Question
we have black dots on our leaves and black larva underneath. there are also green half-inch worms. please advise. jim in Las Vegas.

Answer
Dear Jim, Caterpillars are very fond of petunias and they have located yours.  There are several methods you can use to get rid of them.  The first is just to pick them all off.  It's messy and gross and will take a few days to get them all, and it depends on how many petunias you have.  You can also use BT, Bacillus thuriengensis but that will take several weeks to work.  I would  probably go with a faster acting insecticide to get rid of them before they do much more damage.  I would get whatever is recommended at your local garden center (different chemicals are allowed in different areas).  You may have to spray 2 to 3 times a few days apart to get rid of them all,  but it should be effective pretty quickly.  Good luck, Melissa