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FOWS 2021 Q&A – Invasive forest weeds in Western Washington

Posted by brendan.whyte | March 8, 2021

Invasive forest weeds in Western Washington

Answers by Sasha Shaw, King County Noxious Weed Control Program


Q). How do you control morning glory?

A). Morning glory, also called hedge bindweed, has deep, extensive creeping roots/rhizomes that easily break when pulled. Careful hand-removal repeated whenever you notice new shoots will, over time, reduce the population substantially. Just don’t wait until the stems have grown up and over all your other plants! If there is a large dense patch, you can spread a thick layer of woodchip mulch (perhaps with a layer of cardboard or newspapers underneath) to weaken the plants, and then pull the shoots as they emerge from the mulch layer. The mulch won’t kill the morning glory, it just makes it easier to remove more roots. See our bindweed fact sheet for more details.


Q). Can chickens eat yellow archangel?

A). I’m not sure if chickens can safely eat yellow archangel. It is in the mint family but it isn’t used as an herb. It isn’t listed as a toxic plant but I’m not sure it is common enough for it to be known whether it is safe for chickens. My guess is they would avoid it due to the odor, but probably bet to avoid it if possible.


Q). Would you recommend a mix ratio of glyphosate and triclopyr? We usually do 125gal water to 100 oz roundup pro to 24 oz r-11?

A). The spot spray recommendations I’ve seen for ivy or yellow archangel are usually in the range of 2 to 5% glyphosate plus 1 to 2% triclopyr plus 1 to 2% surfactant, but that’s going to depend on the exact product labels you have so  make sure to follow the label recommendations for spot spraying perennial weeds or brush. To get the actual measured amount, remember the percent is by volume, so divide ounces of herbicide by gallons of spray mix to get the percent. Remember you need to be careful not to exceed the label rate which is usually given in amount per acre. That means you need to know both what’s going in your sprayer and how much you are spraying out. Also make sure to follow the mixing directions, the chemicals can react with each other if you don’t mix them correctly.


Q). How do you control poison hemlock?

A). Poison-hemlock is toxic if you ingest it, so make sure to wear gloves when handling it. Also, if you pull or mow large quantities and in areas with low air circulation you may feel ill from breathing in the odor. That said, it is simple to dig up or even hand-pull plants. They have a large, branched tap root so you can effectively remove the bulk of the root and kill the plant that way. Removed plant material should be discarded in the trash. Mowing is not effective because plants can re-grow. For more detail, see our poison-hemlock fact sheet.


Q). What is the best way to dispose of pulled weeds?

A). It depends on what weeds they are. Most weeds can be put in with clean green yard waste to be taken to a commercial composting facility. Almost all seeds will be broken down in the process so you won’t be spreading weeds that way. You can also do home composting of weeds, but generally you won’t want to use that compost because some seeds may survive if the temperatures don’t get hot enough for long enough. However, if the weeds are regulated noxious weeds in your county, it is best to put them in the garbage instead of yard waste or compost to avoid any risk of spreading them by transport or incomplete composting. This would include things like poison-hemlock and tansy ragwort that are also toxic. Here is a useful handout with more information:


Q). Who is the contact to report weeds in eastern WA?

A). It depends on the county. You can look up your county weed board contact info on the State Noxious Weed Board website.


Q). We have butterfly bush/blackberries/holly/ivy/Scotch broom/et al. The terrain is too steep for mechanical equipment and the area too large for hand removal. We would like to use a brush killer, but we live on the water (Puget Sound) and the area is by our domestic water well. Is there a specific product you would recommend?

A). That’s a tough one. If you are able to use a cut stem treatment on the bushes (cut the stem and apply herbicide directly to the fresh cut stem), then you could use either triclopyr or glyphosate, as long as there was no risk of herbicide getting into the water itself. However, it sounds like an area where herbicide use may be restricted to aquatic products only, which would require the applicator to have WSDA pesticide license and a permit from the Dept of Ecology. Another concern with a steep slope is that if you clear a large area all at once, there may be erosion or slope failure. I would recommend removing the weeds from small areas at a time and replacing with native shrubs and trees as you go to make sure there are roots established to help stabilize the slope. And carefully protect any native and non-invasive plants that are being left. This would be true for either chemical or manual control.


Q). Any tips on eradicating Himalayan blackberry on a 40% slope where there is concern about slope stability?

A). This is similar to the last question. My advice is to do this in stages, one strip of blackberry at a time, and make sure to use erosion control measures on any cleared areas until new vegetation is established. If there are trees or other desirable plants mixed in with the blackberry or along the edges, do your best to preserve those to help maintain the slope. Use control methods that are gentle on the slope such as cutting with loppers or a hand-held brush cutter, and then either using a backpack sprayer to treat the regrowth when it is 2-3 feet tall, or just repeat the cutting several times a year. I don’t recommend digging on the steep slope because that is more destabilizing.


Q). Can meadow knapweed or yellow archangel be eradicated by hand?

A). Meadow knapweed can be dug up and controlled that way, although the roots are large and deep so it will require a shovel and possibly repeat digging if some of the roots remains. Yellow archangel has very thin, fragile roots that tend to break off when you hand pull or dig them up and then the plants regrow easily from those fragments. You can control yellow archangel by hand, but it does require fastidious and repeated effort. It works best in looser, forest soils. In heavy clay soils, it may be very difficult. More info on these plants is on our website.


Q). Is horsetail a noxious weed and, if so, how can it be eradicated?

A). Horsetail is not a noxious weed and there’s no need to remove it unless you wish to. It’s a native plant in the PNW and beneficial in our forests and wetlands. However, in a home garden, yard, or pasture, people do try to get rid of it. It is very difficult to eradicate but you can suppress it with regular cutting. There is some information on horsetail control here.


Q). Can bark mulch be used for weed control? How deep would it need to be applied?

A). Bark mulch can be used, although a better product is chipped up woody material, such as from an arborist or your own wood chipper. It has a mix of wood and green material so it improves soil as well as suppressing the weeds. In general woodchip or coarse bark mulch should be 3-4 inches deep to suppress weeds. Make sure not to pile it up next to tree trunks or shrubs, and don’t use deep mulch over shallow rooted bushes like rhododendrons. Some weeds require deeper mulch, or a layer of cardboard underneath, to suppress regrowth.


Q). Are herbicides really safe for people and the environment?

A). All herbicides come with risks, and each person should research those risks for themselves so they understand how to use an herbicide to minimize risks, or they can decide to avoid herbicide use altogether. Herbicides are heavily regulated by the EPA and our state agencies, and they have detailed instructions for the user to follow to make sure to minimize any risks. Herbicides should never be used in a way not described on the label of the product you are using. Misuse of herbicides greatly increases risks and can cause harm to people and the environment. A good, non-biased source of information on pesticides is the NPIC website. NPIC provides objective, science-based information about pesticides and pesticide-related topics to enable people to make informed decisions. NPIC is a cooperative agreement between Oregon State University and the U.S. Environmental Protection Agency.