Experimenting with herbicide

Most people that know me in real life know that I am an environmentalist even before taking up a career as a botanist, specializing in ecology. I really cannot stand people destroying/degrading the environment through various activities. I love nature and will do everything within my power to conserve nature and the natural environment as much as possible.

^{Front of my apartment.}

I live in a rented apartment whose surroundings is not tiled nor cemented in any form, so I am reduced to manually clearing the surrounding bush at regular intervals, especially during rainy seasons. I have been doing that for more than a year now. Almost everyone that has seen me toiling and sweating while rigorously moving the cutlass to and fro in the process of clearing the bush questioned my judgement of opting for manual labouring when I can just get herbicide and spray the shit out of the troublesome weeds.

For clarity sake, the herbicide is a type of pesticide that is specifically used to kill unwanted plants in form of weeds. Herbicide was derived from two words; 'herb' which mean plants and 'cide' which means to kill. There are wide varieties of herbicides based on how they function, their chemical constituents and the group of plants they are effective on.

Some herbicides operate by inhibiting the synthesis of acetyl CoA carboxylase , a substance that is key in the metabolic process of lipid synthesis within the plant's body. Lipid as a biomolecule is an important component of the plant's cell membrane which acts as a selectively permeable interface in the movement of substances in and out of the cell. However, it is pertinent to note that only acetyl CoA carboxylase of grasses are grass and monocotyledonous plant species are sensitive to this group of herbicide, that of the dicotyledonous plants are immune to it.

Apart from disruption to the process of cell membrane synthesis, some herbicides operate by indirectly inhibiting the synthesis of branched-chain amino acids such as valine, leucine and isoleucine. The process is carried out through the inhibition of acetolactase synthase enzyme which happens to be the first step in the synthesis of the named amino acids. Hence, the synthesis of deoxyribonucleic acids within the various cells is gradually stalled due to the unavailability of the branched-chain amino acids. Unlike the herbicides that inhibit acetyl CoA carboxylase which has effect only on monocotyledonous plant species, this group of herbicides exert their effects both on monocots and dicots. In addition, this group of herbicides is considered one of the safest to use since the acetolactase synthase pathway only exist in plants and not in animals.

Other group of herbicides include but not limited to those that act as inhibitors of photosystem I and II thereby disrupting the process of electron transfer within the cells of the plant, inhibitors of enolpyruvlshikimate-3-phosphate synthase enzyme which is a precursor in the synthesis of tryptophan, phenylalanine and tyrosine and inhibitors of 4-hydroxyphenypyruvate dioxygenase which is an enzyme involved in the metabolism of tyrosine.

Not that I do not know about the use of herbicides which seems to be an easier, more efficient and time-saving option for me instead of the mechanical methods I have been using all these while. Like I said earlier, the ecological/environmental impacts of the various chemicals that make up the varieties of herbicides in the market is the sole reason I have never opted to use it. Some of the impacts that have been deterring me include;

• Depending on the chemical formulation, some herbicides persist in the environment even after carrying out their intended functions. As such, they can become leached deep into the soil and enters the underground water tables, contaminating wells and municipal water system. Sometimes, the persistent herbicides get washed away into a nearby aquatic environment where they become poisonous to fishes and other aquatic organisms. In addition, these group of herbicides might not only kill weeds but also untargeted animals living in the same habitat.

• The use of herbicides can cause a shift in the diversity of plants and animal species within the habitat from broad herbicide-susceptible species to a narrow herbicide-resistant species due to the process of natural selection as postulated by Darwin. According to the theory of natural selection, repeated use of herbicides may cause the death of weak species and emergence and multiplication of the few strong species which become the dominant species over time. As such, the herbicides will cease being effective in the killing of the weed species and the total plant biodiversity would have been narrowed.

However, considering the fact that I hardly get time to mechanically remove the weeds around my apartment recently, I decided to try the herbicide option. I went to the nearby agrochemical merchant, a semi-illiterate man in his late 60s or early 70s by my estimate. I demanded to buy a herbicide but his reply got me a bit confused.

What type would you like? Rapid action or slow action?

From what I have learnt before-hand, I knew I would be needing a herbicide that would be effective in killing both grasses (monocots) and broad-leaf species (dicot). While some are differential, some are specific. This enables farmers to be able to select herbicide of their choice in cases of crop/weed mixture, the crops need to be spared while the weeds need to go. For example, in a maize field where the majority of the weeds are broad-leafed/dicots species, a herbicide that is specific for killing broad-leaf species would be preferred in order to keep the maize plant safe from the harmful effect of general herbicides. If the reverse is the case, a herbicide specific for killing monocots/grasses would be ideal. In a farm where a multi-cropping farming system is in practice, the farmer would have to compromise by either using mechanical means of removing the weeds or find a way to protect the crops from getting in contact with the herbicide.

Some herbicides just need to be in contact with the various plant organs in order to function. Through the organ, they penetrate into various tissues and cells and initiate their various modes of actions. The action of such herbicide is rapid and their effects are also as such. They are generally referred to as contact herbicides. On the other hand, some herbicides need to get to the soil where they are translocated through the roots to the system of various plants before initiating their mode of action. The effects of such herbicides last a while longer than that of their rapid action counterparts. They are generally called systemic herbicides.

^{Appearance of the herbicide}

Back to the response of the agrochemical merchant. I had to think of the best way to explain the exact herbicide I want. I told him I want something that is general (kills monocots and dicots), not poisonous to animals and something whose effects last a while in the environment (will take the weeds some time to grow back). I wanted a systemic herbicide that is generally safe for untargeted organisms in the environment.I also made up my mind never to use the herbicide repeatedly to avoid the ugly situation of a shift in species diversity as well as avoid the evolution of herbicide-resistant species by natural selection. To an extent, I had all my worries taken care of.

I bought the brand offered by the merchant along with a 16L sprayer and headed home. I took my time to read through the label on the herbicide container and to my surprise, there is no instruction as to how to mix (need I say the content is liquid?). I decided to google the brand but could not get the required information, so I took a gamble. I mixed two capfuls of the chemical and mix it with 16 litres of water, sprayed the weeds surrounding my apartment around 10:00 am and then waited in observation.

I am used to seeing the significant effects of herbicides on vegetations as short as the first day of application, especially if the herbicide has been applied early in the morning and it happened to be a sunny day. Towards the setting of the sun, I scrutinized the vegetation around my house for the effects of the herbicide but could not see any. The following day, I observed the same trend and I practically concluded that the percentage by volume of the herbicide used was too low for the spraying to have any effect.

Wait! Not so fast..

I had given up on the effectiveness of the initial spraying and already planning on carrying out another round of spraying with a higher concentration of the herbicide when at the end of the fourth day, I noticed a slight yellowness of some patches of the vegetation (or was it my eyes?). I really cannot say at this point that I got the concentration right. I am still in the process of observing, today being the 5th day and not much changes have been observed that is different from that of the fourth day (see the pic above).

Does systemic action means taking days before the effects start showing?

The observation continues.....

Thank you for reading.

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References

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^{herbicides
science daily}

^{All images were taking using my samsung S4 mobile phone}

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