The problem of the appearance of potatoes in crops of other crops and the need to control it as a weed are typical for regions with mild winters, for example, England or Holland. However, as climate changes take place, potato tubers have begun to winter in the fields of Russia in recent years.
Sergey Banadysev, Doctor of Agricultural Sciences, Doka - Genetic Technologies LLC,
SGC "Doka - Genetic Technologies"
It would seem that a few frosty days without snow cover are enough to destroy the tubers lying on the surface, in the soil the tubers freeze at a temperature below -2оC. It is hard to imagine that during a long and harsh Russian winter there can be no freezing of the soil to such a temperature. Nevertheless, the facts confirm the overwintering of tubers that emerge the next year and become weeds for crops cultivated after potatoes (photo 1).
Studies conducted at the end of the 70s showed that after harvesting potatoes, up to 450 thousand tubers / ha remain on the field, of which 10-20% can come up after a mild winter, and this is more than when planting potatoes. Cultivated potato (Solanum tuberosum) as a weed is quite harmful and reduces the yield of most crops by 20-60%. In Germany, it was found that in the presence of five potato plants per 1 m2 sugar beet yield is reduced by 16 t / ha.
There is an urgent need to apply a set of measures to control, manage (in other words, manage) the problem of potato contamination of agricultural crops. Freely growing potatoes, the weed Solanum tuberosum, have not been identified in any way in domestic science. There is not even a corresponding term, the formulation of the grain theme - "scum" - does not correspond to the essence of the phenomenon under consideration, unlike the English special term Volunteer Potato or German Kartoffeldurchwuchst, Starkekartoffel. Weed potatoes not only reduce the yield of other crops, but crops such as carrots, onions and sugar beets can completely suppress. It devalues the importance of crop rotation for cultivated potatoes, since it can persist for several years and cause significant damage during the next growing cycle in a particular field, because:
- It is a source and accumulator of diseases and pests. In weed potatoes, many pathogens, in particular, silver scab, rhizoctonia disease, verticillosis, wet rot, nematodes and wireworms actively multiply and thus increase the infectious background in the field before the next potato cultivation. Also, volunteer plants are ideal accumulators of late blight and viral diseases. Significantly, many fungicides in subsequent crops have little or no suppression of potato leaf diseases.
- It leads to the mixing of varieties during the next potato cultivation. This is bad for all areas of cultural use, especially if the shape, size of tubers and skin color are almost the same, and therefore manual or optoelectronic separation of impurities of weed potatoes is impossible. In the production of seed potatoes, the consequences are even more serious and may lead to rejection of the lot if foreign plants are not completely removed (photo 2).
To achieve effective control of weed potatoes, it is important to know the main features of its biology. Traditionally, potato tubers die after they receive 50 frost hourly equivalents at or below -2 ° C. At this temperature, death occurs after 25 hours, at –10оC after 5 hours. Practice shows that some varieties of potatoes have a higher resistance to low temperatures and die only at -3-4оC, but this information on varieties has not been officially published. Shoots of weed potatoes appear stretched, depending on the depth of placement of tubers and soil temperature. Tubers from a depth of 20 cm emerge 10 days later than from a depth of 10 cm. Potatoes make their way to the surface and from a depth of 30 cm, so the situation can be fully assessed only after 2-3 months (photo 3).
On crops with an intensive development of the leaf surface, seedlings of weed potatoes appear later due to low soil temperatures during shading. In competitive crops - such as cereals, crucifers - each potato plant produces up to three daughter tubers, rarely more than 1-3 cm in diameter. In less competitive crops, such as cabbage and onions, tubers grow larger and are larger in size.
Child tubers form at the same depth as mother tubers. The initial source of clogging may be botanical potato seeds.
Some varieties, for example, Gala, are characterized by intensive berry formation and leave behind several million seeds per hectare (photo 4,5).
Moreover, these are not seeds of varieties, as is commonly believed in the amateurish environment, but the result of cross-pollination and gene recombination. Each seed is a new and unique genotype; many of the seeds are inevitably distinguished by their high adaptability to the conditions of the wild environment. Botanical potato seeds remain viable for 3-9 years.
Plants from seeds are rather weak and die by 99%. But with stable moisture supply and the presence of light, they can form one small tuber, the offspring of which will already be typical (photo 6,7,8).
