What Is Root Rot? (3 Ways To Prevent It In Your Plants)


If the plants in your house or garden look like they are weak or dying, root rot may be to blame.  This frustrating disease can happen for lots of different reasons, but it is never good.

So, what is root rot?  Root rot is a plant disease that causes a plant’s roots to decay.  Root rot can also cause stunted growth and leaf damage.  Root rot is more likely to affect plants in wet soil.  Some of the fungi that cause root rot can survive for years in soil, and some can spread by root contact or by spores in the air. 

Of course, there are ways to prevent root rot from happening in the first place.  Sometimes a plant can recover, but the best medicine is prevention in this case.

In this article, we’ll talk about root rot, what causes it, and how to tell if your plants have it.  We’ll also look at how to prevent root rot.

Let’s get started.

What Is Root Rot?

Root rot is a plant disease that causes the roots of a plant to decay.  The roots may continue to rot and deteriorate to the point where the plant’s growth is stunted.

roots
Root rot is a plant disease the causes the roots of a plant to decay. It is caused by various types of soilborne fungi.

Sometimes, root rot will resolve itself.  However, in other cases, the disease progresses to the point where a plant can no longer absorb water and nutrients, leading to death.

According to the University of Wisconsin-Madison Extension, most plants are susceptible to root rot, including:

  • Houseplants
  • Ornamentals (both woody and herbaceous)
  • Shrubs & Trees
  • Vegetables
ripe tomatoes on vine
Root rot can affect tomatoes and other garden staples, in addition to houseplants and ornamentals.

The symptoms of root rot can vary considerably, since many different pathogens can cause it.

How Do You Know If Your Plant Has Root Rot? (Symptoms Of Root Rot)

A plant with root rot will often display some or all of the following symptoms:

  • Dark Roots (healthy roots are a lighter color, often white.  You can check this in potted plants by carefully removing the pot to check the outer roots).
  • Stunted growth (slower than usual).
  • Discolored leaves (yellow or red is common, which is often caused by a nutrient deficiency – even with plenty of nutrients in the soil, damaged roots cannot absorb them!  The edges of leaves may also be affected.)
  • Wilted leaves (limp leaves that are wrinkled and hang down instead of standing upright).
  • Dropped leaves (the leaves of a plant may drop off, which can leave some fruit susceptible to sun damage).
  • Reduced yield (due to fewer flowers and fruit, as a result of lower plant vigor).
root rot
As the disease progresses, root rot causes roots to turn brown and mushy.

Sometimes the damage will affect the stem of the plant as well.

The origin of root rot can be difficult to pinpoint, since many different fungi can cause this disease.

What Causes Root Rot?

Root rot is caused by various fungi that live in soil, including:

  • Fusarium – this fungus can affect plants as young as the seedling stage.  Fusarium affects tomatoes, peppers, and eggplants, among other plants and weeds.  This fungus can spread through the air, on surfaces, or by the roots of plants (so don’t put plants too close together!)
  • Phytophthora – this fungus often affects trees, including true firs, Douglas firs, spruce, and eastern white pine, along with many Christmas tree species.
  • Pythium – this fungus can affect turf grass and other plants.  Pythium will decrease root depth and density of infected plants.  Too much water or mulch can cause this disease.
  • Rhizoctonia – this fungus can survive in soil and can cause decay of seeds, seedlings, and established plants.  Rhizoctonia is more common in warm, moist, sandy soil.
  • Thielaviopsis – also known as black root rot, this fungus affects pansies, petunias, and vinca.  Thielaviopsis can also affect many perennial plants.  It is capable of surviving for years in the soil, even without a host plant.  This makes it difficult to eradicate.

You can find a table describing the effects of root rot caused by these fungi from the Michigan State University Extension.

Fusarium root rot
Fusarium root rot can affect both young and established plants.
Image courtesy of user:
Jerzy Opiola via:
Wikimedia Commons: https://commons.wikimedia.org/wiki/File:Fusarium_sp_(4).jpg

However, they suggest that the best way to diagnose root rot is to send a plant sample to your local agricultural extension office.  They can provide a more detailed inspection and analysis to give a definitive diagnosis.

Check out the USDA website to search for agricultural offices by state.

Phytophthora root rot
Phytophthora root rot can cause wilted, yellow leaves and stunted growth.
Image courtesy of user:
H.J. Larsen via:
Wikimedia Commons: https://commons.wikimedia.org/wiki/File:
Phytophthora_root_and_crown_
rots_of_raspberry.jpg

Many of the fungi that cause root rot can infect a variety of plants.  This makes them more dangerous, since they can jump from one plant type to another.

Pythium root rot
Pythium root rot is another disease caused by soilborne fungi.
Image courtesy of user:
Scot Nelson via:
Wikimedia Commons: https://commons.
wikimedia.org/wiki/File:
Awa_Pythium_Root_Rot_–_wilt_on_young_plant.jpg

Some of these fungi produce spores that can travel on the wind or survive in soil for one or more years (even through the winter).

Soil fungi prefer wet conditions to survive and thrive.  Wet soil reduces the space for air, and the resulting lack of oxygen allows soil fungi to thrive.

rhizoctonia root rot
Rhizoctonia root rot causes the roots to turn brown as they rot.
Image courtesy of user:
Ninjatacoshell via:
Wikimedia Commons: https://commons.wikimedia.org/wiki/File:
Rhizoctonia_Root_Rot_on_Corn.png

Soil may stay wet for too long in the following cases:

  • Heavy rainfall (plants in a spot where water flows during heavy rain are more susceptible to root rot).
  • Over watering (keeping the soil too wet for too long by watering too often can cause root rot for indoor or outdoor plants).
  • Poor drainage (heavy clay soil or a container without drainage holes make root rot more likely).

