Black scale mealybug is one of the main pests in Yibin Tea gardens. Recently, various tea-producing districts and counties in our city have entered the spring tea picking period. During surveys of spring tea production, it was found that some areas occasionally experienced harm from black scale mealybugs. To guide tea gardens in scientifically and effectively controlling the Pest and reducing its damage, ensuring tea production and quality safety, the National Tea Industry Technology System Yibin Comprehensive Test Station provides guidance on the symptoms, occurrence patterns, causes, and control methods of black scale mealybugs for reference by tea enterprises and farmers.
I. Symptoms of Damage
The main symptom involves nymphs clustering on the underside of leaves to suck sap and excreting large amounts of “honeydew” on lower leaf surfaces, which can induce sooty mold disease. Severe cases result in the tea garden turning dark, hindering photosynthesis in the tea plants, weakening their vigor, halting new Shoot growth, and affecting tea yield and quality.
II. Occurrence Patterns
1. The black scale mealybug goes through four developmental stages: egg, larva, pupa, and adult. Adults lay eggs on the undersides of mature and new leaves. After a certain period, these eggs hatch into larvae, which crawl short distances to find suitable positions and fix themselves on the underside of leaves until they reach the third instar stage and then pupate in the same spot, eventually emerging as adults.
2. There are four generations per year. Older nymphs mostly overwinter on the underside of old leaves, pupating in March and emerging as adults in April. Subsequently, they lay eggs. The peak period for first-generation nymphs is late April to early May, second-generation nymphs in late June to early July, third-generation nymphs in late August to early September, and fourth-generation nymphs in October.
3. Adults tend to gather on young and tender shoots of tea plants during sunny mornings and evenings but have poor flight capabilities, mostly flying between shoots within the tea bushes. Eggs are mostly distributed on the underside of middle and lower layer leaves; generally, the number of insects is higher where the canopy is dense and shaded.
III. Causes of Occurrence
1. Tea plants in tea gardens are planted densely, resulting in crowded canopies with poor ventilation and light penetration, which is conducive to the occurrence of black scale mealybugs.
2. Inadequate Water and fertilizer management results in weak tea plants with poor disease resistance, making them susceptible to black scale mealybug damage.
3. Long-term use of single chemical pesticides leads to the development of Pesticide resistance in black scale mealybugs.
4. Warm winters and warm, rainy spring weather increase the survival rate of overwintering black scale mealybugs, favoring their occurrence.
5. Black scale mealybugs have a strong attraction to yellow-green leaves and tea varieties with high amino acid content are more likely to attract them.
IV. Control Methods
1. Agricultural Control. During the spring tea harvest, pick fresh leaves frequently and thoroughly, and promptly prune after harvesting to remove eggs laid in the upper layers. Regularly thin out weaker branches in the middle and lower layers of tea plants, removing and disposing of diseased and infested branches outside the tea garden to reduce the number of hosts for black scale mealybugs. Timely clear weeds around the tea rows and garden perimeter to improve ventilation and light penetration. Strengthen fertilization management by applying phosphorus, potassium, and organic fertilizers to strengthen plant vigor and improve disease resistance. Conduct garden closure management from late October to late November using 99% mineral oil + 45% sulfur suspension to reduce the overwintering insect population.
2. Physical Control. Given the strong attraction of black scale mealybug adults to yellow, install yellow sticky boards or predator-friendly sticky traps at the beginning of adult emergence in spring and autumn (late March to early April and late July to early August). For gardens with severe damage the previous year, installation should begin during the spring tea harvest period (early March). Hang the sticky boards 5-10 cm above the top of the tea plants, with a density of 25 boards per mu (about 0.067 hectares), increasing density if necessary in heavily infested gardens. Use sex pheromone lures with the sticky boards, placing the lure core one-third of the way up from the board to disrupt mating and reduce the next generation's nymph population.
3. Scientific Pesticide Application. To control black scale mealybugs, target the young nymph stages of each generation, particularly the first and fourth generations. At the end of the egg hatching period (mid-April), apply efficient, low water-soluble chemical pesticides such as chlorfenapyr, flubendiamide, or buprofezin, or botanical and mineral pesticides like pyrethrin or mineral oil. Rotate pesticides and observe safety intervals. Organic tea gardens should use botanical and mineral pesticides, while EU-exporting gardens should use chemical pesticides cautiously. When controlling adults, sweeping sprays across the canopy are recommended, while for nymphs, side sprays are preferred, focusing on the underside of leaves in the middle and lower parts of the plants. In severely infested gardens within the same region, integrated control efforts are necessary to avoid missed spots.
4. Integrated Pest Management. Adhere to a green control model with prevention as the priority and control as supplementary. Prioritize agricultural and physical control measures, emphasize winter garden closure management, and base emergency pesticide applications on pest monitoring to ensure pesticide residues do not exceed standards. This promotes a dual improvement in tea garden quantity and quality, ensuring tea quality safety.