As you know, farmers do not have easy seasons, but each year brings its own difficulties and problems. How will potato growers in Russia remember the ending 2020?
According to the journal, rhizoctoniasis has come to the fore in terms of the severity of all known "potato" diseases this year. Although the problem did not affect all Russian regions.
The spread of the disease in numbers
According to the Russian Agricultural Center, in general, in the territory of the Russian Federation in 2020, the manifestation of rhizoctoniae remained at the level of 2019 and a predominantly moderate development of the disease was noted. Recall that during the summer of 2019, the disease was detected on an area of 23,30 thousand hectares. In the same period of 2020, the defeat of potato plantings was recorded on an area of 21,47 thousand hectares.
At the same time, an aggravation of the situation was noted in a number of regions.
So in the Central Federal District in 2020, the spread of the disease was recorded on an area of 5,59 thousand hectares (in 2019 - 4,90 thousand hectares). The area of the treated area against rhizoctonia was 1,50 thousand hectares (in 2019 - 0,03 thousand hectares). In the Northwestern Federal District, the spread of the pathogen on potato plantings was detected on an area of 7,56 thousand hectares (in 2019 - 5,01 thousand hectares). The treated area against the disease was 1,79 thousand hectares (in 2019 - 1,30 thousand hectares). In the Volga Federal District, the pathogen affected area of potato plantings was 3,19 thousand hectares (in 2019 - 2,64 thousand hectares). No treatments against the disease were carried out (in 2019 - 1,4 thousand hectares).
But there were also territories where the spread of Rhizoctonia disease decreased.
For example, in the Southern Federal District, manifestations of the disease on potato plantings were recorded on an area of 0,31 thousand hectares (in 2019 - 1,20 thousand hectares). The area of treatments against the pathogen was 0,01 thousand hectares (in 2019 - 1,08 thousand hectares). In the North Caucasian Federal District, no damage was detected on potato plantings (in 2019 - 0,30 thousand hectares). No pathogen treatments have been performed.
In the Urals Federal District, on potato plantations, the disease manifested itself on an area of 2,10 thousand hectares (in 2019 - 3,69 thousand hectares). The area of treatments against the pathogen was 2,36 thousand hectares (in 2019 - 1,63 thousand hectares). In the Siberian Federal District, on potato plantations, the spread of the pathogen was detected on an area of 2,21 thousand hectares (in 2019 - 4,16 thousand hectares). There were no treatments for the disease in 2019 and 2020. In the Far Eastern Federal District, rhizoctonia infection of potato plantings was detected on an area of 0,50 thousand hectares (in 2019 - 1,40 thousand hectares). No treatments against the pathogen were carried out (in 2019 - 0,06 thousand hectares).
Experts of the Russian Agricultural Center of the Russian Federation associate the decrease in the affected areas of potato plantings in the Southern, North Caucasian, Ural, Siberian and Far Eastern federal districts with the prevailing weather conditions during the growing season of plants. In addition, according to experts, the success of many farms in the fight against the disease is explained by systematic work on the processing of fields with plant protection products.
The increase in the area of distribution of rhizoctonia on potato plantings in the Central, North-Western and Volga Federal Districts was caused by prolonged periods of high humidity, as well as with a decrease in the number of plant treatments in the previous year.
It should be noted that the highest infection rate (over 100) in the summer of 2020 was found in the Perm Territory (in 2019 - 29,28). An increase in the infection rate was also recorded in the Republic of Karelia - 1,58 (in 2019 - not met), Vologda - 6,30 (in 2019 - 4,90), Kaluga - 0,24 (in 2019 - not met), Kostroma - 1,58 (in 2019 - 1,29), Tver - 0,04 (in 2019 - not met), Yaroslavl regions - 0,03 (in 2019 - not met) , The Komi Republic - 0,84 (in 2019 - not met), the Mari El Republic - 0,11 (in 2019 - not met), Sverdlovsk - 0,78 (in 2019 - 0,69) and Chelyabinsk regions - 0,81 (in 2019 - 0,36).
The fastest increase in the number of lesions with rhizoctonia was observed in July and August. Frequent changes in air temperature and heavy rains contributed to the active development of the pathogen.
The editors would like to thank the press service of the Russian Agricultural Center for the provided material
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From the point of view of science
Maria Kuznetsova, Head of the Department of Potato and Vegetable Crops Diseases of the Federal State Budgetary Scientific Institution VNIIF, Candidate of Biological Sciences
According to the observations of the All-Russian Scientific Research Institute of Phytopathology (VNIIF), the most significant manifestations of rhizoctonia this year were characteristic of Vladimir, Tver, Yaroslavl, Vologda, Novgorod, Leningrad, Kostroma, Moscow, Smolensk, Pskov and a number of other regions of the country.
