Acibenzolar-S-methyl (Acibenzolar-S-Methyl)

Acibenzolar-S-methyl (ASM or BTH) is a systemic acquired resistance (SAR) inducer widely used in agriculture as a plant activator. Unlike conventional fungicides, it does not have a significant direct action on pathogens, but stimulates the plant's natural defenses.

Common name: acibenzolar-S-methyl

Number CAS: 135158-54-2

Gross chemical formula: C8H6N2OS2

Chemical class: Benzothiadiazole derivative (1,2,3-benzothiadiazole). It belongs to the group of plant defense inducers (FRAC P1). It is classified as a fungicide/plant activator, but its mode of action is indirect via activation of host defenses.

Main names of commercial products in Brazil: Bion 500 WG

Development history: Developed in the laboratories of Ciba-Geigy (now Syngenta) starting in the 1980s. After structure-activity relationship tests with derivatives of 1,2,3-benzothiadiazole-7-carboxylic acid, the S-methyl thioester (CGA code 245704) was selected for its good tolerance in cultures and efficacy in inducing SAR. The first synthesis of the parent acid was described in Ciba-Geigy patents. Commercially launched in 1996 in Europe (Germany) as Bion; later expanded to other markets as Actigard. It is a functional analog of salicylic acid (SA).

Mechanism of action: It induces systemic acquired resistance (SAR) by mimicking salicylic acid and activating the SA downstream signaling pathway (involving proteins such as SABP2 and NPR1). This leads to the expression of defense genes, production of pathogenesis-related proteins (PR-proteins, such as β-1,3-glucanase and chitinase), reinforcement of cell walls (papillae), accumulation of antimicrobial compounds, and, in some cases, stomatal defense. It is not directly toxic to most pathogens (or has a limited effect, reducing mycelial growth, sclerotia formation, etc. in some cases). Preventive application is essential (there is a latency period of hours to days for full activation). Rapid absorption and systemic translocation (acropetal and basipetal).

Control spectrum: Broad-spectrum indirect protection against fungi, oomycetes, ascomycetes, deuteromycetes, bacteria, and some viruses (via plant defense). Examples include powdery mildew, downy mildew, anthracnose, rusts, and bacterial blight. In Brazil, it is used indirectly against angular/bacterial spot, late blight, black spot, powdery mildew, downy mildew, bacterial blight, and golden mosaic virus.

Compatibilities and interactions: Good compatibility with integrated disease management programs (IDM/IPM). Can be integrated with conventional fungicides/bactericides, crop rotation, resistant cultivars, and biological/cultural control—it does not replace them. Low theoretical risk of resistance by pathogens due to its indirect mode of action. Check labels for tank mixtures. Low phytotoxicity at recommended doses (test on ornamentals). Permission for use in the European Union was recently withdrawn due to concerns about endocrine-disrupting properties.

Agronomic positioning: Preventive (apply before pathogens enter). Low doses (generally 15–50 g/ha in Brazil, e.g., 25 g/ha for tomato/cotton). Foliar application (ground or aerial) or, in some countries, seed treatment. Maximum applications per crop are limited by crop type (e.g., up to 10 in tomato/cotton). It complements the routine phytosanitary program and is a valuable tool for resistance management and reducing the use of conventional fungicides.

Other information:

Evaluation of the efficacy of acibenzolar-S-methyl (BTH) as an inducer of systemic acquired resistance against bacterial and fungal diseases of tobacco. The product protected tobacco plants against several pathogens by activating natural defense mechanisms, demonstrating potential as a plant protection tool with a mode of action distinct from conventional fungicides. - DOI: 10.1016/S0261-2194(99)00026-5 -

This shows that acibenzolar-S-methyl induces systemic resistance in cotton against rot caused by Thielaviopsis basicolaThe treatment activated the plant's defenses, reducing disease severity in field and laboratory experiments, positioning it as a promising component of integrated management strategies for root diseases in cotton. DOI: 10.1071/AP05089