What Is Wrong With My Nierembergia?

Are the leaves mottled with yellow, young growth may be narrow and twisted?

Are the leaves curled and distorted?

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

Do the leaves have large, ragged holes in them?

Leaves mottled with yellow usually indicate a Tobacco mosaic virus. There is no cure for viral diseases, remove and destroy infected plants. Presoak seed in a 10 percent bleach solution before planting to prevent problems. Control aphids as they are the most likely carriers of the tobacco mosaic virus.

Distorted and 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.

These symptoms 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.

Large, ragged holes in the leaves are caused by slugs and snails. Slugs and snails feed on the plant leaves usually at night. To control slugs and snails use diatomaceous earth around your plants. You can also handpick them during the night or use shallow dishes filled with beer as a trap.

If your plants have yellow leaves and a stunted look the culprits are whiteflies. These tiny, mothlike flies and their larvae feed by sucking plant juices. Whiteflies secrete honeydew, a sugary substance that makes leaves sticky to the touch. Control whiteflies by eliminating garden weeds and by introducing green lacewings in the garden. Spray infested plants with insecticidal soap every 3 days for 2 weeks.