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Growing Good Food at Home

Dealing with Beet Diseases

A spotted, yellowed beet leaf affected by disease

A spotted, yellowed beet leaf affected by disease

Like all food crops, beets are susceptible to various fungal diseases. Your best weapons against these are best planting practices, which 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 out in some way: repelling pests, attracting pollinators, contributing nutrients to the soil. We discuss this in more detail in the Planting section 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 particular 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>List 2>List 3>List 4> and then back to List 1.

1. Root, Solanaceous (nightshade), & Tuberous Crops

  • beets
  • carrots
  • celery
  • eggplant
  • parsnips
  • potatoes
  • sweet peppers
  • sweet potatoes
  • taro
  • tomatoes

2. Brassicas

  • broccoli
  • Brussels sprouts
  • cauliflower
  • kale
  • kohlrabi
  • mustard
  • radishes
  • 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 crop rotations using the rotation above.
potatoes > broccoli > peas > garlic > tomatoes > Brussels sprouts > beans > leeks

Wondering about corn? Grains have their own complex rotation schedule between one another, though if you have a small backyard garden and aren’t planting different grains in the same place each year, you could add in another rotation, which would be grains like corn and wheat. Plant them after legumes, because legumes leave nitrogen in the soil that grains enjoy.

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 beets deeply about once a week (check the soil for dryness). Do not over-water. Soggy soil invites disease.

Other best practices include:

  • Buy healthy, disease-free seeds from reputable sources
  • Plant your beets in full sun
  • 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 Beet diseases

Here are some of the usual culprits that might infest your beet plants. 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.

Cercospora Leaf Spot

Cause: Fungus overwinters in infected plant material and emerges in warm, humid weather, most commonly after a rainy spell. It does not affect the fleshy root of the plant. This is the most common disease that occurs on beets.

Symptoms:

  • yellow and brown spots on the underside of leaves
  • leaves may curl and turn upward

How it Spreads:

  • fungus overwinters in infected plant material
  • wind, insects, birds

Treatment:

  • removed and destroy infected areas

Prevention:

  • liquid copper fungicide
  • if necessary, sulfur-based fungicide
  • plant disease-resistant varieties
  • remove plant debris
  • rotate crops annually; see crop rotation guidelines above

Alternaria Leaf Spot

Cause: Fungi present after warm summer rain

Symptoms:

  • small black dots appear on leaves, most obvious on the underside
  • light spots with dark borders on leaves
  • spots enlarge as disease progresses, forming a bull’s eye pattern
  • leaves turn yellow between the infected spots
  • will not kill the plant, but can significantly weaken it
  • more than 12 hours of warm rain can distribute spores so much that the plant cannot recover

How it Spreads:

  • rain helps spread spores in temperatures between 65°-75° F.

Treatment:

  • remove and discard infected leaves; this will reduce the number of spores and increase air circulation around plants

Prevention:

  • buy disease-free seeds
  • do not save seeds from infected plants
  • avoid planting in cool, wet weather
  • avoid overhead watering; water at soil level
  • make sure plants have good air circulation and lots of sun
  • rotate crops annually; see crop rotation guidelines above

Ascochyta Blight (Wet Weather Blight)

Cause: Fungi

Symptoms:

  • lesions on stems and leaves early in the growing season
  • light spots with dark borders on leaves
  • small, black fruiting structures embedded in leaves
  • cankers on stems are reddish purple to gray or black

How it Spreads:

  • spores thrive in moist soil and cool temperatures

Treatment:

  • liquid copper fungicide, if infection is severe
  • remove and discard infected parts

Prevention:

  • avoid planting in cool, wet weather
  • plant in well-draining areas
  • treat seeds with fungicides before planting
  • use drip irrigation; avoid overhead watering
  • rotate crops annually; see crop rotation guidelines above

Aster yellows

Cause: Bacteria

Symptoms:

  • hairy, bitter roots
  • yellowed leaves

How it Spreads:

  • spread by leafhoppers, which feed on the plant juices

Treatment:

  • remove and discard infected parts
  • no effective treatment

Prevention:

  • reduce leaf litter and garden debris, where leaf hoppers overwinter
  • install sticky traps to trap leaf hoppers
  • break up compacted soil
  • plant in well-draining areas
  • put straw or aluminum foil under beet plants to confuse leaf hoppers
  • sprinkle kaolin clay on plants to discourage leaf hoppers
  • rotate crops annually; see crop rotation guidelines above

Bacterial Leaf Spot

Cause: Bacteria

Symptoms:

  • leaves have circular spots with irregular edges
  • spots may turn yellow and water-soaked
  • leaf drop

How it Spreads:

  • water
  • wind
  • garden tools
  • thrives in warm, moist conditions

Treatment:

  • remove and discard infected leaves
  • if infection becomes serious, discard entire plant
  • do not compost infected plant material

Prevention:

  • mulch around plants to prevent water from splashing onto leaves
  • avoid overhead watering; water at soil level
  • make sure plants have good air circulation and lots of sun
  • sterilize garden tools before each use
  • spray plants weekly with neem oil or a commercial fungicide such as Bonide Revitalize
  • rotate crops annually; see crop rotation guidelines above

Beet Curly Top

Cause: Viruses

Note: primarily a problem in western U.S. and Canada, and all of Mexico.

