Knowledgebase
Identification of possible invasive aquatic plant #808029
Asked August 25, 2022, 3:30 PM EDT
Good day, I'm hoping you can help me to identify this plant. It showed up for the 1st time this year in my irrigation ditch. After looking through the noxious weed books I have for my area, I contacted my county weed abatement office. I described the plant and said the only thing closest to what I saw was knotweed, and they came and sprayed for it. I checked it yesterday and instead of it being dead or severely knocked back, it's healthy and spreading. After taking photos on site, along with gathering a sample to research, I believe this may be a type of Sagittaria (perhaps Latifolia or Cuneate). Its common names include arrowhead, duck potato, katniss, wapato. The leaf shape is arrowhead; the flower stalk has 3 adjacent stems w/1 flower per stem, every couple of inches up. The flower has 3 white petals w/yellow reproductive organs; the fruit is oval, green with a rough surface. If this is Sagittaria, is there any other information on this other than it's a native species, and it is used as a food source? I'm trying to find out how fast this can grow/spread per season, and if there is a way to control it? I'd hate to destroy it outright, however this is a small lateral irrigation ditch that services several folks. So we can't afford to have it choked out with this plant. I appreciate any help you can give.
Gem County Idaho
Expert Response
Apologies for whatever reason all the photos didn't upload the first time
My guess without keying it out is Sagittaria Latifolia, simply because it is the most common native with all of those characteristics in Idaho. It is a perennial that has a large tuberous root system that spreads through rhizomes. This means that chemical control is pretty much your only effective option. You would need to apply something that has an aquatic label, which means it can be applied over water and not leave residue in the water. Rodeo (a variation of glyphosate) is the easiest option. Be sure to follow the label instructions carefully, because misuse could cause an unintended application to someone's irrigated field. it is also possible to wait until the water is gone out of the ditch, which would simplify the process much more easily. Unfortunately most people are straddling time between an empty ditch and before the canopy senesces for the winter. Hopefully this helps. Best of luck.
