Wednesday, March 2, 2022

Managing Invasives 2022

This is pretty typical of an 'invaded' tree with
Japanese honeysuckle and oriental bittersweet
 twining among its branches.

We’ve been on our central Maryland property for about 9 years now.  From day one we have been battling a slew of invasive species that were covering the ground and trees through the woodland landscape.  While we still have a ways to go I feel that we have made some good progress.  As I am getting ready to start another season managing the landscape I thought I would organize my plan around actions and timing, rather than looking at one species at a time. 


My first activity for the year will be to treat any visible garlic mustard, Alliaria petiolata, with a 2% glyphosate spray.  I'll do this sometime in the middle of March, when the temperatures  will be above 40°F with no rain for a couple of days. I started doing this 2 years ago and it seems to have helped me get the upper hand.  Prior to that I had  been only been pulling up plants in mid-spring as they grew tall prior to blooming. This link to my post on garlic mustard control options describes winter spraying in more detail and shows some of the desirable native species that may be visible at that time.  It also summarizes control options throughout the year.  The timing is critical as it is before the spring ephemerals, like spring beauties and Dutchman's breeches begin to sprout.  This lowers the chances of harming native species.   

Here you can see what a small garlic mustard, Alliaria petiolata,
looks like in winter.  Indian mock strawberry, Potentilla indica,
is also green through the winter.  Unfortunately, that weed is not
 as sensitive to glyphosate as the garlic mustard. 
See this link for methods to manage it.


Cutting woody invasives and vines and stump treating with 20% glyphosate can be done anytime of the year that the temperatures will be over 40°F for a few days in a row.  Winter is a good time to do this as it is easier to get to the base of many or these plants and there is less chance of getting the herbicide on desirable plants.  Particularly troublesome on my property are multiflora rose, Rosa multiflora, oriental bittersweet, Celastrus orbiculatus, Japanese honeysuckle, Lonicera japonica, and to a lesser extent Autumn olive, Eleagnus umbellata.  An excellent reference for managing invasives in the Mid-Atlantic region is Plant Invaders of Mid-Atlantic Natural Areas

In doing dormant season treatments it is critical to be able to distinguish friend and foe.  Below are some images of multiflora rose and other native species that it might be confused with.  

Here is multiflora rose in the winter.  Some distinguishing features are
its round olive green branches and its curved thorns.  The most
distinctive feature are the fringed stipules at the base of the petiole,
shown in the inset above.  It is the only species with this type of stipule.


Most native roses do not have green branches in
winter. Thorn shapes vary.  Here, swamp rose has
straight needle-like thorns.

Cat briar has bright green branches in winter
and it has straight almost pyramidal thorns.

Wild blackberry has smooth red stems in winter
armed with stiff red spines. Older branches
are square with indentions on each face.   

Black raspberry has red canes with somewhat smaller thorns. 
It is distinguished by the white bloom on the older branches 

You can read more about  dormant season treatment of multiflora rose at the link.  This technique is also effective on English ivy, Hedera helix.  Even if you don't use herbicides to treat the cut stumps, cutting vines climbing trees and over shrubs is helpful in controlling the spread of these invasives.  This is because many of these species are only able to bloom on vines that are elevated and/or exposed to plentiful sunlight.

Oriental bittersweet can twine against itself to get
stiffer and climb higher.  I cut these a while back
but left them long so I could easily find them. 
I'll cut them shorter and treat with glyphosate later.

This is typical of the damage that Japanese
 honeysuckle can do to a tree.  This vine can be
 recognized in winter in that it still has leaves and
 the older branches have shaggy bark.  


Around the end of March I will use a brush cutter and mower to cut down last years growth of vines and undesired woody plants in the meadow and woodland edges.  The biggest problem in my meadow is wineberry, Rubus phoenicolasius. In addition to the wineberry there are the aforementioned multiflora rose, autumn olive, and oriental bittersweet.  

Spring mowing and pulling has been pretty effective at reducing wineberry in shady areas. This is a short-lived species and not deeply rooted so it is usually easy to pull up.  Cutting to the ground in spring seems to keep it from blooming, but it is still able to reproduce by it ability to put down roots wherever a branch touches the soil.   It is recommended that mowing/cutting should be done several times each season to be truly effective.  This is particularly true in sunnier areas where the cut plants can rebound quickly.  Oriental bittersweet can also resprout easily after being cut.

Wineberry is easily recognized by its dense
coating of stiff hairs mixed with red spines. 
While formidable in appearance these are
easily crushed with a gloved hand.

I will return about a month later and do a foliar spray on the wineberry sprouts. While burning is not considered an effective option of wineberry control I will test out targeted ‘cooking’ of individual crowns with my garden torch to see if that kills them in place.  (Standard burns do not selectively kill the wineberry, rather it clears out the competition and allows it to grow unhindered.


At about the time that the forsythia is beginning to bloom is the time for me to get started on Japanese stiltgrass, Microstegium vinineum, control.  Stiltgrass has definitely been reduced in the lawn by use of a pre-emergent herbicide originally used for crabgrass control.  It should be applied when forsythia are beginning to bloom.  If you want to be more precise you can use a growing degree day tracker geared toward turf management. like GDD Tracker 4.0The product I use contains only dithiopyr (Dimension™) and no added fertilizer.  Most of my lawn is fescue based and not that hungry for added nutrition.  This link lists some other preemergent products that have shown effectiveness against stiltgrass.  I wrote about my year long plan for controlling stiltgrass in this post.  In the woods pulling and weed whacking, particularly in late summer has reduced, but not eliminated the amount of stiltgrass.  As a result of thinning out the stiltgrass, I am seeing more native species filling in such as white avens and Virginia jumpseed.  I am also seeing an increase in perennial grasses (perhaps a Glyceria species) in areas where stiltgrass had dominated. 

In the sunny meadow stiltgrass has been harder to eliminate.  The preemergent has not been as effective on the rougher soil and I am hesitant to use it every year as it may negatively affect the growth of desirable plants from seed.  Summertime pulling and the addition of tough native grasses and forbs is helping to displace the stiltgrass.  Weed whacking close to the soil level in late summer as the stiltgrass is beginning to bloom is effective.  However this will also damage other desirable species.  The best method or methods to use depend on the situation in a given location. 

Rest of Year

Mid-spring is the time when I will be watch for the rapid growth of garlic mustard as it prepares to flower.  Pulling it out and leaving it in the sun to dry is my method of choice at that time.  

Late-July and August are the time for pulling out stiltgrass as it prepares to bloom.

So there appears to be an awful lot to do, but it is encouraging that I have seen some progress.  I realize that I am talking about using a lot of herbicide, but these treatments are targeted on the actual plants and done at a time that has little negative impact on native species.  In this battle I feel it is necessary to properly use all the tools that are available.  Another aspect of invasive species control, is limited resources, especially time.  It is better to do one area really well, then move on to the next, rather than doing a little bit everywhere.

I wish you all good luck as another growing season is upon us!