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PASMO
In most years, pasmo (Septoria linicola Garass) is primarily a disease of the maturing tissues of the flax plant; however, pasmo can attack seedlings, appearing first as yellow-brown circular lesions on the cotyledons (seed leaves) of young plants. Under warm, moist conditions, infected flax seedlings may succumb to the disease, reducing stands.
With delayed infection, yellow-brown spots appear on older leaves at the lower parts of the plant. Stems are fairly resistant when young and growing vigorously, but they become more susceptible when the plants begin to form bolls. Stem lesions may enlarge rapidly, especially on certain varieties, and extend up the stem to the seed-bearing panicle. In early stages of stem infection, irregular bands of brown characteristically alternate with the uninfected green parts of the stem. The brown lesions run together as the plants ripen prematurely, and lesions may become much darkened by secondary invading organisms.
Pasmo can cause serious damage by reducing yield and quality of seed. Prolonged humid weather during the flowering, boll forming, and maturing stages favors spread and severity of pasmo infection. Spores of the pathogen are carried by wind and rain from plant to plant causing it to spread rapidly. If pasmo infection does not occur until plants have started to mature, only minor damage is likely to result.
Pasmo over-winters on infected straw, stubble and seed. Proper crop rotation, plowing under the flax residues, and use of clean seed aid in controlling the disease. Although no variety is classified as resistant, some are sufficiently tolerant and are not damaged greatly unless conditions are exceptionally favorable for development of the disease.
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