Boscalida (Boscalid)

Boscalid is a systemic fungicide developed by BASF, belonging to the class of succinate dehydrogenase inhibitors (SDHI).

This active ingredient has proven efficacy against a broad spectrum of fungal pathogens in crops such as soybeans, corn, cotton, coffee and vegetables.

Its specific mechanism of action is based on the inhibition of mitochondrial respiration, resulting in energy collapse and cell death of the target fungi.

Chemical characteristics and development

Common name (ISO): boscalida

Synonyms: Endura (trademark of the molecule); Cantus, Collis (commercial product brands)

Number CAS: 188425-85-6

Official chemical name: 2-chloro-N-(4'-chlorobiphenyl-2-yl)nicotinamide

Gross chemical formula: C18H12Cl2N2O

Chemical class: succinate dehydrogenase inhibitor (SDHI) - Carboxamide

The development of boscalid began in BASF laboratories during the 1990s, with the first synthesis being disclosed in patents filed by the company in 1995. This development represented a milestone in the evolution of SDHI fungicides, since the class was previously dominated by carboxin, launched in 1966 with a limited spectrum mainly for the control of basidiomycete fungi.

Research and development of boscalid focused on expanding the control spectrum and increasing potency compared to previous generations of SDHIs. SDHIs with expanded spectrum and potency began to be launched in 2003, when boscalid entered the commercial market. The BASF internal development code for this compound was BAS 510F.

BASF’s development strategy was to create a fungicide that could control pathogens resistant to other chemical groups, especially triazoles and benzimidazoles, which already presented resistance problems in several crops. Boscalid was positioned as part of the second generation of SDHI fungicides, offering greater flexibility in resistance management.

The synthesis process developed by BASF involves a complex reaction using aminobiphenyl with 2-chloronicotinic acid chloride. The preparation of aminobiphenyl requires two steps, including a palladium-catalyzed Suzuki reaction. This synthetic complexity gave BASF an early competitive advantage, enabling it to establish a leading position in the next-generation SDHI fungicide segment.

The commercialization of boscalid was promoted as “the world’s first SDHI chemistry” in terms of broad commercial efficacy, differentiating it from previous, more limited generations. The track record demonstrates consistent efficacy in intensive agricultural systems, solidifying BASF’s position in the systemic fungicide market.

Biochemical mechanism of action

Boscalid acts specifically on complex II of the mitochondrial respiratory chain. The active ingredient binds to the ubiquinone reduction site, preventing the normal functioning of succinate dehydrogenase. This interference blocks the tricarboxylic acid cycle and the electron transport chain.

The Fungicide Resistance Action Committee (FRAC) classifies boscalid as group 7, code C2. This classification indicates a moderate risk for the development of resistance. Cellular energy collapse results in inhibition of mycelial growth, reduced spore germination and blockage of the formation of reproductive structures.

Control spectrum and applications

Boscalid demonstrates efficacy against several economically important pathogens. In soybeans, it controls Sclerotinia sclerotiorum (white mold), Colletotrichum truncatum (anthracnose) and Septoria glycones (brown spot). Cotton presents efficient control of Ramularia areola (ramularia leaf spot). In corn, it reduces severity of Cercospora zeae-maydis (cercosporiosis) and Puccinia sorghi (rust).

The coffee tree represents an important crop for application against Phoma tarda (Phoma spot) and Cercospora coffeicola (cercosporiosis). Vegetables benefit from the control of Botrytis cinerea (gray mold) and Alternaria Solani (alternaria). Fruit trees show a reduction in Monilinia fructicola (brown rot) and venturia inaequalis (scabies).

Recommended doses range from 100-300 g of active ingredient per hectare, depending on the crop and disease pressure. The safety interval ranges from 7-21 days depending on the crop. The re-entry interval ranges from 24-48 hours after application.

Resistance management

There are records of resistance in populations of Botrytis cinerea in protected crops. Other pathogens show reduced sensitivity after continuous use. Proper management requires mandatory rotation with fungicides from different FRAC groups, including groups 1, 3, 11 and multisite (M).

The maximum number of applications should not exceed 2-3 per crop cycle. Mixtures with multi-site fungicides such as mancozeb and copper reduce selective pressure. Field efficacy monitoring allows early detection of resistant populations.

The dosing strategy recommends using the full registered rate. Underdosing favors the selection of resistant isolates. Integrated management programs include cultural practices and systematic monitoring of sensitivity.

Environmental and toxicological aspects

The toxicological classification places boscalid in Category 5 (unlikely to cause acute damage). Persistence in soil has a half-life of between 108 and 365 days, depending on soil and climatic conditions. The adsorption coefficient (Koc) of 1.590 mL/g indicates moderate mobility.

The leaching potential is classified as low to moderate. Soils with a higher organic matter content have greater retention. The risk of groundwater contamination remains limited in clayey soils. Aquatic toxicity requires compliance with protection zones for water bodies.

Compatibility and interactions

Boscalid is compatible with multisite fungicides, triazoles and strobilurins. Permitted mixtures include mancozeb, chlorothalonil, tebuconazole, propiconazole, azoxystrobin and pyraclostrobin. Foliar fertilizers containing micronutrients demonstrate adequate compatibility.

Products with an alkaline reaction (pH > 8,0) are incompatible. Mineral oils in high concentrations may cause phytotoxicity. Formulations containing copper at low pH require prior compatibility testing.

The phytotoxic potential remains low when applied according to technical recommendations. Severe water stress conditions or temperatures above 30°C may increase the risk of phytotoxicity.

Effectiveness and strategic positioning

The optimum temperature for maximum effectiveness is between 15-25°C. Temperatures above 30°C reduce biological activity. Relative humidity between 60-80% favours foliar absorption. Washout resistance is established after 2 hours of application.

The stability of the spray remains adequate at pH 6,0-7,0. Extreme pH values ​​may reduce efficacy. The systemic and translaminar action provides prolonged protection. The residual period extends to 14-21 days.

Strategic positioning varies according to the crop. In soybeans, preventive applications at stages R1-R3 efficiently control white mold. Cotton requires application at the beginning of flowering to control ramularia. Corn benefits from foliar application at tasseling.

Coffee plants respond best to post-harvest applications for Phoma leaf spot. Vegetables in protected cultivation require weekly preventive applications. Fruit trees require application during flowering and fruit development.