Soybean Rust Management Strategies to Protect Yield and Crop Health

Introduction: Why Soybean Rust is a Major threat at this time in 2026?

Soybean leaf rust is a disease that in the past has been known as one of the most serious foliar diseases of soybean crops worldwide. Newer weather patterns, a greater amount of leaf wetness, higher humidities, and other extreme soybean production practices are creating favorable conditions for disease development in the major soybean production areas. With an ever-increasing disease pressure, growers are having more difficulties to ensure their crops stay healthy and profitable.

Soybean rust effects are not just limited to the destruction of leaves. Symptoms may include premature defoliation, a decrease in photosynthesis, lousy pod fill, decreased seed quality and severe losses in yield. Fungicide costs are also higher due to disease outbreaks in many production areas, disease scouting needs in the fields are also higher and harvest efficiency is less as well.

Soybean rust management starts with early detection of disease, preventive protection program and integrated disease management. The initial detection of soybean rust symptoms and knowledge of the disease development are particularly important in ensuring soybean productivity and reducing future economic losses.

Novobac is focused on technologies and solutions for biological crop protection, biological disease management, and sustainable agriculture, which will help our growers in the major agricultural areas of the world.

Soybean rust and the causal agent of the disease

Soybean rust is an Asian soybean rust fungal pathogen, Phakopsora pachyrhizi, that causes the disease. The soybean rust scientific name for the soybean rust is significant since it is known as one of the most destructive foliage diseases of world soybean production.

Soybean rust does not require any soil-borne existence, but is produced by airborne spores that can be carried long distances in the wind. Under adequate environmental conditions spores deposited on a susceptible soybean leaves can cause infection to occur quickly.

There is intense disease pressure and this varies with the geographic areas where soybeans are grown.

Brazil is the world's Soybean Rust hotspot

Brazil continues to be an important epidemic location of asian soybean rust. Soybean diseases are favored for survival and continuous production by warm temperatures, high humidity and repeated cropping. Soybean rust management programs are likely integral elements of annual production in many areas.

Disease pressure is also moderate to severe in certain areas of the United States Midwest during the season.

Soybean rust occurs regularly in the United States Midwest, and is typically triggered by seasonal weather conditions and wind-driven movement of spores. Diseases may develop during summer due to humidity, especially prolonged periods of leaf wetness in the crucial growth phases of the crop.

Disease pressure has been found to be different across various locations, and growers increasingly use integrated disease monitoring and preventive protection programs.

The increase in disease pressure by the Soybean Rust Life Cycle

Knowing the soybean rust life cycle can assist growers in disease prediction and aiding in management decisions.

Spores may lie on the surface of the soybean foliage until they become airborne to begin the disease cycle. Under warm temperature and moisture leaf infection occurs by germination of spores and infection. A larger number of the spores is produced on the diseased leaves and carried by the wind to other plants and fields.

Such multi-cycle spread in the growing season contributes to the very fast spread of asian soybean rust.

Some of the factors that will help speed up the soybean rust life cycle are:

• High humidity
• Frequent rainfall
• Extended leaf wetness
• Dense crop canopies

It's merely moderate to warm with temperature.

Soybean rust can infect several times during a growing season so there is a need for proactive soybean rust management when it comes to reducing disease movement.

Early Soybean Rust Signs Farmers Don't Want to Ignore

Monitoring soybean rust early for adequate management is one of the most critical aspects.

The first signs are frequently as small spots on the underside of leaves—gray, tan or reddish-brown. Small yellow spots may also on upper surfaces of leaves emerge. With advancing disease the number of lesions grows and infected leaves turn yellow and drop early.

The Soybean rust symptoms include:

• Small leaf lesions
• Yellow leaf spots
• Premature defoliation
• Reduced canopy density
• Poor plant vigor
• Lower pod development

A difficulty is that the early signs of soybean leaf rust are similar to other foliar diseases and nutrient deficiencies. Hence, it is important to have regular field scouting in order to have interventions done on time.

Early diagnosis will help in better management of the disease and avoid large yield losses.

Importance of field moisture in the spread of Soybean rust

Asian soybean rust produced by several environmental and agronomic conditions enhance the speed of disease spread. Soybean canopies tend to be thick, creating a moist microclimate which promotes fungal growth and disease incursion. Fungal spores have the potential to germinate more quickly, quicker infecting healthy plant tissues, thereby speeding the disease up in the field under leaves that have been wet for longer periods of time.

Usually the location with the greatest disease impact is the locality where the leaves remain wet most of the time, relative humidity is high, and there is high air moisture content. There is even less air circulation when there are dense stands of crops which further promotes moisture on the leaf surfaces, providing optimum conditions for infection. 

Also, because the disease takes place continuously, with some soybean crops, and where plant density is high, the pathogen can survive and spread from one growth season to the next. Under such conditions, the disease has the opportunity to cause many infections, which means that any soybean rust management strategy is essential for preventing soybean killing infections and maximizing the yield potential.

