Diseases And Problems With Growing Basil

Diseases And Problems With Growing Basil

By: Heather Rhoades

Basil is one of the most popular herbs to grow, but that doesn’t mean there are no basil plant problems. There are a few basil diseases that can cause basil leaves to turn brown or yellow, have spots, or even wilt and fall off. Keep reading to learn more about the diseases that can cause problems with growing basil.

Common Basil Diseases

Fusarium Wilt

Fusarium wilt is among the most common basil diseases. This basil wilt disease most commonly affects sweet basil varieties, but other basil varieties are still somewhat vulnerable.

Symptoms of fusarium wilt include:

  • stunted growth
  • wilted and yellowing leaves
  • brown spots or streaks on the stem
  • severely twisted stems
  • leaf drop

Fusarium wilt is caused by a fungus that can be carried by either the soil that affected basil plants have been growing in or by seeds from infected basil plants.

There is no remedy for fusarium wilt. Destroy infected plants and don’t plant basil or other mint plants in that area for two to three years. Even if a basil or mint plant cannot be hurt by fusarium wilt, they can carry the disease and infect other plants.

Bacterial Leaf Spot or Basil Shoot Blight

This basil disease is caused by a bacteria called Pseudomonas cichorii. Symptoms of bacterial leaf spot are black or brown spots that appear on the leaves and streaking on the stems of the plant.

Bacterial leaf spot occurs when infected soil is splashed onto the leaves of the basil plant.

While there is no fix for bacterial leaf spot, you can minimize the damage by making sure that your basil plants have plenty of air circulation and that they are watered in a way so that the bacteria is not splashed onto the leaves.

Downy Mildew

Downy mildew is a relatively new basil disease that has only started to affect basil in the past few years. The symptoms of downy mildew include yellow leaves that have fuzzy, grey growth on the undersides of the leaves.

Downy mildew is aggravated by overly wet conditions, so if it appears on your basil plants, make sure that you reduce overhead watering and that the basil plants have good drainage and good air circulation.

Other Basil Plant Problems

The basil diseases listed above are specific to basil plants, but there are a few other problems with growing basil that can happen. They include:

  • Root rot
  • Nitrogen deficiency
  • Slugs
  • Thrips
  • Aphids

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Common Problems When Growing Basil

Basil is one of the easiest herbs to grow at home and is far less susceptible to pests and disease than some other herbs. That said, problems can always arise and it’s best to diagnose them right away in order to treat them before they get out of hand. Here’s a list of some common problems when growing basil.

Damping-off is a name given to a condition that attacks the seeds or the roots of young plants during wet, cool conditions. Seedlings may look healthy and then suddenly topple over and die. This is caused by a number of different fungal agents, but if your basil is planted in soil with poor drainage and fertility, it is all the more susceptible. Do not over water. Basil can’t stand sitting in damp conditions. Sterilizing containers before planting basil is also a must, since diseases can hang around for a while even after the previous plant is long gone.

Root Rot
Usually caused by poor drainage and over watering, root rot is another type of fungal disease that will stunt your plants and eventually kill them. They may lose color and begin to die. Roots may appear dark and slimy. Lay off watering. If your soil is poor and your basil does not recover, you may need to replant.

Leaf Spot Disease
Leaf spot is caused by a bacterial infection that causes spots on the leaves and streaks on the stems. Remove any infected leaves as soon as you see them so this disease does not spread. Overhead watering and damp foliage can contribute to leaf spot. Water at the base of the plant and try to water in the morning so the foliage has adequate time to dry throughout the day.

Fusarium Wilt
Sweet basil is most susceptible to fusarium wilt, which causes stunted plants, wilted yellow leaves, twisted stems, brown spots and streaks on the stems, and the leaves to drop. This fungus grows in the soil and can be transmitted through infected leaves. Destroy infected plants and avoid planting in that area for 3 years.

Downy Mildew
Downy mildew is any number of microbes that can attack basil plants. Look for yellow leaves with fuzzy, grey growth on the underside. Good air circulation and keeping the foliage dry is the best way to avoid downy mildew. Remove infected leaves and stems to prevent it from spreading.

Root Knot Nematodes
Nematodes are worm-like creatures that live in the soil and cause your basil to wilt and turn yellow. The roots may be swollen and disfigured when nematodes are present. Till your soil deeply to disturb any possible nematode presence but crop rotation is the best way to avoid them. Otherwise, try growing basil in pots and replanting every year.

Aphids suck plant juice and leave behind a sticky substance called honeydew. They can be found on the undersides of the leaves. They are usually semi-green or yellow (but can be red, black or other colors too), with almost transparent bodies. Blast them off with water. If let be they can do serious damage to your basil plant.

Flea Beetles
Flea beetles chew tiny holes in the basil leaves. They can usually be blasted off with water. Spray them with insecticidal soap if that doesn’t do the trick.

When you shake your basil plant and a ‘cloud’ of insects rise up and then settle back down, you have whiteflies. Much like aphids, they suck the life out of plants if left unhindered. Spray them with water or insecticidal soap.

Snails and Slugs
Chewed leaves accompanied by silver streaks is likely the work of snails or slugs. Pick them off if you see them. Use beer traps or copper fencing if they are a real problem.


Nitrogen Deficiency
Wilting, yellow leaves and poor growth may be a symptom of nitrogen and other nutrient deficiency. Feed your plants with a liquid organic fertilizer that is high in nitrogen to reverse the problem. Disease can also cause these symptoms. So if fertilizing doesn’t correct it, look to nematodes or another problem listed above.

Always plant basil in fertile soil that drains really well.

Water wisely. Poor drainage combined with too much water is one of the fastest ways to see fungus and other diseases settle in your basil.

Harvest regularly. Even if you aren’t using all that much basil, picking leaves often will encourage new growth and keep air circulation good.

Feed or replant container basil to ensure they have all the nutrients they need.

Do not plant too early. Basil does well indoors, so avoid putting it outside before it’s time.

Bacterial Leaf Spot/Basil Shoot Blight

Caused by a bacteria known as Pseudomonas cichorii, this basil disease shows itself as brown or black spots on the leaves, as well as streaking on the stems.

Pseudomonas cichorii does not only affect basil but also chrysanthemums, geraniums, and other ornamental plants. The bacteria is easily spread by water splashing the plant from infected soil. Bacterial leaf spot likes warm and wet conditions

How to Control Bacterial Leaf Spot

There is no way to cure bacterial leaf spot, but there are measures you can take to prevent it and minimize the damage. Remove infected plants as soon as possible.

Gently water the basil plants so that water does not splash up on to the leaves. Use drip irrigation to keep your plants watered if possible. Lower relative humidity by improving circulation of the air. Try to avoid handling the plants when the leaves are wet, as this can spread the disease.

Final Thoughts

For a hardy plant that grows all over the world, it is surprising how sensitive Basil can be. However, it shows off its discomfort with discolored, curling, or wilting leaves and allows its owners the opportunity to remedy the situation.

It’s important to know how much sunlight, water, and care your plant needs so that you can keep it as healthy as possible. Reacting to problems quickly will allow you to enjoy a healthy and productive plant.

If you need more help getting your Basil plant back to perfect health, I’ve written another article about how to fix the most common Basil plant problems.

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