The course of the pathological process of potato rhizoctoniosis is significantly affected by the size of the pathogen population in the soil and on seed tubers. Under Siberian conditions, soil infection plays a more significant role compared to tuber infection, however, at the first stages of the development of the disease, the tuber inoculum is of greater importance.
Taking into account the indicated biological features of the causative agent of potato rhizoctoniosis, in order to reduce the harmfulness of the disease, increase the yield and improve the quality of products, it is necessary to use a set of agricultural practices that reduce the number of the pathogen both on seed tubers and in the soil.
In the absence of an infectious beginning in the soil, potatoes can be grown on barley, oats, rapeseed and mustard, and tubers must be treated with fungicides before planting. Then, in the seedling phase, we can expect the development of rhizoctonia in the range of 9-10%.
When planting untreated planting material, this indicator will increase by 3-5%. If it is not possible to cultivate crops according to the above predecessors, it can be placed on wheat, then the development of the disease will be at the level of 14% with treatment of tubers and 20% without treatment.
If the soil of the fields is inhabited by the causative agent of rhizoctoniosis, then it is better to plant potatoes on such previous crops as oats, rapeseed and mustard. In this case, the development of rhizoctoniosis will reach 13-15% both on plants grown from fungicide-treated tubers and those obtained from untreated planting material.
When cultivating crops for wheat and barley, tubers must be sprayed with a disinfectant before planting, for example, Maxim 0,25 KS, which will reduce potato damage to 7,5%.
By the budding phase - the beginning of flowering on soil free from R. solani, the lowest development of the disease is observed for such predecessors as rapeseed and oats - 16 and 19%, respectively, if the tubers are treated with a disinfectant before planting. This indicator is slightly higher for wheat, barley and mustard - 22-25%. If the planting material is not treated, then by this time the development of the disease on potatoes for grain precursors and mustard reaches approximately the same level of 27-32%. An exception is rapeseed, where the development of rhizoctoniosis is 22%.
Cultivation of potatoes on soil infected with R. solani for oats, rapeseed and mustard in combination with spring dressing of tubers with Maxim 0,25 KS keeps the infection of the crop with rhizoctoniosis at the level of 26-32%. For barley and wheat, this figure is much higher and amounts to 37-44%. Placing potato plantings on infected soil and refusing to treat planting tubers with a fungicide enhances the pathological process. The development of rhizoctoniosis in this case for mustard is 33%, for barley, oats and rapeseed - 37-40, and for wheat - 53%.
The cultivation of potatoes after potatoes leads to a significant damage to plants by the disease throughout the entire growing season.
Cultivation of a crop according to various predecessors, as well as the use of a disinfectant, allows not only to regulate the phytosanitary state of agrocenosis, but also to improve the quality of the resulting products.
The placement of potatoes in soil free from the causative agent of rhizoctoniosis, as well as the use of disinfected planting material, makes it possible to grow it on all of the above grain and cabbage crops. In this case, the yield of healthy tubers ranges from 19-22 t/ha. If the tubers are not treated before planting, then a decrease in the quality of the new crop is observed. The collection of healthy tubers is reduced by 1-3 t/ha, depending on the previous crop.
A completely different picture develops if the soil under the potato is populated by a fungus. In this case, when dressing the planting material with Maxim 0,25 KS, the best predecessors are oats, rapeseed and mustard. They allow you to increase the yield of healthy tubers up to 16-18 t/ha, while wheat and barley - only up to 13-14 t/ha. If the tubers are not treated with a fungicide, then it is also necessary to plant potatoes according to the above predecessors. This allows you to get a crop of quality tubers at the level of 13-14 t/ha. Wheat and barley are much worse predecessors under these conditions: here this indicator will be already 11-12 t/ha.
The cultivation of potatoes after potatoes leads to a significant decrease in the quality of the products obtained.
Only by treating planting material with a disinfectant, you can get 13 t/g of healthy tubers, and in other cases this figure does not exceed 8-9 t/ha.
To obtain consistently high yields of high-quality potatoes in soil free from the causative agent of rhizoctoniosis, spring treatment of tubers with fungicides and the use of wheat, barley, oats, rapeseed or mustard as a previous crop is necessary.
The presence of R. solani in the soil requires a preliminary improvement of the soil with the help of oats, rapeseed and mustard and the obligatory dressing of the planting material.
In the conditions of crop rotations with a short rotation, in order to improve potato plantings from the causative agent of rhizoctoniosis, it is necessary to introduce a phytosanitary precursor (oats, Sarepta mustard, spring rapeseed) and treat the planting material with fungicides. Cultivation of mustard and rapeseed as precursors makes it possible to reduce the density of the R. solani fungus by 50-55% by the beginning of the growing season of potatoes, and 5% of oats. The use of wheat and barley as a precursor is not recommended, as they contribute to the accumulation of the pathogen (the number increases by 16 and 51%, respectively).
A change in the soil population of R. solani under cereal and cabbage predecessors reduces the development of rhizoctoniosis on potato stems at the first stages of ontogenesis by 53-70%, and at the last stages by 31-50% and increases the yield of healthy tubers by 66-86% compared to potatoes placed on potatoes (9,7 t/ha).
The system of crop protection, including the cultivation of potatoes on oats, Sarepta mustard, spring rapeseed and the treatment of tubers before planting with a modern fungicidal disinfectant Maxim 0,25 KS, provides a reduction in the development of the disease by 54-64, 46-67 and 44-61% and increases the yield of healthy tubers by 88, 69 and 76%. The complex of the above methods also improves the quality of the obtained products, reducing its population with sclerotia by 12-14%.
List of used literature:
1. Shaldyaeva E.M. Monitoring of rhizoctoniosis in potato agroecosystems in Western Siberia / E.M. Shaldyaeva, Yu.V. Pilipova, N.M. Konyaev. -
Novosibirsk, 2006. - 196 p.
2. Shaldyaeva E.M. Optimization of the phytosanitary state of plantings
potatoes when using spring rapeseed as green manure
culture / E.M. Shaldyaeva, Yu.V. Pilipova, M.P. Shatunova // Protection
plants in Siberia: Sat. scientific tr. teachers and graduate students of the Faculty of Plant Protection. - Novosibirsk, 2003. - S. 77-83