Erwinia carotovora and Erwinia cypripedii are soft rot pests, they cause soft hazy yellow spots on the leaves. Decomposition usually starts at the base of the leaf; in humid conditions it spreads across the entire leaf leaving nothing but a pulpy mass. On the infested areas a yellow bacterial slime often occurs. When the disease reaches the apical point, it spreads to other leaves and finally the whole plant rots. Bacterioses on young plants in high temperatures, bad light conditions and high humidity can occur during the whole year, but mainly during the winter months and can make the plant die within several days. Erwinia sp. has a very broad spectrum of host plants, among which are nearly all orchid varieties. Acidovorax mainly occurs on Phalaenopsis and Cattleya. However, Cymbidium, Dendrobium and Epidendrum are also mentioned as being host plants. At the beginning of an infestation with Acidovorax usually small dark spots appear on the leaf blade. With a backlight a marked yellow circle around the infection can be seen. Small spots unite to form larger spots and the tissue shrinks while turning black. Decomposition can be limited to individual leaves or spread across the entire plant. In contrast to infections with the anthracnose pathogen Colletotrichum, no ring-formed grouped fruit bodies are found in the infested areas. Infestation with Acidovorax may occur on blossoms. There may be several bacterioses on orchids at the same time. Usually the degree of infestation of the host plant is therefore not directly connected with the respective bacterium, but rather with the conditions of cultivating and climatic conditions and the condition of the plant. Thus, only microbiologic examinations can reveal the type of bacterium that causes a certain disease.
