What Causes Brown Spots on Plants?

Various fungi can cause brown spots on plants. The spots can appear on top or bottom of the leaves. The appearance of the spots may vary, depending on the type of fungus that is attacking the plant, from small specks to larger areas of leaf involvement. Determine which fungus is causing the brown spots, as different fungicides work on targeted fungi. Until the plant is treated, avoid handling the plant, as this can spread the fungus and cause further damage to the plant. Because so many types of fungus exist, the best course of action is to take an affected leaf to a garden store and have an expert recommend treatment.

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Some of the insects that cause brown spots on plants are visible, while others are not. Insects that cause brown spots include thrips, mites, leaf mealy bugs, whiteflies, aphids, scale and nematodes. Most plant insects can be eliminated with insecticides. Plants with nematodes require either professional insecticide treatment or disposal of the plant.

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Bacterial leaf blight and bacterial leaf spot can both cause brown spots on leaves. To treat bacterial plant infections, cut off the affected areas of the plant. Sterilize the clipper between cuts to avoid spreading the bacteria onto healthy plant tissue. Remove the cut plant material from the area.

Multiple environmental factors can cause brown spots on leaves, and most are easily corrected. Sunlight exposure, pH imbalance, nutritional deficiencies, over-fertilizing and cold water can all cause brown spots on leaves. Correct any pH and nutritional issues, or re-pot the plant in fresh soil. Check the care guidelines for your plant and make sure it is not getting more sunlight than what is recommended. Water your plants with room temperature water to avoid brown spots caused by contact with cold water, both when watering the soil and when foliar watering.