In August, with high temperatures and humidity, beware of stem base rot.

As August begins, the weather remains persistently hot, with intense sunlight and occasional heavy downpours. At the same time, August is the peak season for sowing, raising seedlings, transplanting, and managing autumn vegetable crops in the fields.

In mid-to-late August, greenhouse vegetables will begin to be transplanted one after another. At this time, high temperatures prevail, and combined with heavy irrigation following transplanting, runoff from rainfall, or standing water in the fields, the soil surface can easily develop a hot, humid microenvironment, which greatly increases the risk of stem base rot.

If vegetable growers are even slightly careless during transplanting, within a month the crops are likely to experience widespread seedling and plant death, most of which is caused by stem base rot. Stem base rot is a soil-borne disease; the pathogen infects plants directly through mycelial growth and can spread in the field via rainwater, irrigation water, and agricultural tools.

I. Causes of Onset

In addition to the high population of pathogenic fungi in the soil, the main causes of stem base rot include:

(1) With the onset of the high-temperature season, ambient temperatures are elevated, and combined with the use of plastic mulch in greenhouses and inadequate ventilation, indoor temperatures can become excessively high.

(2) Applying a settling‑in irrigation (or seedling‑establishment water) after transplanting results in excessive soil surface moisture.

(3) During the seedling-raising process, a short seedling age and excessive watering result in overly tender seedlings. (Note: If seedlings are too old or become stunted, they recover more slowly and are less susceptible to stem-base rot; conversely, while overly tender seedlings recover quickly, the incidence of stem-base rot also increases.)

(4) Vegetable wounds caused during seedling transportation or transplanting.

II. Precautions for Transplanting

1. Minimize the occurrence of wounds. During transportation, take precautions to prevent damage to the vegetables; when transplanting, handle seedlings gently—avoid pulling them out by the stem. It is recommended to lift the seedlings by pinching the cell tray, thereby preventing mechanical injury caused by excessive pressure on the base of the stem.

2. Prior to transplanting, it is best to till and expose the soil to sunlight for disinfection; avoid flood irrigation, remove diseased or dead plant residues, ensure organic fertilizers are fully decomposed, and minimize or eliminate the use of chemical fertilizers to prevent excessive nitrogen application.

3. During transplanting, avoid planting seedlings too deeply or covering them with excessively thick soil to prevent widespread occurrence of stem base rot (note: this disease is particularly severe in sandy soils). It is advisable to ensure that the soil surface is level with the substrate surface.

4. After transplanting, regularly hoe the soil; it is recommended to “water once and hoe once.”

5. If the temperature inside the greenhouse becomes excessively high, growers are advised not to apply plastic mulch at this stage; instead, wait until the heat has subsided before covering with mulch. For plants that have grown too large, use narrow-width mulch: after suspending the vegetable vines, secure the edges of the mulch with small clips, or lay the mulch between the rows.

III. Chemical Control

1. Before transplanting, you can apply a preventive pesticide spray in advance. For example, fungicides such as carbendazim can form a protective barrier over vegetable wounds, making it more difficult for pathogens to penetrate.

2. Stem base rot should be managed primarily through prevention. The preventive period typically begins about one week after transplanting, during the seedling‑establishment phase, with 2–3 applications of a fungicide via root drenching. For treatment, a fungicide can be applied as a localized flood irrigation to severely affected plants and within a 2–3 meter radius around them; the remaining plants may be treated with hole‑drenching for preventive purposes.

3. When vegetables develop stem-base rot, in addition to applying fungicides, promptly supplement their nutrition and foliar‑apply products such as Nongda Heizefeng and Ye Geili to enhance the plants’ resistance. If the disease is confined to a small area, remove the infected plants, disinfect the soil, and transplant healthy seedlings; treat the remaining seedlings with protective sprays.