Symptoms:

  • leaves crinkle and turn inward
  • small, stunted leaves with purple margins
  • swollen veins on the bottom half of the leaves
  • stiff stems
  • yellowing leave
  • twisted and/or stunted roots

How it Spreads:

  • beet leafhopper spreads virus by chewing on plants

Treatment:

  • remove and discard infected plants

Prevention:

  • buy disease-resistant seeds
  • use floating row covers to protect plants
  • weed frequently to keep soil clear
  • rotate crops annually; see crop rotation guidelines above

Beet Mosaic Virus

Cause: Viruses

Symptoms:

  • small, light-colored spots on the youngest leaves of the plant
  • leaves turn pale yellow between the veins
  • leaf death
  • stunted roots

How it Spreads:

  • aphids

Treatment:

  • disease is not treatable
  • discard all infected plant material
  • do not compost

Prevention:

  • keep aphids away from plants; once aphids appear, plants are at risk of infection
  • use floating row covers with hoops to accommodate plant growth
  • use companion plants like asters, nasturtiums, and nettles to attract aphids away from beet crop
  • plant repellent plants like catnip, dill, and marigold
  • interplant cilantro, cosmos, and geraniums to attract ladybugs—which love aphids
  • spray plants with a mixture of 4 parts mineral oil to 1 part dish soap to smother any insects that land on the leaves
  • do not save seeds from infected plants
  • avoid planting in cool, wet weather
  • avoid overhead watering; water at soil level
  • make sure plants have good air circulation and lots of sun
  • rotate crops annually; see crop rotation guidelines above

Beet Rust

Cause: Fungus

Symptoms:

  • small reddish-orange spots on leaves
  • weakened foliage that breaks off when you try to pull up beets
  • Note: beet roots will still be edible

How it Spreads:

  • fungus thrives in cool wet weather
  • fungus overwinters in plant debris or in seeds

Treatment:

  • remove and discard infected leaves
  • apply foliar fungicide, such as CEASE, twice a week to treat infection

Prevention:

  • avoid overhead watering; water at soil level
  • make sure plants have good air circulation and lots of sun
  • apply foliar fungicide weekly as a preventative
  • rotate crops annually; see crop rotation guidelines above

Beet Western Yellows

Cause: Virus

Symptoms:

  • leaves turn yellow in between the veins
  • older or outside leaves are usually affected first
  • red spots form on leaves
  • leaves become thick and brittle; may turn white

How it Spreads:

  • aphids

Treatment:

  • disease is not treatable
  • discard all infected plant material
  • do not compost

Prevention:

  • keep aphids away from plants; once aphids appear, plants are at risk of infection
  • use floating row covers with hoops to accommodate plant growth
  • use companion plants like asters, nasturtiums, and nettles to attract aphids away from beet crop
  • plant repellent plants like catnip, dill, and marigold
  • interplant cilantro, cosmos, and geraniums to attract ladybugs—which love aphids
  • spray plants with a mixture of 4 parts mineral oil to 1 part dish soap to smother any insects that land on the leaves
  • do not save seeds from infected plants
  • avoid planting in cool, wet weather
  • avoid overhead watering; water at soil level
  • make sure plants have good air circulation and lots of sun
  • rotate crops annually; see crop rotation guidelines above

Damping-off

Cause: Fungi

Symptoms:

  • water-soaked, decomposing seeds
  • infected roots are gray and water-soaked
  • seedlings grow but then collapse and die
  • older plants that get infected are severely stunted

How it Spreads:

  • spores thrive in moist soil and cool temperatures

Treatment:

  • liquid copper fungicide, if infection is severe
  • remove and discard infected parts

Prevention:

  • minimize soil moisture
  • plant in well-draining areas
  • avoid overhead watering; water at soil level
  • treat seeds with fungicides before planting
  • rotate crops annually; see crop rotation guidelines above

Downy Mildew

Cause: Fungi

Symptoms:

  • pale spots or long pale patches on leaves
  • gray-purple fuzzy growth on leaf surface
  • leaves turn pale, then yellow
  • leaf tips collapse

How it Spreads:

  • splashing water (rain, irrigation) disturbs spores
  • cool temperatures favor growth

Treatment:

  • destroy infected plants
  • apply foliar fungicides

Prevention:

  • purchase disease-free seeds and plants
  • plant in well-draining areas
  • avoid overhead watering; water at soil level
  • homemade fungicides
  • choose planting sites with good air movement and no shade
  • rotate crops annually; see crop rotation guidelines above

Powdery Mildew

Cause: Fungus overwinters on infected plant debris and emerges in warm, humid weather

Symptoms:

  • white, powdery patches on leaves
  • leaves may curl and turn upward
  • new shoots appear stunted
  • older infections look like a tan or reddish-brown felt covering; these contain spores
  • heavy mildew infections can stunt a plant’s growth

How it Spreads:

  • fungus overwinters in infected plant debris
  • spores do not need moisture to germinate; often called a “dry weather disease”
  • wind, insects, birds

Treatment:

  • removed and destroy infected plant matter

Prevention:

  • liquid copper fungicide
  • if necessary, sulfur-based fungicide
  • plant disease-resistant varieties
  • remove plant debris
  • rotate crops annually; see crop rotation guidelines above

Which diseases have you had to treat on your beets? Please tell us how you prevent and handle diseases. If you spot other symptoms on your beets that are not mentioned here, contact your local extension center or garden center for a consult—and please let us know what you discover.

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