Causes of the disease
One of the reasons for the active development of Rhizoctonia disease in the current season is the favorable weather conditions for the pathogen Rhizoctonia solani. For example, in the Moscow region, in the second and third decades of May, the air temperature was below the average values of long-term temperatures. The cold snap could not but affect the cultivated crops: potato plants during this period lagged behind in development, compared with the average statistical indicators, by 1-2 weeks, and were weakened. In addition, starting from the third decade of May, as well as in June and July of this year, a significant amount of precipitation fell in the region (against the background of long-term average indicators). All these factors contributed to the early and further intensive development of rhizoctonia.
At the same time, the problem of rhizoctonia is associated not only with weather conditions, but also with a number of equally important reasons. Among them: low quality of seed material; violation of planting dates (we are talking about cases when potato growers begin to plant non-vernalized seed tubers in cold soil), non-compliance with crop rotations, delays in harvesting, etc.
External manifestations
It is known that the fungus Rhizoctonia solani is capable of infecting potatoes at all stages of ontogenesis, from germination to harvest. The disease can manifest itself in the form of black scab, reticular necrosis and deep spotting on tubers, rotting of sprouts, death of stolons and roots. In addition, the symptoms include dry rot of the underground part of the stem - in the form of brown ulcers ("rotten wood") or a grayish-white "felt" plaque ("white leg").
The fungus causes the main harm during the development of seedlings. In wet and cool weather, when the soil temperature is less than 8° C, on the planted tubers, sclerotia (the dormant stage of the fungus) sprout with mycelium, which penetrates the sprouts and leads to the formation of dark depressed spots on them. Diseased sprouts sometimes die before reaching the surface. In warm weather, seedlings can grow into a plant with a shingle lesion on the lower part of the stem, the upper leaves twisted along the vein.
Aftermath
Potato rhizoctonia causes both quantitative yield losses and a decrease in the commercial quality of tubers. Potato yield indicators go down due to the loss of seedlings, damage to stems, stolons and roots, which, in turn, affects the size, number and marketability of tubers.
In Russia, direct loss of yield from rhizoctonia can reach 25%, and the decrease in the marketability of tubers reaches 30%.
Prevention and control measures
To effectively combat the disease, it is necessary to use a whole range of measures:
- Use for planting healthy, preferably certified planting material.
- Priority introduction of early and medium early varieties of potatoes with a growing season of 60-80 days, as well as varieties that are resistant and slightly affected by this disease
- Compliance with crop rotation.
It is important to remember that the Rhizoctonia solani mushroom can persist for a long time in the soil (3-4 years), on potato tubers, its volunteers, and plant debris. The fungus successfully tolerates winter in the form of sclerotia on tubers and in the soil, as well as in the form of mycelium.
In addition, it should be borne in mind that, in addition to potatoes, R. solani is capable of infecting a number of vegetable crops (such as tomatoes, beets and pumpkin), as well as wild weeds (such as quinoa, thistle and horsetail).
Cereals (oats, winter wheat and rye, barley, corn), lupine, alfalfa, and perennial grasses are considered the best predecessors that reduce the infectious stock of rhizoctonia.
- Planting tubers in warm soil in accordance with the requirements for depth and density.
The optimum planting depth is determined taking into account the texture and moisture content of the soil (on heavy soils - the planting is shallower, on sandy loam - deeper). When a crust forms on heavy, floating soils, a necessary stage of work is to harrow the field four to five days after planting and at seedlings, since otherwise the likelihood of plant infection increases.
The optimum planting density from a phytosanitary point of view is 50 thousand tubers per hectare. An increase to 60-80 thousand significantly enhances the development of rhizoctonia on all plant organs.
- The introduction of increased doses of organic fertilizers into the soil and the use of green manure.
It is difficult for R. solani to compete with soil microorganisms; therefore, application of organic fertilizers can reduce the level of soil infection.
The role of siderates is also difficult to overestimate. In many farms, plants from the cruciferous family - Brassica juncea (Sarepta mustard), Raphanus sativus (common radish), Sinapis alba (white mustard), Eruca sativus) - are used as biofumigants against a number of fungal pathogens living in the soil (Rhizoctonia solanic, Colletotrichum , Helminthosporium solani, Streptomyces scabies, Spongospora subterranea) and potato cyst nematodes. At the time of flowering (when more than 50% of the total bloom blooms), the plants are mowed, crushed and plowed. In the soil, secondary plant metabolites (glucosinolates) are degraded to volatile compounds (eg isothiocyanates), which have a fumigating effect on pathogens and nematodes.
- Timely and high-quality cleaning.
Harvesting should not be postponed for more than two weeks after mowing; it is unacceptable to leave small and damaged tubers on the field).
- Using fungicides to treat seed tubers or using them when planting potatoes.
The main task of plant protection chemicals during this period is to reduce the harmfulness of rhizoctonia and other soil pathogens.
The results of long-term tests carried out at VNIIF against an infectious background with Rhizoctonia solani confirm the high efficacy of drugs based on azoxystrobin, fludioxonil, penflufen, fluxapiroxade and other active ingredients in protection against rhizoctonia disease.
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