What to Do About Root Rot in Spring Cabbage Seedlings? Cause Analysis and Control Methods

Cabbage is a very ancient vegetable; people were already turning it into delicious dishes during the ancient Greek and Roman era more than 4,000 years ago. In Europe today, wild cabbage can still be seen growing on those barren, cold chalk grasslands. Cabbage (Brassica oleracea L.) is an annual or biennial herbaceous plant of the genus Brassica in the family Brassicaceae, and it is one of our important vegetables. Apart from Chinese kale (Brassica alboglabra), which originated in China, all the various varieties of cabbage originated along the coast from the Mediterranean to the North Sea. As early as 4,000-4,500 years ago, the ancient Romans and ancient Greeks already cultivated it.

The growing environment of cabbage

Cabbage prefers mild, humid conditions and ample sunlight. It is relatively cold-tolerant and also has the ability to adapt to high temperatures. The optimum growing temperature is 15-20°C. If the fleshy stem enlargement stage encounters high temperatures above 30°C, the flesh tends to become fibrous. It is not very strict about soil choice, but it is best planted in humus-rich clay loam or sandy loam. Cabbage seedlings must pass through vernalization at 0-10°C, then bolt, flower and set fruit under long-day conditions and suitable temperatures.

What to do about root rot in spring cabbage seedlings?

The seedling-raising period for spring cabbage mostly falls in winter, with low temperatures and little sunlight, making various physiological disorders or diseases likely. Although this winter's temperatures were higher than usual, there were many foggy days, and because of the high humidity and weak light, conditions were very unfavorable for cabbage growth. The recent root rot in cabbage seedlings is mainly caused by the following reasons:

Root oxygen deficiency: In low-temperature, high-humidity weather, water evaporates slowly. If the seedbed is watered heavily and the water cannot evaporate in time, oxygen in the soil becomes insufficient, preventing the roots from respiring normally and thereby causing root rot. This winter had relatively little rain and snow, but many overcast and foggy days that lasted a long time, resulting in high humidity in the seedling beds and making root rot likely.

Cabbage black leg disease: In seedlings infected with black leg disease, gray patches appear on the cotyledons and true leaves, with small black dots; on the stem near the ground there are long purplish-black spots that are slightly sunken and can spread toward the roots. In severe cases, all the fibrous roots rot and the plant wilts and dies. The black leg pathogen spreads with water flow, and disease is likely under high temperature (25°C) and high humidity. If the seedling beds are not ventilated in time on sunny days, the disease can become epidemic and lead to root rot.

Cabbage black rot: After infection with black rot, water-soaked lesions appear on the cotyledons, with black necrosis on them. Under high temperature and high humidity, the disease spreads, forming “V”-shaped yellowish-brown spots at leaf margins or veins, and small black dots or streak necrosis on the veins. The pathogen spreads along the veins and petioles, the vascular bundles turn black, and it can extend to the stem and roots. Infection by the black rot pathogen can also cause root rot. If the previous crop in the seedling bed soil was cabbage, the occurrence of black rot will be worsened.

Countermeasures for root rot in spring cabbage seedlings:

In response to the above causes, disease-free bed soil should be prepared before raising seedlings, and the bed soil should preferably be disinfected in advance. It can be sprayed with formalin solution and then sealed for 15-20 days; open it and wait until the smell has dissipated before sowing. When sowing, use medicinal soil made with carbendazim as a bottom layer and top cover, to minimize pathogen infection. After sowing, during the seedling-raising period, pay attention to ventilation and air exchange, maintaining 15°C-20°C during the day and 8°C-10°C at night; the temperature must not be too high. On overcast, rainy and snowy days, strengthen temperature and humidity management in the seedling beds, with special attention to draining moisture. If the seedbed is too wet but cannot be ventilated for long because of low temperatures, plant ash can also be scattered on the seedbed to absorb moisture. Watering of the seedbed must be controlled; for seedling raising in sun-facing beds, watering is generally done only at sowing, transplanting and lifting of seedlings, and at other times generally no watering is done. In greenhouses and hotbeds, watering should also depend on the weather, choosing to water when there are several consecutive sunny days. Keep the seedbed as well-lit as possible; on overcast and snowy days, the seedbed should also be ensured access to scattered light.