Common Disease Problems
Alternaria Leaf Spot: Small, round reddish brown spots with white to gray centers for on the upper surface of the leaves. The lesions may encircle the stems and cause wilt. This disease is worse in warm, wet or very humid weather. Burpee Recommends: Avoid getting water on the foliage. Remove infected plant parts and do not work around wet plants. Provide plenty of air circulation. Contact your Cooperative Extension Service for fungicide recommendations.
Black Root: This mostly affects long rooted radishes. It is caused by a soil borne fungus and causes lesions which expand and girdle roots. Burpee Recommends: Rotating crops. If the problem is persistent try planting round varieties.
Downy Mildew: This fungus causes whitish gray patches on the undersides and eventually both sides of the leaves. Burpee Recommends: Rotate crops with plants in a different family. Avoid overhead watering. Provide adequate air circulation, do not overcrowd plants. Do not work around plants when they are wet.
Scab: This disease causes brown and yellow circular lesions on the roots. The lesions become sunken and cracked, irregular and coalesce. Burpee Recommends: Do not plant radishes or other members of the brassica family in the same area for at least four years. Try container growing.
Yellows: Plants are stunted and develop yellow leaves. This virus-like condition is spread by leafhoppers. Burpee Recommends: Remove infected plants and control leafhoppers. Remove weeds in the area which serve as alternate hosts to the disease.
Common Pest and Cultural Problems
Aphids: Greenish, red, black or peach colored sucking insects can spread disease as they feed on the undersides of leaves. They leave a sticky residue on foliage that attracts ants. Burpee Recommends: Introduce or attract natural predators into your garden such as lady beetles and wasps which feed on aphids. You can also wash them off with a strong spray, or use an insecticidal soap.
Cabbage Root Maggot: These insects live in the soil and feed off the plant roots. Burpee Recommends: Your Cooperative Extension Service may recommend a soil drench prior to planting. A flat band or collar of thick paper around the base of the plants, or floating row covers, may help prevent the adult flies from laying eggs at the base of the stems.
Cracked Roots: This may occur when the roots are not harvested early enough.
Flea Beetles: These small hopping beetles feed on plant foliage. Burpee Recommends: Rotate crops with plants in a different plant family. Use floating row covers to prevent damage to young foliage.
Leafhoppers: Leafhoppers cause injury to leaves and stunt growth. They also spread disease. Burpee Recommends: Remove plant debris. Use insecticidal soaps. Consult your Cooperative Extension Service for other insecticide recommendations.
Why didn’t my radish form a bulb? Radish roots are sensitive to overcrowding and hot weather. Another possibility is the soil was not loose and friable enough.
Why are my radishes woody? Radishes are a cool season crop and will turn woody when they are harvested too late in the season.
My radishes are blooming! Your radishes have bolted, which often occurs when the weather becomes hot. At this point you should pull them up and discard them as they will not be edible.
Can I eat my radish thinnings? Yes, radish sprouts are edible.
Can I grow radishes in containers? Radishes are perfect for container growing. Use a commercial potting mix rather than garden soil and make sure they have enough room to develop fully according to the variety.