Root rot is the most common problem in greenhouse cucumber production, which has been worsening year by year in some areas in recent years, seriously affecting cucumber yield and the economic benefits of vegetable farmers. Therefore, it is necessary to understand the causes of cucumber root rot and take corresponding measures for effective prevention. Cucumber root rot can be divided into physiological root rot and pathological root rot.

1、 Physiological root rot

（1） Root fermentation

1. Causes of occurrence. The root rot of cucumber is mainly caused by high soil moisture, low soil temperature, and insufficient light. The cucumber root system develops poorly under low temperature, excessive humidity, and hypoxia conditions, leading to a decrease in root respiration and absorption capacity. This results in the plant not developing new roots, the original root bark turning brown and rotting, causing the above ground leaves to turn yellow and wither. In severe cases, it can even lead to plant death.

2. Prevention and control measures. When watering, it is necessary to water the cucumber according to its growth needs, ensuring frequent watering with small amounts of water to prevent excessive watering at once. After watering, use a hoe to disperse moisture, enhance soil permeability, and promote the growth of cucumber roots; For plants that have developed root rot, rooting agents can be used to irrigate the roots and promote the development of new roots. A solution of 30% oxytetracycline water at a dilution of 1000 times can be used for root irrigation to prevent infection with root rot disease and also promote rooting and seedling growth.

（2） Burn roots

1. Causes of occurrence. The application of immature organic fertilizer, excessive or uneven one-time fertilization, fertilizer too close to the root system, insufficient water supply after fertilization, etc., can all lead to excessive soil solution concentration, causing root water backflow, root dehydration, poor root development, few lateral roots, yellowing or even decay of root tips. The above ground plants become dehydrated and wilted, with yellowing of leaves. Mild cases can still recover, while severe cases may cause the plants and leaves to turn yellow and eventually die.

2. Prevention and control measures. When fertilizing, do not fertilize too much at once and fertilize evenly; When applying organic fertilizer, it must be fully decomposed. Once root burning occurs, reasonable watering can be used to reduce soil solution concentration and alleviate the harm; Foliar fertilization can also be used to supplement foliar nutrients and alleviate nutrient deficiency symptoms caused by reduced absorption capacity due to root system injuries.

2、 Pathological root rot

The pathological root rot of cucumber is mainly caused by cucumber sickle mycorrhizal rot and pseudomycorrhizal root rot. High temperature and humidity, continuous cropping, low-lying terrain, and heavy soil are conducive to the onset of the disease.

（1） Symptoms of onset

1. Cucumber sickle mycorrhizal rot disease. This disease mainly harms the roots and rhizomes of non grafted cucumbers. In the early stage of the disease, the roots and stem base are soaked in water, which later causes the roots to rot, dry and turn brown. The epidermis at the base of the stem turns light brown and rots, and the vascular bundles at the rot site turn brown and do not develop upwards. The color of the lower leaves of the diseased plant becomes lighter, wilting at noon on sunny days and recovering in the morning and evening. In severe cases, it cannot recover, and the diseased area worsens, producing pink mold like substances, leaving only filamentous vascular bundles, and dying.

2. Pseudo stem point mold root rot disease. This disease mainly harms the roots and rhizomes of grafted cucumbers, and gradually develops after the cucumber bears fruit, causing the roots and stem bases to turn brown and rot. The leaves of the diseased plant wilted during the day, but could recover at night or on cloudy days. After a few days, the lower leaves began to wither and yellow, gradually developing upwards, leading to poor development of the melon strips.

（2） Prevention and control measures

1. Agricultural prevention and control. It can be rotated with cruciferous and lily crops for more than 3 years. Adopting high bed cultivation, watering at appropriate times, watering frequently with small amounts of water, to prevent excessive flooding. Pay attention to moisture removal after watering, and loosen the soil in a timely manner to enhance soil permeability. Soak the seeds in warm water at 50 ℃ for 20 minutes for disinfection. Select disease-free soil as the seedbed or irrigate the seedbed soil with a solution of 200-400 times 50% ammonium permanganate.

2. Pharmaceutical prevention and control. In the early stages of the disease, roots can be treated with 65% mancozeb solution at 500-600 times dilution and 70% methyltobuzen wettable powder solution at 800-1000 times dilution. Each plant can be treated with 0.25 liters of the solution every 7 days. You can also spray the base of plant stems and soil surface with 75% Baijunqing wettable powder at a dilution of 600 times or 50% Duojunling wettable powder at a dilution of 500 times, spraying once every 5-7 days and continuously spraying 2-3 times. It can also be prepared into medicinal soil and sprinkled on the base of the stem.