Effective protection and technology for growing rapeseed
The increase in rapeseed cultivation has led to the spread of economically impactful diseases such as phomosis, sclerotinia, alternaria, root rot, etc. Given that Ukraine's crop rotation is oversaturated with sunflower, and some fungal pathogens are common to sunflower and rapeseed, the problem of protecting crops from their negative impact is extremely relevant.
Statistics show that with an increase in rapeseed crops in the crop rotation of up to 10%, the harmfulness of diseases increases dramatically. Therefore, when planning a high crop yield, it is necessary to provide intensive fungicide and insecticide protection throughout the growing season.
Intense rains at the end of July 2018 provided a good incentive for sowing winter rape on large areas, even in the dry steppe zone. The powerful root system ensured rapid penetration into the deep soil horizons and winter rapeseed formed a powerful and favorable stem with sufficient sugar reserves for wintering.
It was important to prevent premature stem elongation in the fall, which could have been prevented by regulatory products with the active ingredients tebuconazole and protioconazole. Most farms, especially in the south, sprayed rapeseed crops with growth regulators up to 4 times, but this did not always bring the desired effect and the plants “stretched”. This was due to the extended period of active temperatures and the use of not always effective active ingredients in growth regulators.
In addition to stopping the growth point, a modern preparation should contribute to the formation of a powerful root system. If the root survives and the growth point is preserved, the plant will overwinter and the rapeseed will yield a high yield. However, not all preparations stimulate the growth of the root system, especially chlormequat chloride, which inhibits the growth of the aboveground and underground parts of the plant. Tebuconazole is characterized not by an outwardly imperceptible effect on the leaf mass, but by a significant thickening of the root neck and inhibition of the growth point. However, it is necessary to take into account the dose of the drug used for the phase of crop development. Saving on the quantity and quality of active substances can be fatal in maximizing the yield.
The low-frost winter of 2018-19 also contributed to the overwintering of crop plants (even overgrown ones), but pests and diseases that accumulated in the fall on rapeseed crops remained a problem.
Given that rapeseed requires a significant amount of basic nutrients N 60-65 P 35-40 K 60-80 to form 1 ton of grain, it is necessary to take into account the need for S 20-30, Mg 10-12, B 0.1-0.15, Mn 0.4-0.6 when planning a high yield. Only with a balanced comprehensive provision of all nutrients winter rape will maximize its genetic yield potential. Mineral nutrition should be provided in full before the start of intensive crop growth in the spring, as nitrogen deficiency (for example) in the branching phase can affect the yield shortfall by up to 30%. Usually, ammonium nitrate, UAN, ammonium sulfate, urea are effective for spring nitrogen fertilization, which are applied in several stages on thawed soil and at the beginning of crop regrowth.
After the spring vegetation resumes and nitrogen fertilization, rapeseed grows vegetative mass very quickly. An important factor is to regulate the growth of stem mass in order to form simultaneous flowering. This allows for effective control of pests and diseases during the growing season and ensures the simultaneous maturation of all beans in different tiers, which reduces physical yield losses during harvesting. This can be achieved by applying additional chemical plant growth regulators at the beginning of the spring growing season.
The use of tebuconazole and prothioconazole in spring has an advantage over difeconazole, mepiquat chloride, methconazole and chlormequat chloride and provides:
- stimulation of intensive lateral branching (branches of the first and second order)
- strong development of the root system
- control of phomosis and prevention of sclerotinia, alternaria, powdery mildew, cylindersporium
- Increased resistance to lodging and stem breakage.
It is important that these active substances slow down the growth of the central stem until the side shoots grow — simultaneously blooms and fades
We pay special attention to the use of insecticides with fungicidal treatments, as most cryptic bugs, cruciferous fleas, rapeseed borer, weevils and leaf-eating pests are highly active at the beginning of the growing season, and control of these pests prevents mechanical damage to rapeseed tissues. These mechanical damages are responsible for 90% of fungal infections of rapeseed plants.
Currently, the most harmful pathogen is phomosis, which can cause yield losses of 30-50%. Plants affected in the fall often die during wintering or in early spring. Weakened plants are more severely affected during drought, and at the time of harvesting they dry out and have small, unfilled seeds. The root collar breaks and the plants may lie down.
Sclerotinia is one of the main diseases that reduces rapeseed yields by 30-40%. The development of this disease depends mainly on weather conditions, but an important factor is the intensity of the technology (the higher the dose of nitrogen, the higher the risk of the disease), damage to plant stems by pests and plant density (creating a microclimate with high humidity). Thus, the higher the planned yield of rapeseed, the higher the threat of sclerotinia development.
The degree of infection with the disease in previous years is important, as sclerotia can persist in the soil for up to 7-10 years. In the case of returning rapeseed to its original place in the crop rotation after 4-5 years (typical for western Ukraine), the disease is provoked. The provocation is possible due to cracks caused by spring frosts - when intensive regrowth occurs and the temperature drops sharply at night - the parenchymal tissue cracks and infection passes through the cracks.
Genetic resistance to the disease is rather conditional - in the presence of physical damage, infection occurs and damage is noticeable. Most of the registered rapeseed hybrids are medium and highly susceptible to sclerotinia (BSA, Stand, 2016); semi-dwarfs are even less resistant to sclerotinia, which is due to the short flight distance of the spores compared to tall hybrids (Bauernblatt, 11, 2015).
The optimal phase of sclerotinia control is mid-flowering, i.e. more than half of the flowers bloom on the central shoot, the first beans begin to form and flowers on the side shoots bloom. As a rule, one fungicidal treatment with a complex of active substances in the middle of flowering is enough (combined with an insecticide against rapeseed mosquitoes and seed borers - registered for use in bees - thiacloprid) to effectively control sclerotinia and Alternaria. Delayed treatment reduces the effectiveness against sclerotinia and is mainly aimed at alternaria.
The active ingredient thiacloprid is also effective in controlling the larvae that are in the bean. Fluapiram (from the carboxamide group) and a new triazole, protioconazole, are also effective. It is important that the beans remain disease-free until maturity, which reduces the risk of cracking and yield losses from shattering.
The use of a mixture of humates and trace elements (boron, magnesium, manganese) is extremely effective, especially in early spring foliar feeding - it is an additional stimulus for plants to grow intensively, form generative organs, stimulate chloroplast activity, and humic and fulvic acids play the role of antistressants after nighttime temperature drops and after herbicide treatment.
Protection against diseases and pests is only one of the levers to obtain a high quality rapeseed crop - all elements of the technology must be followed. Therefore, if a producer's main goal is to obtain a consistently high crop yield, it is impossible to save on technology and neglect the timing of the necessary treatments with protective agents and mineral fertilizers.
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