2024 Author: Gavin MacAdam | [email protected]. Last modified: 2023-12-16 13:38
Southern late blight of tomatoes occurs mainly in the southern regions of Russia, as well as when this crop is grown in greenhouses. And its active development is largely facilitated by an impressive amount of precipitation and a very high air humidity. Mainly fruits, root parts of stems and roots suffer from this ailment, and not only grown tomatoes, but also seedlings can become infected with southern late blight
A few words about the disease
When infected with southern late blight, constrictions are formed on tomato stalks, similar to those that appear when a black leg is well known to many. However, unlike the black leg, with this disease, constrictions are formed not only at the bases of the stems, but on absolutely any of their parts. In the affected areas, the stalks become noticeably thinner and subsequently break. The lower leaves are characterized by rather rapid wilting, leading to lodging of plants.
On the affected fruits, as such an unpleasant ailment develops, a watery rot of a red-brown or grayish hue appears. And on the fruits growing on the lower branches, the manifestations of southern late blight resemble watery rot with multi-colored concentric zones. As for green fruits, then on them the disease manifests itself in the form of rather extensive spots. At first, these spots are grayish-green in color, and later turn into almost black. Fruit tissues also become watery.
In general, damage to fruits in southern late blight has an external resemblance to the nightshade lesions caused by late blight, however, they differ in the color of the spots (tissues infected with southern late blight are somewhat darker) and in the time of appearance (mostly early periods).
The causative agent of southern late blight is a parasitic fungus called Phytophtora parasitica residing in the upper soil layer (up to fifteen centimeters), the life span of which usually spans a year. It develops most actively if the soil is abundantly moistened, and especially if water stagnates on its surface for a long time.
In greenhouses, where the air humidity exceeds 70%, the disease manifests itself to a greater extent, just like when sprinkling tomatoes. And in open areas, the development of this unpleasant ailment is noticeably promoted by abundant dew with fogs, as well as warm days and cold nights.
How to fight
To increase the resistance of tomatoes to southern late blight, you need to observe the water regime and follow agrotechnical rules. Also, when growing tomatoes, it is extremely important to comply with the rules of crop rotation. The selection of varieties resistant to southern late blight will also be a good measure - least of all, this attack affects such varieties as Leningradsky precocious, Uralsky many-fruited and Leningradsky autumn. It is equally important to disinfect the soil intended for growing tomatoes. And all plant residues from the beds should always be eliminated.
Before sowing, it is useful to soak the seeds for a certain time in a solution of a special preparation "Pseudobacterin-2". And if you water the seedlings planted in greenhouses with a 0.01% solution of sodium humate, the infestation of grown tomatoes with southern late blight can be reduced by 4 - 5 times. In dry seasons, watering is carried out with the addition of copper sulfate in small doses - it will reduce the activity of the disease.
If necrotic spots begin to appear in the area of the root collar, the damaged plants must be removed from the site and destroyed. In no case should they be left for composting. And the surviving cultures are treated with 0.1% copper oxychloride, 1% Bordeaux liquid or 0.5% solutions of Ridomil, Sandofan, Avexil or Oxychoma. When spraying, it is important to pay special attention to the bases of the stalks.
A good effect is also given by spraying tomatoes with a preparation called "Quadris", the treatment with which provides them with rather long-term protection - up to three weeks. And in case of mass infestation of tomatoes, it is advisable to spray with Ridomil Gold (0.25% working solution). Such drugs as "Acrobat" and "Infinity" have also proven themselves quite well. Well, for repeated treatments, you can use various contact preparations.
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