What is Wrong With My Marjoram?

Are there any small, dusty, bright orange, yellow or brown pustules on undersides of leaves?

Are the leaves curled and yellow?

Are the seedlings clipped off at the soil line?

Are the leaves covered in coarse stippling and may appear silvery?

Are the leaves stippled, reddish or yellowish with fine webbing?

Mint rust is a known fungal disease that attacks marjoram. The disease also affects mint and can spread from nearby mint plants. Infected plants and rhizomes should be removed to prevent spread. Heat treatment of roots may help to control the disease, roots should be immersed in hot water at 111°F for 10 minutes, cooled using cold water and then planted as usual.

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.

If the seedlings of your plants are cut off at the soil level, most likely cause are cutworms. These caterpillars can be 1-2 inches long, brown, or gray. 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.

These symptoms may indicate thrips. Thrips are tiny, yellow to black flying insects. They hide under the leaves. 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.

Reddish to yellowish flecks on leaves and webbed foliage is caused by spider mites. These tiny, spider-like pests feed by sucking sap from the underside of the plants leaves causing yellow flecking on the upper leaf surfaces. You can control spider mites by spraying plants thoroughly with water 2-3 times a day for several days. For severe infestations, spray plants with insecticidal soap, or pyrethrin as a last resort.

Some environmental issues may have caused sickly to look in your marjoram. Marjoram is a temperate or subtropical plant and should be grown in full sunlight for best results. Marjoram will thrive in dry, rocky conditions that closely mimic their natural habitat. Plants will grow well in a rich, light loam with a pH range between 4.9–8.7.