Ways to deal with powdery mildew on onions
Powdery mildew on onions, or scientifically peronosporosis, is quite common among diseases in a vegetable crop and poses a threat to the future harvest.
How to deal with powdery mildew on onions
The biological basis of peronosporosis
Such a disease of garden crops, as peronosporosis, is of two types:
- powdery mildew itself, which appears on zucchini, pumpkin and many other melons grown in the beds,
- downy mildew of onions, which most often damages cucumber crops.
In fact, and in another case, peronosporosis belongs to fungal, although it is caused by various families of microorganisms. To combat it, chemicals and folk remedies are used. The difference in powdery mildew on onions and its counterpart, downy mildew, is that outwardly the original form of a fungal disease manifests itself on the outer side of the leaf blade, and with downy mildew, the inner side is affected, subsequently turning upward in the form of spots.
A plant can get sick with peronosporosis not only during the growing season, but also during storage. Many types of onion culture are susceptible to it: shallots, fragrant, leek, batun, slug, chives.
Infection conidia are large enough in size, ovoid and gray in color. At temperatures starting from 13 ° C and maintaining high levels of humidity, peronosporosis is activated and spreads faster.
In drought and hot climates, fungal conidia die when exposed to sunlight, without causing damage to the onion culture. Microorganisms can spread through the air with the help of wind gusts, with raindrops, as well as from a diseased plant to a healthy one through gardening care.
The mycelium can maintain its viability throughout the winter period, settling in the bulbs and root system.
External signs of a fungal disease
Downy mildew onions are affected by round-shaped spots with a pale green color that appear on the foliage. Distinct white streaks look like culinary flour, which can be noted in the photo. Without taking timely appropriate measures, the infectious disease begins to spread to the plant stem.
Over time, these white spots begin to acquire a brown tint, which indicates an overgrown, neglected process; to combat them, chemicals will be required, for example, phytosporin, polycarbacin, arcerid.
Infection on each horticultural crop manifests itself in different ways: on a vegetable marrow it leads to a sharp wilting, on a berry bush it bends branches and shoots, twisting the foliage and covering the berries with a bloom.
If the cause of the disease is an infected seed, then two weeks later - on the 20th day after the onion sprouts, peronosporosis begins to appear on its feathers in the form of large solid gray spots. If the plant is not treated and rescued, as a result of the development of the disease, the feather will wither and sag.
Symptoms and contributing conditions
It is quite problematic to notice the symptoms of the presence of fungi in the planting material: at first glance, the plants affected in the previous sowing period do not lag behind in development, there are no external signs, however, during the period of foliage regrowth in late April - early May, the affected areas become noticeable.
A diseased onion culture stops its growth and development and subsequently withers.
During a period of high humidity, mushroom spores can be seen on the foliage, which outwardly fold into a gray bloom. The mycelium is clearly visible in the morning hours, when the dew has not yet dried. The affected rough surface of the foliage often traps dust and soil dirt between the fungal particles, which makes the onion tops dirty. This appearance serves as an excuse for the gardener to inspect the plant for the presence of powdery mildew on the onion.
After some time, the spots become more noticeable and increase in size, and the foliage begins to dry out prematurely. By the period of foliage dying off, the fungal infection has already penetrated the turnip, stopping growth and storage disturbances.
The infection causes a lot of harm to the testes, which makes the onion arrows turn yellow and break.
A month after planting the onions, green or yellow spots with a gray spore coating begin to appear.
Facilitating conditions
For the development of fungal conidia, there are a number of conditions conducive to their activity:
- they are capable of spreading at night at temperatures ranging from 4-25 ° С,
- humidity indicators from 95 percent or more,
- the presence of moisture residues on the plant at an ambient temperature of 1-28 ° C.
Fungi are able to maintain their viability for up to 4 days. In this case, the incubation period for the development of a fungal disease is on average from 10 days to 2 weeks. Dry hot weather stops the development of peronosporosis.
Agricultural technology in the fight against infection
Prevention of onion disease with downy mildew involves the use of basic agrotechnical measures that allow you to grow a good crop without damaging the plant:
- the vegetable should be planted in places accessible to sunlight, on sandy and loamy soils,
- the bed for planting onions must be provided with drainage and ventilated,
- to quickly dry out the soil layer, weeds are destroyed and watering is not performed before night,
- onions are planted with alternation of garden crops with a change in their growing place,
- when choosing an onion variety for planting, those that have established themselves as resistant to diseases are preferred,
- planting material is warmed up before storage,
- plant feeding with nitrogen-containing mineral fertilizers is carried out only in the initial period immediately after planting, since nitrogen reduces the onion's resistance to fungal infections,
- avoid excessive watering, smoothly moving in the second half of the growing season to regular loosening of the soil layer,
- the affected areas of the onion crop are immediately removed,
- onions are harvested in dry weather, followed by drying until the surface peel is completely dry.
The death of the mycelium inside the onion turnip can be achieved if the vegetable is heated at 4 ° C for 8 hours.
Chemicals against downy mildew
As a remedy for powdery mildew on onions, chemical preparations and folk remedies are often used, which can be carried out as a treatment or as a prevention of a disease.
Use of chemistry
Initial control measures for fungicide treatment are taken even before the detection of a fungal infection, when the onion plant is gaining growth. This is done with the help of Ridomil Gold in the proportion of 2.5-3 kg of the drug per hectare. When processing winter onions from powdery mildew, use the same remedy, starting to water after the appearance of 4-6 onion leaves.
You can achieve maximum efficiency and get rid of fungi if you do several sequential treatments with Ridomil and spray the emerging peronosporosis up to 3 times.
With the active growth of onion crops, when the main vegetative mass has already been recruited, in the fight against powdery mildew on onions, treatment with translaminar Quadris is used, with which onions are sprayed at the rate of 1 liter per 1 hectare with an interval of 10 days a week.
A fungicide called Bravo has established itself well as a remedy that can fight not only peronosporosis, but also gray rot and alternaria.
If the primary signs of powdery mildew are found on the onion, the Bordeaux solution with a concentration of 1% helps the plant to fight it, which can be used only earlier than a couple of weeks before the onion harvest. It should also be remembered that onions treated with Bordeaux liquid are not used on green feathers.
An alternative to this solution can be copper oxychloride in a proportion of 40 g per ten-liter bucket of water, arceride - 30 g per bucket. Onions are processed with these preparations 20 days before harvest.
For the effectiveness of the above solutions, milk or soap is added to them in the calculation of no more than 1% of the total weight.
Processing is carried out at intervals of 1.5-2 weeks and cannot be more often than 2 times per garden season.
Traditional methods
Among the folk remedies for how to deal with powdery mildew on onions, gardeners secrete fermented weeds, half a bucket of which are cut, poured to the brim with boiling water and infused for several days. They are filtered through cheesecloth and the resulting liquid is sprayed with onions. Onions are protected from powdery mildew by fermented milk products in the form of sour milk or sour milk, diluted with cold running water at the rate of 1 to 10.
How to save the harvest is a personal matter for every gardener, fortunately, the choice of means is amazing. The main thing is not to let everything take its course.