Yellow Flag Iris Control: How To Get Rid Of Flag Iris Plants

by johnah on November 15, 2020

How to get rid of yellow flag irises?

The first thing you need to do is to identify your problem plants. You will have many varieties of yellow flags, but they all look very similar. They are all greenish or reddish brown with a few small white spots on their undersides. These little spots are called “flag” because they resemble tiny flags tied together at the top and bottom edges. If you were to tie them into a knot, it would look like a flag.

There are two types of yellow flags; those that grow in groups and those that grow alone. There is no difference between the two except for size. Some varieties may even have stripes instead of flags! The best way to tell which type of yellow flag you have is by looking at its undersides.

If there are several small white spots on the undersides of your plants, then you probably have multiple varieties of yellow flags. If these spots are large and dark, then you probably have only one variety.

You may also notice that some varieties have a distinct odor when touched. These are usually produced by the pseudocorus species. This smell is caused by chemicals called terpenes found in the leaves and flowers of this genus.

Some of the most popular varieties of yellow flags are Yellow Water Flag, also called Yellow Iris (I. pseudacorus), Narrow-leaved Water Flag (I. angustifolius) and Sweet Sedge (I. hexastichus).

Yellow Water Flag is a very common variety with long flag leaves that grow in watery areas. Narrow-leaved Water Flag looks quite similar to Yellow Water Flag except that it is much smaller and has smaller leaves. Sweet Sedge has a very sweet smell and grows in groups. There are other varieties out there that may grow in different places, but they all look quite similar.

The next thing you need to do is to get rid of your yellow flags. I would suggest you wear protective clothing when dealing with this problem. Make sure you wear long pants, long sleeved shirts, shoes and even gloves. Yellow flags have small hairs on them that can cause a skin rash similar to poison oak.

Also be careful when you are using chemicals, especially around water. Always read the label to make sure it is safe to use around water!

Once you have the proper protection, its time to get rid of your yellow flags. Any type of herbicide should work fine. Most people just use Round-up, but there are others that should work just as well. It is best to spray the weeds in the morning when they are still wet with dew.

This will ensure good contact with the leaves and speed up the process.

Be sure to get all of the weeds while they are still small! A larger yellow flag can produce thousands of seeds and it only takes one plant to root to start a new population!

I have heard of people using grass carp to control yellow flag. Apparently the fish like to eat them so it acts as a natural herbicide. It also helps to control the spread of other types of aquatic plants.

There are several ways to prevent the spread of yellow flags in your pond. The best way is to not let them get into your pond in the first place. Be very careful of buying plants from nurseries or other ponds! Most aquatic nurseries don’t screen yellow flags before they sell them to you.

A yellow flag can easily be hidden within the roots of another plant and not even visible to the eye. When you buy a plant, it is always a good idea to cut the plant open and examine the root mass before taking it home. If you find anything that resembles a yellow flag, do not bring it home! Also be careful of other people dumping unwanted plants in your pond.

If you do have yellow flags in your pond, then there are several ways to get rid of them. One of the best ways is to use a grass carp. These fish have been used for years to control various types of aquatic plants. They will eat just about anything they can get their teeth into.

The only problem with using fish is that you need special permits and need to make sure you don’t have any illegal species in your pond!

If you don’t want to fool around with special permits and such, your best bet would be to catch them the old fashioned way. This can be very tedious, but stand the best chance of getting rid of all the yellow flags. I would suggest placing a cup of flour in the middle of some of your infested area. When the flags drift into the flour they leave a white color that makes them much easier to see.

Now armed with a container, you can go through the tedious task of plucking each yellow flag out. You may have to do some weeding to get at all of them. Remember, while you are pulling up yellow flags you should also be removing other unwanted plants. It is much easier to remove everything and start over than it is to continually try to keep up with the maintenance.

If you do any type of grass carp management or hand removal, you need to put some extra time and effort into your aquatic plant control to make sure you get the right plants!

More Info:

Yellow Flag Control

Yellow Flag Images

Water Lilies

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Dear Pond Boss,

I was cleaning out my pond the other day and I came across a couple of

western mosquitofish (Gambusia affinis).

Are these fish harmful in any way?


Johnny Pond Boss

Western mosquitofish are originally from the southwestern united states. They have been used by many pond owners as a means of controlling mosquito larvae. They are very hardy fish and can even survive in droughts by burrowing into mud. They primarily feed on small invertebrates and algae.

They will eat most any food supplement designed for fish, but should only be fed about once a day as they tend to over eat and then waste away (a common problem withFish).

western mosquitofish and pond

Mosquitofish are best used in outdoor ponds that have some sort of filtration system and are properly maintained. Used as a single means of mosquito control, they tend to only reduce the number of mosquitoes around the pond instead of eliminating them.

The best way to get rid of mosquitofish is to place them in a container with a few card board pieces for them to hide in. Then add water and leave it overnight.

Sources & references used in this article:

Utility of unmanned aerial vehicles for mapping invasive plant species: a case study on yellow flag iris (Iris pseudacorus L.) by DJ Hill, C Tarasoff, GE Whitworth, J Baron… – … Journal of Remote …, 2017 – Taylor & Francis

Influence of iron plaque on accumulation of lead by yellow flag (Iris pseudacorus L.) grown in artificial Pb-contaminated soil by S Zhong, J Shi, J Xu – Journal of Soils and Sediments, 2010 – Springer

Comparison of carbohydrate utilization and energy charge in the yellow flag iris (Iris pseudacorus) and garden iris (Iris germanica) under anoxia by AM Hanhijärvi, KV Fagerstedt – Physiologia Plantarum, 1995 – Wiley Online Library

An unusual case of seed dispersal in an invasive aquatic; yellow flag iris (Iris pseudacorus) by JF Gaskin, ML Pokorny, JM Mangold – Biological invasions, 2016 – Springer



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