Invasive Shrub Control Strategies

- Eastern North America has more invasive shrub species plighting native plant communities than any other geographic region in the world.

Some of the most common and aggressive invasive shrubs in Pennsylvania include Japanese barberry, autum olive, privet, shrub honeysuckles and multiflora rose.

Fortunately, most invasive shrubs are easy to control compared to root suckering species like tree of heaven.

If you effectively treat the aboveground parts of invasive shrubs, the roots will die.

When applying control measures, plan to work in the least invaded areas first.

This will help prevent spread and maintain areas of low invasive plants impact.

Next, rescue areas where native plant communities are currently present and competing with invasive plants.

And lastly, take on the most difficult sites, restoring areas dominated by invasives.

Small infestations of young plants, particularly shrub honeysuckles, autumn olives and privets can be effectively pulled by hand.

Pulled shrubs can be piled or left where pulled.

Mowing is often a helpful first approach when controlling invasive shrubs.

It effectively eliminates the shrub canopy and provides access to heavily overgrown sites.

It also eliminates the need to drag and pile or chip the stems.

Smaller stems are readily dispensed with using heavy duty rotary or flail cutters such as brush hogs.

For larger stems, fixed tooth drum type forestry cutters have the capacity to cut down large stems at the ground line and finally chop the debris.

Mowing is imprecise and will likely also remove some native plants.

It is done where invasive shrubs are dominant or where access is a major barrier to other control efforts.

Mowing is not a standalone treatment.

Cut stems of invasive shrubs will resprout vigorously.

It must be followed with a herbicide application to eliminate resprouts.

Treating sprout growth following cutting with either a foliar or basal bark herbicide application is recommended.

The knee to waste high resprouts are easy to treat and can be distinguished from native sprouts you wish to retain, such as shrub dogwoods and viburnums.

Because invasive shrubs have extended leaf phenology, there's a longer operational window to effectively apply herbicides.

Foliar treatments are an option for most species from early June into October.

Foliar spot treatments using a backpack sprayer or mist blower are an effective means to treat sites with low to moderate invasive shrub densities.

Typically there will be several different shrub species present on a site which may respond differently to a given herbicide active ingredient.

Using a mixture of the herbicides glyphosate and triclopyr provides a broader control spectrum than either of ingredient alone.

This mix is non-selective, but with no soil activity poses little risk to non-target plants through root uptake of herbicide.

The addition of metsulfuron provides an added benefit to help control difficult species.

It is especially effective against multiflora rose.

Basal bark and stump treatments are also effective against invasive shrubs and provide year round application opportunities.

Basal bark treatments use a concentrated mixture of the herbicide triclopyr ester mixed in a basal oil.

The mixes apply completely around the lower 12 to 15 inches of the stems.

The bark should be thoroughly wetted but not to the point where runoff is noticed.

Basal bark applications can be applied year round, except when snow prevents spraying to the ground line.

Effectiveness may be reduced if stems are saturated with water at the time of application.

If control efforts remove invasive shrub top growth, then stumps should be treated with a herbicide to prevent resprouting.

Cut the stems close to the soil line and treat the stump.

Oil-based herbicides using triclopyr ester can be applied to the stumps anytime following cutting, and should cover the cut surface, as well as the sides of the stump.

Water soluable herbicides, such as glyphosate or triclopyr should be applied immediately to freshly cut surfaces.

After initial control measures have been applied, continue to monitor the area.

The site must be maintained through periodic re-treatments.

New plants will continually invade sites as birds and other wildlife carry in seeds.

Invasive shrubs are kept under control only through a continued maintenance program.