Southern Rust Confirmed In Southwest Missouri

   Jill Scheidt, an agronomy specialist with University of Missouri Extension, confirmed the presence of southern rust in southwest Missouri fields in Barton County.
   According to Scheidt, southern rust overwinters in warmer climates and spores are blown north on wind currents every year. High temperatures are ranging from 80-90 degrees Fahrenheit and high humidity favor development.
   “Usually southern rust appears too late in the season to cause a significant amount of yield loss in Missouri. However, prolonged wet weather this year has delayed planting, and many late-planted fields could be at risk,” said Scheidt.
   Southern rust is easily confused with other foliage diseases such as common rust and Physoderma brown spot.
   “It is important to differentiate between common and southern rust as common rust is usually present every year, but does not cause economic damage. Identify southern rust by the orange-colored pustules, densely clustered on only the upper leaf surface,” said Scheidt.
   Common rust has brick red colored pustules, sparsely scattered on the upper and lower leaf surface. Pustules can develop on the stalk and husk with both diseases as well.
   Physoderma brown spot is dispersed by wind and occurs when water sits in the whorl for an extended period. Corn is most susceptible to Physoderma brown spot between growth stages V5-V9. Infected leaves have numerous, small lesions that are yellowish to brown and usually occur in broad bands across the leaf. Dark purple to black oval spots occur in the midrib of the leaf and can also occur in the leaf sheath and husks.
   Southern rust affects water use efficiency and uses plant nutrients necessary for grain fill.
   According to Purdue Extension, southern rust reduces yield 25 bushels per acre on susceptible hybrids without fungicide treatment.     Applying fungicides between the silk (R1) and milk (R3) stages when southern rust has been detected are most beneficial.
   Additional applications are likely needed if disease appears before the blister stage. As long as weather conditions are optimal, pustules can produce spores that spread the disease in as little as 7-9 days. Applying a fungicide to field corn within two weeks of black layer is unlikely economical.
   The Integrated Pest Information Platform for Extension and Education (iPiPE) helps track the movement of southern rust throughout the season. Follow the movement at . ∆
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