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Past Articles Library | Plant Diseases & Control | Plant Diseases of Chrysanthemum

When it comes to Chrysanthemums or mums, as they are commonly known, this plant normally does not have any problems as long as they are cared for properly.  This includes pruning, fertilizing, and watering.  Having said that, the list below are diseases that mums can acquire.  To make diagnosis easier, we will work down the plant from leaves to the roots.

Foliage Diseases

Bacterial Blight

This bacterial issue affects leaves, stems, and buds.  It appears as blacking of the plant material from the top down.  This blacking then turns into a wilting behavior of the plant and eventually the plant dies.  This disease survives in plant debris.  To prevent this, clean, clean, and clean.  Tools, and pots will need to be sterilized along with only using plants that have a resistance to this disease.  Control environmental factors such as air circulation around plants by spacing properly, not watering overhead, and keeping humidity low.

If you find these symptoms in your mums, destroy the plants to keep the disease from spreading and killing your entire crop.   

Bacterial Leaf Spot

This bacterial disease appears as brown spots on the leaves that have a yellow ring around them.   These spots typically can be found growing along the veins of leaves.  Once you see this symptom, you will need to destroy the plant along with plants right next to the diseased plant. 

To prevent this plant disease starts with using clean seed, pots, and sterilized soil.  Avoid watering overhead, handling plants when they are wet, and only using disease resistant varieties. 

Foliar Nematodes

Foliar nematodes are little roundworms that live in the soil.  They utilize little streams of water on leaves to transport themselves from one plant to another.  How do you know if you have foliar nematodes?  Well, look at the lower leaves.  If you see yellow to brown spots on the lower leaves then you have a good chance of having foliar nematodes.  These spots will grow until the entire leaf is covered, wilts, and dies. 

Prevention starts with keeping the vegetation dry.  If you notice the damage described above, remove the plant material from the greenhouse or garden space and dispose of it in the trash.  Make sure to clean up any leaves or plant material that may remain.

Gray Mold

This fungus thrives when the weather is cloudy, wet, and humid.  It appears as water soaked spots on stems, petals and leaves.  These spots are brown and once spores are produced can be seen as powdery masses that are gray to brown in color. 

To prevent this starts with proper sanitation.  To begin with, avoid watering from overhead and when watering avoid getting the blooms wet.  Improve circulation by properly spacing the plants and keeping the humidity down.  

Leaf Spots

Leaf spot can be caused by numerous fungi.  The symptoms of this plant disease start near the bottom of the plant and consist of yellowing spots on leaves.  These spots then turn brown and/or black before the leaf dies.  This continues up the plant until all leaves are affected.

To prevent this, first start with proper mum care.  Avoid overhead watering, water in the morning, and avoid splashing water up on the leaves.  If you see yellowing leaves, remove them and throw them away. 

Other Viruses

Mums can suffer from similar plant viruses as tomatoes, and asters.  The reason for this is the fact that many plant viruses are transferred by sucking insects such as aphids, and leafhoppers.  While there is no cure for these viruses and if you have it your only choice is to pull up the plant, there are a few simple ways of reducing the chances of this infestation.  First, make sure the environment is clean.  This includes tools, pots, and even plant material.  Also, make sure to control weeds.  Many of these sucking insects will use these weeds as host plants.  Finally, while this last approach may sound silly, it is important to control the virus carrying insects.  

Powdery Mildew

This fungus appears on the mum as a powdery growth that is white or gray in color.  It attacks the leaves and sometimes the stems.  How do you know if you have this fungus beyond the color?  Take a look at the leaves.  If they are puckered and/or distorted, it is a good chance you have powdery mildew. 

While this fungus loves hot, humid weather, there are a few things that you can do to prevent and/or control.  First, makes sure you have proper air circulation.  Increasing the space between the plants will allow for more air movement and more drying.  When possible, keep the humidity down and increase the amount of light that the plants receive.


Rusts appear in late summer and can be seen as yellowish-green spots on leaves and/or areas of pus like pockets.  If you find this on your mums, destroy the plants immediately and contact your local extension agent. 

Vascular Diseases

Wilts are caused by pathogens in the soil and these pathogens can remain in the soil for years.  Below are two wilts that mums are susceptible to and what to do about it.

Fusarium Wilt

The symptoms of this wilt include yellowing of the leaves that can progress to browning and then death of the leaves.  The plant will also begin to look wilted or water stressed along with stunted growth.  If you cut the stem open and take a look at the vascular system of the plant, you will notice that this system has a reddish-brown appearance.

To prevent this, only use Fusarium Wilt free cuttings, keep humidity down, stop overhead watering, and use only pasteurized soil.  Also, keep the soil pH between 6.5 to 7 and use a nitrate nitrogen fertilizer. 

Verticillium Wilt

This wilt is a hidden wilt that only appears after the blooms have formed.  Symptoms will start with the yellowing of the leaves either along the margins or the entire leaf.   Leaves will eventually die from the bottom up.  Sometimes dark lines can be found along the vascular system of the leaf. 

This wilt is brought on by cool weather that is followed with hot temperatures.  To prevent this, only use pasteurized soil and wilt free cuttings. 

Diseases of Flowers

Ray Blight

Ray blight is caused by Didymula ligulicola.  This plant disease affects both the blooms and the leaves of the flower stem.  Flowers and buds will be blackish and can be deformed.  The leaves on these affected stems can die and/or become deformed.  This disease is spurred on by unsanitary conditions, overhead watering and/or high humidity. 

To prevent this, keep humidity low and give up overhead watering.   Start the crop off right by only using disease-free cuttings.

Ray Speck

Stemphylium lycopersici is the cause of this plant disease.  It appears as brown spots on blooms.  Once these spots appear, the bloom will die.    This disease thrives in wet environments that are kept between 60 and 85 degrees Fahrenheit. 

If you find this disease on your buds and/or flowers, throw the plant in the trash.  Also, improve air circulation between plants by not crowding and stop watering overhead.

Diseases of Roots and Crowns

Mums share the same root and crown diseases that other plants grown for floriculture production do.  This includes Pythium, Phytophthora, and Rhizoctonia.   To aid in the prevention, make sure the area is sanitized and stop watering overhead.

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