There is NO best way to use Sevin. https://www.helpfulgardener.com/forum/vi ... 11&t=57653
is a thread I did on the impacts of various garden poisons. Re the Sevin:
Animal toxicity: Carbaryl is acutely toxic to fish. Carbaryl is acutely toxic to birds, although the dose required to kill most species is greater than that required to kill mammals, fish or insects. Carbaryl also adversely affects birds at lower doses by reducing the population of insects and aquatic invertebrates that the birds feed on. Unhatched and young birds appear to be particularly sensitive to carbaryl exposure. Earthworms are sensitive to small amounts of carbaryl in soil. In field studies, carbaryl treatment reduced earthworm populations by between 50 and 90 percent. Follow-up studies showed that populations took five to twelve months to recover and that the rate at which mineral soil was incorporated into thatch was significantly impaired during this period. It is toxic to frogs, shrimp, crabs, clams, snails, some aquatic insects, and many pond living creatures. Carbaryl is highly toxic to honey bees, certain beneficial insects such as lady beetles, and parasitic wasps and bees.
Plants: While insecticides are not usually assumed to have adverse effects on plants, carbaryl's use as a plant growth regulator (chemical thinning agent) makes effects on other plants unsurprising. It has been shown to decrease germination success, inhibit seedling growth, reduce photosynthesis, and reduce nitrogen fixation. Note that several different people have written in to helpfulgardener to say that their gardens died after being sprayed with Sevin.
Fate in the environment: Because of its chemical characteristics, the U.S. Environmental Protection Agency (EPA) identified carbaryl as one of the pesticides with most potential to leach into groundwater. It has been found in groundwater in California, Missouri, New York, Rhode Island, Virginia, and Wisconsin. Carbaryl was the most commonly detected carbamate insecticide in the 1991 U.S. Food and Drug Administration pesticide residue monitoring program; it was the tenth most commonly detected pesticide. It was also one of eight pesticides detected in baby food samples
It has been banned in Austria, Australia, Germany, Sweden, Angola, the United Kingdom, Denmark, Iran and other places...
AND while it will kill all the beneficial insects in your garden, it is harmless to slugs, which are probably your culprits!