Can Root Rot Fix Itself? (Does It Go Away?)

Sometimes, root rot can fix itself if there is very little root damage and the soil is allowed to dry out.  However, in cases where the root damage is extensive, there is little chance of root rot going away.

rhizoctonia root rot
In cases of severe root damage, root rot is unlikely to fix itself.
Image courtesy of user:
Fk via: Wikimedia Commons: https://commons.wikimedia.org/wiki/File:
Root_of_sugarbeet_root_rot.jpg

Many types of root rot have no treatment, so your best bet may be to remove and destroy infected plants.  That way, you can prevent the spread of the disease to other healthy plants.

How Do You Get Rid Of Root Rot? (Treating & Preventing Root Rot)

There are some chemical fungicide treatments for root rot.  You can learn more about them in this article from the Penn State University Extension.

However, prevention is the best treatment for root rot.  The best way to prevent root rot is to follow these guidelines for plant care:

  • Reduce soil moisture – moist soil that stays wet for too long provides the perfect conditions for the fungi that cause root rot.  Water deeply and infrequently, and allow the soil to dry out a little bit (not dusty bone-dry) between waterings.
  • Improve soil drainage – the best way to avoid wet soil is to improve soil drainage.  If you have heavy, dense, clay soil, you can make it drain faster by mixing in some compost.  You can learn more about how to make soil drain better in my article here.
  • Avoid too much mulch – too much mulch will retain moisture in the soil beneath, which can lead to root rot.  Too much mulch can kill plants in other ways – you can learn more in my article here.
  • Check plants for root rot before buying – look for the symptoms mentioned earlier in the article (yellow leaves, stunted growth, etc.) or take the plant out of its pot to check for brown roots.  If you don’t buy infected plants, they can’t infect your other plants.
  • Choose disease resistant plants – for example, some tomato plants are labelled with an (F), meaning that they resist Fusarium.
  • Use clean soil – if you are starting seeds or potting plants, don’t reuse soil, which may be infected with fungi that cause root rot.   Instead, use sterile seed starting mix or potting mix.
  • Leave enough space between plants – do not overcrowd your plants, or their leaves or roots will touch.  This gives diseases a way to spread more easily.
  • Plant at the proper depth – avoid burying the stems of plants when you move or transplant them.  Otherwise, they might not get enough air, which paves the way for root rot.  One exception is tomato plants, which can produce roots from higher up on the stem if they are buried deep.
  • Do not transplant anything infected with root rot – otherwise, you risk spreading the disease to the plants and soil in other parts of your garden.
  • Clean tools between uses – this includes shovels, trowels, and stakes for supporting climbing plants.  Use alcohol to clean tools and kill fungi that cause root rot.
  • Use new twine or ties – twine can harbor some of the fungi that cause root rot, so use new twine each year instead of reusing the old pieces.
seedlings in seed tray
If you are starting your own seeds, use clean soil in a tray with individual cells. This will prevent the emergence and spread of root rot.

Is Root Rot Contagious?

Many types of root rot are contagious.  The fungi that cause root rot can spread between plants of the same species (or across different species!) in a number of ways:

  • Infected Soil – some of the fungi that cause root rot can survive in soil.  In some cases, they can survive in soil for years, even without a host.  If you move infected soil around or transplant into infected soil, root rot can spread to other plants.
  • Infected Tools – for example, if you dig in infected soil with a shovel, you can spread the fungi that cause root rot to a clean part of your garden.  Clean your tools between uses!
  • Leaf Contact – if plants are too close together, their leaves may touch.  Some of the fungi that cause root rot can spread by spores, which are carried by the wind.  The closer the plants are to each other, the more likely that infections can spread.
  • Root Contact – when plants are crowded without enough space, their roots may touch.  The fungi that cause root rot can spread this way.  When starting seeds, consider using a tray with individual cells to prevent the spread of disease.  When transplanting, use proper spacing to avoid the spread of disease.
  • Transplant – if you transplant into infected soil or use infected tools, you may spread the fungi that cause root rot.
  • Water – when you water (or when rain falls), it can splash up, bringing soil and soil-borne fungi with it.  This can get onto the leaves of plants and infect them with a disease.
shovel
To stop the spread of root rot, clean tools (like shovels) after contact with infected soil & plants.

Can You Reuse Soil That Has Root Rot?

You should not reuse soil that has root rot.  As mentioned earlier, some of the fungi that cause root rot can survive in soil.

Pythium root rot
Some types of root rot can survive in soil for years without a host, so don’t reuse soil that has root rot.

In some cases, these fungi can survive in soil without a host – sometimes for years at a time.  Your best bet is to use fresh, clean seed-starting mix or potting mix to avoid the spread of the fungi that cause root rot.

Conclusion

Now you know what root rot is, what causes it, and what the symptoms look like.  You also know how to prevent it by taking the proper steps to give plants the right environment for healthy growth.

You can learn more about how to promote healthy root growth in plants in my article here.

You can also learn about the best fertilizers for root growth in this article.

I hope you found this article helpful.  If so, please share it with someone who can use the information.

If you want to read some of my most popular posts, check out the “Best of GreenUpSide” page here.  Enjoy!

~Jonathon

jonathon.david.madore

Hi, I'm Jon. Let's solve your gardening problems, spend more time growing, and get the best harvest every year!

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