How to Deal With This Common Fungal Disease

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Don’t you get sick from all the pests and diseases affecting your plants? There are so many bacterial and fungal diseases out there that it’s inevitable that you’ll encounter one (or more) at some point. One of those many fungal diseases is Cercospora leaf spot.

It is a common disease and can be recognized immediately by the small spots it causes. It affects many plants, particularly in the beet and nightshade families, and in some weeds.

What is Cercospora Leaf Spot?

Cercospora leaf spot most often affects plants in the beet family and is spread through fungi. Cercospora beticola. It is contagious and can hide in soil and seeds, and thrives in moisture.

It is widespread in plants such as Swiss chard, spinach and table beets and spreads quickly once established in your garden.

You can also get this disease from fungal species on ornamental plants like hydrangeas. Cercospora Hydrangea. Roses can also get this fungal disease Cercospora rosicola. Eggplant and other nightshades are affected by Cercospora melongenae.

Cercospora leaf spot doesn’t usually kill your plants, but it causes them to lose vigor, making edible plants unattractive. Vegetables like beets will fail to grow to a decent, usable size, and you cannot use leafy greens.

The disease usually takes hold well before symptoms become apparent, so management and prevention are important. It is better to prevent fungal diseases than to fight them once they are already infecting your plants.

What Causes Cercospora Leaf Spot?

Certain conditions cause the fungus to thrive.

These situations include when the leaves of your plants are wet for extended periods at night and there is high humidity.

High temperatures during the day in late summer also play an important role.

The optimum temperature for the spores to survive is between 75ºF and 85ºF. Along with moisture and humidity, they can be spread by rain splash, irrigation, equipment, wind, and insects.

Cercospora is wind-borne, so once it is present, it can spread rapidly via spores. Spraying water on plants is also an infection route. So overhead watering can often create perfect conditions for the fungus. You can also spread it through dirty garden tools.

Severe outbreaks in your garden can occur after extended periods of rain in summer or hot weather. Although a hot summer can often be a boon to the crop, it can also cause many diseases in the garden.

How Cercospora Leaf Spot Affects Your Plants

As the fungal spores germinate, they enter the stomata of the leaves. The stomata are small pores, usually on the underside of the leaves.

The initial symptoms of Cercospora leaf spot are small light brown spots that are lighter towards the center and may have a reddish edge.

How to Deal With This Common Fungal Disease

These lesions spread outwards, becoming attached as they grow. The color changes to gray, and the leaves die off. It can be so dry that it shrinks in your hand when you crush it.

Cercospora spores can survive in soil for up to two years, and because an infected plant produces so many spores, it doesn’t take much infection to produce too many spores in the soil.

Plants commonly affected by Cercospora leaf spot

Many plants are affected by Cercospora leaf spot, and symptoms can vary depending on the plant.


With carrots, the leaves will usually show pointed spots, along the margins. The leaves will also turn yellow and turn. Young leaves are affected more than older leaves. Humid weather after infection will spread rapidly to all foliage.

Spinach, Beet and Swiss Chard

How to Deal With This Common Fungal Disease

With these plants, you will see brown spots with red edges before expanding to cover the entire leaf. Over time the center becomes gray and brittle. Leaves can become woody and bitter and affect the quantity and quality of the crop. Under the right conditions, these plants spread rapidly.


On peppers, lesions develop on leaves, stems and where the two intersect (called petiole). The centers of the wounds completely dry up and break off. They often fall out, leaving a ragged hole.


Okra leaves droop before withering and dying completely. The lesions are much darker than any other plant infection.

Other crops affected by Cercospora leaf spot include:

How to Get Rid of Cercospora Leaf Spot

Before you begin chemical treatment, there are several preventive and environmental strategies you can use to keep the disease under control.

1. Sanitation

How to Deal With This Common Fungal Disease

This is super important. Sanitation includes the garden and the soil as well as your equipment. Remove all debris as it falls on the soil, and make sure you clean your garden tools regularly. Place all leaves and garden waste in the trash or on the fire. Step up your hygiene as soon as you think you may have Cercospora leaf spot.

2. Treated Seeds

Buy and plant certified disease-free or fungicide-treated seeds to avoid introducing Cercospora to your garden. Unfortunately, if you obtain seed from someone who has allowed a plant infected with Cercospora to go to seed, you will likely transfer the fungus to your garden.

3. Rotate Planting

If you have a Cercospora outbreak, it is best to move susceptible plants outside and plant crops that do not host the fungus for at least two to three years. You want to try to eliminate the spores before planting susceptible crops again.

A good crop rotation plan is always a smart idea.

4. Water at soil level

Avoid overhead watering if it will leave the foliage wet for long periods of time. Water at the base of the plant during the day to give the plant enough time to dry out. Remember, wet foliage and high humidity are a playground for Cercospora leaf spot.

5. Trim Away Infected Leaves

Remove leaves if infected. Often you will notice Cercospora leaf spot symptoms early, so remove the affected foliage immediately. Burn it or throw it in the trash, not your compost bin, as this will spread the fungal spores.

Older leaves are more susceptible in the early stages of the disease. As it grows, it will spread to new leaves.

Don’t be afraid removing the entire plant means avoiding the spread of this fungal disease.

6. Don’t Let the Plants Get Stressed

By far, the most common time to get Cercospora leaf spot is at the peak of summer when plants become stressed from lack of water.

Water your plants thoroughly, but at the base, not the top of the foliage.

7. Control Insects

How to Deal With This Common Fungal Disease

Many insects can spread this fungus. I use pyrethrum spray either by itself or added to neem oil spray as a knockdown and preventive combination.

8. Feed Your Plants and Soil

A healthy garden can resist pests and diseases better than one that is struggling and uncaring.

Feed all your plants with a well-balanced fertilizer, not just the ones you harvest for food. Make sure fertilizer or well-rotted manure is dug up before planting. You need to give the plants a good start.

9. Chemical Treatment

Preventive treatment is better than trying to fight Cercospora leaf spot, but sometimes you have no other option.

Regular treatment with a copper-based spray can help control the disease, especially in the early stages of infection.

Potassium bicarbonate can also be effective, but again, the sooner you get treatment, the better. BioWorks makes a product called MilStop that contains this powerful fungicide.

A spray that contains chlorothalonil such as Bonides Fung-Onil can also be used to treat Cercospora leaf spot.

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