Control methods for the Ningxia ground pearl (Porphyrophora ningxiana) pest on licorice
It is distributed in all licorice-producing areas nationwide, generally causing damage from the seedling stage to the mature plant stage. The Ningxia ground pearl has 8 host plant species, all of which are perennial leguminous herbaceous perennials, with licorice suffering the most severe damage, while other hosts are only slightly affected.
(1) Damage period and damage symptoms: Overwintering nymphs can move intermittently when the surface soil temperature reaches 6°C, and become frequently active when the daily average temperature exceeds 12°C, in order to search for hosts. Early March is the initial activity stage, mid-to-late April is the peak period for searching hosts, and by mid-May they have basically all settled. From late May to late July is the pearl body stage (the main damage stage). The symptoms on licorice and other host plants appear after mid-June. After late July, the pearl bodies gradually mature, stop feeding and causing damage, detach from the host and enter the metamorphosis stage.
The damage to licorice varies greatly depending on pest population density in different habitats. In licorice fields that suffered severe damage the previous year, the following year the plants sprout and turn green late, grow weakly, and some are unable to sprout and turn green, with plant rhizomes rotting, and the pest population density that year is also relatively high. In severely damaged fields, the pearl bodies grow larger in mid-to-late June, food intake increases, damage intensifies, and large numbers of plants die; in generally damaged fields, the damage symptoms are not obvious in May to June, and after late June the lower leaves of affected plants can be seen to be withered and yellow, or a large number of functional leaves in the middle and lower parts have scorched yellow leaf margins with green-yellow leaf centers. After mid-July the damage peak is reached, the above symptoms become obvious, individual plants die, and the top leaves of dead plants are of the green-wilt type. From early to mid-August, because the pearl bodies mature and fall off, stop feeding and causing damage, licorice growth tends to improve and stabilize, and some licorice plants noticeably recover normal leaf color and growth vigor.
When the pest bodies are densely clustered, the parasitized licorice roots appear as protruding lumps or lumps, and when they encircle the root for a full circuit they appear as sleeve-like; when the pearl bodies are scattered, they appear as bead-like or tumor-like. The former is mostly seen on the main root, and the latter is mostly seen on string-like rhizomes and lateral branch roots.
(2) Prevention and control: Sow early at the appropriate time, strengthen water and fertilizer management and other field management, promote increased growth, robust and early development, so as to enhance the ability to resist pests and diseases; for perennial licorice, in June carry out deep plowing and heavy harrowing to mechanically kill the pearl bodies, loosen the soil, promote plant growth, and enhance pest resistance; dig licorice in June to July before the pearl bodies have matured, so that the pearl bodies all die because they are detached from the host, which can greatly reduce the occurrence level the following year.
a. Chemical control: Focus on applying pesticide during the adult stage and the activity period of early-instar nymphs after overwintering. Control during the adult stage should grasp the peak emergence period and apply pesticide 1 to 2 times. You can use 4.5% jiadi powder at 2.5 to 4 kg per mu, or spray 2.5% deltamethrin 3000-fold solution. The killing effect on males is relatively good, and the effect on females also reaches more than 72%, and it can reduce egg production and hatching rate, with residual effectiveness.
b. Control during the early-instar nymph stage: Around mid-April, the overwintering nymphs in the soil begin to move and search for hosts. You can apply 50% phoxim emulsifiable concentrate to the roots at 0.5 kg per mu. Generally, you can open furrows before or after rain, apply the pesticide, and cover with soil. If the soil is dry and there is no rain, after applying pesticide at the root zone, irrigate shallowly to bring the pesticide effect into play.
Fumigation control with aluminum phosphide: Make holes and apply 3 to 4 tablets per sq m (each tablet weighs 3.3 g). The application time is the same as above. After application, immediately seal with plastic film for 6 to 8 days. There is no phytotoxicity and the effect is good.