And one more feature - a large supply of carbohydrates in the mother tuber allows plants to regrow and give offspring after pruning, frost, hail damage, Colorado potato beetle, late blight, herbicides, etc.
Effective management of the problem of weed potatoes includes the use of climatic, preventive, biological, agricultural and chemical control methods. An administrative resource is also used in the Netherlands: imposing fines on farmers with more than 2 pcs / m2 potatoes in crops of other crops after July 1.
Climatic Method control refers to unregulated. According to long-term statistical indicators, the climate of the Russian Federation provides guaranteed destruction of tubers that remain in the field for the winter, the depth of soil freezing and the average daily temperatures of the winter months are more than sufficient to destroy the tuber cells. Artifacts observed in recent years are explained by snow falling on unfrozen soil, due to this, tubers that remain at great depths successfully survive the winter, being among plant debris or stones, in dry soil. Biomass and plant debris, permanent and substantial snow cover are effective insulation and significantly reduce the depth of frost penetration. High soil moisture accelerates the death of tubers, as tuber lentils open, while the activity of many putrefactive agents does not deteriorate with a low oxygen content. Mechanical damage to potato tubers remaining in the field after harvesting also increases the damage to tubers at low temperatures and pathogens.
Preventive measures aimed at reducing potato losses after harvesting.
The first step is to select suitable areas for growing potatoes that provide the most uniform plant growth. Processing of ripe soil reduces the number of lumps, the need for separation of which leads to the use of conveyors with increased gaps on harvesting combines and, consequently, increased losses of potatoes. It is advisable to use calibrated planting material so that all plants on the field develop evenly. At the same time, the proportion of small potatoes and its losses are reduced. In the case of planting uncalibrated material, part of the plants noticeably lags in growth and forms small tubers, which inevitably remain on the field. It is important to achieve the closure of the tops in the aisles as quickly as possible, the protective cover of which, especially in dry periods, minimizes unproductive evaporation and counteracts the overheating of ridges and tubers during heat periods. Several days with soil temperatures above 27 ° C cause a secondary cycle of tuber formation or their growth. Late-formed tubers do not reach marketable size due to too short a growing season and form a fraction of losses during harvesting.
The function of ensuring uniform tuber growth is also performed by plant protection. Early infection with late blight not only leads to significant crop losses, but also does not allow the tubers to gain mass, and small tubers are most often lost during harvesting. Effective processing of planting material minimizes the development of rhizoctonia, one of the consequences of which is also an increase in the proportion of small tubers.
Usually, in order to dry the aerial part of potato plants and accelerate the ripening of tubers, it is enough to carry out desiccation, especially twice. For varieties with powerful tops and reliable attachment of tubers to stolons, it is advisable to combine desiccation and mechanical grinding of the aerial mass. If this is not done, then a large volume of stems will prevent the separation of soil and tubers; some of the large tubers, along with the tops, will remain on the field.
But the main "source" of the emergence of losses of tubers (and, later, the appearance of weed potatoes) should be recognized as a potato harvester. The quality of its work in this regard depends, on the one hand, on the conditions of use, which are primarily influenced by the culture of agriculture and the features of the technology used - from soil cultivation to the level of weediness before harvesting and the quality of desiccation. On the other hand, the optimal adaptation and adjustment of the machine to the harvesting conditions prevailing in a particular field is important. Factors to minimize the loss of tubers are also significant:
- the working depth of the coulters should be slightly lower than the deepest tubers;
- the width of the receiving channel should correspond to the width of the row spacings;
- loss of tubers during the transfer of soil from the coulters to the first screening conveyor should be excluded, especially in the area between the copying drums and the cutting discs;
- the selection of the gap between the slats of the screening conveyors should be carried out taking into account the size of the tubers and lumps;
- Devices for separating weed and leaf impurities must be set up;
- the gap between the chippers and the conveyor belts must be maintained at the level of the smallest tuber.
These measures are not always consistent with other goals of successful harvesting, such as high productivity and low tuber injury. For example, a large digging depth on stony or heavy soils disproportionately increases the proportion of impurities, and therefore the load on the separating devices, and increases the risk of damage to tubers. A good balance is required when choosing the clearances on sieve conveyors, since small spacing between bars in high humidity conditions leads to very low screening rates and a sharp decrease in productivity. In general, the significance of all the listed preventive measures is sometimes reduced to zero if the enterprise makes, for a number of reasons, the decision to leave on the field, for example, the entire crop of fraction 50-.
