The satsuma mandarin (Citrus reticulata or Citrus unshiu Marc.) is a relatively cold-hardy citrus tree believed to have originated in Japan. It is prized for its juicy, sweet and nearly seedless fruits. Satsuma trees require protection when temperatures drop below 26 degrees Fahrenheit, but are suitably small enough for indoor container cultivation in cooler regions as long they receive adequate light. Wilted leaves on a satsuma could result from certain diseases, pests or environmental factors. Identifying the probable cause of the wilt allows a grower to adjust care practices or treat the satsuma accordingly.
Environmental and Care Problems
Symptoms of both over-watering and under-watering appear on leaves; over-watering is indicated by leaf yellowing and drop while inadequate water causes interior leaf tissue to collapse and become translucent and the entire leaf to dry out and turn brown. During hot, dry weather, satsuma requires water about twice weekly, although plants grown in containers may require more frequent irrigation. When conditions are cool and wet or humid, satsuma trees may only need supplemental irrigation every several months. Overwatering also leaves a satsuma more vulnerable to root rot diseases. Although a notably frost-hardy citrus, a severe frost can cause leaves and twigs to appear water-soaked, whither, turn dark and either drop off or persist on the satsuma. Root damage in general causes leaf yellowing and dieback.
Pathogens like Phytopthora and Armillaria cause leaf wilt, yellowing and drop. Phytophthora symptoms can appear above ground as gummosis, or foot rot -- when sap oozes from lesions and bark is discolored or dry -- or below ground as root rot. Regardless of the infection type, the satsuma suffers an overall loss in vigor including leaf wilting, yellowing and drop. Trees are most vulnerable to Phytophtora when wounded or if the roots or trunk are subjected to constant moisture. Armillaria root rot, also known as oak root fungus, can destroy an entire root system and is often quite established before symptoms appear. This disease causes small, yellowing leaves, premature leaf drop, dieback and poor growth. Mushrooms may appear at the base of the tree after rain events. Rot-infected trees are difficult to save and usually warrant removal.
Deficiencies or Toxicities
Nutrient deficiencies are most problematic when soil pH or drainage are also issues. A potassium deficiency appears as a yellowing of leaves while the leaf tip and edges bend downward. Light green or yellow leaves, a thin canopy, leaf drop, stunted growth and poor fruit production indicates inadequate nitrogen. Excessive boron or sodium manifests as leaf yellowing or mottling and premature leaf drop.
Nematodes, microscopic roundworms, feed on citrus roots and may plague satsuma in conjunction with Phytophthora root rot. The presence of these pests leads to poor feeder root growth, which results in a general loss of vigor including leaf yellowing or wilt, dieback and decreased fruit size. Heavy whitefly feeding may cause young leaves to wilt. A severe infestation of California red scale, a particularly prevalent pest of citrus in California, leads to leaf yellowing and drop and twig dieback.
Leaf Curling or Distortion
Numerous pests or disorders cause leaf symptoms to develop, though these symptoms are usually more accurately described as distortion, curling or cupping. Aphid feeding, usually concentrated on vulnerable new growth, causes leaves to cup and curl as a result of feeding damage after each flush of growth. The citrus leafminer and Asian citrus psyllid cause twisted, deformed leaves, and the citrus leafminer creates tunnels in the leaf. Thrips feeding cause leaf deformation, while certain caterpillars roll leaves around themselves for protection. Improperly-applied herbicide or growth regulator may also affect leaf growth or shape.
- University of California Riverside Citrus Variety Collection: History of Satsuma
- University of California Statewide Integrated Pest Management Program: Citrus: Identifying Diseases and Disorders of Leaves and Twigs
- University of Florida IFAS Extension: Citrus Problems In The Home Landscape
- University of California Cooperative Extension: Citrus Problem Diagnosis
- Alabama Cooperative Extension System: Crop Profile for Satsuma Mandarin in Alabama
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