Puccinia hordei is a species of rust fungus. Spores created by the rust fungus allow dispersal to other plants. It is prone to predation by rabbits and infestation by rust fungus. The rust fungus "Gymnosporangium cornutum" produces leaf galls. Gymnosporangium clavariiforme is a species of rust fungus which alternately infects Juniperus and hawthorns. This plant is the alternate (telial) host of the Pear Rust fungus "Gymnosporangium fuscum". The stem rust fungus attacks the parts of the plant that are above ground. The study found that the rust fungus showed high levels of extinction in warmer climates. Gymnosporangium libocedri, the Pacific Coast pear rust, is a plant pathogen and rust fungus. As biological control the rust fungus "Puccinia evadens" is used. Other control measures include the rust fungus "Puccinia spegazzinii" and the thrips species "Liothrips mikaniae". He specifically worked with the rust fungus, "Melampsora lini", and the flax host, "Linum usitatissimum".