CSLB C-27 Landscaping ContractorPlanting and LandscapingHard
A client notices that their established avocado tree is experiencing significant leaf drop, branch dieback, and the presence of a white, powdery fungal growth on the leaves. The symptoms are most prevalent during periods of high humidity and moderate temperatures. Which disease is most likely affecting the avocado tree?
- APhytophthora root rot.
- BPowdery mildew.
- CVerticillium wilt.
- DAnthracnose.
Show answer & explanationAnswer & explanation
Correct answer: B. Powdery mildew.
The key symptoms described are 'white, powdery fungal growth on the leaves' and prevalence during 'high humidity and moderate temperatures.' These are classic indicators of powdery mildew, a common fungal disease that affects many plants, including avocado, causing leaf distortion, yellowing, and potentially leaf drop and branch dieback in severe cases.
Why the other options are wrong
- A. Phytophthora root rot causes wilting, yellowing, and leaf drop due to root decay, but not a white powdery growth on leaves.
- C. Verticillium wilt causes sudden wilting, yellowing, and browning of leaves, often on one side of the tree, and vascular discoloration, but no external powdery growth.
- D. Anthracnose typically causes dark, sunken lesions on leaves, fruits, and twigs, often with a 'shot-hole' appearance, not a white powdery coating.
Powdery Mildew Identification
A common fungal disease characterized by a white, powdery growth on plant surfaces, typically thriving in conditions of high humidity, moderate temperatures, and shaded areas.
- Causes a distinctive white, powdery coating on leaves, stems, and flowers.
- Thrives in high humidity and moderate temperatures, often in shaded conditions.
- Can lead to distorted leaves, yellowing, leaf drop, and reduced plant vigor.
- Affects a wide range of plants, including many ornamentals and fruit trees.
Memory trick: Avocado's White Cloud: Humid haze, leaf decay, mildew's way!