Marigolds And Insects

Spider Mites

• Spider mites are especially fond of marigolds. These pests aren't insects, but are related to spiders and ticks. They damage marigolds by puncturing the leaves with their sharp mouths and sucking up the sap. Yellow dots and specks appear on damaged leaves, making them look speckled. If the infestation is severe, the leaves will start looking scorched, and can result in the death of the marigolds. The Stethorus species of ladybird beetles are very effective in controlling spider mites. Hosing plants down with a strong stream of water will also remove mites, if the infestation isn't too severe. Spider mites can be chemically controlled by using miticides.

Japanese Beetles

• Japanese beetles feed on the leaves of many plants, including both the American and the African marigold. The adult beetles are about 1/2 inch long, with metallic-green, oval bodies and copper wing covers. Control Japanese beetles by handpicking them off infested plants. Insecticides need to be applied more than once because most insecticides only last a couple of weeks, and Japanese beetles feed for about 6 weeks. The damage Japanese beetles cause is mostly aesthetic. Even heavily infected flowers usually remain healthy, because beetle infestations usually happen after the leaves have already produced most of the food the plant is going to use. Japanese beetle traps aren't an effective way to control this pest, and gardeners who use them have more of a problem with these beetles than gardeners who don't. That's because while the traps do attract beetles, the beetles don't usually end up going all the way into the trap, feeding instead on nearby plants.

Caterpillars

• Several caterpillars feed on marigold leaves including the cabbage looper, orange tortrix, sunflower moth, tobacco budworm and beet armyworm. Caterpillars chew holes in the flowers and leaves or eat the shoots, buds, flowers and young seedlings. Control them by handpicking them off the marigolds. Pesticides can also be used, and work well when caterpillars are small.

Other

• Marigolds are susceptible to several other insects, including the green peach aphid and the melon aphid, the serpentine leafminer, Western flower thrips and several species of whiteflies. All of these insects puncture the leaves and feeding on the sap. Whiteflies and aphids both secrete a sticky substance called honeydew that attracts fungal diseases. Insecticides aren't usually effective against these pests. Spraying infected plants with water to wash the insects off, and pruning infected leaves and other plant parts, works better to control them.