Marigolds are a popular annual flower grown for their bright colours of yellow, red, white or orange. They grow best in a sunny location with average garden soil. Gardeners use the many types of marigolds for borders and bedding plants and as companion plants in vegetable gardens. Although most are easily controlled, many pests can damage the foliage and flowers of marigolds.
Aphids are soft-bodied insects that feed on the juices of Marigolds. They congregate by the hundreds around the stems and new growth of marigolds. They are tan, black or brown and excrete a sticky substance called honeydew that attracts ants. Although they have many natural enemies, such as ladybugs, their numbers can get so high that other control methods are needed. For organic control try neem oil or insecticidal soap. Also, a strong spray of water usually cleans them off the plant. Chemical control of aphids includes using permethrin powder and sprays or malathion. You should use these only in cases of severe infestation because of their toxicity to beneficial insects that feed on aphids.
Leafminer adults are rarely seen but feed on the sap of plants by piercing their leaves. However, the Leafminer larva make tunnels in the leaf tissue that show up as white squiggly lines running through the foliage. There is no control for leaf miners except to remove infected leaves so larva cannot emerge and multiply. Leafminer damage, although unsightly, is rarely fatal to marigold plants.
Spider mites are the most important pest of marigolds. They cause damage by sucking the juices from the plant. They infect the underside of the leaves, and in severe cases the webbing around the leaves and stems is clearly visible, although the spider mites are very small. Spider mites prefer dusty conditions so keep paths and areas around marigold plants mulched or damp to prevent dust from accumulating on the leaves of plants. Sulphur dusts and insecticidal soap provide some control but cannot be applied when daytime temperatures exceed 32.2 degrees C or damage to plants may occur. A strong spray of water to the underside of leaves can dislodge spider mite colonies and keep them under control.
Snails and Slugs
Snails and slugs eat irregular holes in marigold leaves and chew new flower buds before they open. They feed at night and affect the marigold plants at all stages of development. For control, remove all boards, garden debris and fixtures where the snails and slugs can hide. Hand pick as many as possible when you see them and crush or dispose of them by putting in a plastic bag and placing them in the garbage. Chemical control is most effective by using snail and slug baits that contain iron phosphate, which is not toxic to children and pets.