Occurrence and Control Methods of Common Diseases in the Middle and Late Stages of Pinellia ternata
I. Tuber Rot
1. Cause and symptoms: This disease occurs during high temperatures, the rainy season, prolonged excessive soil moisture, and the tuber and bulbil enlargement stage. In the early stage when the pathogen infects the tubers of Pinellia ternata, irregular black spots appear around the edges of the tubers, and these spots spread rapidly in all directions. After 3—4 days, numerous pathogen spots merge together and continue to infect the interior of the tuber. At this point, the root system of Pinellia ternata begins to shrink, and the above-ground leaves gradually turn from green to yellow and wither. After one week, the tubers of Pinellia ternata become round and blister-like, resembling overripe grapes, with the interior of the tubers filled entirely with black liquid, the entire plant dies, and finally only a thin outer skin remains. The spreading pathogen rapidly infects other tubers of Pinellia ternata, causing the entire Pinellia ternata plot to become infected and rot within a short period. The large tubers rot first, then it spreads to the small tubers, and finally only bulbils smaller than one cm remain. This disease is also currently the most common, difficult to treat, most harmful, and widest-ranging disease in artificially cultivated Pinellia ternata.
2. Control methods
(1) Pay attention to selecting good varieties. For artificial cultivation of 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.”
(2) Disinfect the seed stems before sowing. Soak the seeds in 50% carbendazim for 12 hours; soak in 5% plant ash solution for 2 hours; soak in a solution of 1 part 50% carbendazim + 1 part 40% phosethyl-Al diluted 300 times for half an hour; soak separately in 300-times vinegar and 50 ml/L potassium permanganate to prevent tuber rot and increase yield.
(3) Strictly select the soil and terrain. The soil must be medium loam or loam to ensure good water filtration and aeration; the terrain should preferably have a slope of 10—25 degrees. If the terrain is flat, deeper and densely arranged drainage ditches must be dug.
(4) During continuous overcast and rainy weather and when the soil is relatively moist, as long as it is possible to enter the field for cultivation, carry out various forms of intertillage and soil loosening multiple times to break up 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 tuber rot. Also promptly spray fungicides or broadcast 5 kg/mu of quicklime powder.
(5) Promptly control underground pests such as white grubs and cutworms. Use new pyrethroid pesticides containing 50 g/L cyfluthrin EC, which has an activating effect, can drive pests out of their burrows to come into contact with the pesticide, and rapidly acts on the pests' nervous system, causing poisoning and death. After large-scale field use in the last two years, the control effect was 100%.
(6) Emergency harvest when stems rot. In the middle and late stages of Pinellia ternata growth, if there is continuous overcast and rainy weather and relatively high soil moisture, frequently inspect the growth of Pinellia ternata. If some Pinellia ternata plants are found to have tuber rot, regardless of whether the digging and harvest season has arrived, promptly and decisively harvest them without delay; otherwise, the tubers will rot very quickly, with the large ones rotting first and the small ones afterward, causing reduced yield or even total loss. While carrying out 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 still rot after 1—2 days. Please do not be careless.
II. Viral Disease (Leaf Curl Disease)
1. Cause and symptoms: This disease is caused by Dasheen Mosaic Virus, or DMV, of the Potato virus Y group.
It is mainly due to virus carried in the seed stems of Pinellia ternata or virus transmitted by insects such as aphids. It mostly occurs and spreads in early summer, under high temperature and rainy conditions, and when aphids and other pests appear. After the Pinellia ternata plant becomes diseased, yellow irregular spots appear on normally growing leaves, causing the leaves to become mosaic, shrunken and distorted, curled upward, and the plant to become dwarfed and deformed with poor growth. This disease can also cause large amounts of rot in Pinellia ternata during storage.
2. Control methods
(1) Choose disease-free plots and regions for planting; strictly screen excellent Pinellia ternata varieties.
(2) Apply fermented and thoroughly decomposed organic fertilizer, and appropriately apply additional phosphorus and potassium fertilizer.
(3) Promptly and thoroughly eliminate or prevent the occurrence and spread of aphids and other pests.
(4) After Pinellia ternata emerges, continuously spray 40% dimethoate or 80% dichlorvos diluted 1500 times, once every 7 days, for 3 consecutive sprays.
(5) In the early stage of the disease, treat with new low-toxicity, low-residue agents such as Bingduqing, Keduwei, and Duba, once every 3 days, for 3 consecutive treatments.
III. Damping-off (Leaf Scald Disease)
1. Cause and symptoms: In artificially cultivated Pinellia ternata, this is one of the most common major diseases, and its cause is still under research and observation. It is most likely to occur under high temperature and rainy season conditions with high humidity, especially when ventilation and light transmission are poor, and the disease is severe. In the early stage, green irregular lesions appear on the leaves and petioles, and the color of the lesions then deepens, the affected parts soften, and the leaves droop as if scalded by boiling water, becoming semi-transparent and sticking to each other. This disease develops rapidly and spreads quickly. Once discovered, it spreads very fast, and treatment is troublesome. The soil and air of the entire plot give off a very strong fishy and foul odor.
2. Control methods
(1) When selecting a plot, choose old vegetable land where tomatoes, eggplants, cucumbers, or Chinese cabbage have not been planted in the previous crop, or a plot where the previous crop has not had damping-off, for planting Pinellia ternata.
(2) During the rainy season and high-temperature season, attention should be paid to reducing soil moisture.
(3) After the soil is selected, carry out winter plowing and sunning of the soil clods in winter. Do not apply undecomposed fertilizer, and appropriately apply or do not apply nitrogen fertilizer among chemical fertilizers.
(4) Prevention first. After high temperature and rain before the disease occurs, use 75% chlorothalonil diluted 800 times; 50% thiophanate-methyl diluted 1000 times; agricultural 200 ppm streptomycin, Xinzhimeisu; 300 ppm chloramphenicol; once every 7 days, alternately spraying 3 times. Be sure to spray evenly, with no repeated spraying and no missed spraying.
(5) Recently, trials with 66.5% Previcur diluted 800 times and 72% DuPont Curzate diluted 500 times for spray control have also shown relatively good results.