Guide to Identifying Common Root Disease Symptoms in Vegetables

As the temperature drops, the soil temperature inside greenhouses will also decline day by day, and at the same time various root abnormalities will occur to varying degrees (taking tomatoes as an example) - fusarium wilt, root rot, bacterial wilt and root-knot nematodes are several relatively common root diseases. In addition, various nutrient deficiency symptoms and difficult abnormal conditions that occur in vegetables are also related to root absorption.
　　
1. Bacterial wilt. Symptoms of bacterial wilt: Externally, the most important feature of bacterial wilt is plant wilting. After onset, it appears as wilting of the upper part during the day on sunny days, later spreading from the lower part to the middle, and in some cases one side branch wilts first, while in others the whole plant wilts. For tomatoes showing wilting symptoms, if you cut open the stem base, you can clearly see that the vascular bundles inside have turned brown. It is precisely because these vascular bundles have been damaged that nutrients and water cannot be transported upward normally, which causes the tomato to wilt. Experts point out that if tomato bacterial wilt is not treated in time, after repeated wilting several times, plant death will occur, bringing great losses to vegetable growers. The best way to deal with tomato bacterial wilt is to use chemicals for root drenching.
2. Fusarium wilt. Symptoms: This disease is a vascular bundle disease, mostly beginning to show after transplanting. In the early stage of the disease, leaves closer to the ground turn yellow, and finally become brown and die, with withered leaves mostly remaining on the stem without falling off; in some cases in the early stage of the disease, leaves on one side of the stem turn yellow while leaves on the other side remain normal in color; there are also individual branches where half of a leaf turns yellow and the other half remains normal. When the disease is severe, diseased leaves spread from bottom to top, and finally only a few leaves at the top remain, with all the rest withered and dead. In mild cases, only leaves closer to the ground turn yellow, while the rest remain normal, and flowering and fruiting are no different from healthy plants. The roots of diseased plants show brown rot or localized necrosis. When the stem base is cut open, the vascular bundles are yellow-brown.
　　
The main difference between this disease and tomato bacterial wilt symptoms is that after the plant is affected, the leaves turn yellow and withered. When humid, pink mold-like substances (fungal conidia) often appear at the stem base.
　　
Occurrence and development pattern: The disease is most likely to occur when the soil temperature is around 28°C. High soil water content or abundant root-knot nematodes in the soil, due to poor root development, cause wounds, which favor the occurrence of fusarium wilt. The pathogen infects only tomatoes. In continuous cropping land, the number of pathogens increases year by year, and the disease occurs severely.
　　
3. Root rot. Symptoms: This disease damages the stem base or roots. At initial onset, brown patches appear, which gradually expand and then become sunken. In severe cases, the lesions encircle the stem base or roots for a full circle, causing the aboveground part to gradually wither. When the diseased part is cut longitudinally, the vessels can be seen to be dark brown; later the roots and stems rot, no new roots grow, and the plant dies.
　　
Occurrence pattern: According to relevant information, the pathogen of root rot overwinters in the soil with diseased plant residues, and may also overwinter in incompletely decomposed compost. The following year it produces a large number of conidia that spread through rainwater or irrigation water to cause damage. High temperature, high humidity or relatively low soil temperature favor the occurrence of the disease. If tomatoes after transplanting encounter low soil temperature, excessively high soil humidity, and a long duration, or continuous rainy days with failure to ventilate the greenhouse in time, forming high temperature and high humidity inside the greenhouse, especially after flood irrigation with untimely ventilation, the occurrence and epidemic of this disease will be caused.
　　
4. Root-knot nematodes. Damage symptoms: They mainly occur on the fibrous roots and lateral roots of tomatoes. When root galls are cut open, very small milky-white nematodes are hidden inside. New roots growing from the root galls will be infected again and form root-knot-like tumors. Severely affected plants are short in form, poorly developed, and even prematurely senescent and dead. When the soil temperature is 25-30°C and the soil water content is 40%, the pathogenic nematodes develop very quickly; below 10°C, the larvae stop activity. Their secretions stimulate cell proliferation, forming root knots or tumor-like bodies. Solar greenhouses with dry soil and loose soil texture are suitable for nematode activity, so the disease occurs severely; continuous cropping leads to severe occurrence. These nematodes are mostly distributed in the area where vegetable roots are located, in the 3-10 cm surface soil layer.
　　
In addition, the manifestation of nutrient deficiency symptoms in vegetables is not necessarily actually due to a lack of that element in the soil, but is caused by reduced root absorption capacity resulting from a series of problems such as soil compaction, unsuitable soil pH, or unbalanced soil moisture supply.
　　
5. Soil compaction causing root abnormalities. When soil is compacted, roots cannot develop normally - soil aggregate structure is an important indicator of soil fertility. The destruction of soil aggregate structure reduces the soil's water-holding capacity, fertilizer-holding capacity and permeability, causing soil compaction. Vegetable roots in this state will decline in vigor due to lack of oxygen. Therefore, in routine agricultural management, avoid flood irrigation and use irrigation methods that have as little impact on soil permeability as possible, such as drip irrigation, which is both scientific and water-saving. If heavy rain and other large water inflows flood the greenhouse, drain promptly.
　　
It is generally recommended that in vegetable fields or greenhouses not covered with plastic film, hoeing should be carried out after irrigation, which can both increase soil permeability and reduce soil moisture evaporation.