What Is Wrong With My Leek?

Are there any small white lesions with light green halos on leaves, which may expand slightly as they age?

Are the seedlings dying and the stems are girdled or rotted at soil line?

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

Are the roots light pink, later turn purple, transparent and water-soaked, bulbs shrivel?

Do the leaves have sunken, light-colored spots with concentrically ringed, purple centers?

Have the bulbs rotted in the ground?

Do the leaves have white or translucent tunnels in them?

Are the seedlings stunted or wilting, the plant will commonly break at soil line if an attempt is made to pull it up?

Botrytis leaf blight is a fungal disease that emerges in humid and warm environments. Older leaves are more susceptible to blight than younger leaves. Prevent the disease by planting leeks in areas with good air circulation. Water plants sparsely. Infected plants should be removed. Spray weekly with a copper fungicide until the disease is under control.

If your seedlings are falling over and the stems are girdled or rotted at the soil line, the most likely cause is a damping-off disease. Remove and destroy all infected plants. To prevent damping-off let the soil surface dry between waterings, thin seedlings to avoid overcrowding and do not add nitrogen fertilizers until plants have developed leaves.

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 fungal Pink root disease. Seedlings infected with this fungal disease may shrivel and die. Destroy infected plants. Prevent problems by ensuring good drainage and adding ample organic matter to the soil. Solarization and/or fumigation of the soil can help reduce the levels of pathogen.

A fungal disease Purple blotch causes these symptoms. Spots enlarge and girdle leaves, which wither and fall over. Spray plants with sulfur if the disease is present to keep it from spreading. Cool soil makes plants more prone to this purple blotch. Use a long term rotation with non-allium crops.

White rot disease causes alliums like leek bulbs to rot. Bulbs may be covered with a white fluffy growth. Destroy infected plants, and don’t compost them. Prevent problems by providing good drainage and presoaking seeds in compost tea. Use a long term rotation with non-allium crops.

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.

Onion maggots feed on roots, killing seedlings and older plants. Onion maggots are white and taper to a point at the head. Destroy infested plants. Do not compost them. Apply parasitic nematodes to the soil before planting and cover plants with row cover.

If the leaves are discolored, scarred, and with distorted tissue, the culprits are Onion thrips or Western flower thrips. Severely infected plant parts should be removed and destroyed. Control thrips by introducing lady beetles or lacewings, their natural predators. Insecticidal soap helps in severe infestations.