The Sneaky Invasion of Non-native Cattails

Cattails are aggressively invading many of our state’s best aquatic habitats.

Story and photos by Chris Helzer

Most people reading this probably look at wetlands or lakes with dense accumulations of cattails without thinking twice. After all, cattails are native to Nebraska, and they’re a perfectly normal and healthy part of a wetland ecosystem. Right?

I have bad news. An evil transformation has taken place right beneath our noses. Cattails are no longer benign wetland plants that accent the margins of our favorite water bodies. They’ve become an aggressive occupying force that has invaded many of our state’s best aquatic habitats. Within those wetlands and lakes, as well as slower-moving rivers and streams, this new version of cattail spreads in dense formations. As it does, it chokes out other wetland vegetation and smothers the open water habitat needed by waterfowl and many other wildlife species.

How Did This Happen?

Here’s the quick answer: The native broad-leaved cattail species (Typha latifolia) has been replaced by an invasive cattail species from the east called narrow-leaved cattail (Typha angustifolia). The invader can displace the native species, but it can also hybridize with it, forming an equally, if not more, aggressive organism (Typha x glauca). The invasion has progressed so far that it’s become difficult to find a stand of native broad-leaved cattails in Nebraska.

Because the two species look very similar and the invasion has happened gradually, it’s happened with very little fanfare. Unfortunately, that means there’s been little resistance put up by most land managers and landowners, and many of our state’s best wet habitats are rapidly declining in habitat quality. That’s not universally true, of course. In the Rainwater Basin region, for example, habitat managers have long been fighting against cattails, along with other serious invaders like reed canarygrass that also form thick monocultures at the expense of waterfowl and other wildlife habitat. Other localized skirmishes with cattails are taking place as well, but not at a scale that has slowed the broader invasion.

Invasive cattails haven’t yet reached all the lakes and wetlands across the state, but that result is starting to feel like an inevitability. The best resistance strategy is to employ a search-and-destroy tactic in wetlands where the invaders are just starting to gain a foothold. Spot-spraying with aquatic-labeled herbicides can kill the plants, but that needs to happen when the first small populations appear to prevent them from mushrooming into massive hordes that defy easy solutions.

Once cattails have taken over a substantial portion of a wetland, the objective of a land manager has to switch from eradication to suppression. After several years of establishment, those large populations seem to be immune to complete destruction. Even a few stems that escape a control treatment can quickly initiate a population recovery. More importantly, cattails produce a tremendous amount of seed, which can germinate and fill the space created by its now-dead predecessors. Suppression of large cattail invasions, at least as we currently understand the situation, is a long-term commitment.

Two broad kinds of approaches are generally used to suppress big masses of cattails. The first is the use of an aquatic-labeled herbicide to directly kill the plants. The second is to reduce the storage of carbohydrates by the plants and then either drown them or otherwise kill them when they’re weakened. Those two approaches can be combined, of course, to enhance the effectiveness of herbicide treatments by reducing the vigor of cattails before spraying them.

The use of herbicides often comes with collateral damage. In many cases, the goal isn’t simply to eradicate the cattails, but to replace them with a more diverse plant community, at least along wetland and stream banks. Spraying herbicides that kill both the cattails and their potential replacements isn’t ideal, but it may sometimes be the best available option. Most importantly, it’s crucial to ensure that herbicides used (and any surfactants or other additives) are labeled for aquatic use and don’t negatively impact wildlife, including invertebrates, in the area.

The spring growth of cattails is fueled by carbohydrates stored during the previous growing season. After that pulse of spring growth depletes carbohydrate reserves, the plants spend the rest of the summer trying to rebuild them. Interrupting the summer growth of cattails with practices such as repeated grazing, mowing, disking or others can limit the reserves cattails carry into the winter. In playa wetlands or other sites that often dry up over the summer, those practices are much easier. Other wetlands hold water through most summers, making it much more difficult to attack cattails at that time of year.

If plants can be weakened during the previous summer, it becomes more feasible to drown them the following spring. While it seems illogical that a plant growing in water can drown, cattails need access to oxygen in the air to survive. In the spring, cattails can grow for a little while without oxygen, but need to extend their leaves above the water as soon as possible. The speed and amount of growth they can manage without oxygen is tied to their carbohydrate reserves. If the plants start the season underwater with low reserves of carbohydrates, they may not be able to grow fast or tall enough to break the water’s surface before they drown.

In addition to the energy they get from stored carbohydrates, cattails have one other hack for growing underwater. If the previous year’s dead stems are present, those porous stalks have air trapped within them. Cattails can draw oxygen from those stalks to make more efficient use of their carbohydrates and grow quickly. If those old stalks have been removed, however, cattails that start their year underwater are at a big disadvantage.

The reliance of cattails on last year’s stalks provides an important opportunity for land managers. In addition to reducing stored carbohydrate levels, managers can also burn or mow any stalks left after the end of one growing season so they won’t be there at the beginning of the next. If cattail plants are low on energy reserves and don’t have their backup option for accessing oxygen, it might only take a few inches of water above the base of the plants to drown them.

One of the more active and experimental fights against large scale cattail invasions in the Sandhills is taking place at the Valentine National Wildlife Refuge. Staff there have been employing a variety of strategies to reduce the size, density and impact of cattail patches to improve habitat and provide better food resources for migratory birds. Treatments include grazing, mowing, prescribed fire and herbicides, and combinations of those treatments seem to show the most promise. The results so far have ranged from disappointing to spectacular, but it’s still too early to know why some treatments seem to be effective in one place but not another.

During the summer of 2022, the refuge hosted a field day for wildlife biologists and land managers from across the state. That group visited numerous examples of cattail suppression attempts and discussed how to apply what was being learned to future efforts, both in the Sandhills and beyond. While there was a lot of inconsistency in the effectiveness of treatments, there was also cause for optimism. As an example, the tour stopped at a site that had been a monoculture of cattails for decades but was now covered with a broad diversity of wetland plants, including a few native cattails. It wasn’t clear why that particular treatment had worked there, but not elsewhere, but it was inspiring to see the capacity of wetlands to recover if given the chance.

It’s difficult to prescribe specific approaches for cattail control right now because we still have a lot to learn. What does seem clear is that even the most successful control results on large-scale cattail invasions will be temporary. It will take consistent and repeated efforts to prevent a cattail monoculture from rising again. However, we’re continually improving our techniques and some of the approaches (e.g., grazing) may end up paying for themselves.

While the challenge is great, the cost of doing nothing may be catastrophic. Nebraska has some of the most incredible wetlands on the continent, and they provide tremendous benefits, both to wildlife and people. Saving them from a devastating invasion seems well worthwhile.

Chris Helzer is the Nature Conservancy’s director of science in Nebraska.

Knowing Which Cattails are Native and Which are Invasive

Distinguishing native broad-leaved cattails from invasive cattails can be difficult, but the best clue can be found on the flowering stem. All cattail flower spikes have a section of female flowers, which resembles a hot dog, and a section of male flowers above that. The male flowers drop off after their pollen has been released, leaving what looks like a rough or wrinkled section of stem.

The native broad-leaved cattails have no gap between their female and male flower spikes.

Narrow-leaved and hybrid cattails, both of which are invasive, have a gap of 1⁄2 inch to 4 inches between the bottom (female) and top (male) flower spikes. Unfortunately, cattails — especially hybrid cattails — don’t always make flowers, so the best identification characteristic might not be present. If you’re facing a large, dense colony of cattails that has spread over time, working to suppress that colony is probably a good idea.