Novel thiadiazole compounds are disclosed which contain in the 5 position, C-linked moieties which are either acyclic hydrocarbon radicals or halogenated acyclic hydrocarbon radicals (in which case each halogen is independently selected from F, Cl and Br). These novel compounds also contain an exocyclic nitrogen in the 2 position, and some of them contain the exocyclic substituent: <IMAGE> wherein R3 is a lower acyclic hydrocarbon radical and R4 is either H or a lower acyclic hydrocarbon radical. Synthesis of these compounds is disclosed, including synthesis of those which exhibit isomerism and/or tautomerism. Various of these compounds have various agricultural utilities (e.g. as herbicides, insecticides, acaricides and fungicides), each of them having at least one such biological utility. Methods of using these compounds in phytotoxic fungicidal, acaricidal and insecticidal applications are disclosed.
