Controlling Bacterial Wilt
Bacterial Wilt (BW) is caused by a soil-borne bacterium and is one of the major diseases affecting commercial crops like tomato, eggplant, potato and other solanaceous plants. It is not easy to detect Bacterial Wilt because the symptoms are very different from other wilt diseases. In the case of bacterial wilting, the foliage does not become yellow and spotty as it does with other wilting diseases. Rather, the plant wilts and dies quickly, without much warning.
Favorable Conditions for Bacterial Wilt
The pathogen is primarily spread through the soil and passes through wounds or natural openings into the roots. After an infection, the pathogens multiply and migrate upwards through the vascular system, where they finally block the water transport of the plant. This leads to withering, and usually the rapid death of the plant. The pathogen is released into the soil by infected plants, so that neighbouring plants can be infected via root contacts. It can also be introduced into the plants by pruning wounds. Contaminated water sources, symptom-free, but contaminated seedlings, as well as human contact or machines with infested soil remnants can also be ways for the BW to enter a clean field.
The spread of Bacteria Wilt is encouraged by:
- Inappropriate planting
- Root-feeding insects such as nematodes
- Poor soils (infertile, acidic, heavy clay, poorly drained, bacteria infected)
- Hot and humid weather conditions
- Spread of BW through water runoff
- Weeds that act as hosts without showing any symptoms
- Infected tools, grafts and soil remnants
The expression of bacterial wilting symptoms may vary depending on the crop.
In the early stages of the disease, the first visible symptoms of bacterial wilting are usually seen in the youngest leaves at the ends of the branches. At this point, only one or even half a leaf may wilt and the plants may appear to recover at night in colder temperatures.
As the disease develops rapidly under favourable conditions, the whole plant can quickly wilt and dry out although the dried leaves remain green.
In young tomato stems, for example, infected vascular bundles can appear as long, narrow, dark brown stripes. A collapse of the stem can also be observed in young, succulent plants of highly sensitive varieties.
Methods of Diagnosis
A quick and reliable diagnostic method for bacterial wilting is to cut a wilted runner near the crown of the plant. When bacterial sludge extends from one cut surface to another by bringing both cut surfaces together again for a moment and then slowly pulling them apart again, this is a positive indicator of bacterial wilting.
Another method of detecting Bacteria Wilt is to place the shaft sections in clear water. If the plant is infected, a viscous, white, easily visible sudge should flow from the cut end of the stem into the water after 5-10 minutes.
In general, it's very difficult to control Bacterial Wilt because no single strategy has shown a 100% efficiency. Therefore, a combination of different control measures, including host resistance, cultural practices and the use of chemical or biological control methods, should be part of an integrated pest management approach.
Once the soil is infected, bacterial withering can live on for years without the presence of a host plant. It is therefore strongly recommended to take precautionary measures against BW.
- Try high beds to improve drainage and control root node nematodes that weaken plants and make them more prone to disease.
- Choose resistant varieties
- Keep your soils at a pH of 6.2-6.5 , which is ideal for growing tomatoes and many other vegetables
- Space the plants further apart to ensure good air circulation.
- Keep a keen eye on weed control
- Use 3-4 years crop rotation and cover crops in infested fields to reduce bacteria, weeds and nematodes
- Wash your hands after handling infected plants and pay attention to farm hygiene. Disinfect and sterilize any garden tools that may have been used in infected soil
The fungus Trichoderma viride and Trichoderma harzianum are proven biocontrol agents to fight this disease in an environmentally friendly way. Bacteria such as Pseudomonas fluorescens and Bacillus subtilis act as catalysts for Trichoderma viride and also control some types of nematodes.
- Soil application: Trichoderma virus, Pseudomonas fluorescens and Bacillus subtilis should be mixed separately into 200 kg of manure, covered with Gunny Sacks and stored for 7 days each, 2 kg/acre. During this time, slightly moisten these Gunny Sacks daily so that they can quickly reproduce. On the 8th day mix all these four batches and spread them with FYM or compost all over the field.
- Seed treatment: at 4 to 5 g per kg of seed according to standard wet treatment.
- Seedling root dipping: at 10 g per litre before planting
- After planting: Use alternately, per 1 kg: Trichoderma sp + Pseudomonas & Trichoderma sp + Bacillus at intervals of 8 days
Bacterial Wilt can live on for years without the presence of a host plant. If you have specific questions about products for biological control or about controlling bacterial withering in general, don't hesitate to contact the Plantix experts in the Plantix community.