A Detailed Guide to the Occurrence Characteristics and Control Techniques of the Tea Black Spiny Whitefly

The black spiny whitefly mainly feeds on tea plant sap from the undersides of leaves as larvae and excretes honeydew, which attracts sooty mold fungi and induces sooty mold disease; in severe cases, the tea plants turn pitch black. Affected tea plants have reduced photosynthetic efficiency, lower sprouting density, delayed sprouting, thin and weak buds and leaves, and severe leaf drop, which not only affects tea yield and quality but also seriously affects the vigor of the tea plants.

I. Occurrence Characteristics

This pest has 4 generations per year, overwintering as mature larvae on the undersides of tea leaves, pupating in March of the following year; the peak periods of the 1st to 4th generation larvae are in late May, mid-July, late August, and late September to early October, respectively. Adults have weak flight ability, and eggs are mostly laid on the undersides of leaves by adults and on old leaves. Newly hatched larvae can crawl but soon settle near the eggshell to feed. This pest prefers dense, shaded conditions and is prone to major outbreaks in tea gardens with more leaves in the middle and lower parts of the tea bushes and in tea gardens several years after collar pruning. Within the tea bushes, the pest population is distributed more in the lower part and less in the upper part. The key factors affecting the population dynamics of the black spiny whitefly are environmental conditions and natural enemy factors.

Among environmental conditions, the greatest influences are human factors and the tea garden environment. So-called human factors mainly refer to the unreasonable use of chemical pesticides, especially frequent pesticide application in tea gardens, which kills large numbers of natural enemies of the black spiny whitefly and leads to outbreaks. As for the tea garden environment, the black spiny whitefly generally occurs more severely in densely shaded, damp and shaded tea gardens, and the pest population density in wind-trapped, sun-facing depression tea gardens is often relatively high.

The natural enemy resources of the black spiny whitefly are very rich. According to reports, there are 66 species of natural enemies, including 20 species of predatory spiders, 27 species of predatory natural enemy insects, 8 species of parasitic wasps, and 11 species of parasitic fungi.

II. Control Techniques

1. Protect natural enemies: minimize the number of pesticide applications and the amount of pesticide used in tea gardens to protect and promote the reproduction of natural enemies and give full play to the control role of natural enemies.

2. Agricultural control: for tea gardens with localized occurrence, light pruning can be carried out; for tea gardens with severe black spiny whitefly occurrence, collar pruning should be carried out, and the cut branches and leaves should be collected and treated centrally to reduce the pest population in the field.

3. Biological control: Verticillium lecanii has strong pathogenicity to the larvae of the black spiny whitefly. The suitable concentration for use is 200 million to 300 million spores per milliliter, and the appropriate control period is during the 1st and 2nd instar larval stages.

4. Chemical control: the control thresholds for the black spiny whitefly are: 2 insects per mu to 3 insects per mu for small-leaf varieties, and 4 insects per mu to 7 insects per mu for large-leaf varieties. When the field pest population exceeds the control threshold, chemical control should be considered. The key to chemical control is to grasp the appropriate control period. The appropriate control period for this pest is the late peak stage of egg hatching. If the pest population density is too high, the adult peak stage can also be considered as an auxiliary application period.

The following control agents can be selected: 10% imidacloprid wettable powder 20-30 grams per mu, 98% cartap wettable powder 40-50 grams per mu, 50% phoxim emulsifiable concentrate 100 milliliters per mu. The pre-harvest intervals for the above pesticides are respectively: 7 days, 7 days and 5 days. When spraying, the target must be targeted to improve the utilization rate of the pesticide. For controlling adults, low-volume sweeping spray over the canopy surface is suitable. During the larval stage, side spraying is recommended, with the spray liquid focused on the undersides of the middle and lower leaves of the tea plants.