Biological measures Controls are of secondary importance in the management of Solanum tuberosum weed problems.
Continuous sowing crops are considered the most aggressive, but when growing grains, weed potatoes also manage to ripen normally (photo 9).
Fodder multi-cut crops or pastures are a radical suppression option, but such crops are rarely used in rotations with potatoes. Tilled crops and vegetable crops in open ground do not interfere with the growth and development of potatoes. He manages to form a new crop even in powerful green manure crops of cruciferous plants (photo 10). Therefore, the selection of crops in the context of solving the problem of trash potatoes is only important in combination with the use of effective herbicides.
The hopes that potatoes, left to themselves and deprived of a system of protection, are not justified, will be an easy biological prey for pathogenic organisms - pests and diseases. The prolonged germination process and solitary standing helps him to survive. As a paradox, it is necessary to evaluate the fact that there was no damage to weed potato plants by late blight and Colorado potato beetle in 2019 in winter wheat crops in early August, after three weeks of rainy weather (photo 11).
Agrotechnical methods are largely similar to preventive ones in terms of targeting the reduction of the weed potato population. The most important is the surface tillage after harvesting the potatoes. Against the background of the increasing harmfulness of the weed, the understanding of the need to abandon plowing in order to leave all tubers in the upper soil layer, where they are destroyed by frost, quickly became established. In the context of the problem, the most effective are double row discs and tooth cultivators. Tubers left on the surface and partially damaged are susceptible to disease and decay, especially in warmer regions. Shallow placement stimulates friendly early germination and makes it more efficient to apply continuous herbicides or undercut cultivators before seeding subsequent crops.
One of the safest and most effective ways to manage the problem of weedy potatoes is manual weeding, but it can only be recommended for small areas, due to the high complexity of the process.
When growing row crops, trash potatoes can be controlled by re-cultivation (if you do not take into account the plants in the rows of crops). It is not difficult to completely eradicate weed potatoes with pruning crops in a fallow field. Four cultivations at a height of 10-15 cm (no more than 6-8 leaves) are enough to completely deplete the plant and prevent the formation of new tubers. However, a fallow field after potatoes is a wasteful land use option, it is recommended only in extremely difficult cases, for example, after a mild winter with a short crop rotation pattern in seed production.
Chemical control of potato weed suggests the widespread use of germination inhibitors, soil fumigants, continuous herbicides, soil and leaf selective preparations. Plant Growth Inhibitors with AI Maleic hydrazide (Phazor), when applied to green plants about two to three weeks after full flowering, is absorbed by the leaves and translocated into tubers, preventing their germination by 70-80%. Soil fumigants achieve the same goal no less effectively (but in the Russian Federation there are no approved drugs).
Herbicides are capable of completely destroying weed potatoes only in combination and with repeated use. The stock of nutrients in the mother tuber allows plants to recover from doses of herbicides that are lethal to other weeds. In addition, the late appearance of potatoes in many crops makes the successful application of herbicides unacceptable due to the fact that the crops are already at their optimal stage for treatment. Accordingly, if herbicides are applied to the main crop in a timely manner, then the consequences of treatment do not affect part of the weed potato plants: by this period they simply do not germinate. Therefore, soil herbicides applied pre-emergence are generally insufficient to control voluntary potatoes. Potatoes are resistant to most post-emergence herbicides.
It makes no contextual sense to use AI on other crops used in potato growing (metribuzin, rimsulfuron, etc.). At the same time, there is extensive foreign information that some active substances are effective in controlling weed potatoes if they are used at the beginning of tuberization (initiation of tubers). If the herbicide is used earlier (before the initiation of the tuber), the mother tuber can germinate again. The use of the herbicide later than at the start of tuberization cannot prevent the formation of daughter tubers.
Herbicides used on specific crops may also be allowed to work with others. Most tolerances mean “suppression,” not total control of weed potatoes. It is necessary to take into account information about the aftereffect of specific AI other crop rotation crops, in particular cultivated potatoes or vegetables.
In conclusion, it should be emphasized that potato as a weed is becoming a serious problem for cultivated potatoes and other crop rotation participants. Today it is difficult to prevent the spread of weed potatoes in crops; therefore, it is necessary to use the whole range of effective suppression and control measures.