Brazil has cleared its first ascaroside-based biofungicide, opening a new biochemical mode of action against Asian soybean rust (Phakopsora pachyrhizi) and corn leaf blight. The regulatory decision, reported this week, marks the first commercial approval of the ascaroside class in any major row-crop market.

What is an ascaroside biofungicide?

Ascarosides are small-molecule signalling compounds first characterised in nematode biology. Research has shown that certain ascarosides trigger plant defence responses, leading to their development as crop protection agents. Unlike conventional fungicides, which target pathogen metabolism directly, ascaroside products act as elicitors — compounds that switch on the plant's own immunity pathways.

This mechanism places ascarosides in a distinct category from established biofungicides based on Bacillus subtilis, Trichoderma harzianum or Streptomyces species. Each of those microbial classes has a different mode of action, but none mimic the signalling chemistry of nematode-derived molecules.

Why these two target diseases matter

Asian soybean rust remains the most economically damaging foliar disease in Brazilian soybeans. Outbreaks in epidemic seasons can cut yields sharply if left uncontrolled, and growers in the Cerrado typically budget two to three fungicide sprays per season to manage the pathogen. Resistance pressure on the most-used modes of action — including QoIs (strobilurins), DMIs (triazoles) and SDHIs — has intensified over the past decade, raising the per-hectare cost of rust programmes and pushing growers to seek rotational tools.

Corn leaf blight, driven primarily by Exserohilum turcicum (Northern corn leaf blight) and Bipolaris maydis (Southern corn leaf blight), attacks the crop's photosynthetic leaf area and shortens the grain-fill window. Maize in central and southern Brazil faces two production cycles per season, multiplying disease pressure on the second crop (safrinha) that follows soybeans.

What changes for growers

The Brazilian Ministry of Agriculture's clearance allows the product to enter the commercial distribution chain. Growers will need to wait for label specifications — application timing, dose per hectare, compatibility with tank-mix partners and pre-harvest interval — before planning the first sprays.

For resistance management, ascaroside elicitors behave differently from single-site fungicides. Elicitor products work best as protectants, applied before infection pressure peaks, and agronomists generally recommend rotating them with conventional modes of action rather than substituting one for another. Brazilian cooperatives already operate rust spore-monitoring networks across Mato Grosso, Goiás and Paraná, and these will shape the timing of the first commercial applications.

What to watch next

Watch for product registration documents to specify the active molecule, formulation type and registered crop-pest combinations. The manufacturer has not yet announced hectare pricing, packaging volumes or distribution partners, but commercial launches typically align with the September soybean planting window in central Brazil.

Independent efficacy trials from Embrapa, state research organisations and university extensions will follow the first commercial use. Growers should look for multi-site trial data covering both soybean rust and maize leaf blight before committing a large share of their programme to the new class.