Peronosporosis of cucumbers and methods of dealing with it
Peronosporosis of cucumbers, or downy mildew, is a dangerous disease that can destroy all plantings and spread very quickly. The disease causes a mushroom-like organism that parasitizes exclusively on pumpkin crops. It is difficult to treat it, in most cases the affected plants die. The main methods of prevention are the treatment of seeds before planting, regulation of humidity and the implementation of agricultural regulations.
Peronosporosis of cucumbers and methods of dealing with it
Described ie diseases
The causative agent of downy mildew is psevdogrib or mikoid Pseudoperonospora cubensis Rostowz, of a kind Psevdoperonospora class Oomycetes.
microorganism can exist and develop only disease in tissues and host authorities. It affects only pumpkin plants: cucumbers, zucchini, watermelons, melons, pumpkin, squash. The leaves are attacked by a pseudo-fungus, less often ovaries and flowers.
The fruiting bodies of the microorganism formed on the leaves of cucumbers produce oospores in early autumn. They fall into the ground, where they are able to overwinter even in fairly severe frosts. In spring, when the temperature rises to 12-18 ° C, oospores turn into zoospores.These are small unicellular organisms with two flagella, able to swim in water. That is why the disease most often develops with increased humidity of air and soil, in rainy summers.
Falling with a drop of water on the lower part of the leaf of a cucumber, the zoospore penetrates the stomata (plant organs that play the role of gas exchange). Inside the peronospore leaves forms a mycelium. Mycelial hyphae grow in the intercellular space, and its lateral processes penetrate the cells. False mushroom literally sucks out a cucumber, takes water and nutrients from the cells.
The overgrown mycelium comes out, it can be seen on the bottom of the leaf in the form of a fluffy coating with black dots. This plaque contains millions of oospores.
The pathogen is carried by the wind and parasitic insects. With its development, new leaves are constantly struck. If there is a lot of rain in the summer, up to 15 generations of a pseudo-fungus can develop on one plant.
A number of conditions are necessary for the development of downy mildew on cucumbers:
temperature difference (at night – about 13-18 ° C, in the daytime – 20-23 ° C);
cold dew in the morning;
crowding of plants in the garden;
watering with cold water.
Cucumbers in poorly ventilated close greenhouses are often affected. The weather also matters: in the cold rainy summer, downy mildew threatens pumpkin crops more than in the hot and dry.The risk of the disease increases when aphids and other pests parasitize on cucumbers.
False powdery mildew does not appear immediately on cucumbers. The incubation period lasts approximately 3-10 days, depending on the air temperature. Optimum conditions for the growth of mycelium occur at 15-20 ° C. Most often, the pathogen is affected by cucumbers in the second part of summer, when nights become cold, more often rain falls.
The main symptoms of peronosporosis progress very quickly, cucumbers can die in 1-2 days. Here is how powdery mildew manifests itself:
yellow-green spots appear on the top;
a gray coating on the bottom;
black under the magnifying glass on a gray coating specks in which oospores ripen;
spots increase in size, become gray-brown;
the leaf is deformed and dries;
the flowers of the plants turn black and fall off.
On an open bed in the southern regions, signs of downy mildew may be slightly different. Yellow spots are very small, the leaves themselves become coarse, dark green.
As a result of loss of foliage, photosynthesis is sharply reduced. Fruits get less nutrients. The cucumber itself is not affected, but it ceases to grow and loses taste. Together with fallen leaves, the infection enters the soil and can be there for 4-6 years.
Cure the disease
К treatment should be started as soon as possible
If the first signs of the disease become noticeable, treatment should be started immediately. The chances of saving the plants are small, but worth a try.
First of all, remove the affected leaves. Powdery mildew on cucumbers spreads very quickly. It does not appear immediately, because the bushes should be regularly checked and new leaves with spots removed. After this, the culture is necessarily treated with fungicides. The most effective means are:
In the initial stages of the disease, you can also use traditional methods of combating plant fungi. To do this, cucumbers are treated with the following means:
soda (25 g) with soap (5 g) dissolved in 5 l of hot water;
copper sulfate (10 g), dissolved in 10 l of water;
sulfur solution (50-80 g / 10 l);
bordeaux liquid (100 g / 10 l of water);
chloroxide copper 0.4%.
