Fight late blight and brown rot in tomatoes

Late blight is a highly infectious tomato disease that can spread rapidly. We give tips on the prevention and control of the fungal disease on tomatoes.

There are numerous tomato diseases, but late blight and brown rot are probably one of the most serious. By Phytophthora infestans, an egg fungus (Oomycet), disease usually occurs in tomatoes (Solanum lycopersicum) and potatoes (Solanum tuberosum), but also other nightshade family (Solanaceae), such as Physalis (Physalis sp.) and paprika (Capsicum annuum) on. The rot usually appears shortly before the harvest or afterwards in the warehouse and causes massive harvest losses. The generic name Phytophthora comes from the Greek and means "plant destroyer", the species name infestans indicates the high infectivity of the disease. In 1845 this disease in potatoes caused the great famine in Ireland. The best way to combat the disease is prevention, because if it breaks out, it can hardly be dealt with. It is just as important to recognize an infestation at an early stage, because this is the only way to contain it quickly and prevent it from spreading to healthy plants. In this article you will learn everything about late blight and brown rot, their typical symptoms in tomatoes and the measures to be taken to control them.

Recognizing brown rot in tomatoes: symptoms and damage

The following symptoms occur with late blight and brown rot on tomatoes:

• From summer to autumn: In the early stages of the tomato brown rot, you can first see it on the leaves brown to black, damp patches of dead tissue, usually quickly spreading from the tip spread.
• Wilt of the leaf and later of the whole plant.
• Underside of leaf: Sometimes whitish fungus coating that is slightly mildew remind.
• Stem: Black-brown, sharply demarcated spots that can discolor the entire stem.
• Fruits: yellowish spots that later turn brown and sink in; Affected tomato fruits initially feel hard on the brown spots, later they either rot on the diseased plant or shortly after harvest in the warehouse.

The entire tomato crop can be affected by tomato rot within a very short time, because the spores are transmitted by wind and water splashes during the warm season. In dryness and heat above 30 ° C, the infection is initially stopped, but it progresses rapidly at lower temperatures.

Prevent tomato rot

Once you see symptoms of late blight on tomatoes, combating them is extremely time-consuming and many of the agents of choice are anything but environmentally friendly. The best way to combat it is therefore prevention. In the following paragraphs we explain various measures that can prevent the infestation in advance.

Brown rot-resistant tomato varieties

The targeted selection of varieties is one of the most important measures to prevent tomato brown rot. For planting tomatoes in unprotected open ground, resistant or tolerant varieties should be used be selected, because then the fungal spores usually have no chance to gain a foothold and the plant infested. Some wild relatives of our cultivated tomatoes, such as the Humboldt tomato (Solanum humboldtii) or varieties of Currant tomato (Solanum pimpinellifolium) are largely resistant to Phytophthora infestans. In addition, tolerant and resistant varieties have been bred for many years, both solid and hybrid seeds. The seed-resistant tomato varieties, for example, have proven to be robust against late blight and brown rot "De Berao", "Sunviva", "Primabella" and ˈResibellaˈ. Among the hybrid varieties we find other resistant crosses, such as the varieties "Philovita", "Phantasia F1" and "Vitella F1".

The right choice of location against brown rot on tomatoes

As explained above, the spores outlast from Phytophthora infestans, the cause of brown rot in tomatoes, in the soil as permanent spores or on potato tubers or old roots. Crop rotation therefore helps a lot in preventing tomato rot. Tomatoes should not be planted after potatoes or other nightshade plants (such as peppers, aubergines, physalis). You should also not follow up on infected tomatoes. In particular, high humidity and wet leaves over several hours at pleasantly warm temperatures favor the brown rot infestation. Therefore, the location should ideally be protected from the weather, especially from rain showers. An outdoor rain canopy can significantly reduce or delay the infestation of tomato latex.

Low planting density to prevent brown rot on tomatoes

If the plants are too close together, diseases such as the brown rot in tomatoes can spread quickly. After rain, the plants dry off slowly because the air can circulate poorly. Wet and moist tomato leaves are ideal attack surfaces for the water-dependent fungal spores. The longer it takes until the plants are dry again after morning dew or rain, the longer the fungus has time to infest. To ensure good drying and air circulation, tomatoes should be planted about 80 to 100 cm apart.

Correct pouring behavior

The fungal spores of the tomato brown rot are quickly transferred from the ground to the lower leaves through splashes of water. If the plant is watered overhead, the spores also get from infected leaves to still healthy ones. Here you can start with a better watering technique: The plants should only be watered in the root area. Neither should it splash when watering, nor should the leaves of the tomato be wetted with irrigation water. For more tips, check out our article on the right one Pouring and mulching tomatoes.

Strengthen tomato plants against late blight

If the tomato plant is well cared for and provided with sufficient nutrients, pests and pathogens generally have a difficult game. Potassium plays an important role in the stability of plant tissues. Fungi and other pathogens cannot penetrate stable cell walls as quickly or at all and infect the plant. A good supply of potassium, like ours Plantura organic tomato fertilizer thus prevents diseases such as late blight and brown rot. Important tips on Fertilizing tomatoes can also be found in our special article.

Herbal fortifications also help to keep the plant healthy, so they have a preventive effect against tomato rot, but usually no longer if there is a visible infestation. Good home remedies for tomato brown rot are about weekly injections Horsetail Broth or garlic or Onion peel tea. Both should prevent the growth of pathogens, supply the plant with trace elements and thus strengthen it. The biological agents Chitoplant made from crab shells and ENVIrepel based on garlic also show a good defense against tomato late blight.

Important: The egg fungus persists both in the soil and on plant debris. Therefore, never dispose of leaves and fruits infected with tomato late blight on the compost or leave them in the garden. It should be disposed of with the residual waste as soon as possible. The scissors used for this should also be disinfected afterwards.

Combat brown rot on tomatoes

Fighting late blight and brown rot in tomatoes is time-consuming when the first symptoms appear and requires immediate action. There are some fungicides for this purpose that can also be used in the home garden. If you want to combat late blight in tomatoes biologically, the arsenal of means is unfortunately very limited. In experiments by the State Institute for Agriculture (LfL), that was the case in the biological field Plant strengthener horsetail extract is effective even after a visible infection and was able to prevent the leaf attack reduce significantly. Horsetail extracts can be purchased as well as made by yourself.

Conclusion: The best way to combat late blight and brown rot on tomatoes consists primarily of preventive measures such as choosing the variety, choosing the location, observing the crop rotation and taking the right care.

Not only pathogens can afflict our tomato plants and destroy the harvest. the Flower end rot comes about, for example, due to a lack of nutrients. You can find out how to recognize this disease and how to effectively prevent and fight it in our special article.