Alternariosis, also called Negrón or Alternaria, is the fungal attack of the genus Alternaria solani, which often affects the cultivation of tomatoes, eggplant and potatoes. Since it is a disease that appears when the crop cycle is already in an advanced state, its effects are often confused with signs of maturation. It should be noted that Alternariosis is favored by periods of humidity and drought , as well as temperatures above 20 ° C.
This fungus has spread throughout the world and, in ancient times, it was given very little importance, since its symptoms were associated with the senescence of the plant and, therefore, it was not considered as a disease. Currently, the damage it produces is known and, therefore, it is given importance.
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What are the symptoms of Alternariosis?
- Symptoms of Alternariosis in the leaves: it usually produces concentric spots of brown color that affects the older leaves . Also, if the conditions are favorable, these spots will expand throughout the plant. Leaf lesions rarely have circular shapes, because they are restricted by the main nerve areas. In the vast majority of cases, these spots appear around flowering and increase as the plants mature, reaching the point of coming together and generating a great deterioration that eventually causes them to die.
- Symptoms of the Alternariosis in the tubers: it generates superficial lesions of dark color that, they sink of irregular way, and present borders of tanned color, slightly raised. Although they do not rot the tuber, they do deteriorate their appearance.
- Development of the disease:the fungi that produce the Alternariosis can survive in the stubble of crops that have been parasitized by them, such as clamidospores and in seeds. The development of the Negron is totally linked to high humidity and temperatures ranging from 25 ° C. Storms and sprinkler risks in the morning cause the disease.
How to prevent this disease?
As in the vast majority of fungal diseases, prevention is the best method to avoid its devastating effects. Therefore, below, I propose the following measures for you to apply.
- Remove all plant debris after harvesting the crops, especially in those specimens that already show symptoms of Alternariosis.
- Use tuber seeds that are certified to ensure their good health.
- Let the tubers mature properly before beginning harvesting, to avoid damage during harvest.
- Make a crop rotation, keeping the vegetation healthy to provide all the nutrients that the crop needs.
Plants that are not well fed will be the most prone to the attack of the Alternariosis . Treatments should be done periodically every 10 or 15 days with fungicides such as Maneb, Zineb, Mancozeb, Benzimidazoles, etc. The best treatment to prevent Alternariosis is by applying copper oxychloride every 15 days.
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Tomato plant control
Although there are some varieties much more tolerant than others, there are currently no varieties capable of having acceptable genetic resistance. Therefore, the most effective method is the use of preventive fungicides, the best being Captan, Chlorothalonil, Mancozed and Estrobilurina, and the most currently applied.
Inspect the crop at least twice a week and if you use spray, you will have to water early so that the plants can air properly. Use healthy seeds, increase organic matter and do not forget to control the nematodes.