A new bio-rational fungicide formulation of potassium bicarbonate for horticultural crops, vines and ornamentals Dr Jean-Pierre Laffranque and Dr Steve W. Shires Potassium bicarbonate is a naturally occurring inorganic salt found in soil, water, sediments, plant and animal tissues. Registered by both CODEX and the EU as a food additive, classified as GRAS (Generally Recognised As Safe) in the USA. Indistinguishable from natural potassium and bicarbonate, therefore exempt from residue tolerances (MRLs) in USA. Mode of action related to osmotic and pH effects on fungal hyphae and spores, non site specific, therefore resistance is extremely unlikely. Research to find a formulation that gives optimum spreading and penetration carried out by Cornell University and Church & Dwight Co. Ltd Soluble powder formulation containing 85% potassium bicarbonate, is now registered and commercialised in the USA, and is being developed in Europe under the brand name of Armicarb 85SP ®. 13 field trials were conducted in Austria (2), France (5), Spain (1) and Switzerland (5) in 2003 and INTRODUCTION VINE POWDERY MILDEW (Uncinula necator) APPLE SCAB (Venturia inaequalis) Two field trials in Belgium in 2002 and two in Austria in 2004 Standard reference product: Captan at 1000 g a.i./ha and Kresoxim- methyl at 100 g a.i./ha A total of 10 or 11 sprays were applied at 7 to 12 days intervals. Potassium Bicarbonate application rate: 4250 g a.i./ha in Austria and Switzerland; 5100 g a.i./ha in France and Spain  3 to 10 applications at 8 to 14 day intervals  Comparison with standard reference products: Sulphur at 10 kg a.i./ha; Spiroxamine at 250 g a.i./ha; Penconazol at 25 g a.i./ha Crop selectivity was generally good, although moderate phytotoxicity observed in two trials that had been sprayed twice within two days Potassium bicarbonate at 4250 and 5100 g a.i./ha provided good control of powdery mildew (Figs. 1 and 2) Overall efficacy was numerically but not statistically slightly lower than the standard products French trials confirmed that potassium bicarbonate performs best when applied preventatively STRAWBERRY POWDERY MILDEW (Sphaerotheca macularis) 10 trials were conducted in France (7), Belgium (2), Spain (1) Strawberries were grown under plastic. Application rates for potassium bicarbonate were between 2125 to 4250 g/ha. Two to eight sprays at one week intervals High crop selectivity High scab infestation Potassium bicarbonate activity similar to standards (Fig. 3). Grapes infected with powdery mildew Apples ab aa ab aa Reference products: Penconazol or Spiroxamine Untreated check severity (pest pressure): Bunches: 33%Leaves: 51% Untreated check severity (pest pressure): Bunches: 51%Leaves: 27% Reference products: Captan and Kresoxim-methyl Untreated check incidence: Fruits: 100% Leaves: 100% Untreated check incidence: Leaves: 72% CONCLUSIONS The recently developed 85SP formulation of potassium bicarbonate provides commercially acceptable control of some key diseases. In vines, potassium bicarbonate applied at 4250 to 5100 g a.i./ha gave similar or only slightly reduced control of powdery mildew compared with the standards. In apples, 3825 to 4250 g a.i./ha of potassium bicarbonate gave similar control of scab on fruits but slightly inferior on leaves compared with the standards. In strawberries, 2125 to 4250 g a.i./ha provided high powdery mildew protection Potassium bicarbonate is a naturally occurring inorganic salt and the concentrations used in agriculture are unlikely to have any adverse effects on man or the environment. Exemption from residue tolerances have been granted in the USA and a similar request has been made to the European authorities. Other trials ongoing in Europe are demonstrating interesting efficacy against powdery mildew in vegetables (e.g. cucurbits) and Botrytis in vines. Formulated potassium bicarbonate at 3 kg/ha Untreated check Efficacy trial on Cucumbers Powdery mildew (Erysiphe cichoracarum) RESULTS on Vine Powdery Mildew RESULTS Crop selectivity was excellent in all trials Potassium bicarbonate gave good control in all French trials where natural substrate was used In Spain potassium bicarbonate was superior to the standard sulphur and in Belgium it was superior to myclobutanil but inferior to kresoxim-methyl (Fig. 4) RESULTS