Competitive interactions among free living organisms such as plants and algae are known to be regulated by rates and ratios of environmental nutrient supplies1. Micro-organisms that rely on a host for their reproduction cycle hijack host metabolic machinery, as well as host resources in metabolites, enzymes and proteins. As the synthesis of these molecules requires nitrogen and phosphorus, altered host nutrients supplies have been hypothesized and thereafter shown to influence microbial dynamics, based on the response of single and a group of micro-organism species2. Yet, rates and ratios of nutrients supplied to hosts could also mediate the interactions among co-occurring micro-organisms. Understanding these effects would be an important advance because interactions among co-occuring microbes can alter both host population dynamics and epidemiological processes3. The objective of our study was to determine the outcomes of nitrogen and phosphorus addition to plant hosts on infection rates of and interactions among two plant virus species.