Flax rust fungus is a disease that affects the flax plant. This parasitic fungus is responsible for damaging the foliage, stems, and seeds of the flax plant. Some synonyms for the term "flax rust fungus" include Linum rust, Melampsora lini, and flax leaf rust. This fungal disease can cause significant yield losses in flax crops, reducing the quality and quantity of flaxseed and fiber production. Symptoms of flax rust fungus include yellow-orange pustules on the underside of leaves and stem lesions. Fortunately, controlling the spread of flax rust fungus can be achieved through crop rotation, resistant varieties, and the use of fungicides.