As our volunteers know, we do a lot of manual pulling of invasives and have professional services cut larger woody invasives.  The goal is to minimize the use of pesticides and herbicides due to their negative impact on the environment and our health. We do use herbicide on the cut stumps of woody invasives like Honeysuckle and Tree of Heaven to stop regrowth. It is not a good option to spray large swaths of herbaceous vegetation due to drift and run-off.

We have a considerable stand of poisonous hemlock, which carries its own health risks when exposed to its sap. It’s not something that is easy to pull. Being in the same family as carrots, it has a deep taproot. And it shouldn’t be tackled with a weed eater or handled due to its neurotoxic chemistry. So, we are going to treat it with herbicide.

I spoke with Ken Cooke, our conservation advisor, with Friends of Wolf Run. Here are his recommendations.

Since we are working close to the stream, we will use an “aquatic approved” 53.8% glyphosate. The isopropylamine (IPA) salt form pf glyphosate is what gives it the "aquatic" label designation under its EPA registration.

That designation is meaningful because it authorizes use on emerged vegetation in or adjacent to water bodies. All 53.8% glyphosate IPA salt concentrates share the same regulatory basis. Some formulations, like Airmax, contain no surfactant. For effective foliar uptake on Poison Hemlock — which has a distinctly waxy stem and leaf surface — a surfactant must be added to the mix. And for any application near a water feature, that surfactant must also carry an aquatic use authorization. Standard POEA-based surfactants (like those in consumer Roundup products) are not appropriate in aquatic or near-water settings.

Mixing and application instructions for Poison Hemlock

Timing = SPRING

Glyphosate is most effective on Poison Hemlock in the rosette stage (year-one basal growth) or in early spring of the second year before the plant bolts and begins to flower. Effectiveness drops significantly once flowering and seed set are underway. The herbicide needs time to be absorbed through the foliage.

Mix Rate = 1.5% Glyphosate + Surfactant

For spot treatment of Poison Hemlock with 53.8% glyphosate, mix approximately 2.5 to 3 oz of concentrate per gallon of water (roughly a 1.5% solution). Add 0.5 to 1.0 oz of Plex Mate per gallon of spray solution. Add the surfactant last, after mixing the herbicide with water, to minimize foaming.

Application = Fully Wet all Plant Surfaces

Apply with a backpack or hand-pump sprayer to thoroughly wet all leaf and stem surfaces of actively growing plants. Glyphosate is non-selective, meaning it kills everything, so take care to avoid overspray onto desirable native vegetation. Do not cut or mow treated plants for at least 14 days after application; the herbicide needs time to move systemically from the foliage into the root system.

Follow-up Required

Poison Hemlock seeds can remain viable in the soil for several years. Even a successful treatment this season should be followed by a site check next year for new rosette emergence from the seed bank.

Personal Protection Equipment (PPE) Required

Poison Hemlock is highly toxic. Wear gloves, long sleeves, and eye protection when working in infested areas regardless of whether you are spraying. Avoid any contact with sap from cut or damaged stems.

Health Concerns Around Glyphosate

One more item I want to make sure is on your radar before you use these products — the health risk and the personal protective equipment the label requires.

You may be aware that glyphosate has been the subject of considerable regulatory controversy, particularly between the US and EU. The short version is that the two regulatory systems evaluated somewhat different things. The US EPA assessed glyphosate as an isolated active ingredient and, as of its most recent review, concluded it is "not likely to be carcinogenic to humans" when used according to label directions.

The EU's concerns, and the IARC Group 2A "probable carcinogen" classification issued in 2015, were driven in significant part by studies of the complete formulated product — particularly formulations containing a surfactant called POEA (polyethoxylated tallow amine), which showed higher cytotoxicity in laboratory studies than glyphosate alone.

The EU has since specifically restricted or banned POEA-based surfactants.

This distinction is relevant when looking at available products. The products listed below (and the one we are using in the greenspace) does not contain POEA.

Farm General Aquatic Herbicide contains no surfactant whatsoever — only the glyphosate IPA salt and an inert carrier.

Plex Mate is a non-ionic, plant-based surfactant that is specifically not POEA chemistry, which is why it carries the aquatic authorization. The combination we use is among the lower-risk glyphosate formulations available commercially and is in better standing with respect to the EU concerns than standard consumer Roundup products.

There is also active litigation in the US against Bayer (Monsanto) alleging links between glyphosate exposure and non-Hodgkin lymphoma and chronic lymphocytic leukemia. Juries have found in favor of the plaintiffs in the cases that have gone to trial. Science remains genuinely contested at the regulatory level. I cannot tell you the specific risk level — only that the products selected minimize risk relative to the alternatives, and that label-compliant PPE further reduces exposure meaningfully.

Required PPE per the Product Label

The EPA-registered label specifies the following minimum PPE for applicators and handlers:

• Long-sleeved shirt and long pants
• Shoes plus socks (closed-toe — no sandals)

Additional label requirements:

• Wash hands before eating, drinking, chewing gum, using tobacco, or using the toilet.
• Remove clothing or PPE immediately if pesticide gets inside, then wash thoroughly and put on clean clothing.
• After application, bag and wash your field clothing in hot water with a standard laundry detergent. Do this separately before laundering with household items.

For early re-entry to treated areas (within 4 hours of application), the label additionally requires:

• Coveralls over long clothing
• Waterproof gloves
• Shoes plus socks

More Reasons to be Careful

Ken also gives us his recommendation beyond the label when working in a Poison Hemlock infestation. Poison Hemlock itself — independent of the herbicide — is highly toxic through skin contact and inhalation of sap, particularly from damaged stems.

• chemical-resistant gloves (nitrile or neoprene) and
• eye protection (safety glasses or splash goggles)
• N95 or P100 half-mask respirator

The gloves and eye protection protect you from both hazards simultaneously. A disposable N95 or P100 half-mask respirator is worth considering if you are working in dense stands on a warm day when volatile compounds from disturbed plants may be present in the air. Think of it like working in a bar with secondhand smoke.

Some Good Herbicide Options Include

1. Farm General Aquatic Herbicide, 53.8% Glyphosate — 1 Gallon (Amazon ASIN B07NNX6NY6). Same active ingredient, same IPA salt formulation, same aquatic label authorization at a lower cost per ounce and in a much more useful volume for ongoing restoration work.
   https://www.amazon.com/Farm-General-Herbicide-Glyphosate-1-Gallon/dp/B07NNX6NY6/
2. Plex Mate Aquatic Surfactant — 8 oz (Crystal Blue, available on Amazon). Plex Mate is a non-ionic surfactant purpose-formulated for aquatic herbicide applications. It carries no water use restrictions beyond those of the herbicide it's mixed with, making it the correct companion product for near-water treatment. At 0.5–1.0 oz per gallon of spray solution, 8 oz will provide more than enough for your treatment area.
   https://www.amazon.com/Sanco-Industries-Surfactant-Herbicides-Non-Ionic/dp/B0049ACIX4/

Supply List

• 2.5 gallons of Glyphosate (Aquatic Formulation)
• 8 oz. Surfactant (Aquatic Formulation)
• Blue marking dye for cut stump treatments
• Spray bottles and buckthorn daubers for application
• Funnel for pouring
• Reusable arm’s length gloves
• A box of kitty litter for spill control
• Two rolls of paper towels for cleaning up after mixing
• A gallon jug of tap water for your rinse and mixing water, separate from the garden hose you use for watering plants you don't want to kill (for obvious reasons)