Knowledge from Olle Garden Bed:What Are the Black Spots on Cauliflower and Is It Safe to Eat?

Cauliflower can be a challenging vegetable, so seeing your hard work stained with black spots can be devastating. What do these black dots mean? How can you get rid of them?The following content also has some reference value for raised garden beds.

There are several reasons why your cauliflower may have black spots. Many fungal diseases, such as black leg, Alternaria leaf spot, ring spot, Downy mildew or white mold, can cause dark lesions on leaves or heads.

Even if you have harvested cauliflower, it will still suffer oxidation or mold in the refrigerator.

Fortunately, you can solve this problem and cauliflower is still edible.

Continue reading to learn how to identify the problem you are dealing with, how to preserve cauliflower crops, and some tips to prevent future black spots.

Fungal disease is the main cause of black spots in cauliflower

There are several different fungi that can infect your cauliflower, causing black spots. Soil borne fungi exist in the soil and can be splashed onto crops during rainstorm.

Spores can also be spread through the air, introduced into your garden by the wind or blown from one plant to another.

When the weather conditions are cool and humid, fungi can attach to the leaves of plants and infect them through lesions in the tissues.

Most fungi thrive at temperatures ranging from 15 ° C to 21 ° C (59 to 70 ° F). If conditions remain moist and cool, fungi can quickly spread from plants to plants and infect the entire crop.

Fungi can also attach to your gardening tools and be carried from one plant to another, so make sure to clean your equipment, such as scissors and shovels, after handling sick plants.

There are many fungal diseases that can cause black spots on your growing cauliflower.

Some can damage the leaves, while others can infect the head. You should distinguish each fungus by certain signs so that you know which problem you are dealing with.

The fungi that cause black spots on cauliflower are:

Black leg disease

Alternaria leaf Spot

Circular point

Downy mildew

White mold

Let's take a look at how to identify each disease, as well as ways to prevent fungal diseases and keep cauliflower safe.

Black leg disease

Black leg, also known as stem ulcer disease, attacks the stems and leaves of cauliflower plants. Leaf damage is usually identified by a usually dirty white area covered with small black spots and yellowed leaves.

The lesions on the stem can be various shades of brown, accompanied by small black spots in the affected area.

The black spots are very small, sometimes only visible with a magnifying glass, and pink liquid often seeps out from the spots.

Black legs may cause stem atrophy and death in seedlings. If a plant grows to maturity, it will form ulcers, which usually worsen the stem and cause cauliflower to die.

Black legs can remain dormant in the soil throughout the season and can also be spread through the air between plants.

Poor quality seeds can also be contaminated by black legs, so your plant is destined to fail even before it begins to grow.

This is a very detailed article about rapeseed black legs, which has many similarities with infected cauliflower.

Black legs are often confused with Rhizoctonia solani, which is very similar but does not have black spots in the lesion.

Alternaria leaf Spot

Streptomyces brassicae and Streptomyces brassicae, like most fungi, prefer cool weather for their leaf spots, but they can also tolerate warm temperatures.

Its ideal range is 15.6 ° C to 25.6 ° C (59 ° F-78 ° F) and can thrive in humid environments. It produces target shaped spots on the leaves, with a brown concave center surrounded by a yellow halo.

Streptomyces can also infect cauliflower itself, causing black spots. A single bud or curd will turn black and often spread to a large area of the head.

The lesion is usually superficial, and the infected area can be cut off, so the head can still be consumed.

Circular spot

Brassica mold, ring-shaped spots do not affect the head itself, but its leaf damage is often confused with Alternaria leaf spots. Circumferential lesions are gray concentric rings with small black or white spots.

Although not usually fatal, ring-shaped patches can inhibit development and slow down plant growth, which can be very problematic during short growth seasons.

Downy mildew

Parasitic Hyalulosporidia and Downy mildew can infect cauliflower and other brassica at any time during their growth. Its spores are spread through the air, although they can survive in the soil and require water to adhere to the leaves.

You can identify Downy mildew by the discolored patches at the top of the leaves and the white fuzzy growth at the bottom.

Severely infected leaves will wither and fall off. Cauliflower itself may also be infected, individual buds (or curds) may turn black, or the entire bottom of small flowers may have black and moldy growth.

White mold

Sclerotinia Sclerotiorum&Sclerotinia minor Although this fungus does not cause black spots, it leaves black pods. This fungus covers the lesion with fluffy white mold.

If left unchecked, mold will develop black sclerosis (a tightly packed food store for fungi), which is roughly the same size as a grain of rice inside white mold.

Fungi can survive in soil for several years, so rotation is very important.

Can you still eat infected cauliflower?

In most cases, broccoli infected with black spots can still be consumed. You can discard infected leaves and trim any spotted flowers.

