Identification and Treatment for House Plant Diseases

Indoor Plant Disease Prevention

Healthy indoor plants will be able to resist and fight off pests and diseases much better than weak plants. In order to keep your house plants strong you need to meet their cultural requirements, which involves using proper soil, avoiding drafts, not crowding plants and then keeping a good balance of temperature, humidity, light, water and drainage. A diseased plant by AnnaAll plants have different requirements and if you aren't sure what these are, be sure to check out our Plant Hub to find out what balance and care your particular plant needs to thrive.

Chances are though you are on this page because prevention is too late and you have been afflicted with something nasty and want a treatment now! Trust us when we say, we feel your frustration. All is not lost however and the rest of this page gets to grips with this.

Diseases

The eight most common ones are listed below along with a suggested treatment and the identifying symptoms. If you're having problems with something different let us know and we will try and help you out. Sometimes your plant will have a pest problem rather than a disease in which case you will need to head on over to our pest guide .

Crown and Stem Rot (Basal Stem Rot)
Grey mould (Botrytis)
Nutrient deficiency
Powdery mildew
Rust
Sooty Mold
Viruses
White Mold


Crown and Stem Rot (Basal Stem Rot)

This is caused by fungal mycelia which lives in most soils. It normally lives peacefully with the plant, however when conditions become very damp through overwatering, cool conditions or poor ventilation it rapidly multiplies and infects it.

Symptoms

Black or discolored rotten patches at the base of the plant. It normally effects the base because this is the closest part to the soil and therefore the fungus, although it's possible other parts will be infected instead. Succulents and cacti are most at risk.

Treatment

If the base stem has been effected there is very little you can do because the only treatment is to cut out the rot and dust with an anti fungicide such as sulphur. Obviously if you are cutting out the base you will kill or topple over the plant, it's therefore worth taking cuttings from the healthy parts and trying to propagate replacements.



Grey mold (Botrytis)

Botrytis thriving on a strawberryGray Mold or Grey Mould is caused by airborne fungal that land on damaged or dying tissue. Small wounds are normal on plants, if it is healthy and the conditions are reasonably dry it shouldn't be a problem. The issue arises when the plant is weak anyway and the surrounding atmosphere is humid and cool.

Symptoms

Soft rotting patches which are soon covered in a grey fungus. In addition you should be able to find the point of disease "entry", i.e. there will more than likely be dead brown patches on the leaves or stems, white or pale brown spots on flower petals or rotting on bulbs etc.

Treatment

Remove the infected parts of the plant. You may have to throw it away completely if it has got out of hand. Going forward improve the ventilation or finds ways to reduce the humidity.


Nutrient deficiency

If you have never fed or repotted your plant then a nutrient deficiency is quite probable. Nutrient deficiency in a plants leavesThe majority of plants make their own food through photosynthesis, however small levels of nutrients are needed to sustain that new growth and to ensure a healthy look. The nutrients are found in the soil but once they are gone they are gone and therefore it's important they are replaced either by a fertiliser or by changing the soil occasionally.

Symptoms

There are many symptoms of nutrient deficiency in house plants, although as a general rule you will be experiencing unusual or poor growth. The leaves may be very small with odd shapes, the colour of the plant may be dull or transparent in places. No flowers or flowers which are discolored or aborted before they can open can also be symptoms.

Treatment

The immediate treatment is to either fertilise using an all purpose mixture or to repot using fresh compost. Choose only one to start with, rather than both at the same time as this could result in too much fertiliser which can damage the plant further. The rule of thumb is to wait at least 8 weeks before you start fertilising newly repotted plants.


Powdery mildew

Photo showing Powdery mildew leavesFortunately powdery mildew is often disfiguring rather than fatal, nor is it overly common on indoor plants because it's caused by fungi spores that travel through the wind. Obviously if you have been summering your houseplants outdoors then you increase your risk. Warm, damp locations and plants which are situated very close together all increase your chances of the fungi taking hold and spreading.

