Black Spots on Arugula: 5 Common Causes and Solutions

Black spots on arugula leaves can be caused by various fungal and bacterial diseases, or pests. This article outlines the five most common causes and provides effective solutions to manage and prevent these issues, ensuring a healthy and appealing arugula crop.

Key Takeaways

  1. Alternaria Leaf Spot: Prevent by providing ample space for plants, watering at the base, and using citric acid-based fungicides. Infected leaves should not be consumed.
  2. Bacterial Leaf Spot: Prevent by heat-treating seeds, avoiding wet foliage, and using neem oil spray. Infected leaves should not be consumed.
  3. Downy Mildew: Ensure good air circulation, water at the base, and use organic fungicides. Affected leaves should not be consumed.
  4. Blight: Avoid excessive watering, ensure good air circulation, and consider using raised beds. Blight-affected leaves can be consumed if not severely wilted.
  5. Aphids: Control with neem oil sprays, gentle washing, and introducing ladybugs. Arugula with aphids can be consumed after thorough washing.
black spots on arugula

While your plant might still be edible (in some cases), you may pretty much pass the distinctive-tasting veggie up because of the unsightly spots on the leaves, especially when you’re planning a salad.

In this article, we will explore the most common causes of these spots and provide effective solutions to address them.

Black Spots on Arugula Leaves: 5 Causes and Solutions

1. Alternaria Leaf Spot

One of the primary culprits behind spots on arugula leaves is Alternaria leaf spot, a fungal disease.

It manifests as small reddish-brown spots on the upper surface of the leaves, often with white or gray centers.

If left untreated, these spots can spread and encircle the leaves, leading to wilting.

black spots on arugula

Solutions

Prevention is crucial in managing Alternaria leaf spot.

Since this fungus thrives in warm and wet environments, it is essential to provide sufficient space for your arugula plants to breathe and avoid overcrowding.

Additionally, watering the plants at the base rather than overhead can help prevent the leaves from getting wet.

Using an organic citric acid-based fungicide can also aid in killing Alternaria and other fungal diseases.

If the infection persists, it is best to remove the infected parts or plants altogether to prevent further spread.

Can You Eat Arugula with Alternaria Leaf Spot?

It is advisable to avoid consuming leaves affected by Alternaria leaf spot.

This fungal disease causes rapid wilting and renders the arugula leaves unsuitable for consumption.

black spots on arugula

2. Bacterial Leaf Spot

Another cause of brown spots on arugula leaves is bacterial leaf spot, which, as the name suggests, is a bacterial disease.

It results in brown, water-soaked spots that eventually cause the leaves to turn yellow and wilt.

Solutions

To prevent bacterial leaf spot, treating arugula seeds with heat before planting is recommended.

Soaking the seeds in water heated to 100-122 degrees Fahrenheit for approximately 15 minutes helps eliminate bacterial leaf spot and potentially other diseases without damaging the seeds.

Avoiding wet foliage and watering only at the base of the plants can help prevent the spread of bacterial leaf spot.

Rotating planting locations and using neem oil diluted in water as a spray can also aid in combatting the disease.

If these measures fail, removing infected parts or plants is crucial to halt further infection.

black spots on arugula

Can You Eat Arugula With Bacterial Leaf Spot?

Similar to Alternaria leaf spot, it is best to refrain from consuming arugula leaves affected by bacterial leaf spot.

The disease causes rotting and wilting, making the leaves unfit for consumption.

3. Downy Mildew 

Downy mildew, another fungal disease, can cause brown spots on arugula leaves.

What sets it apart is the presence of white mildewy spots on the undersides of the leaves.

Solutions

black spots on arugula

Downy mildew thrives in environments with poor air circulation and excessive moisture.

To counter this, ensure that your arugula plants are adequately spaced apart to promote air circulation.

Watering near the base and avoiding wetting the foliage further prevent the disease from spreading.

Using the organic fungicide mentioned earlier can help treat downy mildew.

If all else fails, removing the infected parts or plants is necessary to prevent the disease from spreading.

Can You Eat Arugula with Downy Mildew Spots?

It is advisable to avoid consuming arugula leaves affected by downy mildew.

The disease causes wilting, rendering the arugula leaves unsuitable for consumption.

4. Blight

black spots on arugula

Blight, a fungal disease that resides in the soil, can be challenging to treat or prevent.

It leads to the formation of brown or brown-gray spots on arugula leaves, resulting in wilting.

Solutions 

To combat blight, avoid wetting the arugula leaves excessively and refrain from overwatering to prevent the roots from sitting in excess water.

Providing ample room for the plants will promote air circulation, thwarting blight development.

Planting arugula in pots or raised beds also hinders blight growth.

Using an organic fungicide as soon as blight is detected can help restore your arugula plants.

If the infection persists, promptly removing infected plants will prevent the blight from spreading.

If arugula is grown in the ground, consider planting elsewhere and leaving the soil empty for a period to allow the fungus to die out.

black spots on arugula
Credit: Kat Med/Unsplash

Can You Eat Arugula with Blight Spots?

For the most part, arugula with blight spots is safe to eat as long as the leaves have not wilted significantly.

While the spots may not be visually appealing, they do not pose harm to human health.

However, it is advisable to avoid consuming leaves that are mostly affected by blight spots.

5. Aphids 

black spots on arugula
Credit: Viktor Forgacs/Unsplash

Although not a disease, aphids are pesky pests that can be troublesome.

These tiny insects feed on arugula leaves, leaving behind discolored spots that can be white, yellow, or light green.

They also produce a sticky white residue on the leaves, aiding in their identification.

If left unchecked, aphids can cause the plant to wilt by devouring the leaves.

How to Treat Aphids

To combat aphids, using a neem oil solution in a spray bottle is highly effective.

Spraying the arugula leaves with this solution will kill the aphids and prevent their eggs from hatching.

Alternatively, gently washing the plants can dislodge the aphids.

Be cautious not to damage the leaves, as this can facilitate the spread of diseases mentioned earlier.

black spots on arugula
Neem Oil

Combining the washing with the neem oil spray provides a comprehensive solution for aphid management.

Introducing ladybugs into your garden is another natural and efficient method to control aphids.

Ladybugs prey on aphids without causing harm to arugula plants. You can purchase ladybugs online to bolster your garden’s ecosystem.

Can You Eat Arugula with Aphids on It?

In short, you can still consume arugula with aphids, provided you wash them off thoroughly.

Avoid consuming wilted leaves and be sure to clean your arugula before consumption.

While aphids are safe to eat, they are not particularly appetizing.

Final Thoughts

Arugula is a delightful addition to any garden, but it requires care and attention.

By understanding the causes of spots on arugula and implementing the appropriate solutions, you can enjoy a thriving arugula crop that is both delicious and visually appealing.