Horseradish Common Disease Problems
Bacterial Leaf Spot: First signs are small translucent spots with a broad yellowish edge that slowly enlarge and become angular or irregularly circular with a reddish center. It thrives in cooler temperatures.Burpee Recommends: Remove infected plants and do not plant horseradish in the same area. Avoid overhead watering. Do not work around plants when they are wet.
Cercospora Leaf Blight: Small flecks which develop a yellowish halo appear on the leaves and turn brown and coalesce. They cause the leaves to wither and die. Burpee Recommends: Remove infected plants and destroy all plant debris.
Root Rots: A number of pathogens cause root rots. Burpee Recommends: Practice crop rotation and do not plant related crops in the same area for several years. Pull up and discard infected plants. Make sure your soil has excellent drainage. Contact your Cooperative Extension Service for recommendations.
Rust: A number of fungus diseases that cause rust colored spots on foliage and stalks. Burpee Recommends: Plant resistant varieties. Practice crop rotation. Remove infected plants.
Turnip Mosaic Virus: This causes ring spots and mosaic or mottling on the leaves and black streaks on the leaf stalk. Burpee Recommends: Remove infected plants and discard.
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 Looper: These worms are green with a white stripe on either side, about 1-1.5 inches long. Burpee Recommends: Hand pick. Floating row covers can help prevent their laying eggs on the plants.
Flea Beetles: These small hopping beetles feed on plant foliage and may spread diseases. 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.
Slugs: These pests leave large holes in the foliage or eat leaves entirely. They leave a slime trail, feed at night and are mostly a problem in damp weather. Burpee Recommends: Hand pick, at night if possible. You can try attracting the slugs to traps either using cornmeal or beer. For a beer trap, dig a hole in the ground and place a large cup or bowl into the hole; use something that has steep sides so that the slugs can’t crawl back out when they’re finished. Fill the bowl about ¾ of the way full with beer, and let it sit overnight. In the morning, the bowl should be full of drowned slugs that can be dumped out for the birds to eat. For a cornmeal trap, put a tablespoon or two of cornmeal in a jar and put it on its side near the plants. Slugs are attracted to the scent but they cannot digest it and it will kill them. You can also try placing a barrier around your plants of diatomaceous earth or even coffee grounds. They cannot crawl over these.
My roots arrived with a mold on them, will they be OK to plant? Yes, this is most likely a surface mold that will not affect the plants. It comes from the roots being in transit several days in warm conditions without adequate air circulation. If the roots are not mushy or do not have a foul odor, wash off the mold and plant.
Can I grow horseradish in zone 10? No, horseradish is only recommended to zone 9 because the plants require cool falls and winters for the best flavor.
How long before I can harvest my horseradish? Do not harvest horseradish the first year as this will weaken the plants. Wait until the end of the second year after planting to harvest.
How do I get the hottest horseradish? For the hottest horseradish, use the roots as soon as possible after harvest, the heat fades the longer the roots are stored. Roots should be creamy white when cut. The pungency also begins to wane when fresh crushed horseradish is exposed to air. When making your own sauce, add vinegar to stabilize the flavor about three minutes after grating. Add 2-3 tablespoons of white distilled vinegar and ½ teaspoon of salt to each cup of grated root.
Are the leaves edible? Yes, the fresh leaves may be used in salads.