The Q&A Archives: Herb Diseases

Question: I have an indoor herb garden with a number of problems. One problem that I have is with lemon thyme and a crawling thyme variety. The stem near the new small leaves at the end of the branch will begin to turn brown, neck down, and consequently the leaves will die. I've noticed small flying insects around them and have begun spraying with an organic pesticide with botanical pyrethrins. I also have some browning and brown spots forming on the leaves of basils. Finally white spider web like films form on my mint leaves. What are these diseases, and how can I stop them?

Answer: Herbs grow best in full sunshine and need good air circulation between each plant. If your herbs are crowded together, they may be showing their distress by developing fungal diseases. Thyme likes soil on the dry side and basil appreciates rich, moist soil. If the plants are sharing the same pot, the watering conditions won't suit them all. Since summer is when the plants put forth their greatest surge of growth, your plants are probably craving sunshine. Why not try potting each up in its own container and placing them outdoors in full sunshine, at least while the weather is warm. You can always bring them back indoors in the autumn and winter them over inside. Webbing on the mint leaves is probably from spider mite insects. These are late season pests that suck juices from leaves. You can wash them off the leaves, or cut the mint plant back to remove the infestation. Mist your plants regularly to discourage spider mites (they love dry conditions).

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