How to prevent anthracnose disease in tea trees

Anthrax is not only a common fungal disease in tea leaves, but also an important limiting factor affecting tea yield, quality, and ecological security in tea gardens. It forms a significant seasonal epidemic peak in spring and autumn (especially during the plum rain and autumn rain periods.

Disease onset conditions and seasonal patterns

Tea anthracnose fungus is a typical high-temperature and high humidity pathogenic fungus, and its nutritional growth and sporulation activity are regulated by temperature and humidity conditions. The suitable temperature for the growth of tea anthracnose mycelium is 25-28 ℃, while the germination of conidia and the formation of attachment cells require a continuous relative humidity of over 80%. This specific requirement for environmental conditions is highly consistent with the suitable temperature for tea growth (20-30 ℃) and the microclimate conditions of the tea garden canopy, which together lead to diseases.

Clear seasonal epidemic peaks are formed in spring and autumn (especially during the plum rain and autumn rain periods:

• In spring (February April), the temperature rises and stabilizes at around 20 ℃. The mycelium in the overwintering diseased leaves resumes growth and produces conidia, which spread to the sprouting spring shoots and tender leaves through wind and rain, becoming an important source of infection at the beginning of the year. At this stage, the stratum corneum of the tender leaves has not completely embolized, forming a clear host susceptibility window. Pathogenic bacteria are prone to invade, and the disease rapidly increases in April and May, forming the first peak of the epidemic.
• In summer (June to July), although hyphae can continue to grow at around 25 ℃, conidia are sensitive to high temperatures and can die in 10 minutes at 50 ℃. Short term high temperatures (>30 ℃) in summer can to some extent inhibit the spread of the disease, but the local microenvironment formed by canopy shading can still maintain the survival of pathogens at suitable temperatures, allowing hyphae to grow at low speeds or remain dormant in leaf tissues, preserving the bacterial source for reinfection in autumn.
• In autumn (August October), as the temperature drops and autumn shoots sprout, the conidia produced by the diseased remains spread again, completing the reinfection cycle and forming the second peak of the epidemic.

Compared to temperature, humidity is often a key factor limiting the rapid spread of tea anthracnose disease. The propagation and germination of conidia depend on water droplets or high humidity microenvironments. When the relative humidity is ≥ 85%, the germination rate of spores significantly increases. Therefore, reducing the canopy humidity of tea gardens and shortening the water holding time of leaves are important entry points for preventing infection in agricultural control. This humidity dependence leads to significant regional differentiation in tea regions with different climate types.

Infection process and dynamic development of disease spots

The infection process of tea anthracnose follows a cyclic pattern of “attachment invasion expansion manifestation”. Spores spread through wind and rain to the soft hairs on the back of tender tea leaves. When the temperature and humidity conditions are suitable, the spores start to germinate and extend into the bud tube. The top of the bud tube differentiates into attachment cells, which then enter the host tissue by directly penetrating the stratum corneum or stomata/wounds, completing colonization and causing leaf lesions.

During the infection process, pathogenic bacteria secrete extracellular enzymes such as keratinase and pectinase, which break down the polysaccharide components in the cuticle layer and cell wall of tea leaves, thereby breaking through the physical barrier of tea plants and completing tissue colonization.

Prevention and control techniques for anthracnose in tea trees

1. Chemical control

Chemical control has the characteristics of fast onset and stable prevention effect, and is suitable for emergency control of tea anthracnose in the initial and epidemic stages. However, it should not be used as a long-term single dependent prevention and control method.

Existing research has shown that 30% ether fungicide wettable powder, benzofenapyr, and pyriproxystrobin have strong inhibitory effects on C. camelliae (a dominant pathogen of tea anthracnose) and can be used as important candidate agents for chemical intervention in the early stages of the disease. In the early stages of the disease, spraying a certain concentration of pyrazole ether fungicide suspension or phenylene ether cyclohexane water dispersible granules can effectively curb the spread of the disease.
In terms of the development of new formulations, nano Cu (OH) 2 can induce pathogenic bacterial cell membrane rupture, DNA damage, and oxidative stress (inhibiting SOD activity and promoting MDA accumulation) to cause their death. To delay the development of drug resistance, rotation of medication should be implemented based on the mechanism of action of the drug (such as alternating the use of methoxyacrylates and triazoles). At the same time, specialized additives and precise spraying techniques can be combined to reduce pesticide use, while maintaining control effectiveness and reducing residual risks.

