Invasive Plant News

Consider this recent article from the Journal of Applied Ecology: Estimating and influencing the duration of weed eradication programmes.  The article asks a very simple question: based on the past performance of a weed eradication program at a site, how long will it take to get rid of a targeted weed?  The model was applied to two invasive plants.  For one of the plants, chromolaena (Chromolaena odorata), the study estimated it would take a minimum of 23 years with (stepped-up efforts) and 248 years based on the results from the current program!

This may seem discouraging.  However, the study suggests many possible paths forward including: (1) total eradication is not practicable, but weed control is; (2) total eradication is not practicable and efforts should be focused elsewhere; or (3) more needs to be done, for example, at high-value sites.

The authors include: F. Dane Panetta, Oscar Cacho, Susie Hester, Nikki Sims-Chilton, and Simon Brooks.

For more information on chromolaena (Chromolaena odorata) as an invasive plant, read TT Struhsaker, PJ Struhsaker, KS Siex, Conserving Africa’s rain forests: problems in protected areas and possible solutions (free PDF). Biological Conservation, 2005; 123 (1): 45–54.

Using herbicide to control invasive weed trees such as buckthorn in the springtime can be tough.  The sap in the weed tree is rising, and it can be hard to get the herbicide down to the roots.

What can be done in the spring to woody invasive species?  Spring is a

Fig. 1 Tall Stumps Cut in May 2011

great time to cut the tops off woody invasives such as buckthorn and leave what I call a “tall stump.”  The tall stump should be at least waist height or higher as shown in Fig 1.  (NOTE: DO NOT cut the woody stem at ground level!  If you do this, most woody invasives will either form a bush around the short stump or will send suckers up from various parts of the root.  This is an absolute mess, so be sure to cut high and remove all the branches left on the tall stump.)

Why cut tall stumps?  First, it weakens the weed tree.  In the spring as the tree begins to leaf out,  sugars stored in the roots are being translocated to the crown.  By removing the crown near the time of leaf out, you have removed the primary springtime storehouse of sugars.  See Fig. 2.  Crown removal not only depletes this sugar sink; it also forces the tree to exert energy and develop new branches and leaves precisely at the time when its new leaves should be photosynthesizing.  This weakens the tree and makes it much easier to kill later in the season.

Second, invasive weed trees can form a real thicket.  Sometimes you can barely move through them.  By topping the trees, you clear out a lot of the branches.  This makes it much easier to come back in the fall or even winter to apply herbicide.

Fig. 2 Topping a Tree in Springtime When Sap Is Rising

Third, its a great way to divide up tasks.  It’s always hard to do both cutting and herbicide application simultaneously especially in a heavy thicket of woody invasives.  Moreover, the best time to do herbicide applications is generally the fall or early winter.  With the tall stump method, you are clearing brush and applying herbicide at the optimum times.

Finally, you can save time and use less herbicide.  In the fall or winter, you can do either a traditional cut stump or  frill method.  The application should be more effective – because the weed tree is weakened and you should be able to use less herbicide.

This presentation I did at the Midwest Meeting for the Society for Ecological Restoration earlier in 2011 explains the method in more detail.