Like all food crops, radishes are susceptible to various fungal diseases, however they’re quite the tough crop. Because of their short growing period, they don’t have much time to develop some of the more complicated diseases that others in the Brassicaceae family do.

Your best weapons against the diseases that could arise, particularly in winter radishes that have a longer growing season, are best planting practices that help prevent disease in the first place.

This is especially important, as there are no fungicides approved for home use for many diseases.

These best practices are aimed at producing strong, healthy plants that can withstand disease, and at avoiding situations that contribute to the development of disease. They involve keeping plants clean, dry, and undamaged.

Companion Planting: Each crop has a garden buddy that helps in some way: repelling pests, attracting pollinators, contributing nutrients to the soil. We discuss this in more detail in the article Planting Radishes in the Ground or in Raised Beds of this collection. You can also review our Food Gardening Network Companion Planting Chart for a full list of good planting partners for your garden.

Crop Rotation: As tempting as it might be, it’s best not to grow the same crops in the same soil—open garden, raised bed, or container—for more than one growing season. Each plant takes certain nutrients from the soil and leaves others behind. Some crops are susceptible to soilborne diseases or pests. For these reasons, you want to rotate your crops from growing season to growing season. This will help ensure better soil health and healthier, more productive harvests. This practice applies primarily to annual crops; perennial crops can usually continue to grow where they’re planted.

Now, in a perfect gardening world, you would be able to implement a crop rotation plan that spans decades. There are some soilborne diseases that can live in the soil for up to 20 years!

Even so, it’s a good idea to switch things up from season to season. Here’s a list of vegetable crops by category. The general rule of thumb here is to plant crops from one list in the growing space of the crops in the following list in the next growing season. So, you would go from List 1 to List 2 to List 3 to List 4 and then back to List 1.

1. Root, Solanaceous (nightshade), and Tuberous Crops
• eggplant
• beets
• carrots
• celery
• parsnips
• potatoes
• sweet peppers
• sweet potatoes
• taro
• tomatoes
2. Brassicas
• radishes
• broccoli
• Brussels sprouts
• cauliflower
• kale
• kohlrabi
• mustard
• rutabaga
• turnips
3. Legumes and Pod Crops
• broad beans
• lima beans
• okra
• peas
• runner beans
• snap beans
4. Alliums
• bulb onions
• garlic
• leeks
• oriental bunching onions
• scallions
• shallots
• welsh onions

Here’s a short example of common crop rotations:
potatoes > corn > cabbage > peas > eggplant > beans > root crops > squash/potatoes > onions.

If you can’t do a complete crop rotation, consider alternating what you grow from one season to the next—a virtual crop rotation of sorts. With containers and raised beds, you have the option of changing out the soil, depending on what you want to grow there. Some container soil, especially, will be severely depleted of nutrients at the end of the growing season and should just be replaced.

Mulch: Mulch can help with water retention—but be vigilant and check for insect or fungal activity.

Watering: Water your radishes regularly and keep the soil moist but don’t over-water. Soggy soil invites disease. Radishes want about 1 inch of rain or watering every week.

Other best practices include:

• Buy healthy, disease-free seeds from reputable sources.
• Plant in sites with good drainage; if planting in open ground, choose a higher spot for better drainage.
• Check plants regularly for signs of disease.

Common Radish diseases

Here are some of the usual culprits that might infest your radishes. Remember, it’s important to remove infected plant material (leaves, roots) to prevent the spread of disease once it’s found its way onto your plant. The best way to prevent these diseases is through crop rotation every year.

The great news about radishes is that if you plant spring radishes, they have such a short growing period that if you harvest regularly and don’t leave plants to bolt or compost in the soil, you can avoid most diseases. However, like all plants, there are some they are more prone to disease.

Alternaria Blight

Cause: spores from the fungus Alternaria dauci

Symptoms:

• small, yellow, raised lesions on the stem, then on seed pods
• pods may become black and shriveled
• infected seeds will not germinate

How it Spreads:

• spores germinate in water-logged soil and get in through wounds in the bulb, stems, or leaves

Treatment:

• a sulfur-based or copper fungicide sprayed directly on leaves

Prevention:

• hot water treatment of seeds
• tested, disease-free seeds
• fungicides like Difolatan, Dithane M 45, and Ridomil are used commercially
• crop-rotation

White Rust

Cause: a fungus-like microorganism, Albugo candida, that breeds in many plants and spreads

Symptoms:

• white raised masses of spores on the undersides of the leaves that can be small and get larger

How it Spreads:

• as the spore masses get larger, they burst and release the spores into the air
• high humidity is an ideal conductor for growth while cold will slow the progression
• will live in the soil for years

Treatment:

• fungicides

Prevention:

• grow white rust-resistant varieties of all crops to reduce presence in the area, as it can affect other plants too
• rotate crops annually; see crop rotation guidelines above

Radish Black Root

Cause: a fungus-like organism called Aphanomyces raphani

Symptoms:

• rotting of radishes with black holes
• deformed inedible radishes
• wilting and yellowing greens
• black veins

How it Spreads:

• when roots are transplanted
• wind and water
• insects
• in the soil for 40 to 60 days

Treatment:

• destroy and remove infected crops

Prevention:

• rotate crops every year
• don’t plant with other crucifer-type plants
• provide excellent drainage
• plant resistant varieties like White Spike and Red Prince

Radish Mosaic Virus

Cause: a virus that is spread mostly by aphids

Symptoms:

• small circular lesions near veins in leaves
• leaves that are mottled in color
• stunted growth

How it Spreads:

• aphids
• seeds from infected plants

Treatment:

• remove infected plants and do not compost them

Prevention:

• do not compost infected plants
• do not use seeds from infected plants
• use clean and disinfected gardening tools
• plant virus-resistant varietals
• row covers, which can reduce insects
• reduce weeds, which may reduce aphids
• soak seeds in a 10% solution of bleach before planting

Radish Phyllody

Cause: a hormonal imbalance often caused by phytoplasma or viral infections

Symptoms:

• grey or purple coloration
• at time of bolting, flowers are green, thick, and knobby because they are sterile

How it Spreads:

• insects
• viral infections

Treatment:

• remove and destroy infected plants

Prevention:

• there are no ways to prevent it

Clubroot

Cause: a fungal infection

Symptoms:

• yellow leaves during the day that spring back up at night
• stunted plants
• distorted roots

How it Spreads:

• in the soil for up to 10 years

Treatment:

• destroy crops and do not plant radishes in same bed

Prevention:

• solarize your garden bed for best results
• add lime to soil to reduce spores by raising pH to 7.2.

Which diseases do you find affect your radish crops most? Or have you been lucky and avoided them so far?