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My favorite dog walking route has become fraught with peril. Wild parsnip, with its pretty yellow umbrella-shaped flower clusters, is blooming along the path in abundance.

That's a problem because wild parsnip produces a toxin that causes phytophotodermatis. Contact with the plant sap increases the sensitivity of skin to ultraviolet (UV) light and can result in severe blistering.

If that isn't enough of a threat, healthy stands of poison hemlock stand nearby in wicked allegiance. Poison hemlock's fern-like foliage and white filigreed flower may look harmless, but the weed's name bears a deadly promise.

The weeds aren't new on the landscape. But the problem seems to be growing. This year I'm finding both weeds liberally dispersed along roadways and field edges.

Some theories say efforts to protect nesting birds and plants that attract butterflies and pollinators through naturalizing roadsides have contributed to the increase of these weeds. Mowing at the wrong time and spreading the seed may be another factor.

Joe Boggs, an assistant professor with Ohio State University Extension based in Hamilton County, hopes awareness of the dangers will lead to caution around these weeds. Boggs has excellent photos and resources online to help identify these potential troublemakers. (See https://bygl.osu.edu/…)

"Once these plants start flowering, it is really too late (in the season) to eradicate," Boggs told DTN. "However, the good news is both weeds respond very well to a wide range of post-emergent herbicides if applied at the correct time," Boggs said.

Mowing is not a safe option with wild parsnip because of the extreme risk posed by the sap, he cautioned. String or blade trimmers are also potentially hazardous. Even cleaning mower decks or blades can expose operators to the blister-inducing sap.

Boggs wrote that mowing could be an option for poison hemlock, but he recommended personal protective equipment (PPE) and shrouded mower blades. Poison hemlock sap does not cause blisters but can mechanically aerosolize and pose an inhalation risk, he noted.

Boggs said an alternative strategy is to mark the areas that need control and come back later with herbicides. Wild parsnip development from seeds to flowers usually follows a biennial life cycle. Seeds most commonly germinate in the spring and the first year is spent in the vegetative stage as a low-growing basal rosette. The rosettes use carbohydrates acquired through photosynthesis to produce a robust root system.

"Some recommend making (herbicide applications) in the fall," Boggs said. "However, I see better results in the spring just before the plants bolt because you will eliminate both the seedlings and the plants as they start to rise before flowering." Boggs called it "exploiting the lifecycle" of the weed.

Just taking out the weed isn't always enough, Boggs said, noting that these weeds seem to be more opportunistic than competitive. "Setting up competition (i.e. seeding grasses) is another component to management," he added.

ADDITIONAL INFORMATION

-- For more information on these weeds go to Boggs' blog at https://bygl.osu.edu/… and https://bygl.osu.edu/…

-- Find a previous DTN article on wild parsnip here: " Wild Parsnip Warnings," https://www.dtnpf.com/…

-- Purdue University information on poison hemlock can be found here: https://www.purdue.edu/…

Controlling poison hemlock in pastures requires additional considerations, since livestock are susceptible to it. For more resources go to:

-- https://utbeef.tennessee.edu/…

-- https://extension.missouri.edu/…

-- https://extension.umn.edu/…

Pamela Smith can be reached at pamela.smith@dtn.com

Follow her on social platform X @PamSmithDTN

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