Source(s): Wayne McLaurin, Professor Emeritus of Horticulture, The University of Georgia, College of Agricultural and Environmental Sciences
Herbs are generally resistant to garden pests and diseases. As with growing any plant, thorough soil preparation, good cultivation practices, adequate watering, and good drainage keeps most herbs growing well and trouble free. A few pests occur, however.
Because the leaves of herbs are used throughout the season, chemical sprays and dusts generally should not be used. Organic materials, such as Bt (Bacillus thuringiensis), insecticidal soaps, herb/spice decoctions, and soapy water may also be used, but a simple spray of water is enough to wash away many pests. A few herbs do succumb more than others to garden problems.
Caterpillars — Identify caterpillars as harmful before trying to eradicate them. Black Swallowtail caterpillars are found on dill, fennel, parsley and related plants. In many gardens dill and parsley are planted especially to attract this butterfly.
Leaf Hoppers — Because they “hop” to various parts of the plant or to other plants, leaf hoppers can spread plant diseases as well as inflict damage from their own sucking feeding habits. They may infest almost any plant but often can be controlled by water sprays.
Leaf Miners — These burrowing insects that leave white “trails” all over the leaves of parsley and lovage can be persistent. While commercial growers use floating row covers to prevent this pest, the herb gardener will more likely clip back or replant when miners attack established plants.
Aphids; whiteflies — Good air circulation helps prevent these insects on more susceptible plants, such as germander and monarda; once discovered, they can usually be washed away with a spray of water.
Rust — A fungal disease found on mint, lemon balm, and similar plants, rust is usually not destructive of the entire plant. Because mints are so persistent and propagate through underground runners (stolons), rust-infected plants can be cut back to the ground and allowed to resprout.
Mildew — Lemon balm, monarda, and yarrow may show signs of powdery mildew. Thinning, clipping off the infected parts, and clipping adjacent plants back to increase air circulation are usually effective.
Further research is needed to verify claims of the effects of companion plantings. Plants said to repel pests or otherwise appear beneficial to other plants include chives, nasturtiums, mints, pennyroyal, garlic, tansy and French marigolds. Other herbs may affect some plantings negatively.
Resource(s): Herbs in Southern Gardens
Center Publication Number: 260