Rot of Pinellia ternata tubers in the late growth stage: growers need to pay attention to prevention and control
Causes of the disease
When Pinellia ternata grows to August-October, that is, when the rainy season arrives, the second-, third- and fourth-generation bulbils formed by Pinellia ternata planted in early spring and the first- and second-generation bulbils formed by Pinellia ternata cultivated in summer rapidly expand and form tubers, and the small mother corms used as seed during cultivation are also expanding themselves. This period is the stage of fastest tuber growth in Pinellia ternata, and also the period when the tubers have the weakest ability to resist external infection. The larger the tuber, the weaker its resistance; the smaller the tuber and the bulbils, the stronger their defensive ability. The rapid growth of underground Pinellia ternata tubers of various specifications requires absorbing large amounts of oxygen and organic matter from the soil. During this period, microorganisms in the soil are also quite active and reproduce fastest, and they also need large amounts of oxygen while releasing various harmful gases and substances. During this period, when there is continuous rain, high soil moisture or soil compaction, and gases in the soil and air cannot be exchanged in time, the Pinellia ternata tubers that are in the rapid expansion stage, because the protective layer of the outer skin has a weak ability to resist infection, a large number of harmful gases and pathogens in the soil can easily invade the Pinellia ternata tubers and spread rapidly, causing the tubers to rot within a relatively short time. In mild cases, 80% rot within one week; in severely affected plots, all Pinellia ternata tubers rot within 3-5 days, and the soil and air of the entire plot give off a fishy, foul odor. This causes total loss of Pinellia ternata. At harvest, after all the hard planting and management, only some bulbils and a portion of small tubers can be harvested, causing serious losses to Pinellia ternata production. This rot disease is one of the main bottlenecks restricting Pinellia ternata production.
Symptom characteristics
In the early stage of pathogen infection of Pinellia ternata tubers, irregular black spots appear around the tubers. These spots spread rapidly in all directions. After 3-4 days, numerous pathogen spots join together and continue to infect the interior of the tuber. At this time, the root system of Pinellia ternata begins to shrink, and the aboveground leaves gradually turn from green to yellow and wither. After one week, the Pinellia ternata tuber becomes round and blister-like, as if it were a fully ripe grape, and the inside of the tuber is entirely black water. The whole plant dies, and finally only a thin outer skin remains. The spreading pathogen will quickly infect other Pinellia ternata tubers, and within a short time the entire Pinellia ternata plot becomes infected and rots. The soil and air of the cultivated Pinellia ternata area give off a foul, fishy odor.
Prevention and control methods
Variety selection: When planting Pinellia ternata, choose varieties with strong disease resistance and vigorous growth, such as excellent varieties with leaf shapes like "narrow three-leaf" and "willow-leaf shape", and select disease-free tubers or bulbils as seed corms.
Seed corm treatment: Before sowing, the selected seed corms must undergo seed corm treatment and disinfection, such as sun-drying the seed and seed dressing with chemicals, to prevent the seed corms themselves from carrying pathogens.
Land selection: Pinellia ternata must be planted on loam or sandy loam with a pH value between 6.5 and 7, and the plot must not have previously had root rot or rot disease. In areas with abundant autumn rain, the selected plot should have a 20% slope. In plain areas and relatively flat plots, when planning the early stage of Pinellia ternata cultivation, a drainage ditch 30 cm wide and 30 cm deep should be left every other intercropping bed to ensure that during continuous rainy weather, the water in the soil of the Pinellia ternata field can thoroughly seep into the drainage ditch and be discharged from the plot in time.
Remedial measures: When encountering continuous rainy weather and relatively moist soil, as long as it is possible to enter the field for cultivation, carry out multiple forms and multiple rounds of intertillage and loosening of the soil to break the compacted soil layer, allow harmful gases in the soil to escape, let fresh oxygen from the air enter, and increase gas exchange between the soil and the air. This measure can effectively prevent and reduce the occurrence of rot disease.
Emergency harvest of rotted stems: In the middle and late stages of Pinellia ternata growth, if there is continuous rainy weather and relatively high soil moisture, frequently inspect the growth of Pinellia ternata. If some Pinellia ternata plants are found to have rot disease, then regardless of whether the digging and harvesting season has arrived, an emergency harvest should be carried out in time without delay. Otherwise, the tubers rot very quickly, with the large ones rotting first and the small ones afterward, causing reduced yield or even total loss. At the same time as the emergency harvest, the Pinellia ternata tubers dug from the wet mud should immediately be peeled and processed, because at this time the fresh tubers are still rotting internally. If not processed, most tubers will rot within 1-2 days. Growers are urged not to be careless.