Where do they come from? There a plenty of ways the bad guys get transported. Birds and wildlife can be the vehicle of transportation, whether stuck on their body somewhere or if they ate the plant and go to the bathroom at your pond.
Some are actually dumped into pond, maybe as a good gesture but can ruin the pond rather quickly. For instance someone with an aquarium or small Koi pond deciding they’ve had enough of it and dump their water, fish and plants into a pond. What happens is the aquariums and koi pond have opportunity to get these really cool looking exotic plants because of color or shape but they are imported from out of the states and can be invasive or fast spreaders.
Wind/weather also plays a part in the vehicle of spreading plants, tornadoes, hurricanes, up drafts and storms can pull plants and seeds out of the pond and ground and carry them for miles and be dropped off in your pond.
On with our Phragmites story. A year ago we had a few geese stop by but only for a little while and they would be on their way once the fountain came on or we shooed them off. So for these few visits they did leave behind their little nutrient bombs so this is who I can say left the seeds behind for the Phragmites to grow.
Maybe I made a mistake to see how far this plant would go in one season because in a few months it went wild. One little stalk fell into the pond and grew about 20’. I thought it was just floating but NO. At each point or knuckle of the stalk it dropped down roots to the bottom of the pond. Then along the ground I pick up a stalk only to find it was 20’ some feet long as well with the same thing going on dropping down roots along the length of this stalk.
I did hand picking and tried to get all the roots but they spread thru rhizomes, long roots spreading horizontally along the ground which can infest an area extremely fast by popping up another stalk where ever it pleases, plus the thousands of seeds the produce. At least I got them before the seed or flower started.
This year they’re back, plus what was in the water came back too, looks like more digging to do and wade out in the water and pluck them before they spread more. Yes chemical treatments are available so far I’m sticking to my plan of not using chemicals in my ponds.
Options for control is to continue to hand pull and dig up the roots which is the way I’m working on the now since they are just getting started and a small group of plants. But if you have a large stand or group of these Phragmites an option is to use a chemical, the same you would use for cattails, called Shoreline Defense.