Marigolds are easy to grow and often recommended for beginning gardeners. They bloom all season long, require little care and compared to many other plants have very few problems. They are not exempt from common plant diseases and pests, however, despite their reputation as a repellent for mosquitoes, rabbits and deer.
Common garden pests that attack other plants can also damage marigolds. These include aphids, spider mites, thrips, leaf miners, grasshoppers and slugs. Most of these pests prefer other plants, but will eat marigolds if favourite plants are not available. The exception is spider mites. Dry conditions often result in a spider mite infestation, which can kill the marigold plant. Spraying plants with water daily to rinse away pests, misting plants with a soapy spray to kill soft-bodied insects and using insecticides for severe infestations can help keep pests from destroying marigolds.
Several types of wilt, tomato spotted wilt virus, southern bacterial wilt and Verticillium wilt. All of these infections are characterised by leaves suddenly wilting and the plant beginning to die. Unfortunately, none of these types of wilt can be treated. An infected marigold should be removed and destroyed to avoid spreading the problem to nearby plants. Prevent wilt by controlling insects and ensuring the plants have good soil drainage. Avoid planting marigolds in locations where other plants have succumbed to wilt.
Root rot is one of the most common rot problems in marigolds. It is caused by overwatering. Water plants only when soil begins to dry and make sure the soil is well-drained. Other rot problems that affect marigolds include stem rot, cottony rot and Pythium root rot. Although these rots represent different types of fungus, nearly all can be prevented by giving plants the proper amount of water. Make sure the soil is not soggy and well-drained.
Leaf Spot and Mold
Marigolds are susceptible to Alternaria leaf spot, bacterial leaf spot, grey mould and smut. While these problems appear in different forms, they all cause unusual spots or mottling on the leaves of the plant. Prevention is the only treatment for these problems. Treat marigold plants with a antibacterial and anti-fungal sprays before planting. Keeping insects at bay can also help reduce the chance of infection. Plants affected by leaf spot or mould should be removed and destroyed.
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