Downy mildew will cause the most serious damage to the head itself. Unless the whole head is shaped, the infected area can be removed and the head can be eaten.

How to prevent cauliflower fungal diseases

The best way to avoid black spots on cauliflower is to prevent fungi from entering your garden or field. Here are some tips to prevent fungal infections in gardens:

1: Planting disease-resistant varieties

If you know that your garden is sensitive to certain fungi, please plant broccoli varieties that are resistant to diseases. Most reputable seed companies list which varieties have disease resistance.

2: Do not use a sprinkler to water

Most fungi adhere to leaves when they are damp, so please water the soil instead of the plants. Head watering devices, such as sprinklers, soak leaves and splash contaminated soil onto them.

A better choice is to immerse the water into the soil through a soaking hose. They also provide water directly to the roots and help save water by reducing evaporation.

3: Spacer plant

Fungi prefer cool and humid conditions. Tightly spaced plants create an environment that expels air and sunlight while capturing moisture, so please space the plants so that sunlight and air penetrate underneath the leaves to warm and dry the area.

Space cauliflower at least 45 centimeters to 60 centimeters (18 to 24 inches) apart.

4: Crop rotation

Most fungi can survive in the soil for several months, sometimes for several years. Do not plant cauliflower on the same plot for 3 to 4 years to ensure pathogen death.

Please remember that cauliflower is a part of the Brassica genus, so you also want to avoid planting cabbage, mustard, broccoli, and other Brassica plants in the area.

5: Infected plants that have been eliminated

If your cauliflower is indeed sick, please immediately remove any infected leaves. If the disease has really taken root, please remove the entire plant.

Do not discard infected leaves in compost, as the heat generated during the composting process may not be sufficient to kill pathogens.

On the contrary, completely remove diseased plants from the garden or burn them.

6: Companion planting

Companion planting is the practice of planting two crops together so that they benefit each other.

For example, try planting garlic or other onion plants with cauliflower because it has a high sulfur content, which is a natural fungicide.

Another benefit of partner planting is that it "confuses" pests and diseases. By planting several crops at the same time, if sugar beets or legumes grow among them (to name just a few), fungi that like cauliflower are unlikely to take root.

Good companion plants or cauliflower include dill, mint, chamomile, rosemary, sage, scallions, legumes, beets, cucumbers, radishes, carrots, celery, lettuce, and spinach

Avoid planting cauliflower near eggplant vegetables (tomatoes, potatoes, eggplants, chili peppers) as they can make the soil acidic and not suitable for cauliflower, winter melon, and strawberries.

Treating Fungi in Cauliflower

But what should you do when the fungus has already controlled your cauliflower crop? Before you grab a bottle of dangerous chemical fungicides, try one of these natural homemade fungal therapies:


Neem oil

baking soda

Garlic spray

Cinnamon spray

mouth wash

Black dots in storage

Perhaps your cauliflower crop has passed its growing season and has flaws. But now it's in your refrigerator and it's starting to form small black spots! What happened? What should I do?

Your cauliflower is likely experiencing oxidation or starting to mold.

Both of these are the most common in long-term storage of cauliflower, making it more likely to purchase cauliflower from stores, but it may also occur on your own products.


Oxidation is the result of exposure to light and air, similar to how avocado or apple slices turn brown when cut and left on a cabinet.

In addition, condensation usually causes water to settle on the head, so try removing excess water from the head of the refrigerator.

Oxidation can cause small brown or black spots on the buds, or curds (which are small balls bouncing throughout the kitchen when cut).

They usually turn light brown from a single bud, but they can turn black and even spread to the entire small flower.

Can oxidized cauliflower be eaten?

yes! Oxidized cauliflower is completely edible, although brown or black spots may not have the best taste, especially when they are large.

Carefully scrape off black spots with a sharp knife, or cut off any large areas.

However, oxidation is the beginning of decay. If these areas start to become mushy and have an unpleasant odor, then they have already started to rot.

You can still remove decaying fragments, but if the affected part covers most of it, it would be safer to discard cauliflower.

Black mold

Sometimes, the black spots on cauliflower are actually caused by black mold rather than oxidation. You can easily identify black mold through its slightly blurry appearance.

Can you eat moldy cauliflower?

If the moldy spots are still small, just remove them like oxidized cauliflower and thoroughly clean them.

However, if black mold infects a large area of the head, it is much safer to throw it away. If consumed in large quantities, it can be very dangerous.


Whether it's white, yellow, or purple, the healthy cauliflower heads sprouting from the dense leaves are all worth seeing.

But after weeks of patient cultivation, when the perfect head is stained with unsightly black spots, it is a shame.

Through good garden management and prepared natural fungicides, you can combat these diseases and maintain healthy and strong growth of cauliflower.