Plants classified as invasive species or “invasives” cannot be collected, transported, imported, exported, moved, bought, sold, distributed, propagated or transplanted, according to Douglas Cygan, Invasive Plant Coordinator for the New Hampshire Department of Agriculture.
So how do they reproduce themselves?
You don’t want to know. Or in the case of the Derry Conservation Commission, Derry Garden Club and Go Green Committee, you do. The Conservation Commission hosted Cygan last week and invited the other two groups and the general public to hear what they can do about controlling and eliminating invasives in their personal and civic gardens.
One invasive plant can produce up to 2.5 million seeds, as opposed to a native plant’s thousands, Cygan said. The seeds of the invasive are borne by the wind or buried in the ground, to reproduce for another day. They can also be propagated by unsuspecting homeowners when the homeowner attempts to chop down the plant. Chopping, Cygan said, only helps it to propagate further.
The plants are fast-growing, with the ability to produce many seeds and offspring, he said. The Norway Maple’s seeds can be carried by both wind and water, while the Purple Loosestrife seeds can float.
And an invasive plant can appear in another form or “cultivar,” he said. For example, the Norway Maple has a cultivar called the Crimson King, with brown-purple foliage, he said, adding, “But its genetic makeup reverts back to the Norway Maple.”
There’s a number of reasons for not wanting that to happen, Cygan observed. Invasives inhibit the growth of native vegetation, eliminating species diversity. They disrupt the ecological process by taking more than their fair share of light, water and nutrients; they affect wildlife habitats; they can alter the soil chemistry; they can lead to crop losses; and they can even cause structural damage.
“In Europe, if you want to buy a property that contains Japanese knotweed, you will not get a mortgage,” he said.
They can even affect human health, he observed, noting that the “Japanese Barberry” creates a habitat for deer ticks and also for the white-footed mouse, another host for Lyme disease. Giant Hogweed is also dangerous, creating burns on human skin for anyone who touches it without protective covering.
Cygan reviewed the ways of controlling or eliminating invasives in New Hampshire, including chemical, mechanical and natural remedies.
Mechanical remedies include a “weed wrench,” a tool effective with woody invasives. Conservation member Dennis Wiley observed that the Commission owns two of the gadgets and will loan them out to homeowners.
The wrench is a good tool for getting every bit of a plant, Cygan said. “Don’t leave anything behind – it will regenerate,” he cautioned. Don’t even sever the roots, but lift the plant out whole, he said. The so-called “fork-spade” is effective for this, he said.
“Cutting is useless – it only propagates growth,” Cygan said.
Chemical remedies are good with some invasives but must be approved by the state Division of Pesticides. Also, he said, pesticides on a public area can only be applied by a licensed pesticide applicator.
Natural, biological remedies are also good, such as importing leaf-eating beetles to deal with purple loosestrife.
Cygan advised home landscapers and gardeners to be cautious about earthen fill, hay or straw, because these could hold the seeds of a future problem.
Japanese knotweed has been a particular focus of the Derry Conservation Commission. It can propagate when well-meaning homeowners take a load of brush to the dump and a piece falls off the truck, he observed, adding, “It’s diabolical.”
For more information, e-mail [email protected] or call 271-3488.
