with it come/comes?

I came across a sentence in scientificamerican

Summer’s here and with it come picnics, barbecues and of course Salmonella.

Why not comes but come? I found there are

Here Comes the Boom. Here comes the sun.

When to use come and when the other?

It's because picnics and barbecues are plural.

Consider:

Picnics come in the summer, the sun comes at dawn.

When the noun is singular, we conjugate with comes; when the noun is plural, we conjugate with come.

Every Wednesday, five of my friends come over – Jane comes with Harry, but David and Betsy come with Linda.