Abstract: Biochar (charcoal) is the solid co-product of biomass pyrolysis (thermaldecomposition in the absence of oxygen). Amendment of soil with biochar is known to improvesoil tilth, nutrient retention and crop productivity. We studied the effect of soil-applied biochar onplant productivity and plant foliar diseases. Biochar amendments to sand at levels of 1-3 weight% enhanced the growth of tomato and pepper plants. In addition, suppression of the powderymildew caused by Podosphaera aphanis on strawberry plants grown in commercial coconutfiber:tuff growing mix was observed. Resistance was maximal with 3% biochar amendment aslong as 6 months following planting. Reduction rates were 20 to 93% depending on the biocharpercentage and sampling date. However, gray mold caused by Botrytis cinerea on strawberryleaves was not reduced upon biochar treatment. Similarly, root-nematode Meloidogyne javanicawas not affected by biochar amendments in tomato grown in sandy soil. Biochar amendmentsmoderately enhanced abundances of culturable general bacteria and Bacillus spp. but had noapparent effect on other tested culturable microorganisms. Studies designed to clarify theimportant systemic resistance metabolic pathways and its elicitors are underway. Biochar in soilhas a very slow turnover (half-life of 1000s of years), and therefore, when introduced to soil itresults in quasi-permanent sequestration of carbon. Soil treatment with biochar can thus serve asa climate change mitigation tool and an agriculture adaptation tool.