- How does phytotoxicity manifest itself after the use of clomazone?
- Can discoloration indicate potential growing problems?
What factors contribute to phytotoxicity after clomazone?
Discoloration after clomazone is a fairly common phenomenon. This is also due to the scale of its use. While metazachlor or pethoxamid are often used interchangeably in technologies, clomazone is the most popular component of soil technologies. Hence, characteristic discoloration after its use is most often noticed on plantations. However, it does not have to appear at all. However, everything depends on the applied dose and soil. In the case of phytoxicity after the use of clomazone, we will observe leaf bleaching, it always starts from the edges of the leaf blade. If the bleaching is significant, the entire leaf may take on a characteristic white (sometimes cream) color.
When is the risk of clomazone phytotoxicity greatest? First of all, when all of the following conditions are met:
- high dose of active substance;
- rainfall after treatment, especially heavy rainfall;
- light soil;
- omission of adjuvants in the procedure.
If all of the above factors occur, we can be sure that phytotoxicity will occur. We are seeing it now in the southern regions, where heavy rainfall occurred at the end of last week (in some parts of the country, it also occurred a few days after sowing). However, it is not the case that the above-mentioned factors necessarily occur together. Their simultaneous occurrence, however, increases the probability of phytotoxicity.
The discoloration itself did not have to be observed immediately after emergence. Especially if there was no rainfall after the herbicide treatment. It may be that phytotoxicity is observed only after 2-3 weeks from emergence. It all depends on how quickly rainfall occurs. Nevertheless, chloromaozn is taken up during germination and emergence. Therefore, in the absence of rainfall at this very moment, the chance of phytotoxicity occurring is significantly reduced. If we observe this phenomenon at a certain time interval from emergence, it is rather on plants that emerged slightly later (or generally started the germination process with a delay).
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The most dangerous uncontrolled movement of substances
The greatest scale of discoloration will concern places where the active substance has accumulated (so-called headlands, headlands, wedges).
If no adjuvant was used, precipitation even a dozen or so days after sowing could still move the active substance in an uncontrolled manner to other places, sometimes additionally leading to a large concentration in one point. Then it may happen that in one place we have a multiple of the permissible dose.
Meanwhile, it is the dose that decides how dangerous phytotoxicity will be to rapeseed. Discoloration alone does not indicate that phytotoxicity will affect yield. Generally, there are no reports of chloromaozin reducing the yield potential of rapeseed due to such an undesirable effect. The discoloration will disappear – depending on the scale on which it appeared on the plants – within a dozen or so days, sometimes within a few weeks (the higher the dynamics of plant development, the faster they will cope with phytotoxicity). If it is cool, we can observe slight discoloration for up to 4-5 weeks.
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Clomazone dangerous in high dose
Some studies indicate that a threefold dose of clomazone can be destructive for rapeseed. Destructive, meaning that it can cause the plants to die. Following this line of thinking – discoloration is not dangerous if there has not been a large accumulation of clomazone. Using label doses of this substance, there is no risk of damaging rapeseed. However, phytotoxic phenomena can be dangerous in places where the active substance has reached a much larger amount than the permissible dose, e.g. in valleys as a result of runoff. Generally, however, there is no indication that phytotoxicity as a result of clomazone has a negative impact on yield. However, the potential harmful effects of phytotoxicity cannot be completely discounted. This phenomenon can be dangerous in the case of high intensity, i.e. large concentration on a given unit of crop area, and at the same time unfavorable weather conditions (drought, low temperatures). Then the processes inside the plant are disrupted, and they are additionally exposed to pests, which also weaken the plant.