Cedar, more accurately known as juniper, can be a very difficult plant to control. It is a very aggressive woody plant that grows here in Texas. It is often viewed as invasive because if left unchecked it can quickly take over a pasture chocking out any grass growth.
Along with quickly taking over a pasture it has been shown to be a very thirsty plant. I knew a rancher near here that when he started removing cedars on his place he had a spring start producing water again.
While getting control of cedar is possible it is not a one-and-done type of thing. It will take many applications to get this little pest under control.