Provided herein is a dual amplification method for identifying plant pathogens by analysis of pathogen DNA in an unpurified nucleic acid sample from the plant. Pathogen-specific and/or plant-specific primers are used to generate a first set of amplicons that are further amplified in a second amplification step using fluorescent tagged pathogen-specific primers. Fluorescent amplicons thus generated are hybridized with pathogen-specific nucleic acid probes that are immobilized on a solid support using bifunctional polymer linkers. The hybridized microarray is imaged to obtain fluorescent images of the amplicons and the nucleic acid probes, which are superimposed to detect the pathogen present in the plant. Also described herein is a method to identify a plant by analysis of plant DNA and a method to simultaneously detect both plant DNA and pathogen DNA in a single assay.