Marigold Bug Control

Chewed Foliage Edges

• Caterpillars are likely the culprit if your marigold is suffering from chewed edges and holes in the leaves. Caterpillars are best managed by hand. Remove the pests, drop them in a plastic bag and dispose of them securely in the garbage. If your caterpillar infestation is heavy, spray the pests with a bacterial product containing Bacillus thuringiensis. As the caterpillars eat the bacteria, they will become sick and die within a couple of days.

Holes in Leaves and Flowers

• Although Japanese beetles prefer to dine on roses, they will often settle for marigolds if no roses are nearby. Japanese beetles, large and easy to spot, are best removed by hand. Pick the pests off your marigolds, then drop them in a bucket of soapy water and discard the drowned bugs. For heavy Japanese beetle infestations, apply an insecticidal product containing pyrethrin or pyrethrum. Use the product according to the directions on the label.

Discolored, Curly Leaves

• Although aphids usually avoid marigolds, the pests can bother a plant that is stressed by lack of light, inadequate water or excessive heat. The tiny insects are usually green, but can also be white, brown, red or yellow. Aphids are easy to spot as they gather in clusters to suck the sap from the undersides of leaves or young stems. If you catch the infestation early, spraying the plants forcefully with a strong stream of water will often dislodge the pests. Otherwise, treat the marigolds with an insecticidal soap or an insecticide containing pyrethrin or pyrethrum.

Deformed or Stunted Blooms

• Leafhoppers are brightly-colored, winged bugs that will cause marigold's leaves to roll and twist. Often, the leaves will turn a purple color before turning yellow and dropping off. Blooming is inhibited, and any flowers that manage to bloom soon wilt. The best way to control leafhoppers is to improve the overall health of your marigold plants. Otherwise, natural controls such as spiders help keep leafhoppers under control. Although insecticidal soap may help, pesticides aren't recommended, as pesticides kill beneficial insects as well as harmful pests.

Stippled or Webbed Plants

• Spider mites are about the size of a grain of pepper, but the tiny bugs leave telltale signs such as small white dots, yellowing leaves and the appearance of fine webs. Usually, spider mites are successfully removed with a strong stream of water directed onto the plant every other day for three to five days. If the spider mites are stubborn, treat them with a horticultural oil or a spray containing pyrethrin or pyrethrum.