With these tools it is advisable to process the bushes twice, and then repeat the procedure after a week.They also recommend cultivating the soil. If the downy mildew of the cucumber hit most of the foliage, it is better to destroy the entire planting, the struggle for its survival in this case is practically useless. The tops are completely burned, the soil is dug up and disinfected. At this point, it is advised not to plant pumpkin crops for another 3-4 years.
How to prevent peronosporosis
To prevent peronosporosis of the cucumber, a number of actions are taken:
proper agricultural technology;
seed treatment before planting;
antifungal treatment for Prevention.
Let’s take a closer look at the listed preventive measures against downy mildew.
When growing cucumbers, crop rotation should be followed. It is undesirable to plant a crop on the same site for several years in a row after pumpkins, zucchini, watermelons. The break between sowing these crops should be 3-4 years. It is best if onions, garlic, carrots grew in the garden before the cucumbers.
If the cucumbers do not grow in the open ground, but in the greenhouse, it must be carefully processed after harvesting and before planting the seeds in spring. It is important to provide enough space for the bushes and not to plant them too close to each other.
Preparing the soil
In autumn, remove all the tops from the plot. If the plants were infected, they must be burned. Dig the earth to a depth of 25-35 cm.It is possible to treat the soil with 1% potassium permanganate, 2–3 copper sulfate, or any preparation with fungicide. This will not only kill the spores of the pseudo fungus, but also the causative agents of other diseases of cucumbers. The soil in greenhouses should be especially carefully treated.
The causative agent of downy mildew can parasitize seeds, although they practically do not change their appearance. To get rid of the false fungus, you need to take some measures before planting. You can place the seeds in hot water at 50 ° C for 15 minutes. You can also soak the seed in 1% potassium permanganate or Trichodermin solution for 2-3 hours.
Regular ventilation will prevent the plants from getting sick
So that the adult plants do not get sick, they are planted in the ground as early as possible and covered with a film . It is important to combat insect pests and weeds in the garden. Watering cucumbers should be moderate, you can not pour cold water under the bushes. If they grow in a greenhouse, there should be kept humidity at 80%, temperature in the range of 21-24 ° C, regularly aired greenhouse.
Preventative treatment of plants
to prevent infection, it is necessary to process cucumbers with fungicides several times a season. Use the same drugs as for treatment, but a little in lower concentrations.You can use some folk recipes:
Take 10 drops of 5% iodine, add 1 liter of skim milk and 9 liters of water.
2 cups of ash pour 2-3 liters of boiling water, after 20-30 minutes filter through cheesecloth, add 10 liters of cold water.
About 200-300 g of dry onion husks pour 10 liters of water and slowly bring to a boil, then insist 1-2 days.
Take 1 part of cow manure and 3 parts of water, breed, insist 3-4 days, dilute 7-8 liters of clean water.
It is necessary to process cucumbers with these means for 2-3 days in a row, then replay ryat treatment a week later. The advantage of folk methods is that they are environmentally friendly. Unfortunately, reviews say that such methods of struggle are not very effective. Ready-made drugs act on the pathogen much better.
Peronosporosis of cucumbers appeared in Russia in the 70-80s. He became the cause of the decline in productivity, the death of entire plantations. Since it is quite difficult to fight the disease, varieties with high resistance to the pathogen have been developed over the past decades. The most stable and popular of them:
Boy with a finger;
Hybrid varieties of cucumbers are also highly resistant to the pathogen.Among them are:
Green Wave F1;
Emerald City F1;
First Class F1;
None one variety or hybrid does not give a 100% guarantee that it will not fall ill with downy mildew, therefore you should adhere to all the above recommendations even when growing resistant varieties of cucumbers. To prevent the disease is much easier than to cure.
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