Fig trees (Ficus carica) are prone to developing brown spots on their leaves. This common issue affects both indoor container plants and established outdoor trees, signaling problems ranging from cultural stress to biological attacks. Accurately identifying the cause of this discoloration is necessary for an effective solution. The appearance, location, and texture of the brown spots provide clues to determine if the fig is struggling with a pathogen, an environmental imbalance, or an insect infestation.
Brown Spots Caused by Fungal and Bacterial Pathogens
Fungal diseases are a widespread cause of leaf spotting on figs, thriving in warm, humid conditions. Fig rust, caused by Cerotelium fici, is a common pathogen that initially appears as small, yellowish flecks on the upper surface. These develop into distinctive, raised, reddish-brown pustules on the leaf underside, causing leaves to yellow and drop prematurely.
Cercospora leaf spot is characterized by angular, reddish-brown lesions. As these spots enlarge, they often develop a light tan or gray center surrounded by a dark brown margin, sometimes creating a yellow halo. Anthracnose, caused by Glomerella cingulata, presents as slightly sunken, irregular brown spots, often beginning near the leaf margins. These spots can merge to form large, necrotic areas, causing the leaf edges to dry out.
Environmental Stressors and Cultural Issues
Non-biological factors related to care and environment are often the primary culprits for brown spots, especially for container-grown figs. Inconsistent watering can cause edema, which occurs when roots absorb water faster than the leaves can transpire it. This causes leaf cells to burst, manifesting as small, reddish-brown, corky, or blister-like spots, particularly on new foliage.
Sunburn or heat stress results in large, bleached, silver, or light tan patches that appear quickly after a sudden increase in direct sunlight. This damage is dry and crispy to the touch. The accumulation of mineral salts from water or fertilizer can cause necrosis, visible as uniform browning and crisping along the leaf tips and outer margins. Sudden cold snaps can also cause dark brown or black necrotic areas on the foliage, often resulting in immediate leaf drop.
Damage from Pests
Certain insect infestations lead to brown discoloration through feeding damage or residue. Spider mites use piercing mouthparts to extract cell contents, causing minute, yellow or light brown pinpricks known as stippling. Severe infestations result in a dull, bronzed, or silvery appearance, often accompanied by fine, silken webbing on the undersides of the foliage.
Scale insects are immobile pests that appear as small, smooth, oval-shaped brown bumps attached to stems and leaf undersides. They suck sap, leading to leaf yellowing and stunting, and excrete honeydew. This sticky substance supports sooty mold, a black fungus that covers the leaf surface, appearing as dark blotches. Fig mites cause a generalized brown discoloration and roughening of new growth called russeting or bronzing.
How to Diagnose and Treat the Problem
Accurate diagnosis begins with a systematic inspection of the affected leaves. Note the location and texture of the spots: raised, rusty spots concentrated on the underside suggest fig rust. Blister-like spots on new growth point toward edema, while dry, crispy spots along the margins or tips indicate watering or nutrient issues.
If the spots are minute pinpricks or accompanied by webbing, spider mites are the probable cause. Treatment must be tailored to the specific diagnosis. For fungal diseases, improving air circulation through selective pruning and removing infected leaf debris is necessary. Applying a copper or sulfur-based fungicide can help control the infection’s spread.
Environmental issues require cultural adjustments. Edema is managed by establishing a consistent watering schedule and ensuring excellent soil drainage. Sunburn requires moving the plant into filtered light or gradually acclimating it to higher light levels. For pests, physically wiping the leaves with insecticidal soap or horticultural oil, such as neem oil, is effective. Sanitation and providing preferred growing conditions are the most reliable long-term treatments.