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dealing with invasive asiatic smart weed #813305

Asked October 05, 2022, 4:20 PM EDT

m being invaded by asiatic smartweed how do i combat it?

Washington County Maryland

Expert Response

Several smartweed species look very much alike, frustratingly, so if you have an invasive species like Oriental Smartweed and not the native (or even undesirable amounts of the latter), you can either dig them out, repeatedly cut them down until they stop resprouting, or treat them with herbicide. Both our most widespread native and the common invasive species are annuals, so will die on their own this winter. In that case, if you can keep them from going to seed by cutting them back for now, the only herbicide you might need would be a pre-emergent to prevent germination of next year's generation in spring. Product choice will depend on where the plants are growing (lawn, garden, etc.). If there are too many to mow-down or pull up, you can use a contact herbicide to kill the top growth so they don't go to seed (assuming they haven't already). Organic herbicides can be a useful approach for this, but be mindful that they are non-selective so will damage any desirable plants the spray contacts. Follow all label directions for any herbicide chosen.

If you wish to avoid herbicide use, just pull the plants up now (they won't grow back) or next year, when seedlings appear, keep cutting them back to remove foliage so they can't photosynthesize. Since the repeated removal of their foliage deprives the roots of energy, they will stop resprouting eventually. (Annual weeds are much easier to eliminate in this way than perennial weeds, so this may not require many repeat attempts.)

Depending on where these are growing, smartweeds generally like damp to wet soils, so if this is an area of lawn or a garden bed that isn't a purposeful rain garden, perhaps something needs to change in the drainage patterns of that part of the yard to keep it from staying that moist. See if any nearby roof downspout outlets are flooding an area with extra water. With a change in conditions that lets the soil dry more between rainstorms or irrigation sessions, the seedlings may not return if conditions don't suit them.

Miri

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