From QDMA. https://www.qdma.com/hack-squirt-timber-stand-improvement/
Effective Herbicides

�All herbicides are effective on a certain number of species,� said Jim, �but fortunately the new ones like Arsenal AC have a wide range of effectiveness and can be used at low concentrations and wider cut spacings. That has been a real plus to this method. With Arsenal AC, we�ve gone to wider spacings, which means a lot less time at the tree and a lot less energy expended.�

Arsenal AC calls for one cut per 3 to 4 inches of tree diameter at breast height (DBH). So, a 4-inch diameter tree would need one cut. The mixing rate for Arsenal AC is 10 percent, or one part herbicide to nine parts water.

Keep in mind that Arsenal AC is soil active and can injure or kill non-target plants if accidentally spilled or washed off equipment near desirable plants.

Two other herbicides used widely for bark injection are Garlon 3A and 2-4,D Amine, although Arsenal AC seems to have the widest range of species effectiveness. With any herbicide, consult the label for a list of species that are killed by the product. Every herbicide is better at killing some species while less effective on others. Also be sure to wear appropriate clothing and protective equipment as recommended by the label.

50% Garlon 3A
40% Water
10% Arsenal AC
MIX IN THAT ORDER!

You really don't have to worry about non-target kill; especially cross species kill.

50% Garlon 3A
40% Water
10% Arsenal AC
MIX IN THAT ORDER!

You really don't have to worry about non-target kill; especially cross species kill.

How would be the best way to apply?
Can I just spray the ground in the middle of the bushes and let it sink in and kill them by the roots?
I have tried spraying the entire bushes while live and green but it worked a little but not worth doing because sometimes it doesn't kill
I have been hack and squirting and done a few drill and fill the hole. I have been using GLY at full strength. A few bushes are showing a little sign of death but most look the same as the day I did the treatments.
I would like to have something that I can ground treat that works. They are so bushy that you can't get to the base of the trees to hack and squirt.
Seen a product called Pronone Power Pellets and you place a pellet or two at the base of a tree and it kills them over time. They are really proud of their product and is way to expensive for me.

How would be the best way to apply?
Can I just spray the ground in the middle of the bushes and let it sink in and kill them by the roots?
I have tried spraying the entire bushes while live and green but it worked a little but not worth doing because sometimes it doesn't kill
I have been hack and squirting and done a few drill and fill the hole. I have been using GLY at full strength. A few bushes are showing a little sign of death but most look the same as the day I did the treatments.
I would like to have something that I can ground treat that works. They are so bushy that you can't get to the base of the trees to hack and squirt.
Seen a product called Pronone Power Pellets and you place a pellet or two at the base of a tree and it kills them over time. They are really proud of their product and is way to expensive for me.

If that’s the approach you want to use, Remedy Ultra + Diesel fuel as a basal bark treatment is your best bet. Works best on thin barked species like privet and especially when there are multiple stems. Wet each stem from the root collar up to about 12-15”.

For larger stems, use the hack and squirt mix mentioned. Use a good sharp hatchet like a Fiskars or Eastwing. I’ve tried the drill/fill and gas success, but I think the hatchet is faster.

If you can't inject the bark, then there are mixes where you can do a basal bark treatment. Basically a herbicide mixed with diesel so it can penetrate the bark. Don't know the exact mix options off the top of my head but they will be easy to find on internet.

You can use a foliar application with a number of products like Pasture Guard, Crossbow and Remedy. Check the label for recommended surfactants, but if they are compatible I’d use something with methylated seed oil as a component.