Answer: The blotch diseases are fungal leaf diseases similar to Tan Spot and Septoria, but they affect only barley. There are three blotch diseases to be aware of: Net Blotch, Spot Blotch, and the Spot Form of Net Blotch. Temperatures of 68° to 77°F and 100% relative humidity are ideal for spore production.
Spores are spread by wind and rain, with barley residue serving as the main source of infection for subsequent crops.
Organic control practices to prevent Net Blotch include the following:
• Use resistant cultivars.
• Bury crop residue and destroy volunteers.
• Use balanced applications of nitrogen and phosphorus. Heavy nitrogen applications create conditions favorable to outbreaks of this disease.
• Follow a crop rotation that includes at least two years of non-susceptible hosts. Barley should not follow barley, particularly if disease levels were high the previous year.
• If barley must be grown in two successive years, use a susceptible cultivar the first year and a resistant type the second.
• Use pathogen-free seed if possible.
You can learn much more in the ATTRA publication Disease and Insect Management in Organic Small Grains. It outlines various strategies that make up a good organic disease and insect management plan, and describes some specific diseases and insects that affect small grain crops. Although this publication pertains to various regions of the country, the main focus is on the Plains states—where most organic small grains are grown.
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