Many farmers ask themselves the reason behind curled leaves in their lemon,oranges,tangerines and lime trees.Citrus leaf curl is caused by many different things, making positive identification of your problem is important before you can determine how to treat leaf curling on citrus. Identifying your tree’s underlying problem is the first step to restoring its foliage’s glossy green color and natural form.
Pests and insects
Sucking insects such as aphids, whiteflies and mites feed on citrus leaves by sucking out plant juices. Check the undersides of leaves for signs of infestation. If infestations are caught early, sucking insects can often be removed or discouraged using a strong stream of water. Eliminate Argentinian ants in areas around infested citrus trees. Several species of common garden pests can attack citrus trees feeding on the liquid running through the leaves. Aphids, spider mites, citrus leaf miners, scale insects and mealy bugs are a few of these sap-sucking pests that will cause the leaves to curl, wilt. Pests feed on citrus leaves and suck the sap from transport tissues. This can cause deformations of leaves causing curling, cupping, wilting and discoloration. This will not kill the tree, but they will reduce the yield.
The adult citrus leaf miner, a tiny night flying moth do not suck on leaf juices, but their larvae tunnel through leaf tissues as they grow, forming serpentine mines in the tender new leaves of all varieties of citrus leaving a silver trail in their path.
The mining causes the new flush to twist and curl and prevents it from expanding fully. Introducing predatory insects that feed on the sap-sucking pests will help keep their numbers in check. Ladybugs, predatory wasps and green lacewings are a few of these predatory insects that help control pests naturally. You don’t need to use insecticides because the pests rarely threaten the citrus tree’s life. If you decided to use insecticides to treat the pest, apply horticultural oil, insecticidal soap or neem oil to the citrus on a cool, calm day 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.
Several fungal diseases will cause the leaves of citrus tree to curl, distort, yellow, wilt and drop prematurely from the tree. Bacterial blast and botrytis disease are two of these fungal diseases that lead to leaf curling. Bacterial blast starts out as black lesions on the petiole and moves to the axil. The infected leaves will curl, wither and drop. Protecting the citrus tree from high winds will help reduce the chance of bacterial blast. Apply Bordeaux or copper sprays to trees infected with bacterial blast. Botrytis disease attacks citrus trees that have damage or injuries. Grayish, velvety mold begins to grow on infected areas causing leaf discoloration, curling and possible twig dieback. Botrytis disease will also cause an increase in fruit drop. Keep this fungal disease at bay by preventing mechanical injury to the tree and protecting it from rot and frost. Applying copper fungicide before rainy or foggy weather helps prevent the fungus from reaching the blossom or fruit stage.
Insufficient soil water is probably the most-common general cause of curling citrus leaves. This can occur at any time of year, but is most common with trees in areas that aren’t regularly irrigated, during long periods without rainfall, and during hot weather. A citrus tree that does not get enough water becomes water-stressed and the leaves begin to dull and curl. As the time passes, these leaves will dry, become crisp and fall from the branches. If the citrus still doesn’t receive proper water, flowers and fruit will drop prematurely, and the life of the plant is threatened. The amount of water depends on the citrus type, time of year, weather and size of canopy.
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.
Potassium Deficiencies in Citrus Trees
If deficient in potassium, the citrus leaves show a yellow cast that are bent downward at the tip. Check the soil ph. Feed with fertilizer high in potassium.
Phytophthora Root Rot
Too much water can cause the roots of your orange tree to rot. Phytophthora fungi live as spores in the soil, and moist conditions provide an opportunity for it to thrive. Signs of phytophthora root rot include the leaves turning pale green or yellow and eventual decline in growth and tree health. Ensure your orange tree has well-drained soil and cut back on watering to prevent further damage. Severe infections may be treated with fungicides containing mefenoxam or fosetyl-al.