Marigolds are amazing little flowers. Not only are they extremely low-maintenance, but they’re also so easy to grow that they’re often people’s first experience in growing plants.
But that’s not to say they’re completely without problems.
In fact, a wide range of diseases can harm your marigolds, but the good news is that most of them are easily preventable.
What Diseases Attack Marigold Plants And Flowers?
The vast majority of diseases targetting marigolds are due to poor care methods.
Of these, the most common cause is overwatering, which is preventable using the soak-and-dry method.
Botrytis Blight (Botrytis cinerea)
This fungal disease occurs as a result of overwatering or abnormally damp conditions.
The fungus was named after the fact that it most commonly affects grapes, but it can also target a wide range of plants, especially food crops.
Once infected, marigolds will exhibit patches of brown, rotting tissue.
In the middle of these spots are silvery spores.
There’s no effective cure for botrytis blight, and it’s best to immediately remove and destroy any infected plants.
However, neem soil soaks have been known to reduce the risk of developing this fungus when used as a general preventative.
Additionally, proper watering techniques can help minimize the risk of botrytis blight.
This disease can be caused by a range of fungal infections and is technically a symptom rather than its own disease.
A plant with collar rot will begin to develop black lesions on the stem below its flower buds.
As collar rot is caused by overwatering, you should employ good watering habits.
Additionally, infected plants will need to be destroyed.
Discard the soil the plants were in to avoid infecting any future plants.
This fungal disease is caused by several fungi and will most often target seedlings.
As the name implies, it’s caused by exposing the plant to excess moisture.
The exact symptoms can vary depending on the strain of fungus involved.
Some potential symptoms include:
- Fungal leaf spots
- Lesions at the base of the stem
- Wire-stem (where the stem becomes thin, tough, and wiry)
- Visible mold
- Root rot.
Proper watering and using only sterile soil are the keys to preventing this disease.
You should remove any infected seedlings nads discard them along with the soil they were in to prevent spread.
Edema (AKA Oedema)
This isn’t so much a disease as a common reaction to overwatering.
When a plant absorbs too much water, some of the cells in its leaves can burst.
This causes blistering on the leaf surface, which can eventually become necrotic.
Proper watering techniques and spacing can both eliminate the risk of edema.
If a plant develops this condition, repotting (or replacing the soil with drier soil) will help prevent further blisters, while removing any affected leaves can help keep your marigold healthy.
Flower Bud Rot
This fungal disease causes flower buds to wither and turn brown, while the leaves may become necrotic along their margins.
More mature buds, meanwhile, may simply fail to open.
Left untreated, the plant will eventually die.
This disease can be treated using fungicides, although you may need to destroy any plants where the infection is widespread.
Fusarium Wilt (Fusarium oxysporum)
The nasty fungal disease affects a wide range of plants, including marigolds.
It often begins with chlorosis, a condition where the plant can no longer produce enough chlorophyll, and the leaves will become paler.
The leaves will wilt, beginning with the older ones, while younger leaves may become stunted.
Necrosis along the margins and leaf drop soon follow, ultimately resulting in the plant’s death.
While you can combat this disease, it can survive for long periods in barren soil.
As a result, it’s best to destroy the infected plant and its soil.
Proper watering techniques and well-draining soil will help minimize the risk of developing this disease.
Not caused by any single fungus, this condition gets its name from the powdery white to light gray mold that develops on an infected plant’s leaves.
In most cases, the presence of powdery mildew is a side effect of a plant infestation, as honeydew is a prime breeding ground for the fungi.
If not treated, powdery mildew will eventually stunt any infected leaves or buds, causing them to die.
This is a surface infection, so normal preventatives (such as neem soil soaks) won’t treat it.
However, a soil soak can be used as a preventative against the pest insects that create honeydew.
Additionally, neem foliar sprays have shown some effectiveness in killing powdery mildew, as do fungicidal sprays.
You may also wish to remove any heavily infected parts of the plant.
One of the most dreaded diseases, root rot, can be caused by both fungi and bacteria, making it more difficult to treat.
Possible symptoms include:
- Signs of underwatering despite getting plenty of water.
- Wilting, visible cottony fungus on the soil surface.
- A foul odor comes from the soil.
It’s most often caused by overwatering, and the most common treatment is to uproot the plant, remove any visibly infected roots, sterilize the root system, and replant in sterile soil.
Southern Bacterial Wilt
This disease tends to affect marigolds being grown in warmer regions primarily.
The disease causes wilting and stunted growth, and affected leaves usually turn light yellow or grayish-green.
It doesn’t take long for this disease to spread, and it can kill a marigold within just a couple of weeks.
Unlike fungal infections, there’s no cure for southern bacterial wilt, so you’ll want to remove and destroy affected plants as soon as possible.
However, there are numerous cultivars with increased resistance to bacterial wilt, so consider using those if you live in an area prone to this disease.
Like fusarium wilt, this disease is caused by members of the Verticillium genus.
Both the symptoms and treatment options are the same as fusarium wilt, although the infections tend to be a little less intensive.
Some cultivars are being bred to resist verticillium, which can still be prone to fusarium.