Symptoms

A white film which looks like a light dusting of flour coats the leaves, over time the white may dull and become darker. If left unchecked it will spread over the entire plant, stems, flowers etc.

Treatment

Remove the badly infected mildewed leaves with care (you don't want to be acting like an artificial wind by blowing the spores around other plants) and then spray with a product containing Myclobutanil, Penconazole, Flutriafol or lightly dust the leaves with Sulphur to give control.


Rust

Rust on the leaf of a RoseRust is a common disease on Roses outdoors but inside, it's rather rare. If you grow Roses, Chrysanthemums, Pelargoniums or Fuchsias as houseplants you will need to watch out for infection as eradication is very difficult. Therefore if Rust is suspected you must isolate it from other houseplants to prevent it spreading.

Symptoms

Brown rings or spots on the leaves. They usually start on the underside although in more advanced stages they can appear on either side. Leaves may fall prematurely without any yellowing before hand and often when you gently brush past.

Treatment

Normally control is all you will achieve, however in any event you should carefully remove the infected leaves and try not to shake or knock the Rust spores from the discs as this will just spread the infection to other parts of the plant. If this doesn't work, any chemical product containing the following should help, Mancozeb, Penconazole or Flutriafol.


Sooty Mold (or Mould)

Sooty mold on an Umbrella plants leavesThis is a disease which has a very visible presence. It's not actually a direct attack on the plant but rather on the honeydew that is produced as a waste product by several pests, such as Scale. The honeydew is a clear substance but at certain visual angles you can see it as a sticky looking residual. As soon as the room because humid and less ventilated, perhaps as Winter approaches and we close our windows and switch on the central heating, the fungus takes hold and all the previously clear residual turns greeny black and moldy.

Symptoms

Black or dark green soot like spots or in extreme cases it will coat almost entire leaves.

Treatment

It does not directly harm the plant however it is horrible and unpleasant to look at. You can remove it by wiping over the leaves with a damp cloth. Afterwards rinse the leaves with clean water. Ensure you eradicate the pest problem at the same time to prevent future attacks.



Viruses

Plant Virus in an orchid leafViruses are a broad topic, the symptoms are varied and most types of plant are effected from time to time. They are typically spread by pests such as Aphids or by the plant being in close proximity to one that has already been effected. Therefore prevention is a must.

Symptoms

There are many symptoms of a virus and they can appear differently depending what type of plant has been infected. Growth may be stunted, twisted or distorted. Leaves may be yellowed or mottled in spots, mosaics or streaks. Any flowers may become streaked or not developed correctly i.e. they may mature and open but still be a green colour.

Treatment

There is no cure. If the symptoms can't be tolerated then you will need to throw it away. Don't try to propagate any part of the plant before hand as there is a high possibility the virus will remain and prosper in the new plants.


White Mold (or Mould)

"What is the white mold growing in my plant's soil"? Is one of our frequently asked questions. White mold in house plant soilIt's another fungus that quickly colonise the soil surface when conditions are moist, humid and over watered. Ventilation is also typically poor therefore it tends to appear more in cooler months of the year when everything in the home is shut up tight. Don't worry as White mold is basically harmless to plants and people.

Symptoms

The surface of the soil is coated in a white fluffy substance that looks like cotton wool.

Treatment

No need to reach for the sprays here. All you need do is gently rake up the effected soil using something like the end of a pencil or pen. You don't need to pick it out or anything like that so it's a very easy job. The raking could free up the fungal spores into the air though so do be careful not to inhale them as they may potentially trigger allergies and aggravate asthma. Think about maybe moving your plant to a more ventilated space or try and free the growing medium by making it more "open".


Also on OurHousePlants.com

Photo credit of the first diseased plant Anna
Photo credit of Botrytis on a strawberry Rasbak
Photo credit of Sooty mold Amnon Shavit


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