In focal areas from mid-June, outside usually only in August 1 millimeter large, breaking pustules with rust - brown uredospore powder . First on middle and lower leaves, later on all above-ground parts of the plant. Toward maturity, black, breaking pustules with teliospores . On the underside of the leaf of the intermediate hosts in June, sulfur- to orange-yellow, cup-shaped spore beds (aecidia).
The fungus only overwinters with teleutospores and is obligatorily changing host. Towards the end of May, the intermediate hosts are attacked, from which the aecidiospores trigger the first infections on maize after 2 weeks . The uredospores then formed can re-infect the maize directly. Teleutospores develop on aging leaves.
The initial infection of maize means that infected sorrel species are present within a few meters. An epidemic epidemic is favored by repeated high humidity for several hours per day, as well as through dense corn. Individual varieties are more susceptible. Their inbred lines used for seed production are particularly at risk .
In herd areas, pushing back the intermediate hosts through targeted weed control in maize fields, taking into account the marginal strips. Avoiding susceptible varieties and their seed production in infected areas. Plow in crop residues cleanly.
Chemical control is possible, but is only possible in the production of seed maize and only with a special permit.
- Häni, F. and colleagues: Integrated plant protection in arable farming, Zollikofen Switzerland.