Soybean diseases in Argentina and fungicide resistance

Argentina harvested 50.1 million tonnes of soybean in 2025/26. The Buenos Aires Grain Exchange projects 53.6 million tonnes for 2026/27. The crop is large, and a great deal of the national economy depends on it.

Margins, however, are tight. Rosario Stock Exchange data shows a net margin of about USD 385/ha on owned land, but roughly USD -20/ha under lease. A grower on leased land has almost no room for error, and even a grower on owned land feels every avoidable loss.

With so little room, any loss that can be controlled has a direct effect on whether a field makes money. That is why disease deserves a place in the planning, not only in the response.

The same logic applies to the cost side of the budget. A fungicide programme that fails because the pathogen has adapted costs the grower twice: once for the product and once for the yield it was meant to protect.

Annual losses from disease are estimated at 8-10% of total production. Weather and prices are outside a grower's hands. Disease is different, because it can be watched for, planned around and managed. That makes it one of the biggest controllable losses in the crop.

These are estimates, and the real figure changes with the season, the region and the pressure from each pathogen. They are a reason to take disease seriously, not a forecast for any single field.

A useful habit is to keep a record of what each field showed, season by season. Over time that record tells you which diseases keep returning, and it gives your agronomist something firmer than memory to work from.

Four diseases appear again and again in the reported evidence. A figure such as "up to 80%" is the top of a reported range, not an average, so read each one as a sign of what a bad season can do. The four are listed below.

The late-season diseases matter for a different reason. They add pressure to a crop that is already working hard to fill its pods, so they deserve the same attention as rust, even though their reported loss figures are less dramatic.

1. Asian soybean rust — reported losses of up to 80%.
2. Frogeye leaf spot — losses of 15% to 40% in Argentina.
3. Septoria brown spot — a late-season disease that adds further pressure.
4. Cercospora leaf blight — also a late-season disease that adds further pressure.

Foliar fungicides remain the main control tool. Growers rely heavily on a few chemical families: triazoles, strobilurins and carboxamides are the most commonly used, and triazole-strobilurin mixtures are the most widely applied.

Relying on a narrow set of chemistry has a cost. When the same modes of action are used season after season, the pathogen populations that survive are the ones that tolerate them. This is how resistance builds, and it builds in the field long before it is easy to see.

The evidence says the limits of that reliance are now showing. Resistance mutations to strobilurins and benzimidazoles have spread through Cercospora populations. Researchers have also confirmed strobilurin resistance in Septoria brown spot for the first time in Argentina.

Argentine scientists themselves have called for work on biological control, induced plant defences and new fungicide mixtures. Their message is that no single tool will solve the problem. A programme built on several tools is more durable than one built on a single product, and it gives each tool a longer working life.

For product choice and use in your own fields, follow the registered label and local extension advice.

Growers need chemistry that works in a different way. Fertivero's R&D team is evaluating chemical families with different modes of action for soybean disease management. The three families are listed below.

These families are under evaluation. They are not products, and we do not describe any of them as proven in Argentine fields. A different mode of action is a reason to test a molecule carefully, not a result. Each family has to show, in data, what it does and where it fits alongside the tools growers already use.

1. Quinone outside inhibitors (FRAC 11A) — being evaluated for activity where strobilurin resistance exists.
2. Picolinamides (FRAC 21) — these act at a different site in the fungal respiration chain.
3. Oxysterol-binding protein inhibitors (FRAC 49) — aimed at oomycete diseases such as Phytophthora root rot.

SYGOPLUS is Fertivero's global R&D programme, run with international laboratories, and it is in development. Under SYGOPLUS we screen new molecules and formulations against the pathogens that Argentine growers actually face, and we build resistance-management programmes around them. Global R&D runs from Copenhagen, and its locations include Argentina.

We make no performance claim until trials support it. Every candidate goes through laboratory, greenhouse and multi-location field testing, and is registered with SENASA before sale. Registered before sold.

Our approach is to learn from the field first, then apply the science. Healthier soybean crops mean stronger harvests and better returns for Argentine growers, and that is the aim of this work. If you grow soybean in Argentina and want to share what you are seeing, write to info@fertivero.com.

1. Buenos Aires Grain Exchange — 2026/27 soybean production projection
2. Rosario Stock Exchange — net margin data for soybean on owned and leased land
3. Published estimates on the 2025/26 Argentine soybean harvest, annual disease losses and reported loss ranges for Asian soybean rust and frogeye leaf spot
4. Published research from Argentine scientists — resistance mutations in Cercospora populations, confirmed strobilurin resistance in Septoria brown spot, and calls for further work
5. FRAC — fungicide mode-of-action group codes 11A, 21 and 49