What Causes Black Spots on Kale and What to Do About Them

Discovering black spots on kale leaves is a common issue for gardeners and grocery shoppers. These blemishes raise questions about their cause and whether the kale is still good to eat. This guide will help you identify the likely culprits behind the spots, determine the edibility of the affected leaves, and learn how to manage and prevent this problem in your garden.

Common Causes of Black Spots on Kale

Black spots on kale are frequently caused by fungal or bacterial diseases. One fungal issue is Alternaria leaf spot, which appears as small, circular, dark spots that develop target-like concentric rings. These spots can range from purplish-black to brown, and as the disease progresses, the centers may dry out and fall away, leaving a hole. Another fungal problem, Anthracnose, presents as small, water-soaked spots that darken to black and become sunken.

Bacterial diseases also affect kale. Black Rot, caused by the bacterium Xanthomonas campestris, starts as yellow, V-shaped lesions along the leaf edges. As these lesions grow, they move toward the leaf’s center, turning black and causing the tissue to collapse. Bacterial Leaf Spot, caused by Pseudomonas syringae, results in tiny, black to purplish spots on the leaves, which may be surrounded by a yellow halo.

Pest infestations can also lead to black spots. Cabbage aphids feed in dense colonies and can be mistaken for spots themselves. Their feeding damages leaf tissue and they excrete a sticky substance called honeydew, which promotes the growth of sooty mold, a black fungus that covers the leaf surface. Flea beetles chew numerous small “shot holes” in the leaves, which can appear as dark specks from a distance.

Is Kale with Black Spots Safe to Eat

The decision to eat kale with black spots depends on the extent and nature of the damage. If you find only a few small, dry spots on an otherwise firm and healthy-looking leaf, it is safe to consume. You can trim away the spotted sections with a knife before washing and preparing the rest of the leaf.

You should discard the kale if the spots are widespread, mushy, or accompanied by a slimy texture or an unpleasant odor. These are signs of a more advanced decomposition or a severe infection, which could affect the flavor and quality of the kale. Trust your senses; if the kale seems off in any way beyond the isolated spots, dispose of it.

Preventing Black Spots in Your Garden

Preventing the conditions that favor fungal and bacterial growth is the most effective way to keep black spots off your kale. Key strategies include:

• Provide adequate spacing between plants to promote good air circulation, allowing leaves to dry quickly after rain or watering.
• Water plants at their base directly onto the soil, rather than overhead. Watering in the morning gives the foliage time to dry in the sun.
• Implement crop rotation by avoiding planting kale or other brassica family crops, like broccoli and cabbage, in the same location for at least two to three years. This disrupts the life cycles of soil-borne pathogens.
• Keep the garden clean by removing and destroying any plant debris at the end of the season to eliminate overwintering sites for pests and diseases.
• Select kale varieties noted for their disease resistance. Checking seed catalogs or plant tags for information on resistance can give your garden an advantage.

Managing an Existing Problem

If you notice black spots on your kale plants, taking immediate action can help control the spread. The first step is to remove any affected leaves as soon as you see them. This slows the disease’s progression and prevents it from spreading to healthy foliage on the same plant or to neighboring plants.

For fungal issues that persist, organic treatments are an option. Sprays containing neem oil or copper-based fungicides can be effective when applied according to the product’s label instructions. These treatments work best when applied at the first sign of disease and may require repeat applications.

In cases of a severe infestation, it may be necessary to remove the entire plant. This prevents the heavily infected plant from acting as a reservoir for the pathogen. Destroy the plant and do not add it to your compost pile, as this can perpetuate the disease cycle.