Fungicide Not Working? Pathogen Resistance Is Not Always to Blame

The Polish agricultural portal topagrar.pl has published guidance on fungicide performance, that is, products used to control plant diseases. It stresses that a spray failing to deliver the expected result does not necessarily mean the pathogen has become resistant to the active substance. Resistance to crop protection products is already clearly visible on some farms, while on others it may emerge in future unless it is prevented.

In Poland, pathogen resistance to fungicides is noticed less widely than weed resistance, but it should not be dismissed. As Paweł Talbierz puts it, resistance is the consequence of mistakes made over many years, which can stem from both deliberate decisions and lack of knowledge.

Check the application first

Before concluding that a pathogen has adapted, it is worth verifying that the treatment was done correctly. Relevant factors include spray timing, the growth stage of the crop and the disease, and the choice of product for the situation in the field. Water quality, nozzles and the way the mixture is prepared also affect efficacy. Combining several products in one tank can be convenient, especially when weather limits separate passes, but not every combination works as expected because different formulations may be incompatible. The result should therefore be assessed after spraying.

Crop rotation and rotating active substances

Diverse crop rotation is one of the basic tools for reducing disease pressure. Frequent repetition of the same species, particularly in intensive cereal rotations, can help pathogens persist. Diversity also helps with weeds and makes protection planning easier.

Protection should not rest on a single active substance. Repeating treatments with the same substance or mode of action increases selection pressure on pathogens; regular use of tebuconazole without rotating to other modes of action is given as an example. Rotation does not mean choosing the most expensive products, but matching them to the crop, the disease and the conditions.

Prevention rather than late intervention

Once a disease is visible, controlling it effectively can be difficult. This applies, for example, to septoria leaf blotch in cereals, where protection must be planned preventively. Even for diseases that can be treated curatively, the protective action of a fungicide matters, since limiting pathogen development early reduces selection pressure.

An effective anti-resistance strategy requires correct diagnosis, proper timing, careful spray preparation, rotation of modes of action and well-thought-out crop rotation. Only after reviewing the whole process can resistance be assessed as a cause. The publication will discuss the issue on 25 November 2026 in Poznań at the 11th Farmers and Agribusiness Forum.