Investigations on the Efficacy of some Natural Chemicals against Powdery Mildew [Uncinula necator (Schw.) Burr.] of Grape

The efficacies of Na2SiO3, K2SiO3, KH2PO4, NaHCO3 and di-1-p-menthen against powdery mildew caused by Uncinula necator (Schw.) Burr. were investigated on Vitis vinifera L. spp. c.v. Yuvarlak Cekirdeksiz and compared with the efficacy of sulphur and penconazole. The investigation was carried out during 1998– 1999 under glasshouse condition and in two vineyards in Manisa and Izmir/Turkey. When applied to potgrown plants before inoculation with the fungus, NaHCO3 and Na2SiO3 reduced the spore formation ability of colonies for 4 days on young leaves and NaHCO3, KH2PO4, Na2 SiO3 and di-1-p-menthen reduced the spore formation ability of colonies for 7 days on old leaves. In vineyard trials, all the test chemicals showed low efficacies against leaf infection. However, bunch infections were inhibited by fungicide application with the alternation of KH2PO4 – di-1-p-menthen and the mixture of KH2PO4 + sulphur(S) (WP), as effectively as by the alternate application of penconazole – sulphur. NaHCO3 and K2SiO3 + S (WP) were less effective in the vineyard with high disease incidence. The test chemicals had no effect on the sugar content of berries and did not cause any toxic effect or residue problems in the leaves and bunch. It is, therefore, suggested that Na2SiO3, K2SiO3, KH2PO4, NaHCO3 and di-1-p-menthen could be included in the spraying programmes against powdery mildew with sulphur, synthetic fungicides or they could be used in suitable mixtures and alternations with each other.