[MAIPC] Fallopia japonica

[Judy Fulton]

Andrea,

You've given me some useful information. I haven't seen Reynoutria x 
bohemica in the wild that I know of, but I've heard that it's hard to 
distinguish from R. japonica. I also find it somewhat difficult to ID 
plants from pictures, and the photos that were sentto me don't show much 
detail. My understanding is that the easiest characteristic for 
distinguishing among R. japonica, sachalinensis and x bohemica are the 
hairs along the veins on the leaf undersides, but those hairs aren't 
visible in the photos (see Flora of North America: 
http://www.efloras.org/florataxon.aspx?flora_id=1&taxon_id=250060601 and 
Weakley's Flora of the Southern and Mid-Atlantic States, page 800: 
http://www.herbarium.unc.edu/flora.htm).

I thought that the plants in the photos appeared to have leaves in the 
size-range for R. japonica; however, it's conceivable that they are 
bigger. (In the close-up photo it's hard to compare leaf size to what I 
assume is a 4 x 4 upright or to the boards on the deck because of 
foreshortening. I ended up trying to look at the leaf shadows against 
the boards to determine size.)

How sure are you that the plants in the photos are Reynoutria x 
bohemica? What are the specific leaf size and shape characteristics that 
you are using to distinguish between R. japonica and x bohemica? 
Weakley's Flora of the Southern and Mid-Atlantic States says that R. x 
bohemia has "mid-branch leaf bases usually slightly cordate", whereas R. 
japonica has "mid-branch leaves truncate (to very broadly V-shaped)". I 
can make an argument that the mid-branch leaves in the close-up photo 
look slightly cordate, but I'm not sure, and there are plenty of similar 
leaf shapes online that are attributed to R. japonica. Can you recommend 
a key with a more definitive description that I can use in the future? 
I'm planning to collect samples of some knotweed near me to key it out 
and see whether it's japonica or x bohemica.

Thanks again,
Judy
____________________________________________

Judith P. Fulton
Consultant, University of Maryland Extension
Master Gardener, University of Maryland Extension
Chair, Maryland Invasive Species Council Subcommittee on Invasives Lists
410-337-3701
jfulton5 at gmail.com

On 9/6/2016 11:35 AM, Locke, Andrea S wrote:
>
> In addition to the methods provided, I’ve found success using 
> stem-injection with glyphosate, especially for areas adjacent to 
> water. My understanding is also that japanese knotweed (/Reynoutria 
> japonica/) doesn’t produce viable seed, however giant knotweed (/R. 
> sachalinensis/) and the hybrid bohemian knotweed /(R. x bohemica/) do. 
> Looking at the photographs provided, this is probably bohemian, not 
> japanese. Leaf size and shape are good characteristics to use for 
> differentiation. In my area, bohemian is the most common knotweed, by 
> far.
>
> Andrea Locke
>
> WNY PRISM Coordinator
>
> 716.878.4708
>
> lockeas at buffalostate.edu
>
> *From:*MAIPC [mailto:maipc-bounces at lists.maipc.org] *On Behalf Of 
> *Judy Fulton
> *Sent:* Friday, September 2, 2016 12:00 PM
> *To:* MAIPC <maipc at lists.maipc.org>
> *Subject:* [MAIPC] Fallopia japonica
>
> I was recently sent the attached two photos of what looks like 
> Fallopia japonica (aka Polygonum cuspidatum and Reynoutria japonica), 
> which were taken in May. Apparently, the homeowners, whose property 
> borders Back River in Baltimore County near Rock Creek Park, Maryland, 
> are quite pleased with their decision to plant “Japanese bamboo” to 
> reduce erosion.
>
> I’m concerned because Fallopia japonica can live in salt environments, 
> such as salt marshes. I’ve been informed that the mouth of Back River 
> is at the southern edge of the fresh water zone of the Chesapeake Bay 
> with average salinity of 6 ppt, but salinity can range from <1 ppt to 
> 10 ppt depending on weather conditions.  I’m assuming that the pieces 
> of rhizomes that might break off in a major storm could survive in 
> Back River to colonize other areas, especially if the storm reduced 
> the salinity in the river. Does anyone know if this is correct? Also, 
> would the seeds remain viable if they were transported to another 
> location by Back River?
>
> If the homeowners were convinced to remove their Fallopia japonica, 
> what would be the best way to eradicate it so near the water? 
> Something like Rodeo plus a non-ionic surfactant?
>
> Thanks for your advice.
>
> Judy
>
> ____________________________________________
>
> Judith P. Fulton
> Consultant, University of Maryland Extension
> Master Gardener, University of Maryland Extension
> Chair, Maryland Invasive Species Council Subcommittee on Invasives Lists
> 410-337-3701
> jfulton5 at gmail.com <mailto:jfulton5 at gmail.com>
>

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