How To Save The Crop Of Potatoes And Tomatoes From Late Blight

2024 Author: Sebastian Paterson | [email protected]. Last modified: 2023-12-16 13:47

The Leningrad Region is considered to be one of those potato and tomato growing zones where the harmful effects of late blight disease on them are considered a frequent occurrence (every 2 years), especially if varieties that are susceptible to this common pathogen are grown, or if a warm and humid summer is established.

As a rule, on potatoes, the disease manifests itself first in early varieties, then it moves on to later varieties. Under conditions favorable for the development of this disease, the gardener in 1-2 weeks can lose not only recently normally vegetating tops, but also get a serious infection of the crop of tubers intended for long-term storage. In case of late blight disease, 3/4 of the leaf surface of potato tops completely stops increasing the yield, while its damage is 50-80%. Infection of tomato plants is usually observed 2-3 weeks after the appearance of late blight on the tops of potatoes. When infected during the filling period, tomato fruits do not ripen, turn brown and are not suitable for nutrition.

Fungal infection of late blight can persist in the soil in the form of conidia and mycelium for a short period, as well as on plant debris and tubers. At the beginning of the growing season, from diseased seed tubers, it gets to the shoots, from the tops - to the tubers of the new harvest. But more often the initial source of infection of the pathogen in the field is the infected and germinated tubers, carelessly thrown by the gardener near the potato plantings.

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In warm rainy weather in our region, the defeat of the leaves and stems of potatoes by late blight due to the appearance of a new (more aggressive) race can be expected already in the phase of full germination (even before the beginning of budding). Symptoms of the disease are noted on the underside of mainly the lower tiers of leaves in the form of dark brown spots with a light bluish bloom (mycelium), which then quickly capture the entire leaf mass of the bush. The sporulation of late blight is especially noticeable - the bordering of the spot with a delicate bloom of white color - in the early morning after the dew falls. The mycelium is a characteristic feature of the disease.

The spread of the fungus infection occurs with spores, which are quickly spread from the affected potato tops by wind or spray of rain from plant to plant, from site to site throughout the district, falling on healthy plants of new plantings of this crop, as well as tomato. This phenomenon is facilitated by warm daytime weather, when spores are blown off diseased leaves by ascending air currents. Their active germination is facilitated by a temperature of 10 … 20 ° C and high air humidity.

If such favorable conditions are repeated for 3-5 days in the morning, there is a widespread infection of potato and tomato plantings, especially unstable varieties. Flowing down with drops of dew or rain onto the soil surface, spores, possessing special flagella for movement, penetrate with water flows through the soil and infect tubers. Hard dark spots appear on the surface of diseased tubers; they spread into the tissues with brown uneven "tongues". The active spread of late blight on potato plantings will show the gardener how seriously he picked up varieties for growing - resistant or susceptible, since the use of immune varieties is considered the main measure of combating mycosis.

Slowing down the process of infestation of potatoes with late blight and saving it is possible only by spraying plants with fungicides that are allowed for sale in the retail network. Solutions of drugs applied to the tops of potatoes prevent spore germination and protect the leaves from infection, but they are not able to kill the mycelium and do not cure the disease of potatoes. If we carry out preventive treatment of healthy tops before the onset of late blight, then significant crop losses can be prevented. The protective effect of the treatment lasts 12-14 days. The effectiveness of one-time treatments of potatoes in a plot with resistant varieties is somewhat reduced if they are surrounded by neighboring, uncultivated plantings of this crop, especially with susceptible varieties, which serve as constant intensive sources of infection. It is useless to process already heavily infected plantings.

Late blight (brown rot) is called the most widespread and dangerous tomato disease (destroys up to 50-60% of the crop), affecting stems, leaves and fruits. Sometimes the last for 1-2 days completely turn black and become unfit for food. Late varieties or plants of late planting suffer greatly in tomato. The most favorable conditions for the development of this disease occur in the second half of summer and autumn, when the daytime temperature is quite high (20 … 22 ° C), and the nighttime temperature is low (10 … 12 ° C). With such a temperature difference, dew falls out, which contributes to the massive development of sporulation of the pathogen and the active re-infection of plants. Outbreaks of this disease usually occur after prolonged rainy weather, especially with fog and dew.

The spread of late blight usually begins with the upper layer of leaves and goes to the lower ones. In diseased leaves, large brown spots are located mainly along the edges of the leaf blade: on the lower side, the fungus (at a relative humidity of 75%) forms a delicate white mycelium with spores; such leaves dry out quickly. With the advent of a new aggressive race, causing the formation of long dark brown elongated spots on the petioles, as well as on the stems, leading to the appearance of constrictions on the latter and, as a result, to the death of the plant within several days, the control measures became somewhat more complicated.

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If potato growers can still get away from a strong tuber disease with the help of high hilling of their bushes, then vegetable growers cannot mechanically protect the opened tomato fruits. Some of them, trying in vain to protect tomato plants from late blight, even stop growing it. On fruits, the disease that begins during the growing season manifests itself in the form of rot - brown rounded spots, and with early damage the fruits may have an ugly appearance: the tissue from their surface and inside remains solid. If there are no symptoms of late blight on the fruits of an infected plant, the latter can quickly appear during transportation and ripening, since conditions favorable for the development of infection are created during these periods. Fruit re-infection usually does not occur during storage.

In general, it is not supposed to grow a tomato after or next to a potato, but where can you go from that?

To prevent the disease, it is necessary to qualitatively destroy every autumn, it is better to burn all plant residues, dig up the plot well and observe crop rotation, returning the tomato to its old place only after 3-4 years. In our zone of strong spread of the disease, before the appearance of its signs, plants are fed with phosphorus and especially potassium fertilizers, which increases their immunity. At the beginning of flowering, foliar top dressing with a 0.5% superphosphate extract is useful (50 g is poured into 1 liter of hot water, infused for a day; the settled solution, without shaking, is drained and diluted tenfold with water). When spraying, 0.8-1 l of this solution is consumed per 10 m². At the beginning of fruit formation, tomatoes are fed with potassium sulfate (10-15 g / m²).

Preventive spraying with fungicides is carried out when the first symptoms are detected on potato bushes (1% Bordeaux liquid, copper oxychloride, cuproxate). 3-4 spraying is done per season (the interval between treatments is 10-14 days, in rainy weather - 7 days). Bordeaux liquid can be used no later than eight days before harvesting, copper oxychloride and cuproxate - for 20. Fruits from treated plants must be thoroughly washed with water. Some gardeners get a good effect when spraying plants during the period of fruit setting on the second bunch with infusion of garlic every 12-15 days (up to five times).

With the threat of a strong development of late blight, some gardeners practice early harvesting of fruits, and before ripening (to prevent disease) they immediately rinse with water and keep them (1.5-2 minutes) in hot (60 ° C) water. When laying tomatoes in a box with a lid for ripening, they additionally sprinkle the fruits with crushed garlic (10 g per 10 kg). In areas where late blight is especially harmful, it is preferable to cultivate early varieties.