Pacific Pests, Pathogens & Weeds - Mini Fact Sheet Edition

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Maize American corn rust (042)

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Photo 1. Spots of American corn rust, Puccinia polysora, on lower leaves of maize.

Photo 2. Golden brown pustules of American corn rust, Puccinia polysora, on the underside of a maize leaf.

Photo 3. Puccinia polysora pustules (uredinia) on maize.

Photo 4. American corn rust, Puccina polysora, on the stem or stalk of maize.

Summary

• Worldwide distribution. On grasses and some relatives of maize (but not reported in the Pacific islands). It does not have another host for part of its life cycle as does Puccinia sorghi. It lack the stages of life cycle that Puccinia sorghi has on Oxalis (see Fact Sheet no. 225).
• Spots in large numbers on both sides of the leaves and stems, brown, round to oval up to 2 mm, bursting open, spreading spores in the wind that eventually landing on maize, geminating and infecting though natural openings.
• Warm humid weather favours disease. But usually infection comes late so impact is slight. However, in 2008 However, in 2008, a new strain was recorded in the US to which most hybrid maize varieties were susceptible. Fungicides were needed to provide control.
• Cultural control: plant far away from infested crops; plant in drier times of year; use varieties bred for resistance to rust diseases; destroy volunteers; collect and burn trash after harvest.
• Chemical control: usually not needed, but if required: copper or mancozeb.

Common Name

American corn rust, maize rust, southern rust

Scientific Name

Puccinia polysora. Another rust, Puccinia sorghi (common rust of maize) occurs worldwide (see Fact Sheet no. 225). Often the two rusts occur together, requiring microscopic examination to tell them apart.

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