One of the frequent signs of early failure in semitransparent wood coatings is colonization by “black stain” fungi, such as Aureobasidium pullulans. A laboratory method evaluating the ability of various wood coating formulations to inhibit the growth of black stain fungi on artificially weathered, coated wood in petri dishes was developed. Meaningful results were obtained after only 6 weeks of incubation. Selected biocides and biocide combinations formulated in a semitransparent coating including selected combinations of diiodomethyl-p-tolylsulfone, 3-iodo-2-propynyl butylcarbamate (IPBC), propiconazole, tebuconazole, thiabendazole, fludioxonil, chlorothalonil, oxine copper, copper metal, and naphthoquinone were evaluated. Combinations of propiconazole with IPBC and propiconazole with IPBC and thiabendazole were most effective in this test. Further work is needed to evaluate the use of other coatings and test fungi with the laboratory test method and to evaluate the performance of the best-performing biocides in field exposures.