- Heavy weed infestation after rapeseed harvest is associated with, among others, with the emergence of self-sowing plants.
- Post-harvest weed control prevents, among other things: water losses.
Weeds need to be given time after harvesting
If we plan to apply a non-selective herbicide (glyphosate) after harvesting rapeseed, there is some time before the application. Remember not to do any cultivation after harvest. The weeds themselves should grow back appropriately, i.e. reach a minimum height. And so in the case of proper couch grass – it should be at least 10 cm, and the remaining monocots should be at least 5 cm. In turn, dicotyledonous weeds (including rapeseed that emerged after harvest) must have two true leaves.
Glyphosate is absorbed only by green parts of plants (stems, leaves, shoots, but also non-woody bark). From the place of collection, it is transported in the plant, also to underground parts. The plant dies gradually, and the full effect is achieved after about 3 weeks (sometimes earlier, but the speed of action depends not only on the dose, but also on weather conditions). The first discolorations on the plant will be visible after about a week.
When applying glyphosate, it is very important to use an additional preparation supporting this substance. Sometimes the choice falls on, for example, ammonium sulfate, but a better solution may be to administer an adjuvant with glyphosate.
The appropriate dose of water is equally important. In the case of glyphosate, the spray liquid flow rate is 100 – 150 l/ha. In this way, we obtain a higher concentration of the applied herbicide.
If perennial weeds appear on the plantation, we use higher doses.
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This year's rapeseed harvest is expected to be lower than last year
Mechanical protection has its advantages but also disadvantages
There is also mechanical protection. It has its advantages, but also has some problems. First of all, tillage has to be done several times, and the minimum is usually two passes, e.g. with a disc harrow. Secondly, they require quite a lot of time, if we are talking about two or three runs. Additionally, frequent trips contribute to the soil drying out. When deciding on mechanical weed control, you also need to demonstrate knowledge of the weed seed bank. If there is couch grass in the plantation, the best solution is not to use e.g. a disc disc, which will cut the rhizomes and contribute to compensating for the couch grass weed infestation.
However, which option we choose after the harvest is a highly individual matter. There are supporters of treating rapeseed stubble with glyphosate – this treatment is generally supported by the speed of action and a much smaller number of passes over the stubble.
Please note that heavy weed infestation may result from the emergence of self-seeded rapeseed plants. With a yield of 3 t/ha and harvest losses of only 1%, we have on average 30 kg of rapeseed seeds sown on each hectare. This is a very large plant density – after all, the standards during sowing are much lower and if converted into kilograms, it is usually in the range of 1.5 – 4 kg/ha, which gives us a plant density of 30 – 70 plants per meter. Here, the plant density can be several times higher on average, which means significant water losses from the soil.
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How much does a disc stubble cultivator cost? We are checking 
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Advantages and disadvantages of catch crops
