Herb Problems and Solutions


Symptoms: Brown leaf tips

Possible Culprits: Excessive fertilizer, watering, high level of fluoride, boron, or copper in the water

Susceptible Herbs: All plants

Solutions: Change watering and fertilizing habits. If symptoms persist, test water quality.

Symptoms: Poor growth, yellowing leaves, new growth shrivels and dies

Possible Culprits: pH imbalance, lack of nutrients, poor drainage

Susceptible Herbs: All plants

Solutions: Check drainage; test soil. Amend with appropriate additives or repot plant to provide better drainage.


Symptoms: Stunted and deformed leaves and stems; plant parts covered with sticky, dark substance

Possible Culprits: Aphids: suck sap from plants, producing a sugary “honeydew”

Susceptible Herbs: Calendula, mint, oregano, and rosemary

Solutions: Spray plants with water or insecticidal soap. Or wipe affected areas with a cotton swab soaked in rubbing alcohol.

Symptoms: Wilted leaves, possibly coated with sooty mold; plant loses vitality and eventually dies

Possible Culprits: Whiteflies: feed on undersides of leaves and can cause extensive damage

Susceptible Herbs: Calendula, lemon verbena, and rosemary

Solutions: Spray plants with water. If indoors, lower growing temperature to decrease whitefly activity. Encarsia formosa, a species of tiny predatory wasp, can be an effective control outdoors.

Symptoms: Yellowish or silvery leaves; severe yellowing and rusty spots; fine webbing on leaves and stems

Possible Culprits: Spider mites: tiny pests puncture plant leaves and stems and feed on sap

Susceptible Herbs: Mint, oregano, parsley, rosemary, sage, and thyme

Solutions: Apply horticultural oil or insecticidal soap. Wash plants with a mild solution of dish detergent and water. Prune heavily infested branches and isolate infested plants.

Symptoms: Holes at edges of leaves; plants are eventually defoliated

Possible Culprits: Japanese beetles: metallic green insect with copper-colored wings that feed on leaves

Susceptible Herbs: More than 200 plant species including basil, borage, and foxglove

Solutions: Remove from leaves by hand. Control larvae with parasitic nematodes and the bacteria milky spore.

Symptoms: Yellow foliage; plants lose leaves, weaken, and die

Possible Culprits: Scale: minute, sap- feeding insects

Susceptible Herbs: Wide range of plants, including bay and rosemary

Solutions: Remove with a soft-bristled toothbrush dipped in rubbing alcohol or insecticidal soap spray. Plant herbs to attract beneficials. Horticultural oils may help.


Symptoms: Irregular holes in the middle or at the edges of leaves; plants may be defoliated; shiny slime trails on and around plants

Possible Culprits: Snails and slugs: pests eat seedlings and soft-tissued parts at night and on cloudy, damp days

Susceptible Herbs: Bee balm, calendula, sage, and sorrel

Solutions: Remove by hand daily, then weekly, when numbers drop. Edge beds with copper strips or diatomaceous earth. Trap with boards and rocks, or sink beer-filled saucers set into the ground with the rims at soil level.


Symptoms: Yellow, drooping foliage; plants turn brown and die

Possible Culprits: Verticillium wilt: a fungal disease

Susceptible Herbs: Mint and many other plants

Solutions: Plant disease-resistant varieties.

Symptoms: Weakened stems with flowers develop a fluffy gray or white growth, which spreads to fruits

Possible Culprits: Botrytis blight: a fungal disease

Susceptible Herbs: Rosemary, scented geranium, and many other plants

Solutions: Destroy infected plant parts. Promote air circulation around plants by cutting back or removing plants that crowd each other.

Symptoms: Yellow or white spots on surface of leaves; crusty orange or yellow bumps on undersides; plants become stunted

Possible Culprits: Rust: a disease caused by 4,000 or so related fungi

Susceptible Herbs: Germander, mint, and yarrow

Solutions: Destroy infected plant parts. Promote air circulation around plants by cutting back or removing plants that crowd each other.

Symptoms: Gray or white powdery growth on leaves; new leaves are distorted in shape; poor growth and low yield

Possible Culprits: Powdery mildew: a fungal disease that thrives in hot weather

Susceptible Herbs: Bee balm, catmint, germander, and lemon

Solutions: Promote air circulation around plants by cutting back or removing plants that crowd each other. Spray affected plants with sulfur, lime-sulfur, horticultural oil, or a weak solution of baking soda and water.

Symptoms: Yellow foliage; brown coloration along leaf edges; plants wilt and become stunted; roots soft and waterlogged

Possible Culprits: Root rot: a fungal disease

Susceptible Herbs: Oregano, rosemary, sage, tarragon, and thyme

Solutions: Use sterile potting soil when propagating plants. Avoid overwatering, but do not let plants dry out between waterings. Remove and destroy affected plants.

Symptoms: Yellow stunted leaves; wilting

Possible Culprits: Nematodes: microscopic wormlike creatures feed on roots, leaves, and stems and spread readily in water and on tools

Susceptible Herbs: Calendula and parsley

Solutions: Remove and destroy infested plants. Amend soil with compost, organic fertilizers, and products containing seaweed.