Causes and Control Methods of Ginger Bacterial Wilt

1. Symptoms

The pathogen attacks the roots and the underground and aboveground stems. The affected underground fleshy stem initially becomes water-soaked and yellowish-brown, loses its luster, and then the internal tissues gradually soften and rot, leaving only the outer skin. Squeezing the diseased part exudes a dirty white turbid juice with a foul odor; the affected roots also turn pale yellowish-brown and eventually rot completely. The affected aboveground stem turns dark purple, and the internal tissues turn brown and rot, leaving fibers behind. The affected leaves appear wilted, turn pale yellow, with curled edges, and eventually the whole plant dies.

2. Pathogen

This disease is caused by infection with the bacterium Pseudomonas solanacearum. The optimum temperature for its growth and development is 28-29°C, with a maximum of 40°C and a minimum of 4°C, and a lethal temperature of 52-53.3°C (10 minutes). In a dry state at around 30°C, the bacterium loses its viability after 3 days. The bacterium can grow within a pH range of 4.05-9.5, but pH 5.4-7.3 is most suitable. Besides harming ginger, the pathogen can also infect eggplant, chili pepper, tomato, potato, and others.

3. Sources of Inoculum and Transmission

The pathogenic bacteria exist in large numbers in the soil of diseased ginger fields and in the tissues of diseased ginger rhizomes, and can survive in soil for more than 2 years. Contaminated ginger seed is the main source of primary infection and is spread over long distances through the transport of ginger seed. After planting the following year, the pathogen from diseased ginger seed or contaminated soil first invades the base of the underground stem of ginger plants under suitable environmental conditions, or directly causes disease in the underground ginger rhizome. Comparing diseased seed and contaminated soil, diseased ginger seed is more likely to cause disease and does so more quickly; both are important sources of inoculum that cannot be ignored. The ginger bacterial wilt pathogen, like other rod-shaped bacteria bearing flagella, must have water present in order to spread and proliferate. It generally spreads through irrigation water, surface runoff, underground pests, and rain splash. Planting susceptible varieties, continuous monocropping in diseased soil year after year, using contaminated ginger seed, improper fertilization, and high-temperature and high-humidity environmental conditions all readily cause the occurrence and epidemic of ginger bacterial wilt.

4. Disease Conditions

First, there must be a source of inoculum (diseased ginger seed and contaminated soil); second, there must be suitable environmental conditions for disease development. Environmental conditions mainly refer to climatic conditions such as temperature (air temperature and soil temperature) and rainfall. Generally, when the 10-day mean temperature reaches around 24°C, the disease begins to become epidemic; at around 28°C combined with sufficient rainfall, waterlogging forms in the field, and the disease develops and spreads rapidly. Experimental observations show that, given the presence of a source of inoculum, temperature (especially soil temperature) and rainfall are two important factors leading to disease epidemics, with the most severe outbreaks occurring when ginger fields are waterlogged after rain and then exposed to scorching sun. In addition, improper irrigation before and after ginger seedlings emerge has a certain triggering effect; improper cultivation management or the length of crop rotation are both closely related to disease occurrence. When the mean soil temperature is above 25°C, the incubation period is generally 6-8 days, with a minimum of 3 days and a maximum of 11 days; at 15-20°C it is 41 days, and below 15°C disease rarely occurs. High temperature and high humidity, with alternating sunny and rainy weather, especially drastic fluctuations in soil temperature, favor the occurrence and epidemic of this disease. The amount of rainfall and how early or late the rain falls are also related. From June to July, if rainfall reaches about 100 mm within 10-12 days, diseased plants can appear in the field; about 1 week after heavy rain, a peak of disease incidence appears in the field. Continuous cropping, low-lying land, heavy clay soil, no mulching, and excessive application of N fertilizer result in high disease incidence; the earlier the central diseased plant appears and the more times the pathogen re-infects, the more severe the disease occurrence.

5. Patterns of Occurrence and Decline

Ginger bacterial wilt in open-field cultivation generally begins to occur from mid-May to early June. Because temperatures are relatively low and rainfall is scarce during this period, the disease occurs sporadically and spreads slowly. Late June and early July are the period when central diseased plants appear and central disease clusters form over large areas, and late mid-July to mid-September is the peak period for the occurrence and epidemic of ginger bacterial wilt. At this time, the climate is high-temperature and high-humidity, and it is the period of vigorous formation and enlargement of ginger rhizomes; the pathogen easily invades, infection is rapid, and in severe cases the entire field can be lost within about 15 days. The entire disease peak can last 50-60 days. After mid-September, as temperature decreases and rainfall diminishes, the disease gradually abates, and after mid-October disease occurrence stops. The entire disease period lasts about 140 days.

6. Integrated Control Measures

The control strategy must be considered as integrated measures based on agricultural control, creating as much as possible environmental conditions unfavorable to disease occurrence, and vigorously coordinating all links.

6.1 Select disease-resistant varieties. Resistance differs among varieties; varieties such as Yiwu Shoujiang, Xinchang Small Bamboo-edge Ginger, and Zhejiang Tieganqing are relatively resistant.

6.2 Select disease-free ginger seed. Establish disease-free seed retention fields and select disease-free ginger seed. Any ginger rhizome that is water-soaked, has skin that easily falls off, or when broken open shows dark brown ring patterns and exudes white juice when squeezed by hand is a diseased ginger rhizome and must not be planted.

6.3 Disinfection treatment of ginger seed. The method is the same as for seed selection and disinfection.

6.4 Crop rotation. Choose plots with high terrain and good drainage, apply 100-150 kg of quicklime per mu after deep plowing, form high ridges, increase the application of phosphorus and potassium fertilizers or cover with shade, and implement crop rotation of 2-3 years or more, avoiding continuous cropping or interplanting with Solanaceae crops.

6.5 Strengthen field management. Pay attention to drainage of ginger fields, strictly control irrigation of ginger fields; generally use manual watering, and strictly prohibit flooding irrigation of the whole field. Use deep furrows and high beds, and promptly drain accumulated water after rain,

Apply heavy basal fertilizer and light, skillfully applied topdressing; avoid excessive application of nitrogenous chemical fertilizers, and increase the application of phosphorus and potassium fertilizers and coarse residue manure. Upon discovering a central diseased plant, immediately pull it out, take it out of the field together with the soil in the planting hole for disposal, and disinfect the nearby area with fresh lime.

6.6 Chemical control. At the full seedling stage, drench the planting holes with 300 kg per mu of 500-fold diluted 78% Jiangwenning. At the early stage of disease, drench the holes or spray with 300-500-fold diluted 78% Jiangwenning, once every 5-7 days, for 2-3 consecutive times, or drench the holes with 3000-fold diluted 72% streptomycin sulfate, or drench the holes with 3000-fold diluted 1000-unit Xinzhi meisu, or drench the holes with 300-fold diluted 90% fosetyl-aluminum soluble powder, which can relatively effectively control the damage of ginger bacterial wilt.