Renee, locusts are, in the broadest terms, "broadleaved plants". As such, any of a number of phenoxy herbicidal preparations will do them in. It may take a few whacks at it, but should eventually work. That way, you needn't kill your lawn.

+oM

I second the suggestion to use a broadleaved weedkiller designed for lawns. The suckers will translocate the chemical through the entire root mass and kill it, but it will take a couple of applications. You can also, of course, carefully apply in other locations, avoiding desirable plants.

Liable to be a black locust rootstock you are dealing with and not Purple Robe.

Sorry to hear about your pain. I always liked the look of this tree but had trouble locating one and heard about the sucker problems.... (and the locust leaf miner problem around here) so never actually planted one.

It's too late for you, but what do people think about girdling a tree like this and letting it die first before cutting it down? That's what I did for some alianthus and it seemed to spare me any sucker headaches.

A sight certain to quake the stoutest heart is not the locust leaf miner but the locust borer...the adult is fully an inch and a half in length and brightlt cilored in yellow and black, leaving holes in the trunk a half inch in diameter.

Yeah, it be time to break out the 2,4-d...also known as a phenoxy herbicide. Girlding is okay...if you treat the cut with round-up or one the 2,4-d relatives...otherwise the suckering is likely to occur.

Thank you for the encouragement. I will spray rather than pull for a while. The zoysia does not take kindly to broadleaf weed killers, but I can paint the stuff on the locust suckers.

You know, I have an old regular Black Locust that my grandfather planted over 40 years ago, and I have never had any suckers. This led me to believe that locusts don't sucker here, which is why I took a risk on the Purple Robe. What a mistake. That rootstock is a whole different animal than my grandpa's locust.

Renee

i have tried painting.. the glove method.. and dripping ..

the only one you control completely.. is dripping ..

both the cotton glove on a chem glove and the paintbrush.. themselves.. drip all over the place ...

it doesnt matter what you put in the applicator ... someone once told me to dilute and mix both 2,4d and roundup.. i dont know about that ...

ken

Variable suckering is seen in other species of trees as well. If the suckers you have now have the same foliage and thorns etc. as the suckerless black locust, then the suckers are black locust.

There are lots of Purple Robe and other locusts here with few or no suckers.

I have two purple robe and one golden locust that we planted when we moved in ten years ago. While happy with the rapid growth, shade, and blooms of these trees; I am constantly cutting down shoots throughout the yard. It has grown in to the neighbors yard, and he's allowed one to grow to a height of about 10 feet. If I apply an herbicide to the suckers that are growing in my yard, do I risk killing the one in the neighbors yard? Strangely enough, one sucker started growing in a part of the yard that was still open, and I didn't cut it down. It's now dieing on its own !
(talk about a black thumb).

Recent discussions of Purple Robe, on another plant enthusiasts' list indicate that 'on its own roots' it's a suckering nightmare, far surpassing anything black locust ever even thought about...

That is very exciting to think about

Can anyone tell me if the suckers of the Red Robe will ever bloom? We have a large area where we have let several of the suckers grow, we have trimmed them so they are trees and they don't bloom in the spring like the mother tree. TIA for any advice

The suckers might not be old enough.

Also, see Embothrium's post above (7/23/12) - suckers from the rootstock are probably black locust, not Purple Robe.

Here's some valuable help from an Arborist exprience with dealing with suckers from a dead Robinia tree.

Number 1 advice, don't plant one of these monsters. If you are mad enough plant one and run into trouble, his advice is-

Saplings:

- Allow saplings to grow to about 20-30 cm. This allows it to form a decent amount of foliage for maximum absorption of herbicide. Here, blackberry killer can be used. Give the sapling a good soaking front and under leaves if possible.

- Do not slice saplings at the base and spray as it will only allow a limited amount of herbicide to be absorbed.

Roots:

- . Carefully brush away soil or dig around the base of the dead stump till you find as many thick feeder roots as you can.

- Drill holes into the root 5-10cm apart at roughly 0.5 - 1cm depth or until you just pass the Cambiun layer.

- Spray Roundup (he told me the standard pre-prepared spray bottle from the shops is fine). The Roundup needs to have a drop or two of dishwashing detergent added to it, which works to wash away any protective crystals the roots form to try and inhibit absorption. Shake the bottle to distribute.

- Then spray into the holes a couple of times more that day.

- The next day, drill holes in between the holes and spray again.

- I would be tempted to do it a third day as well to make sure this horror plant is dead once and for all.

Good luck everyone!