The Carlisle Mosquito Online

Friday, October 27, 2006


Backyard action plans for invasive plants

The natural landscaping around Carlisle is beautiful. Most homes have conventional suburban landscapes consisting of foundation plantings, lawn, planting beds and ornamental trees. In my opinion, however, it is the surrounding native vegetation that really frames the home and provides year-round visual interest. It would be wonderful if these woodland borders could be left to themselves, but unfortunately without intervention all of these areas will eventually be overrun with a tangle of invasive plants.

Our native forest edges that offer views and afternoon strolls are being replaced by some very nasty thickets and obviously the remaining interior forest sections are also being compromised. To help Mosquito readers identify these plants, I have assembled a "rogues gallery" of invasives with cooperation from the Conservation Commission. The display can be found at the Town Hall flag pole through next week.

History of invasive plants

Most of our woody invasive plants have been intentionally introduced over the last century for either erosion control or landscaping. The postwar building boom, agricultural decline and suburban landscaping interest combined to accelerate the invasive march over the local landscape. Because most people have difficulty detecting changes in trees and shrubs from year to year (seasonal changes are much more dramatic), invasive plants have stayed under the public radar. Many of them are pretty, they seem to have always been there and appear to be minding their own business. Why all the phobia?


The answer lies in taking a careful look at the landscape not from year to year but from decade to decade. Within that time frame, these invasive plants are not minding their own business, while our beautiful landscape is being destroyed.

Carlisle's worst invasives

In my opinion the worst offenders in our area are:

Bittersweet. This climbing vine overruns and kills large trees. Once established, replacement tree seedlings cannot survive. The proper name is Oriental Bittersweet.

Buckthorn, Glossy or Common. Ironically we seem to have more Glossy than the Common species but there are not any good Buckthorns. These plants thrive along the woodland edge and then penetrate into the forest interior threatening native shrubs and trees. Although birds will take and disperse the fruit, it has low nutrient value.

Multiflora rose. This is actually a rootstock that has escaped from hybrid rose gardens. Yes, it has delightful flowers and nice red fruit, but it forms violent tangles that impede walking and over-tops native plants.

Barberry. Generally Japanese Barberry, but again no reason to get into modifiers — they're all bad. These brutal plants form dense thickets transforming diverse forested lowlands into very unpleasant places.

Honeysuckle. All types are bad. Some sections of abandoned Carlisle farmland are completely dominated by this plant. Walking through them is impossible.

Norway maple. You could argue that at least this invasive plant is a tree of some stature, but unfortunately it poisons the soil to kill its competition (plants use herbicides too). Its wildlife contribution is zero when compared to the native Red and Sugar maples.

Purple Loosestrife and Common Rush (Phragmites). If you don't remember wide expanses of wildlife-nurturing wetland cattails from your youth I suppose these plants are attractive but because they are both so ecologically barren compared to our native wetland plants I find them depressing.

Burning Bush. This plant is only just starting, but there are woodland areas where these are rampant, for example bordering Green Cemetery.

Autumn Olive. It is similar to Buckthorn in terms of habit — another bad plant just getting started in Carlisle.

Japanese Knotweed. The stems look similar to bamboo; once established they keep on spreading.

Garlic Mustard. Undoubtedly several other herbaceous plants should be on this list, but my experience has been mostly limited to trees and shrubs. This new but very aggressive biennial plant has a scary capacity to thrive in a shaded forest floor and form extensive mats.

All of the above plants are on the Massachusetts Prohibited Plant List (, a better-late-than-never law banning the import and sale of invasive plants.

Control Measures

To protect our local landscape from these invaders:

• Consider ripping out listed species from your planted landscape.

• Take a survey along the edge of your yard. Fortunately most properties only have three or four prevalent species. I'll guarantee that you have at least two.

• Crosscheck identification as needed against the rogues gallery at the Town Hall or any of the numerous invasive plant web sites. The Nature Conservancy's is my favorite (

• Obtain Cons Com approval prior to working in or near wetlands.

• Dispose of seeds and viable cuttings responsibly so that you do not spread plants to new areas.

Autumn Olive
• Hand pulling smaller plants is very effective, especially if the disturbed soil is covered over with leaf litter / mulch. Weed Wrench is a very effective tool for some larger plants. Hand pulling is highly recommended when small pioneer Purple Loosestrife or Common Rush is found in an otherwise pristine wetland. Garlic mustard can be pulled easily.

• Cut and cut again. This can be frustrating for some plants such as Buckthorn but it certainly slows all plants down. This is an excellent method for reducing the amount of seeds dispersed from landscape plants such as Barberry and Burning Bush if you can't bear to rip them out entirely.

• Herbicide spraying of low-lying invasive plants is ecologically justifiable in my opinion if the label is followed (location, time of year, weather conditions, concentrations, species) and complete eradication followed by zero tolerance within a clearly defined area is the plan. Round-Up and Brush-B-Gon are common choices.

• Cutting and stump-treating taller plants when hand pulling or spraying is not an option. Brush-B-Gon is labeled for this technique but note that the plant must be active (not dormant) and herbicide must be applied while the cut is still fresh. Cutting tools include loppers, hand saws and chain saws. Some weed whackers can be fitted with brush blades, a bit dangerous but very effective."Tree mowers" are available for when the job appears overwhelming.

• Cut and then spray when the plant resprouts — some plants such as Multiflora Rose and Honeysuckle are very difficult to stump-treat.

• Basel bark herbicide formulations allow you to treat standing plants with very limited quantities. These products are marketed for use with hand sprayers, but I consider hand painting to be more ecologically responsible. This method works well on thin-barked taller plants such as Buckthorn, Norway Maple and Autumn Olive. I use an oil-based herbicide applied with a paint roller that I call the Buckthorn Deathstick. E-mail inquiries are welcome. This method allows you to kill the plants without having to simultaneously deal with moving the brush and treating the often difficult-to-locate stumps. The formulation is effective year-round and can also be used effectively on dried stumps. Dead plants can be left standing to decay in place.

• Natural controls. For all the plants listed above there is only one natural control on the horizon — a beetle that is an effective predator of Purple Loosestrife. For limited, isolated plants, however, I strongly recommend hand pulling ASAP.

• Professional services. Make sure that hired herbicide applicators are licensed as required by law and can identify a Buckthorn from a Honeysuckle and a Barberry from a Winterberry. Otherwise you risk wiping out everything and thus encouraging another invasion.

Patrolling your woodlands on search and destroy missions might be just another tedious chore but on a pleasant day I find it infinitely more enjoyable than flossing teeth or changing the oil. Whatever time and energy you can commit to the battle against invasive plants will be rewarded with prettier, more sustainable landscape.

Note: John Bakewell operates Carlisle Arboriculture. He can be reached at

2006 The Carlisle Mosquito