Why are my large green tomatoes falling off the vine?

Question

They are staked up.

Answer 1

Cut worms - very green in color and hard to spot unless you look close.

Dont rule out an angry night squirrell or bird. Cover with chicken wire will fix that.

Water if anything will ensure proper nutrient flow to the fruit and develop stong branch structure and NOT weak stems that would cause faling fruit. This of course making the assumption that you are an average gardner that waters adequatly as most if anything tend to overwater.Yes ,water more when fruit develops as we all know tomatoes are 70% water so they need it during this stage.

Its a pestt none the less

Answer 2

Sounds like lack of water to me.  How often have you been watering?  Or how often does it rain..Tomatoes can take up to two gallons of water per plant per day if you have really warm or hot weather.  Make sure they have ample water and plenty of mulch.  Also make sure you inspect regularly for insect pests.