Invasive plants in Pennsylvania

by Stephen Wagner

The McKean County Conservation District has partnered with Penn State’s Education Extension to talk about some of the most invasive plants in the commonwealth. The Conservation District worked in concert with the Allegheny Plateau Invasive Plant Management Area to bring us this information. Madeleine Stanisch, a resource specialist with the district, hosted the session.

An invasive plant spreads aggressively, grows rapidly and displaces native plants. It’s likely to cause ecologic or economic harm via damage to the wildlife habitat. “Japanese knotweed, for example,” Stanisch pointed out, “is highly invasive because it’s the only thing growing. It out-competes everything else because sunlight can’t get below the big leaves on it.”

Invasive plant advantages go into the game full tilt, with seeds transported by wind, water, animals and people. Couple that with fewer, if any, native controls (insects, disease, herbivores and other plants) and you have a problem.

Citing Japanese knotweed as a primary villain, Stanisch noted, “Everyone has seen this plant. It grows everywhere – along stream banks, in disturbed soil. It grows in people’s yards. It isn’t picky where it grows. Originally from Asia, it grows on the sides of volcanoes, so its root system is enormous. It’s difficult to treat because people think that if they’ve treated the top, they’ve done their job.”

The root system has to be killed because it’s so extensive. It prefers shaded soils along rivers and streams, and reproduces by plant fragments and rhizomatically.

A lookalike is common pokeweed, but it is native and beneficial. It’s notable for its purple berries on red stems.

Japanese stiltgrass is “kind of like an early detection/rapid response plant for an area,” Stanisch said. Not quite as invasive, it populates roadsides and wooded areas. It prefers moist soils but tolerates drier sites, and invades floodplains, forests and uplands.

Deer-tongue grass is nearly a twin to stiltgrass, and is a native plant.

Bush honeysuckle, with its red berries, starts growing about midsummer. “It’s the first green thing I see in the spring,” Stanisch said. “There are a lot of different species of honeysuckle, and a lot of them are invasive.” If you cut into a non-native variety stem you’ll find a hollow pith. The natives ones are not hollow.

How is wildlife affected by these plants? Some birds, like the Baltimore oriole and the cedar waxwing, can change color based on their invasive dining diet. The tip of the waxwing’s tail can change from yellow to orange by eating the aforementioned berries.

Glossy buckthorn is another invasive that small birds and animals abet by distributing seeds. With its red to purple fruits, it leafs out earlier and longer than native vegetation. Its habitat includes nutrient poor soils, full sun and dense shade, and it’s found in every environment from swamps to wet meadows. There are two buckthorns – the common/European and the glossy. The main difference is that the common has toothed margins, and the glossy doesn’t.

Goatsrue “looks a lot like crown vetch but is larger than crown vetch,” Stanisch said. It grows along stream banks and in moist areas and flowers from May to August. It boasts a 27-year seed bank. “What that means is that if a seed doesn’t germinate, it can stay in the soil for that long.” It is toxic to livestock, and therefore subject to the Pennsylvania Noxious Weed Control Law. Just because it has turned into hay doesn’t mean it’s lost its toxicity, so beware.

One advantage of Tree of Heaven is a near extreme tolerance of poor soils. This up to 80-foot tree will grow through cracks in the pavement. It can produce 300,000 seeds a year. Stanisch’s way of identifying Tree of Heaven is to take a leaf and crumple it. “The resulting smell is like bad peanut butter,” she said. It is the preferred host tree of the spotted lanternfly – “a double whammy that we definitely want to keep out of the area.”

A common lookalike is the staghorn or the smooth sumac, Stanisch noted. Unlike the Tree of Heaven, it only attains a height of 15 to 30 feet, and it’s often mistaken for walnut or butternut trees.

“Japanese barberry is pretty widespread at this point thanks to birds eating the berries off of it,” Stanisch said. Like many of its invasive relatives, it is shade tolerant, drought resistant and found in wooded habitats, wetlands and disturbed areas. Japanese barberry is associated with higher tick population. Mice will eat the berries and any ticks that are on the mice drop off into the bush. Knowing how bad Lyme disease can be, Stanisch advises to stay out of the woods if you don’t have to be there.

2021-06-10T12:51:17-05:00June 10, 2021|Mid Atlantic, Western Edition|0 Comments

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