Spores are wind dispersible and can spread great distances, leading to a quick infection of seemingly healthy fields.

These risk factors can provide insight for growers to beef up soybean rust management programs in advance of large crop losses.

Traditional approaches for controlling soybean rust and why they have failed

Usually, a traditional disease management programme includes field monitoring, resistant varieties, crop rotation and soybean rust fungicides application.

Soybean rust fungicides have still an areal role in the management of the disease; however, there are challenges that continue to be present if soybean growers are depending heavily on fungicides. Frequent fungicide treatments may lead to pathogen population buildup of fungicide resistance, and also cost more to produce crops. 

Environmental conditions (e.g., high rainfall, extended leaf wetness duration and close disease advance) also may hinder or diminish efficacy of management, and may restrict management timing. A significant number of producers have shorter treatment windows (time between planting and disease system) to get the right disease suppression timing. 

Therefore, today soybean rust management relies on an integrated approach that employs the use of fungicides in combination with preventative surveys, resistant varieties and biological disease management strategies to improve ongoing soybean rust control and minimise losses from Asian soybean rust epidemics.

Poor control has been reported by many growers when environmental conditions are conducive to disease growth.

For this reason, biological soybean rust management methods are now becoming an integral component of current soybean rust control methods in addition to conventional fungicide applications.

A combination of various disease management techniques often gives greater long-term protection than is available with chemical control tools.

Trichoderma harzianum is used as a Biological Disease Protection Mechanism

Biological disease management is an important element to sustainable soybean growing.

Trichoderma harzianum, soybean rust fungicides, is one of the most well-established fungi beneficial for biological disease suppression. The fungus, an endemic agent, provides beneficial effects to plants via several mechanisms in order to increase crop resistance towards diseases.

Trichoderma harzianum helps:

• Welfare against plant pathogens.Welfare with plant pathogens.
• Cover seedbed and plant root and crown with soil.
• Produce beneficial enzymes.
• Induce resistance mechanisms in plants. Improve root development.
• Improve crop vigour.

Biologicals add to disease management on long-term sustainable basis and part of managing diseases. Biological methods are becoming useful throughout the world soybean rust control programs and soybean leaf rust and other leaf diseases.

Explore how HarzShield can help with sustainable Soybean Rust management strategies

Novobac HarzShield is the biological soybean rust control solution for plant diseases, which was developed based on Trichoderma harzianum technology. It’s HarzShield is an integral component of disease protection programs implemented by growers in soybean-producing countries throughout Brazil, the United States, Canada, India and Latin America.

The biological disease management programmes have been proven to have a potential in supporting natural suppression of disease in the root zone and in the rhizosphere and in this way they have a potential to increase more sustainable crop protection. Beneficial microorganisms build a protective biological barrier around plant roots, possibly lowering disease pressure and helping to obtain better root health. 

Besides disease control, these biological methods can also help improve the overall health of plants, increase their root ability, and boost the plant's resistance when growing conditions are trying. 

Biological tools can be used to complement crop monitoring, cultural practices and timely interventions as part of integrated disease management strategies to achieve reduced reliance on repeated chemical applications, promote long-term soil health and sustainable agriculture productivity.

Many growers are applying HarzShield (soybean rust fungicides) with traditional soybean rust fungicides in order to create more robust disease management strategies.

The product is suitable for programs aimed at conducting sustainable agriculture for rapid long-term management of soybean rust and overall soybean health.

Developing an Integrated Soybean Rust Management Strategy for 2026

Next is the need for a long-term disease control approach, which goes beyond reactive fungicide applications. As growers become more successful, more and more of them are implementing various management practices simultaneously to form a complete disease prevention scheme.

A good, integrated management approach consists of:

Regular Field Scouting

Provide regular inspections on fields for onset of soybean rust.

Resistant Varieties

Use soybean varieties that are more resistant to disease if available.

Canopy Management

Correct ventilation to minimize humidity, leaf wetness.

Timely Disease Protection

Use preventive measures before the disease becomes problematic.

Biological Disease Management

Incorporate biological materials, e.g. Trichoderma products, into disease prevention programmes.

Environmental Monitoring

Monitor weather conditions conducive to disease development.

These will help to lower long-term disease pressure and enhance yield stability and sustainability.

Integrated soybean rust management programs are critical to the protection of productivity and profitability on soybean farms as asian soybean rust continues to pose a risk to soybean production globally.

Reference:

• Baan, Samen. "Effectiveness of biological control of trichoderma harzianum on soybean leaf rust disease and the production in west papua lowland, indonesia." Biodiversitas Journal of Biological Diversity (2020).
• Jahagirdar, Shamarao. "Bioformulations and indigenous plant protection measures in enhancing the vitalities of bio-control agents for induced systemic resistance suppressing Asian soybean rust in India." Proceedings of the Dubai: International Conference on Biological, Civil and Environmental Engineering, Dubai. 2014.