- Humidity during treatment is crucial for pre-emergence herbicide protection, but it is not the only factor that determines the success of the application.
- What times of day are best for soil protection?
Although soil treatments do not have a rigid time frame in terms of time of day, the conditions in which we apply herbicides immediately after sowing are crucial to the effectiveness of the treatment. Application in the middle of the day will not necessarily be a good solution in every case. Similarly, before heavy rainfall.
The procedure is performed with good hydration.
The most important factor in the case of soil-applied crops is humidity. In fact, it is this parameter that determines the feasibility of implementing a pre-emergence herbicide. If the soil is dry, we give up on soil-applied crops. Even sowing rapeseed in such conditions is a difficult challenge, because emergence may be uneven. But the procedure itself is also a big risk due to the certain probability that it will end in failure.
The applied herbicide (actually the active substance) must be absorbed by the soil profile and then transported to the place where the weeds germinate. If there is little moisture in the soil, the transport of the herbicide is disrupted – instead of reaching the place of action, it concentrates at the place of application. Yes, some of the active substance will reach the driving weed seeds, although in many cases it will not be a dose that will be able to combat them. Therefore, if despite difficult conditions, we want to perform a soil treatment, it is definitely better to do such an application in the early morning hours, with heavy dew. An evening application will also be a good solution, i.e. when the dew is already appearing. Then the active substance is not exposed to such a large melt to strong sunlight and high temperature. Generally, it is always worth using soil treatments in conditions of a high dew point.
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Do heavy rains improve the humidity situation?
When soil-applied, we also avoid high temperatures.
High temperatures that occur during the day will also not be conducive to protection. Here, let us note that even with good soil moisture, the herbicidal effect may be poor if the treatment is performed at high temperatures. The active substance must be bound to the soil. And of course, moisture is needed for good binding. But also the right temperature. If the mercury levels are too high, some of the active substance may not reach the ground at all. In turn, the part of the herbicide that has not evaporated as a result of high temperature may be insufficient, because the working fluid will evaporate from the soil due to the temperature and high sunlight.
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Heavy rains have crusted the soil, possible overseeding of rapeseed
Do not perform treatments before heavy rains
We have already written about soil crusting in the context of the risk of stopping germination. However, heavy rainfall is also dangerous for herbicide protection. While the herbicide applied in drought conditions cannot be activated, after rainfall, transport in the soil improves, and therefore the applied active substance is transferred to the place of action. But this happens in the case of calm rainfall. If heavy rain occurs after the treatment, there is a certain risk of moving the active substances too deep into the soil profile. Then, there is also excessive concentration of the herbicide in certain points of the field, in such a situation we will often observe a strong phytotoxic effect. In one place there will be too much active substance, while from other places it will be washed away. If we observe warnings of heavy rains in the forecast, it is worth waiting for this moment. It is true that we do not have much time for soil protection – in many cases we are talking about three days after sowing. So if we still have a time buffer, let's wait until the potential heavy rains have passed. These are of course not good for rapeseed that has just been sown, but in the event of the need to reseed the plantation, the task will be easier, and we will also avoid the need for repeated comprehensive protection. It is better to perform the procedure after rain, on moist soil. Nevertheless, "calm" rainfall after soil application is most advisable.
During the day, soil treatment only at appropriate temperatures
If the moisture is adequate and the daytime temperatures do not exceed the maximum for the given herbicides (information should be found on the labels), then the treatment can be performed during the day. It is good that there is no strong sunlight during it. However, let us pay attention to the complex action of the active substances. For example, when applying a mixture of clomazone with pethoxamide, the maximum temperature is 20 C (25 C for pethoxamide and 20 C for clomazone). These are the maximum temperatures. If it is hot during the day, then only in the evening hours (or very early in the morning) will we be able to apply at optimal temperatures.
At night the temperature drops, so the active substances do not evaporate. In the morning, we have the best moisture. Both evening and early morning treatments will be the best solution in most cases. At the same time, the time of day itself, although important, is not decisive. Even in the evening hours, we should not perform a treatment using clomazone if the mercury readings still exceed the thermal maximums.
At the same time, regardless of weather conditions, it is worth adding a soil adjuvant to the treatment. This will improve the concentration of the agent at the site of action, bind the substance better with the soil, and also reduce the risk of herbicide washing out due to wind-blown rainfall (although it will not completely reduce such risk).
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