From 2009 to 2011, freshly harvested processing tomatoes from California commercial fields were surveyed for mold species present in the mature fruit. Molds were recovered from the majority of fruit that had visual symptoms of black mold and other decays and from about a quarter of randomly sampled, asymptomatic fruit. Alternaria, Fusarium, and Geotrichum spp. were the most commonly recovered fungi in both symptomatic and random samples. Based on pairwise statistical analysis, the frequencies of 2 different fungal genera in a composite 11 kg-sample were, in general, statistically independent events, with the exception of a weak association between the incidence of Geotrichum with Alternaria, Cladosporium, or Stemphylium. The mold genera distribution data in this study provide the processing tomato industry with a valuable informational resource that can be used in the management of fungal infection in both the crop and in the final thermally processed finished product. Because of the relative abundance of these fungi, this survey supported the development of genera-specific immunochromatographic diagnostic assays to detect and quantify mold occurrence in Californian processing tomatoes as a potential alternative to the current subjective visual methods, which are characterized by imprecision and nonuniform species sensitivity. A simulation of 1 million 11 kg-composite samples based upon the distributional survey data projected that a multiantibody immunochromatographic assay using monoclonal antibodies for Alternaria, Cladosporium, Fusarium, and Geotrichum could successfully detect the presence of mold in 94% of moldy processing tomato samples collected randomly at harvest.