Collocations for harmful - adj.

be, prove
The spraying could prove harmful to humans.

become
consider sth
She actually considered fresh air harmful.

extremely, very
particularly, positively
These products are often positively harmful.

quite
possibly, potentially
A lot of these chemicals are potentially very harmful.

(not) necessarily
Not all virus infections are necessarily harmful to vines.

intrinsically
environmentally, socially
These pesticides are environmentally harmful.

to
pesticides that are harmful to the environment

Harmful is used with these nouns:
bacteria, chemical, consequence, effect, emission, influence, insect, mutation, pesticide, radiation, ray, side effect, substance, waste