Is it correct to say in Russian something like "как следствует из его отчёта" instead of "как следует из его отчёта"? What's the base form for "следствует"? Is it "следствовать"? I can't find it in any available dictionary.
It seems that Lomonosov used the word следствовать in 1749 in a different meaning
"о том следствовать начинает автор ..." (the author starts to investigate that)
In XIX century, "следствует" was used instead of "следовать" in the meaning "ought to",
"я отдам там, кому следствует" (I will return it to whom I ought to)
but never in the meaning of "to follow". In modern times, this word disappears from literary language, but as you see sometimes people use it. Maybe in error, maybe because it still exists in some dialects.