WHAT CAUSES ORANGE TREE LEAVES TO CURL?
Orange trees not only produce delicious citrus they also make striking landscape plants for the garden. Unfortunately, orange trees can become invested with pests or become infected with a fungal disease that causes their leaves to curl. It is essential to identify the problem with the trees in order to treat the leaves with either pesticide or herbicide.
There are four major reasons for leaf curl in orange trees:
Curling citrus leaves with yellow, brown, or grey spots may be sunburned. This usually occurs on outer leaves that are exposed to the longest periods of direct sunlight during warm-to-hot weather, usually on the south and west sides of trees.
A section or two of sunburned leaves usually doesn’t pose a serious problem for mature trees. Provide shade. It may be beneficial to allow sunburned leaves to persist on the tree until weather cools. If a layer of sunburned leaves is removed, the leaves beneath them may also become sunburned.
Water stress is probably the most obvious reason for leaf curl on a citrus. Lack of water will eventually affect the flowers and fruit which will drop prematurely. The amount of water an orange tree needs depends on the type, time of year, weather and the size of the tree.
As an example, an orange tree with a 14-foot canopy needs 29 gallons of water a day in July when it is dry! Overwatering can affect the orange tree as well. Be sure to plant the tree in an area of excellent drainage. Remember, citrus trees don’t like overly wet feet.
Citrus canker is a fungal disease that causes discoloration and curling of orange tree leaves. Swelling on branches and twigs along with the curled leaves are good indications that the tree has a fungal disease. Bacteria survive in lesions; the main method of spread is via wind driven rain; bacteria may enter through pruning wounds. Treatment generally includes pruning off the cankers and applying a fungicide to the tree.
If the disease is introduced to an area, all infected trees should be removed and destroyed; in areas where disease is endemic, windbreaks can help to reduce disease severity; cultural control of the disease should focus on controlling leaf miner populations, utilizing wind breaks and applications of copper sprays
Sap-sucking pests like aphids, mites and psyllids feed on citrus leaves by extracting the juices directly from transport tissues. As populations grow, they can cause deformations including curling and cupping in leaves, as well as discoloration.
When you notice your citrus leaves are curling, check their undersides carefully for tiny pests feeding in clusters. If you spot them, spray your citrus tree with insecticidal soap or neem oil, making sure to coat areas where pests were spotted. Repeat this treatment weekly until your citrus plant begins to recover and all signs of insects are gone.
Citrus leaf miners are another insect pest of citrus, but instead of sucking on leaf juices, the moth larvae tunnel through leaf tissues as they grow. These tunnels are highly visible on leaf surfaces, appearing as undulating white or yellow lines on the green leaf surfaces. Citrus leaf miners are difficult to treat successfully; it’s generally recommended that you allow them to run their course since most citrus trees can tolerate a significant leaf miner load.
Citrus leaves may curl in response to cold weather. Many types of citrus withstand overnight frost or short periods of frost. Blossoms and fruit of most citrus are sensitive to frost. Dead leaves that still attached at the tops of trees and outer canopies after periods of cold weather may indicate frost damage.
Cover canopies with cloth or plastic sheets overnight to protect them from mild frost. Most types of citrus trees recover well after minor frost damage.