Tea grey blight is one of the most serious diseases affecting tea leaves, also known as tea shoot blight, primarily caused by the plant pathogenic fungus Pestalotiopsis sp.. This disease mainly affects mature and old leaves but can also infect young shoots, causing leaf withering, shedding, and even death of the entire plant, significantly impacting tea yield and quality. In recent years, there have been reports in China identifying a diversity of pathogens causing this disease, with multiple species within the genus Pestalotiopsis showing significant biological differences, making control challenging.
Currently, chemical fungicides such as carbendazim, thiophanate-methyl, copper compounds, and others are primarily used for control, while biofungicides like pseudomonads, bacilli, and antibiotics (such as Wuyi mycin, camellia saponin, kasugamycin, and nisin) and extracts from approximately 30 plants, including Datura, are increasingly being applied. This article discusses the distribution and damage of tea grey blight, the biological characteristics of its causative agents, and epidemiological patterns, and proposes integrated control measures to provide guidance for practical disease management.
I. Distribution and Damage
Tea grey blight is widely distributed in tea-growing regions, including India and Japan, and occurs in all tea-producing areas in China. On young shoots, mature, and old leaves, the disease produces circular or irregular spots that range in color from yellowish-brown to dark brown, with small black ink-like particles (the conidiomata) arranged along concentric rings. The center, margins, or entire surface of the spots may appear grayish-white. A characteristic symptom is the formation of clearly visible concentric rings (Fig. 1-A to C), resembling the annual rings on a tree trunk's cross-section, hence the name; however, some infected leaves show no concentric rings, only scattered black conidiomata (Fig. 1-D to F). Spots of varying sizes often merge into larger lesions in later stages (Fig. 1-E), leading to leaf fall. Severe cases cause twig dieback and weaken the growth of the tea plant, resulting in yield losses of 10% to 20% in tea-growing regions worldwide.
Fig. 1 Symptoms of field damage caused by tea grey blight
II. Biological Characteristics of the Pathogen
The disease was first discovered in Kagoshima, Japan, in 1973 and named Zonate leaf spot. The causative agent of tea grey blight belongs to the genus Pestalotiopsis (Ascomycota), which exhibits diversity, with Pestalotiopsis theae (Sawada) Steyaert and Pestalotiopsis longiseta (Speg.) K. Dai & Tak. Kobay being dominant species. The former is widely found in major tea-producing countries like India and China, while the latter is prevalent in tea-growing areas in Japan. Additionally, nine species within the genus Pestalotiopsis have been recorded globally as causing similar symptoms in tea leaves; three new genera of fungi (Monochaetia Camelliae Milei, Pseudopestalotiopsis Camelliae sinensis, and Neopestalotiopsis clavispora) have also been identified as pathogens causing tea grey blight.
Pestalotiopsis theae, as a dominant species, forms colonies with smooth edges and distinct concentric rings after seven days of growth, with black particles in the center and a pale yellow underside (Fig. 2-A). In later stages, the concentric rings become less apparent, but the black conidiomata enlarge and distribute randomly on the agar plate (Fig. 2-B). Conidiomata are flat and glossy black, containing numerous conidia (Fig. 2-C to D). Conidia are fusiform, colorless, and contain four septa, with tapered ends, an inverted conical basal cell that is transparent and has a thin, smooth wall, and 2-3 cells at the apex that are black to dark brown. The size of the conidia is (24.0-28.0) µm × (6.6-8.0) µm, and 2-9 appendages are produced on the apical cell (Fig. 2-E to F).
Note: A, B – Colony morphology of the pathogen; C, D – Conidiomata of the pathogen; E, F – Conidia of the pathogen (scale bar: 3 μm).
Fig. 2 Morphological observations of the pathogen causing tea grey blight
III. Epidemiological Patterns
Tea grey blight is a high temperature and high Humidity type of disease, with temperatures between 25-28°C and relative humidity of 85-87% favoring infection. Pathogens overwinter as conidia or mycelium attached to diseased leaves; the following year, when temperature and humidity conditions are suitable, conidia are produced.
The pathogen typically initiates infection from the leaf tip or margin, or through wounds on mature or young leaves, and after a 1-2 week incubation period, causes leaf disease and lesion formation. The conidiomata are spread by wind and rain, allowing for multiple re-infections.
IV. Control Measures
1. Agricultural Control
First, select resistant varieties. Generally, small- and medium-leaf varieties have stronger resistance to tea grey blight compared to large-leaf varieties. Tea gardens with recurring severe infections can be replanted with resistant small- and medium-leaf varieties. Second, implement appropriate cultivation management practices, such as applying fungicides immediately after pruning to protect the plants and minimizing wounds caused by improper agricultural operations to reduce the chance of infection. Avoid excessive nitrogen fertilization in tea gardens and increase potassium content appropriately to enhance the resistance of tea plants through balanced nutrition.
2. Chemical Control
In the early stages of the disease, apply fungicides promptly. Options include 1% kasugamycin suspension concentrate at 1,000-1,500 times dilution, 3% polyoxin D wettable powder at 300-500 times dilution, 25% difenoconazole suspension concentrate at 1,500-2,500 times dilution, and 25% pyraclostrobin suspension concentrate at 1,000-2,000 times dilution. For winter dormancy, use 45% lime-sulfur crystals at 200-300 times dilution.