The most commonly reported symptoms of suspected citrus disease are related to discoloration of the leaves. More than 60 percent of reports submitted through the Save Our Citrus program cite spotted or blotched leaves, or leathery leaves with yellow or clear veins.While these symptoms are telltale signs of citrus greening disease, abnormal looking citrus leaves can also be the result of other factors such as unfavorable weather or overwatering. Additionally, other severe citrus diseases such as citrus canker and sweet orange scab can cause lesions on the leaves. This can make it difficult to distinguish serious disease from harmless environmental conditions. Remember, if you do suspect your tree may be infected, please don’t hesitate to report it. A mistaken case of disease is harmless compared to an undetected disease that spreads to other healthy trees. Here are some tips to tell the difference:
Cold weather can cause citrus leaves to curl. Cold can cause the tissue in the leaves to dry out leaving a burnt appearance. If possible, cover citrus trees if you expect a freeze.
Sunburn can leave yellow or brown leathery spots on the fruit and leaves, likely on the south and west sides of the tree. Too much heat can cause leaves to curl.
Overwatering is another common cause of unhealthy looking leaves. Too much water can cause leaves to curl, turn yellow, and drop. If you suspect overwatering, reduce your watering schedule and look for signs of improvements. Also make sure your tree has proper drainage.
Sooty Mold is the result of massive, superficial fungal growth commonly occurring on the upper surfaces of leaves, fruit, twigs and small branches. Sooty mold develops on the honeydew produced by insects such as aphids and white flies. Controlling insect populations is the best way to control sooty mold.
Citrus Greening Disease. Check leaves and fruit. In addition to leathery leaves with yellow veins, leaves may show an asymmetric blotchy mottling, which is the most characteristic symptom. Fruit of trees infected with citrus greening may be small and lopsided, or retain green color on the bottom rather than fully ripening to the expected yellows and oranges.
Citrus Canker Disease is a bacterial disease of citrus that causes premature leaf and fruit drop. The main symptoms are raised, corky, water sunken lesions on the leaves, stems and fruit of citrus trees. A yellow halo maybe be evident on leaf and fruit, but not on stems.
Sweet Orange Scab is a fungal disease that results in unsightly, scab-like lesions developing on fruit rinds and, less often, on leaves and twigs. Rusted colored lesions have been observed on the lower side of the affected leaves.
Magnesium (Mg) deficiency results from translocation (the transport of all dissolved material within a plant) from the leaves to developing fruit of new leaves on the same shoot. Mature leaves may show a triangular green pattern along the mid-rib (an inverted V). Mg deficiency may be caused by the presence of citrus greening disease. If you suspect this is the case, check for the presence of the blotchy mottle (uneven spots) symptom on leaves of previous flushes (fresh leaf growth).
Zinc (Zn) deficiency is one of the most damaging and widespread citrus nutritional disorders. A distinctive yellow mottle (uneven spots) is observed on reduced and pointed leaves: green veins with interveinal yellow spaces. This deficiency may be caused by the presence of citrus greening disease. If you suspect this is the case, check for the presence of the blotchy mottle symptom on leaves of previous flushes (fresh leaf growth).
Manganese (Mn) deficiency occurs in young, enlarging leaves on which dark green areas along the mid-rib and main lateral veins can be observed accompanied by light green interveinal areas. This deficiency may be caused by the presence of citrus greening disease. If you suspect this is the case, check for the presence of the blotchy mottle symptom on leaves of previous flushes (fresh leaf growth).