Thursday, August 28, 2008
Careful use of chemicals can kill locust trees once and for all
John Arbogast
Landscape consultant John Arbogast answers your questions every Thursday. Send questions about your lawn, garden, plants, or insects to:
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5102 Greenfield St. SW
Roanoke, Va. 24018
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Q: My husband and I bought a new house last October in Lexington, Ky. Halfway through our backyard was a row of locust trees. I believe they were black locusts but we aren't certain. We decided since they were in the middle of our yard (and close together) that it would be wise to have them removed and plant trees toward the back of our property line. We hired a company to remove the trees and also paid to have them grind the stumps. Since then, we've had topsoil brought in and sod laid. We are finding out now that we are getting little tree sprouts all along the row of trees that we removed. We were under the impression that since we had the stumps ground, we wouldn't have this kind-of problem. My question is: is there anything I can put on the yard that will kill the underground stump and root system for good that will not destroy our grass? And if not, what are your recommendations?
A: As I’ve said before, I can’t guarantee that you’ll get rid of black locust trees once and for all because nature has made them one of the fastest “re-greeners” in the natural process of reforestation. Sprouts could be emerging from viable ripe seeds left in the ground or from live sections of roots with live buds that were not destroyed through the stump grinding process.
I'd let the sprouts emerge and grow into trees with trunks and leaves so you can use one of the commercially made “brush killer” or “stump killing” herbicides in the spring.
Then find a commercial lawn service that has the required pesticide applicator license in your state and can apply in the spring a potent, restricted pre-emergent weed killer formulated to kill locust seeds as they sprout.
I believe your best bet is to chemically treat a freshly cut stump in the spring. Absorption of the chemical onto the stump only moves within the plant downward to the roots and will not carry the risk of poisoning the soil or adjacent plants.
Commercially available “brush killers” also can be used as “over-the-plant sprays,” although this method carries the risk of injuring nearby plants.
Here in Virginia, the 2008 Virginia Tech Pest Management Guide recommends the brush herbicide containing the active ingredients 2,4-D + 2,4-DP +dicamba as a spot spray or the non-selective herbicide known as Roundup as a spray targeted at locust sprouts.
Along with frequent lawn mowing, applying a multi-ingredient broadleaf lawn weed killer may also starve the locusts' photosynthesis factory. Scan the containers of residential-use tough lawn weed killers in garden departments to select the best one that could work without hurting the grass.
Pre-emergent plant killers work by killing the new sprout at the point of seed germination. This type of product affects only plants from seed, so it should be very safe for your existing lawn.
I’m recommending that you hire a knowledgeable lawn service worker who has the necessary pesticide applicator’s license in your state, which gives them legal permission to purchase and apply potent restricted-use chemicals.
