- Southern rust causes light orange or brown pustules on the top of leaves, whereas common rust forms on both sides.
- Selecting hybrids with higher tolerance to southern rust and applying a foliar fungicide if disease is present or anticipated are the best management options.
Common and southern rust do not overwinter in central corn growing areas. Windblown spores overwinter and move in from southern geographies in
early June until mid-July. While common rust typically isn’t an economic concern in commercial corn hybrids, southern rust can seriously impact susceptible hybrids. The impact on yield potential from southern rust is dependent on how early infection occurs, severity of the infection and how far up in the canopy infection moves.
In July 2020, southern rust was found in north-central KS with additional reports along the NE/KS border. Reports of southern rust were made earlier in the season than in previous years, sparking the potential for higher risk of infection.
Disease Symptoms
- Southern rust causes light orange or brown, densely packed, clustered pustules only on the top of leaves and are small relative to common rust. Pustules can also be found on the stalk, husks and leaf sheaths. Heavy leaf pustule presence can lead to leaf blight, which is ultimately what causes yield reduction in the corn plant.
- Common rust forms on both sides of the leaves, where they begin as small, brownish-red circular lesions and are more sparsely spread throughout. As the lesions mature, they elongate to approximately 1/4-1/8” in length and form a yellow halo around the edges. The pustules will typically turn black by the end of the season. Younger leaves are generally more susceptible to the disease.
- Symptoms of both pathogens are usually the heaviest post-tassel stage.
Environmental Triggers- Southern rust is more likely to develop in moderate temperatures ranging from 77-82° F, whereas the risk of common rust is higher when temperatures are cooler, about 60-75° F.
- Heavy dews, high relative humidity, above-average soil nitrogen levels and late-planted fields can increase chances of southern and common rust.
- Due to the wind-dispersed nature of the pathogens, optimal wind conditions can produce new common and southern rust infections about every 7-14 days throughout the growing season.
Fungicide ApplicationsDuring the season, scout fields based on hybrid susceptibility (Table 2) for disease presence. If southern rust is confirmed early enough and the environmental symptoms outlined above exist, consider applying a foliar fungicide to help prevent disease (Table 1).
Golden Harvest® recommends
Trivapro® fungicide at 13.7 fl oz per acre for southern rust through the R1 (silking) stage. Delayed applications of Trivapro can allow southern rust to establish and reduce yield potential. Trivapro fungicide offers residual control of southern rust from the tassel stage through grain fill.
Miravis® Neo and
Quilt Xcel® are also labeled for southern rust.
For more insight and management advice on southern rust and common rust, contact your local
Golden Harvest Seed Advisor.
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