2. Biological control

The core of biological control lies in reducing the infection and expansion ability of pathogens through microbial antagonism, inducing systemic resistance, and regulating the microecology of tea gardens.

• After spraying the spore suspension (1 × 104 cells · mL-1) of antagonistic fungi Aspergillus niger En10 and Talaromyces sp. En12 on tea leaves, the lesion area was significantly reduced, and the inhibition rates against pathogenic bacteria were 59% and 44%, respectively.
• Trichoderma inhibits pathogens through heavy parasitism and antimicrobial activity. The field efficacy of Yunnan Trichoderma fermentation broth against anthracnose in tea trees reached 68.55%, and the yield of tea leaves increased by 15.92% compared to the control.
• Trichoderma harzianum also exhibits broad-spectrum antagonistic activity against the genus Colletotrichum.
• Bacillus subtilis exerts disease prevention effects by secreting lipopeptide antibiotics, polyketide compounds, and inducing ISR.
• Bacillus velezensis YJK1 is a highly efficient biological control strain screened in recent years, with an inhibition rate of 70.7% on the growth of C. camelliae hyphae. Its fermentation broth has a significant inhibitory effect on spore germination, and it maintains high activity even after 80 ℃ heat treatment and UV irradiation, demonstrating good environmental stability and potential for field application.
• Pseudomonas is an important biological control bacterial resource in the rhizosphere and leaf zone of tea plants. In the application of biological control of tea tree anthracnose, Pseudomonas aeruginosa is often used as a component of composite agents in combination with Bacillus subtilis and Trichoderma. There are few reports on the field efficacy of using it alone to control tea tree anthracnose.

The field efficacy of biological control agents is greatly affected by environmental factors such as temperature, humidity, and ultraviolet radiation in tea gardens, and their onset rate is slower than that of chemical agents. Currently, they are mostly used as preventive measures in the early stages of disease occurrence, or in combination with low-dose chemical agents to prolong the efficacy and achieve reduced and increased efficacy.

3. Agricultural prevention and control

The main goal of agricultural prevention and control is not to directly kill pathogens, but to construct a “plant pathogen environment” collaborative regulation system through agronomic means such as improving resistant varieties, optimizing cultivation management, and regulating microecology, in order to reduce the probability of disease occurrence.

(1) Grafting resistance mechanism

Research has found that grafting the susceptible variety Qianmei 818 onto the resistant rootstock Qianmei 419 can reduce the diameter of disease spots by 98.7%.

(2) Cultivation management

On the basis of clarifying the background of variety resistance, scientific cultivation and management can further enhance the growth of tea trees, reduce canopy humidity and pathogen sources, thereby weakening the conditions for pathogen infection and expansion. The regulation of tea garden microenvironment directly affects the intensity of disease occurrence. Excessive soil moisture can weaken the respiratory function of roots, leading to weakened tree vigor; The newly pruned branches and young tea trees after pruning form a susceptible window period due to incomplete keratinization of the leaf cuticle and high moisture content. Nutritional imbalance, especially high nitrogen potassium ratio, may inhibit lignin and cellulose synthesis, reduce leaf mechanical strength, and make tea trees more susceptible to pathogen infection.

Production should be carried out on slopes with loose soil, abundant organic matter, and good drainage. Reasonable and dense planting (row spacing of 1.5-1.8 m) should be carried out to optimize group ventilation and reduce canopy relative humidity. Controlling the nitrogen potassium ratio and increasing the application of potassium fertilizer (K2O, 100-150 kg · hm-2) can enhance physical barriers by strengthening lignin synthesis. In winter, the use of stone sulfur agents or mineral oil to clear the garden, combined with the removal of diseased leaves, deep burial or incineration treatment, can significantly reduce the overwintering bacterial source base.

The intercropping mode can indirectly improve the ecological regulation ability of tea gardens against anthracnose by improving soil fertility, optimizing canopy microclimate, increasing biodiversity, and enhancing tea tree growth. Studies have shown that intercropping leguminous plants in tea gardens can enhance soil nitrogen content and improve soil fertility structure through the nitrogen fixation effect of rhizobia. Intercropping ornamental tree species such as cherry blossoms and osmanthus flowers, or fruit trees such as citrus and peach can not only provide shade for tea trees and alleviate sunburn damage during high temperature seasons, but also loosen soil and enhance air permeability through deep root activity, preventing soil compaction.