Plants produce numerous organic compounds that have antimicrobial activity. (Borchardt, 2008b; Gillitzer et al. in review) These natural products are found in tissues and structures throughout the plant, including the stems, berries, mature/young leaves, and roots. The many native and naturalized plant species that grow throughout Minnesota are a potential source of chemicals with antimicrobial properties that could be useful in medicines, cosmetics, preservatives or pesticides. Identification of antimicrobial compounds from a wide array of plant tissues and numerous plant species requires screening of numerous extracts from many different plant sources for their biological activity. Alamar Blue (AB), a nontoxic, water soluble dye, changes color from indigo blue to fluorescent pink in the presence of living cells. This color change is an accurate indicator of the fungistatic activity of plant extracts, via respiration, dissolved in a solution of water, nutrient broth, and AB. Phytopthora sojae is a soil borne plant pathogen and major cause of soybean crop loss. Zoospores are a motile reproductive stage of P. sojae critical to the infection process.