Symptoms of the disease are mainly observed in the form of round to oval white pustules beneath the epidermis of the leaves. The pustules are organized in clusters parallel to the leaf veins on both sides of the leaf. As they enlarge, they become purple to black and eventually burst, leaving a conspicuous bright opening lesion at their center. When the attack is severe, pustules coalesce, leading to premature leaf fall. The fungus is highly destructive and can cause severe yield losses if it infects plants before the flowering stage.
This fungus is sporadic and only occurs in the warm, humid tropics of the American continent. It is an obligate parasite that cannot complete its life-cycle without a suitable host. It cannot overwinter in soil or on plant debris, thus interseasonal infections in the same field can be avoided easily. It is mainly spread from plant to plant or between different areas by wind. Tropical rust is favored by elevated temperatures (22 to 30 °C), high humidity and high levels of solar radiation. The presence of water on the leaf surface triggers spore germination. Tropical rust mainly occurs when maize is planted in low altitudes late in the season.
No alternative treatment against Physopella zeae is known. Please get in touch with us in case you know of any biological treatment that may help to fight this disease or reduce its incidence.
Whenever possible use an integrated approach with preventive measures along with available biological treatments. Foliar application of fungicides can be effective when the first symptoms appear in high value crops. Fungicides containing azoxystrobin, tebuconazole, propiconazole or combinations thereof can help to control the spreading of the disease.