trees during the growing season reduced (P<0.05) the incidence of rotted nuts during cold storage in 2 out of 5 trials, or 1 out of 3 trials respectively. In one trial, nut rot was reduced from 42.6% in unsprayed trees to 23 or 23.6% in nuts from trees sprayed with benomy l or phosphorous acid respectively. Prochloraz sprays were not effecti ve. At harvest kernel nut tissue from trees sprayed with benomyl, proc hloraz or phosphorous acid showed residues of <0.03, 0.14 or from 16 t o 145 mu g/g respectively. Trunk injection with imazalil or phosphorou s acid at flowering in December did not control the disease, although in 1 trial, phosphorous acid reduced rot levels in stored nuts from 51 .1% in untreated trees to 41.8% (P = 0.088). Imazalil treatments cause d leaf scorching and in some cases limb death above the point of injec tion. Occasional slight leaf scorching was associated with some phosph orous acid injections. Residue studies showed that phosphorous acid mo ved into nut tissue, but showed little lateral redistribution around t he tree.