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Lawn Problem with Invading Plants

Hi Doug, from Penticton B.C. in zone 5 have a lawn problem. Many years ago not knowing the invasive nature of sumac I planted half a dozen plants on an ugly clay bank behind my lawn. They were very pretty in the fall and stabilized the bank but when they started a major invasion of the lawn I cut them down and gave the stumps a shot of full strength roundup to kill them. No dice, they continued their invasion of the lawn to the extent that not even constant mowing dicouraged them. The lawn is now more brown than green and the sumac roots are living very happily. Can you suggest any remedy short of plowing up the lawn and reseeding? There is another culprit too on another part of the lawn, a trumpet vine, almost as invasive is sending up shoots ten feet into the lawn. So far it has not turned that part of the lawn brown but can foresee another major problem developing. An article on invasive species would probably help a lot of ill-informed gardeners like myself. Any suggestions will be appreciated. Henry

Doug says


Invasive plants are indeed a pain in the garden anatomy.   Interestingly enough - one gardener's treasure is another's thug and depending on where you live - your thugs will be different.   In a USDA zone 3, English Ivy is a houseplant while in a USDA zone 6, it can be a noxious weed invading everywhere.   So telling people to "avoid this plant or that plant" is pretty useless gardening information.

The problem of course is that an organic solution to this problem is a bit difficult.  It involves a consistent amount of work and persistence over several years.  Constantly digging and removing suckers and never allowing any survivors to set seed.  Plants like the two you mention do throw underground shoots and this is a major problem for gardeners - you gotta get 'em early or they'll be a big headache.  

You can use an organic "burn" type of spray with products that contain high concentrations of acetic acid (vinegar).  Repeated spraying of the foliage will weaken these plants and they'll eventually die off.    You'll have to spray several times a season to control them and you'll have to remove the adult plants as well as they won't stop throwing babies.
On the chemical front, pne of the uses for Roundup that I have used in the past is to paint it in its concentrated form (not the ready-to-use dilution) onto the freshly cut stumps of woody plants.  This is - to the best of my knowledge at time of writing - a registered use for the product and is listed on the label as acceptable.   Cut and paint.

So your sumac and trumpet vines could be cut and then painted to kill the root systems.  You might find you have to redo this if you don't get them all the first time.  I have killed off large silver maple roots this way (the ones invading my septic beds)  

I confess I have mixed feelings about using Roundup.  In my case, I had to figure out a way to kill off the roots without messing with the main trunk.  The tree was down but the roots were so intertwined with the septic that digging them up was impossible without a $25K septic rebuilding job.   So I used it but it's a slippery slope.  Where do you justify using chemicals and where's the line for not using them.  Tough call but in my case, $25K and safe application system (painting using appropriate personal protection versus spraying) were the dividing, practical line.

Your call is somewhat similar except it isn't economic.  It's cosmetic.  And I rarely recommend chemicals for other than persistent woody problems when we're dealing with cosmetic problems.

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Invading Trumpet Vine