Physoderma stalk rot (Physoderma maydis) stalk breakage at lower node (Sept. 2014, Iowa). The nodes at which breakage occurs are black (Figure 2) and some stalk rot of the pith may be present (Figure 3). Infection usually occurs earlier in the season V3-V8. Physoderma Node Breakage RATINGS :1 = POOR 9 = EXCELLENT R = RECOMMENDED HR = HIGHLY RECOMMENDED NR = NOT RECOMMENDED 12 3456789. Small, water Small yellow spots appear first at the base of the leaf and over time turn brown in color. Physoderma brown spot and stalk rot of corn caused by Physoderma maydis in Iowa. node rot phase can cause stalk breakage, so it’s important to continue monitoring corn fields throughout the fall. Physoderma Brown Spot and Node Breakage Small yellow spots appear first at the base of the leaf and over time turn brown in color. •Since 2013, the disease has been frequently associated with infection of lower nodes resulting in stalk breakage at later reproductive growth stages. P. maydis produces resting spores called sporangia, which allow the pathogen to persist in soils for up to 7 years in the absence of corn. Photo courtesy of Dr. Alison Robertson, Iowa State University. Infection of lower nodes can result in PSR. Physoderma Brown Spot and Node Breakage Small yellow spots appear first at the base of the leaf and over time turn brown in color. Figure 1. 62A28. The fungus survives in crop residue and may be more common in continuous corn and conservation tillage systems. This weakens the nodes causing them to become brittle and snap when pushed (Figure 4). Infected nodes become weakened over time and snap easily when pushed. Alright welcome from the field this week My name is Nick Benson here in Northeast Iowa Today, I'm over by Arlington, Iowa today. Infection at lower stalk nodes causes stalks to become weakened and subject to snapping.Extremely wet weather appears to be a causal factor of Physoderma stalk rot and breakage. Walking field across Southwest Iowa the past two weeks in September there have been a number of fields with plants that area easily snapped or broken-off at the base (1 st or 2 nd node) when pushed off the center of the row. Generally, losses are related to lodging. The fungus survives in crop residue and may be more common in continuous corn and conservation tillage systems. Microscopic examination of the symptomatic tissue reveals thousands of light brown sporangia (Figure 4 and 5). First symptoms noticed are corn plants that break at the first or second node (Figure 1). The nodes are easily snapped when the plant is pushed, giving the impression that hybrids simply have a greensnap issue. Physoderma brown spot lesions. When temperatures are warm (75-85°F) and sporangia are saturated in water for at least 72 hours, they germinate and release copious amounts of motile zoospores. Spots in the mid-rib of the leaf become reddish to Page 1 of 2 Figure 3. SYMPTOMS. 110-112 Day Maturity. 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