What Is Wrong With The Leaves Of My Arugula?

Do the leaves have visible damages like holes or tunnels in them?

Do the leaves have white or translucent tunnels in them?

Do the leaves have tiny holes in them?

Do the leaves have large holes and a green caterpillar is present?

Are the leaves distorted and yellow, clusters of small insects are present?

Are there any small translucent spots on leaves, spots later turn black?

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

Are there any brown to tan concentric rings with yellow edges on leaves, centers of lesions developing gray to brown soft fungal mold?

If the leaves have white or translucent tunnels in them the culprits are leafminers. These tiny white, maggotlike larvae feed inside leaves. Prune off and destroy all infested leaves. Cover plants with row cover until flowers open to prevent adults from laying eggs on plants. Certain nematodes can attack leafminer larvae inside leaf tunnels.

Tiny holes in leaves are caused by Flea beetles. These tiny, black, brown, or bronze beetles hop when disturbed. Larvae are small and white, feed mostly on the undersides of leaves. Prevent problems by covering young plants with row cover. Control severe infestations by spraying or dusting plants with pyrethrin.

Cabbage looper is a pale green caterpillar with white lines running down either side of their body. Looper populations are usually held in check by natural enemies, but if they do become problematic larvae can be hand-picked from the plants. The application of BTK will effectively kill younger larvae.

Large, ragged holes in the leaves are caused by slugs and snails. Slugs and snails feed on the plant leaves usually at night so you usually can't see them during the day. To control slugs and snails use diatomaceous earth around your plants. You can also handpick them during the night or use shallow dishes filled with beer as a trap.

Distorted, yellow 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.

Bacterial leaf spot causes circular translucent spots scattered over the leaf surface between the veins. These spots turn brownish-black and may spread to form large patches of dead tissue. To prevent the spread of this disease, avoid working around wet plants. Remove and destroy affected parts. Spray Bordeaux mix on remaining plants.

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.

These symptoms indicate Alternaria leaf spot. Warm, wet conditions favor this fungal disease. Spray infected plants with copper and/or sulfur to prevent further disease development.

If there are pale yellow areas on upper leaf surfaces and white blisters on the undersides of the leaves the culprit is a fungal disease White rust. Disease development is favored by cool weather and periods of extended rainfall. Destroy infected leaves or plants. Remove weeds and any horseradish debris from around plants. Avoid the use of sprinklers for irrigation. Thin plants to increase airflow.