2024 Author: Gavin MacAdam | [email protected]. Last modified: 2023-12-16 13:38
Alternaria is otherwise called black spot or dry spot. This very dangerous disease is found literally everywhere, but in the southern regions the damage from it is noticeably higher. It mainly affects plants of the Solanaceae family - tomato, potato, belladonna, henbane, etc. The stems, leaves, and tubers of plants equally suffer from Alternaria
About the disease
Alternaria manifests itself on completely different parts of plants, not only in the form of brown spots, but also in the form of unpleasant necrotic spots with fragments of dead tissue. On the damaged tissues, concentric brown spots begin to form, covered with a dark bloom consisting of fungal spores. If humidity and temperature are very favorable, then such spots can be noticed already two to three days after infection. After a couple of days, smoky-gray conidia with longitudinal (usually few of them) and transverse (from one to nine) septa or even without them begin to appear on specks that have reached 3 mm in diameter. All damaged parts of plants are characterized by fragility and fragility.
On the surfaces of potato tubers struck by the disease, slightly depressed spots of irregular shape are formed - they are distinguished from healthy parts of the tubers by the fact that they are noticeably darker than the peel. In addition, on the surface of large spots, it is often possible to notice parallel directed wrinkles located in a circle.
Onion infected with Alternaria, watery spots appear, on old leaves quickly transforming into brown ones, surrounded by a yellow zone. Subsequently, expanding, the spots become oblong-ovate and have a pronounced concentric zoning. The beginning of the development of such spots often falls on the tips of onion feathers or on their middle parts; when the middle parts are infected, feathers usually break at the spots where spots are formed. On the neck of the onion, constrictions are formed, gradually affecting the scales on the bulbs. As a result, the leaves die, the bulbs decrease in size and rot when they are harvested and stored.
When tomato crops are infected, the development of spots is almost always noted on the fruits, and when cabbage is infected, on the heads of cabbage.
The fungus-causative agent of Alternaria overwinters on seeds, as well as on plant debris. It penetrates into plants directly through the cuticle or through the stomata, if droplets of moisture do not dry on them for more than two hours. In the intercellular spaces, the development of the mycelium starts. Fungi secretes alternaric acid, which causes necrosis of leaves, petioles and stems.
Such an unpleasant disease as Alternaria is spread by all kinds of insects, raindrops or wind. The spread of the disease is also greatly facilitated by damage to vegetation by all kinds of pests, various viral infections, as well as a lack of nitrogen. The incubation period is three to eight days.
A particularly strong manifestation of Alternaria occurs in hot weather, accompanied by dew and heavy rains.
How to fight
If possible, you should try to select plant varieties that are resistant to such an unpleasant disease, and also use only healthy planting material. The storage regime of seeds must be correct, since often the disease spreads with them. It is also important to observe the rules of agricultural technology - watering, planting density and other factors have a significant impact on the state of vegetation. It is not recommended to plant potatoes next to tomatoes.
All weeds, even those that grow in the aisles, must be removed without fail. Remnants of vegetation should be buried deep enough (about 50 cm) into the soil. Aphids and other pests should also be dealt with; it is not forbidden to do this with the use of insecticides. Correct mineral nutrition will also help to increase the immunity of plants.
You can spray vegetation with such biological products as Planriz, Agat-25, Baktofit, Integral, etc. If you spray with chemicals, then you should pay attention to Bravo, Ridomil Gold MC, Maxim. Spraying is carried out throughout the growing season. Also, a good effect can be achieved using a fungicide called Quadris.
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