Zinnia Leaf Curling

The National Garden Bureau named 2011 the Year of the Zinnia.

Zinnias are easy to grow from seed. They produce a variety of vibrantly colored flowers on long stems that range from 8 to 48 inches in length. The size of the flowers can be as small as 1/2 inch or as large as 5 inches in diameter. Zinnias are prone to several diseases, including one virus disease that causes the leaves to curl. Another problem that leads to curling leaves is attack by aphids.

Aphids

The black bean aphid is a pear-shaped insect that grows to be about 1/8 inch long. It has an olive-green or black body and damages zinnias and other hosts by sucking the sap out of the leaves and spreading the beet western yellows virus. Aphids excrete a sweet, sticky substance called honeydew, which attracts the growth of black sooty mold. Symptoms of aphid infestation include curling, yellowing or distorted leaves. In addition, the leaves may wilt. The aphids can usually be found on the bottom sides of leaves, along with white skins discarded by previous generations.

Aphid Control

Control aphids by spraying your zinnias with a strong spray of water to knock them off your plants. Don't use excessive levels of nitrogen fertilizer because aphids reproduce faster when exposed to high levels of nitrogen. Avoid using pesticides as they will also kill beneficial insects that eat aphids, including ladybird beetles and parasitical wasps. If chemical control becomes necessary, use neem oil or insecticidal soap because they don't leave a poisonous residue and will have less impact on beneficial insects.

Leaf Curl

Symptoms of zinnia leaf curl virus include leaves that curl upward or are yellow and stunted with ringspots. Leaves may also look mottled with dead edges, or the veins may turn a lighter green. Zinnia leaf curl virus, which is also known as tobacco curly leaf virus or eggplant yellow mosaic virus, is spread by the beet leafhopper, a small light green or yellow wedge-shaped insect about 1/8 inch long. The leafhopper has to feed on a diseased plant for only one minute to spread the disease for the rest of its life.

Leaf Curl Control

There is no cure for zinnia leaf curl virus, but infections can be reduced by controlling leafhopper infestations and weeds that the leafhopper uses as alternate hosts. Providing young plants with shade will help deter leafhoppers because they prefer sunny locations. Insecticides can be used for control. Consult your county extension for recommendations for your local area. Infected plants should be removed and destroyed as soon as they're discovered.

References

• University of Idaho: Tobacco Leaf Curl Bigeminivirus
• New Mexico State University; Curly Top Virus; Dr. Emroy L. Shannon; May 2001
• Kansas State University; Zinnias
• University of California Statewide Integrated Pest Management Program: Sugarbeet Curly Top
• California Department of Food and Agriculture: Curly Top Virus Program Details
• University of Arizona Extension: Diseases of Pepper -- Curly Top Disease

Resources

• Iowa State University Extension: Zinnias
• University of Idaho Pest Management Center; Sugarbeets -- Black Bean Aphid
• University of California Statewide Integrated Pest Management Program: Aphids