Previously classified as a fungus, and sometimes called water fungus, Pythium is a type of plant parasite. Since Pythium is a genus, there are dozens of species classified under this name, and they affect all kinds of plants. One thing to keep in mind is that one species – Pythium insidiosum is a pathogen that animals need. However, the other dozens of species are usually parasitic. They are often passed on from the feet of the fungus gnat.
The major thing that Pythium is famous for is causing root-rot, something that can do serious damage to plants and rocks. Most of the time, at least in the United States, root-rot is caused by the species Pythium irregulare, P. aphanidermatum, P. ultimum and P. cryptoirregulare. Species of Pythium can be found in all sorts of soils, sand, ponds, streams and sediment beds as well as in the dead roots of last year’s crops. You will almost never get this problem from commercial potting soils but can be easily introduced through walking on your mix or letting your pets roam free on it, as well as by using dirty pots and tools that could contain Pythium.
Symptoms of Pythium
So, what symptoms might you experience if you have a case of the Pythium parasite infesting your plants? There are a number of warning signs to look out for. Here are just a few that should give you a good indication of whether or not you are currently experiencing an infestation from one of the dozens of species of harmful Pythium.
The root tips of the plant are brown and dead. Obviously, this will require that you pull up the roots and look at them, but this should be a symptom you should check after you have noticed some of the others on this list.
During the day you notice that your plants seem to wilt, but they get better overnight.
You notice that some plants are much smaller and not as healthy as the ones around them.
Your plants die, but only after turning yellow.
There is brown tissue outside of the root and you can pull it off and expose the vascular tissue beneath.
If you look at root cells under a microscope, you will notice round spores that have thick walls.
What to do if you Have Root-Rot
Unfortunately, if root-rot has already taken hold, you may not have much success in removing it. Most experts highly recommend that you do everything you can to prevent root-rot in the first place, because once you get it, it can be almost impossible to eradicate. Let’s first discuss what kind of things you can do to prevent root-rot and then talk about some of the things that might work to kill the parasite once it has infested your plants.
Preventing Root-Rot in the First Place
One of the things that you can do to prevent root-rot in the first place is using potting soil that has been pasteurized using heat. What you want is for it to have been heated up to 180 degrees for about 30 minutes. You don’t want any more than that, or any hotter, because it will kill the good bacteria in the soil.
Check your irrigation water carefully if you are getting it from a pond. Pond water can leak sediment through the intake pipe. If you are experiencing a Pythium parasite infection and you think that your irrigation water might be to blame, you should treat it before using it to water your crops or plants. Filtering the water through something like a sand filter will get rid of the parasite before it reaches your crops.
If you are using a flood and drain irrigation system, check your reservoirs. You might have to keep them covered to prevent debris from getting in. You should also pass water through some kind of a filter when it returns so that the potting soil and plant matter can be eliminated from the water before it gets into the reservoir.
Clean all of your tools, pots, benches and anything that could pass on the parasite with a disinfectant. You should also clean your irrigation pipes, reservoir beds, benches and flood and drain floors once in a while as well.
If you have a greenhouse and you have had root-rot from Pythium before, consider adding some type of fungicide to your crop cycle as soon as you can. For example, you can add these bio-agents to potting mix before the transplant, as well as afterward. You might need to apply them more than once and keep in mind that you can’t use pesticides for about two weeks prior to, or after, adding the fungicide to your potting mix.
If you want to get rid of root-rot after your plants have already been infected, you’ll have a hard road ahead of you. The first thing you want to do is watch out for the warning signs. If your crops or plants seem stunted or have wilted, the first thing to do is check the roots for root-rot. If you do, you may be able to act in time to save your crop. Remove the plant from the container and look for brown roots that are mushy, look for brown lesions on the roots or discoloration. If the roots appear to be decaying, you may have root-rot and if you can detect it early enough, you might be able to get rid of it.
The best way to get rid of Pythium root-rot is using a fungicide as mentioned in the section on preventing it. If the parasite infection hasn’t reached an unmanageable stage, you might be able to kill it with the fungicide. Some of the products on the market are fungicides that contain these products, which have been shown to be most effective at getting rid of root-rot. However, again, bear in mind that it is much easier to prevent it in the first place than to kill it once it happens.