Why Does My Fennel Look Sickly?

Are there any small, necrotic flecks on leaves that develop a chlorotic halo and expand into tan brown necrotic spots?

Do the leaves have pale areas on upper surfaces and "downy" patches underneath?

Are the leaves covered with white powder?

Are the leaves pale on their upper side and are there any dusty blisters on the undersides?

Are the leaves curled and yellow?

Are there singular, or closely grouped circular to irregularly shaped holes in the foliage?

Are the seedlings clipped off at the soil line?

Cercospora leaf blight is caused by a fungus that can be introduced through infected seed and spread by wind or water splash. Plant only pathogen-free seed from a reputable nursery. Apply copper-based foliar fungicide if the disease emerges. Rotate crops to non-umbelliferous varieties.

Pale areas on upper surfaces of the leaves and "downy" patches underneath are caused by Downy mildew. This fungus spreads quickly during cool, wet nights and warm, humid days. Leaves will wilt and die. Remove and destroy all affected plant parts and encourage good air circulation around plants by thining them. Water plants early in the morning to make sure they dry before nightfall.

White, powdery patches on the leaves are caused by a fungal disease Powdery mildew. Powdery mildew usually appears in damp places. Encourage good air circulation around the affected plants by thining them and any surrounding plants. Water plants from bellow to keep foliage dry. Any affected leaves should be cut off and removed.

Likely cause for these symptoms is a fungal disease - Rust. Provide good air circulation around plants by thining them. Avoid making leaves wet when watering. All infected leaves should be removed. Spray leaves with sulfur early in the season to prevent rust or to treat mild infections.

Distorted, curled leaves are caused by aphids. These tiny insects cluster under leaves and on growing tips where they feed on plant sap. Leaves, stems, and buds get distorted, and later leaves and flowers drop from the plant. You can control them by washing them off the plant with water spray. Insecticidal soap should be used with severe infestations.

Armyworm is a known pest of fennel. This insect can go through 3–5 generations a year. Organic methods of controlling armyworms include biological control by natural enemies that parasitize the larvae and the application of BTK spray (Bacillus thuringiensis).

If the seedlings of your plants are cut off at the soil level, most likely cause are cutworms. They feed at night by cutting off young plants and sometimes eating them whole. During the day, they are hidden below the soil surface. Control them by introducing parasitic nematodes to the ground. Using BTK spray on the ground will also control their numbers.

Yellow, stunted plants and roots that have swollen galls indicate root-knot nematodes. Other symptoms are plants wilting during bright, hot days. Prevent root-knot nematodes by applying chitin or introducing parasitic nematodes to the soil before planting. Solarizing the soil also helps in preventing root-knot nematodes.