Fungicide

Fungicides fall into two broad functional categories. Contact fungicides (copper, sulfur, chlorothalonil, mancozeb) form a protective barrier on the leaf surface and kill spores on contact; they must be applied before infection and reapplied after rain. Systemic fungicides (triazoles, strobilurins, SDHIs) are absorbed into plant tissue and move with the xylem, providing both preventive and short-term curative action (typically up to 72 hours after infection). Biological fungicides (Bacillus subtilis, Trichoderma species, Gliocladium) suppress pathogens through competition, antibiosis, or induced plant resistance.

Resistance is the central challenge of modern fungicide use. Fungal populations evolve resistance rapidly — strobilurin resistance in wheat septoria emerged within 7 years of widespread use; triazole sensitivity has shifted in most European wheat regions. Resistance management relies on (1) rotating fungicides with different FRAC mode-of-action codes, (2) tank-mixing multi-site protectants with single-site systemics, (3) limiting applications to 2–3 per season per mode of action, and (4) integrating cultural controls (resistant varieties, crop rotation, residue management) to reduce fungicide reliance.

Economic use depends on disease-pressure forecasts and economic threshold analysis. Preventive calendar spraying often over-applies, wasting €50–200/ha per season on unnecessary sprays. Weather-driven disease models (Blitecast for potato late blight, FHB-Risk for wheat fusarium, Mills period for apple scab) forecast infection windows and trigger sprays only when conditions favor disease. These models typically cut fungicide use 30–50% while holding yield (Penn State Extension, 2023). AI-powered vision systems can also detect early symptoms from smartphone images, enabling rapid-response sprays before disease spreads beyond economic threshold.