Field Facts: Soybean Rust
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Soybean rust made its way to the southern United States in the early 2000s and has been spreading north with each growing season. This disease can cause 50% to 80% soybean yield loss under favorable conditions.1,2
- Common name: Soybean rust
- Scientific name: Phakopsora pachyrhizi
- Symptoms: Lesions appear as irregularly shaped spots that develop spore-containing pustules. These lesions, usually confined to the veins or close to the veins, gradually increase in size and turn brown or reddish as the disease progresses.
- Conditions for development: Cloudy, moist conditions and humidity over 75% increase disease risk. Plants are most susceptible during reproductive stages.
Fast Facts on Soybean Rust:
- Soybean rust is an airborne fungal disease that causes lesions on the leaves, stem and pods; premature defoliation; fewer pods; lighter seeds; and poor seed quality.
- The disease is difficult to detect, as it commonly develops in the shaded, moist conditions of the lower canopy. Detection involves being vigilant for hot spots, or clumps of diseased plants, and systematic field scouting.
- Yield loss due to soybean rust depends on timing of infection, amount of leaf area damaged and location of damaged leaves on the plant.
- If significant damage to upper leaves occurs early in the life of the variety, yield losses may be higher.
- If damage is confined to lower leaves of the plant or occurs in the later reproductive stages of development, little economic loss would be expected.
Control Tips:
- Soybean rust must be diagnosed early for successful management.
- In low pressure situations, vigilance is imperative. Warning systems and systematic scouting programs can be used to stay on top of the disease.
- In high-pressure situations, carefully timed preventive measures are essential. Cultural practices, such as alternate host elimination, can contribute to disease prevention, but chemical control also will likely be necessary.
- Two to seven fungicide applications should be applied at regular intervals (14 to 21 days) at or before the R1 growth stage.
- Because of the frequent need to apply fungicides, measures should be taken to manage resistance development.
- Reach out to your local Corteva Agriscience representative or reference our Corn and Soybean Disease ID Guide for more information.
1Malvick, D. 2018. Soybean rust. https://extension.umn.edu/soybean-pest-management/soybean-rust
2 Schnepf, R. 2005. Asian Soybean Rust: Background and Issues. https://nationalaglawcenter.org/wp-content/uploads/assets/crs/RL32225.pdf