If you have drip emmitters then the pressure should be on the whole system. Sounds like not enough pressure. How ever if you are just dripping out of 1/4 inch lines then you won't be able to control it with out getting some 1/4 inch cutoff valves. They sell them at Slowes or the Depot home or any place that sells irragation supllies. One on each line and then you can control the flow on each line the way you like.

By the way in a sea of green where plants are at different stages of life, How do you flush just the ones that are readdy to harvest ?