Leaf Curl - Causes of Leaf Curl

Causes of Leaf Curl

When a virus is the cause of leaf curl in a plant, usually an insect will carry the virus to the plant. This is such the case in sweet potato leaf curl, carried by the sweet potato whitefly. The whitefly also has been found to transport the leaf curl virus to tomatoes. This has been seen since 1997 in Florida, and has since spread to other southern states. The virus was recently seen in South Carolina, and with the abundance of whiteflies in the state, has the potential to spread out of the southeastern United States. The Geminiviridae virus has also been seen to spread by the transport of nursery soils. The virus appears to stay in soil, and when a new crop is planted, affects the new host.

When a whitefly (and some other carriers of viruses) eats leaves on an infected plant, the virus enters its saliva and is spread when the fly eats at a healthy tree. This explains the rapid amount of trees infected in a given area.

When a fungus causes the sickness, a different process occurs. The fungus (Taphrina deformans) causes the whitish bloom that covers each leaf as infection progresses. This color is made of asci that break through the cuticle of the leaf. One asci consists of eight ascospores that create conidia, which are ejected in early summer and moved by methods of rain and wind. It is believed that this fungus survives the winter by staying on the surface of the new host plant, such as on bark or buds. In the spring, new buds are affected by the conidia as the leaves come out of the buds. The fungus produces the ascospores on the surface of the already infected leaves. Often the disease does not occur every year due to the variances in temperature and weather from year to year. The fungus has higher infection rates following cooler winters, has optimal temperatures for infection, and requires rain.

Other common diseases caused by ascomycetes include: the Dutch Elm Disease, Chestnut Blight, Leaf Spot, and Ergot.