Identifying Fungal Diseases in Vegetables

Plants, like any living creature, are susceptible to diseases if not cared for properly. One of the main challenges in vegetable gardening is to identify and treat vegetable diseases. Vegetable plants commonly suffer from fungal, bacterial, or viral attacks. These diseases inhibit the normal growth of the plant and turn the natural functions within the plants topsy-turvy. Most fungi and bacterial infections live off the plant\’s store of food to survive. Viruses tend to stunt plant growth or foliage deformity.

The most common type of diseases in plants is fungal diseases. Because they are unable to produce their own food due to the fact that they lack chlorophyll, they rob their host plants of nutrients. While some fungi are beneficial to gardeners and only feed on dead or decaying matter (thus helping in decomposition and re-establish minerals and nutrients to the soil), others are destructive in the garden. Below lists some of the more common fungal diseases (such as blights, botrytis, clubroot, damping off, leaf and pod spots, mildews, and wilts), how to identify them, as well as prevention methods.


  • caused by Alternaria solani.
  • Infects tomato, potato, eggplant, horse nettle, and black nightshade.
  • occur on the plant at all stages of development. Early blights causes a decrease in fruit quantity and quality.


  • collar rot in young plants (a dark, sunken spot on one side of the stem which grow completely around the stem or weaken the stem, \’choking\’ the plant to death.
  • 1/2″ diameter leaf spots that foes from dark to light brown in a concentric rings (like a target)
  • target spots on fruits and stem end of infected fruits; can appear leathery and covered with a velvety mass of black spores.


  • Avoid using disease-infected seeds and transplant; use resistant variant.
  • Limit leaf wetness (water early in the day and at the base of the plant)
  • Keep area clean of weed through out planting period and debris after harvest.
  • Do not plant near tomato or potato plants.

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  • also known as grey mould, it is a common vegetable disease that affects plants such as lettuces and tomatoes.
  • They thrive in cold, damp conditions.
  • Early symptoms include brown-spotted or blotchy leaves, followed by a fluffy grey mould which jills plant tissue underneath.


  • keep plant foliage dry
  • clear vegetable garden of debris at the end of the gardening season
  • destroy affected plant matter.

Image credit: Rasbak/


  • caused by Plasmodiophora brassicae
  • symptoms are club-shaped swellings on the roots; wilting, yellowing, and stunted growth of aboveground parts.
  • attacks broccoli, cauliflower, and cabbage.


  • grow plants from seed on your own
  • buy seedlings from a reputable grower.
  • Raise the pH of the soil above 7.2 as clubroot do not thrive on acidic soil.

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Leaf and pod spots (anthracnose)

  • occur on beans, broccoli, cauliflower, cucumbers, peppers, and tomatoes.
  • The fungi invade the roots of plants and causes a rot of ripe fruit
  • Symptoms include round 1/2″ diameter fruit spots; with center of the spot may becoming tan and flecked with small black specks. In wet conditions, a mass of slimy salmon- colored spores may emerge.
  • You may also find small, round brown leaf spots (with a yellow ring around them).


  • Use disease-free and resistant seed and grow them yourself.
  • Irrigation should be done at the base near the soil, not over the plant.
  • Reduce weeds..

Image credit: Franciscosp2/

Downy mildew

  • Commonly attacks lettuce, peas, onions and spinach.
  • Symptoms include yellowing leaves with a grey or white mould on the underside.
  • tiny black fungi spots may be discovered on older leaves
  • Cause: wet foliage, watering plants with sprinkler that wets the whole plant.


  • use drip irrigation or container watering.

The healthy looking strawberry plant was grown in soil treated with methyl bromide alternatives. The other is from untreated and unfumigated soil and is infested with Verticillium wilt.

Image credit: Brian Prechtel/

Fusarium wilt
and verticillium wilt

  • symptom include leaf wilt that turns from yellow to brown.
  • Fusarium wilt is prevalent in warm climates. Verticillium wilt is common in cooler regions.
  • Can be spread by insects such as cucumber beetles and squash vine borers.


  • Grow disease-resistant varieties
  • Destroy infected plant material.

The above outlined fungal diseases are only a few that are common. There are diseases caused by bacteria and viruses that are not covered in this article. Knowing how to identify the malady that is attacking your vegetable crops is important so that you can take the proper measure to treat it as well as prevent future reoccurrence. There are many online references as well as reading materials on the susceptibilities of the vegetables, which ever it is that you choose to grow. By being able to identify early symptoms, you may be able to save your crop by stopping the spread to other crops in your home garden.