We can't see enough detail to determine the plant's ID, though it does look a bit like Johnsongrass, an invasive species. (We're not convinced the pictured weed is a grass, though, as the base of the leaf blade doesn't look quite right.) If this is not a grass, the plant may need to come into bloom before we can come up with an ID, since flower traits are very important when identifying plants with similar-looking foliage.

Miri

Hello Michael,

Thank you for the additional photos and information. Our new suspect for the weed's ID is Japanese Bloodgrass (also called Cogongrass, Imperata cylindrica), as it is known to be tenaciously weedy and has similar characteristics to the plants pictured (like the rhizomes and slightly off-center prominent white midvein in the leaves).

Grassy weed ID involves using fine details like the presence/absence of (or traits of) a ligule, auricles, vernation, sheath, collar, and others. Examples of what to look for are shown on the linked pages below:

• Grassy Weed ID -- Ohio State
• Cool-season Turfgrass ID -- Penn State (even though this focuses on turf, the same structures are still used for identifying weed grasses too)

We are checking with Extension weed specialists and will let you know what they think as soon as we hear back from them.

Miri

Two of our weed specialists agree that the visible traits appear to align with Cogongrass, though they can't see enough detail in the images to be more certain about that tentative ID. Since Japanese Pachysandra can be aggressive and might spread into natural areas, removing all plants from that area (which may help you dig most of the weedy grass out so what's left is easier to address) might be the most effective eradiation approach (or first step towards eradication).

If needed, you could try again with a systemic herbicide, using (if the product label allows) a surfactant addition to help it stick to the leaves without dripping off as quickly. Surfactants, also sometimes sold as "spreader-sticker," are sold alongside pesticides at garden centers since they two are often combined. Some formulations of herbicide might already contain a surfactant agent, though, which is why you'd need to see if the label encourages the addition of one or not for hard-to-kill weeds.

Another option, again if you sacrifice the Pachysandra as collateral damage, is to try smothering the patch so that the grass is starved of light. We'd suggest mowing it as low as possible in that case, then covering it with a light-blocking tarp for several weeks to exhaust the root energy stores. Since it's a creeping grass, though, there is a risk of some areas moving out of the dark area to get light, unless it can be monitored carefully and kept covered. How long that process would take is hard to predict, and even if it weakens the grass and it still regrows once the cover is removed, at least then it might be easier to dig out or treat with a systemic herbicide at that point.

Miri

Dear Miri,

 

           After I said that I haven’t seen this weed flower – it now has a flower !

 

See pic’s attached.

 

Thank you, 

Hello Michael,

Thank you for the additional photos. They do appear to be the seed heads / flowers of Cogongrass (also known as Japanese Bloodgrass), as we suspected earlier. The fact that the grass blades are starting to blush deep red-purple also supports that ID, since the cultivar widely grown of that grass (before it was banned in Maryland) has red-pigmented leaves.

Miri