Pesticides with herbicidal, fungicidal and algicidal activity contain isothiazolyl-ureas of formula (I): (where R1 is =4C alkyl, alkenyl or alkynyl; R2 is 2-5C alkoxycarbonyl, 2-5C alkanoyl or COOH; R3 is H or Me; R4 is H, 1-4C alkyl or MEO; R5 is 1-4C alkyl). Cpds. (I) are new, with the exception of (I) where R1=R5=Me, R3=R4=H and R2=COOEt. Cpds. (I) are useful as (a) selective herbicides for pre- and post-emergence weed control; e.g. the effective pre-emergence application rate of 1-methyl-3-(3-methyl-4-ethoxycarbonyl-5-isothiazolyl)-urea (Ia) is 1 kg/ha against Echinochloa crusgali and 0.5 kg/haagainst Alopecurus, Apera and Digitaria, while its lethal application rate is 15 kg/ha for maize, 6 kg/ha for rice, 20 kg/ha for cotton and 2 kg/ha for wheat; (b) algicides, e.g. the MIC of (Ia) against Chlorella pyrenoidosa is 2 ppm; and (c) fungicides; e.g. the activity of (Ia) against Plasmopara viticola and Sphaerotheca fulginea is superior to that of dinocap.
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