By Kudakwashe Gwabanayi
If one is to spend just five minutes in an agricultural chemicals shop these days, chances are very high that two or three farmers would have walked in and asked for herbicides, or anything that can do away with weeds.
Weeds have really become a menace for this farming generation.
Wikipedia defines a weed as a plant considered undesirable in a particular situation, “a plant in the wrong place”.
Examples commonly cited are plants unwanted in human-controlled settings, such as farm fields, gardens, lawns and parks.
In the same way, volunteer crops (plants) are regarded as weeds in a subsequent crop.
This means that maize in a sugar bean field is a weed.
Because of the rainy season, where theare is uncontrolled fall of water in the fields, undesired plants, particularly annual grsses are growing where they are not desired by farmers.
Whilst during the dry season farmers may use drip irrigation systems that water only the desired crop to choke weeds, or mulching to cover areas where weeds would grow so that they do not get sunlight, these methods are inapplicable during the rainy season.
It therefore means one can either remove weeds by using chemicals or do it mechanically, that is using a hoe or cultivator.
Now, because we are using more fertilisers — and of different types — the grass is quickly outgrowing the wanted crop because fertilisers do not select which plants to feed.
Lack of manual labour and in most cases poor planning, the farmer is left with no option but to rush to get herbicides.
Whilst there are many post emergency chemicals that can deal with weeds, the anxiety that follows the purchase and subsequent use is really not worth it for the farmer.
At times it rains heavily just after applying the herbicide and it is washed away and you may be forced to re-apply it.
In other instances, it does not rain at all, yet some herbicides require that the grass or the weeds are relatively wet before you apply them.
Add to this, the salesperson in the shop does not really tell you the side effects of the weeds, nor do they tell you that after applying certain herbicides in maize for example, you cannot plant potatoes or any tubers that grow underground.
Some maize herbicides are incompatible with other crops.
They will force you to plant maize only in that field for at least two years as the residual effects die away.
Usually, farmers find out the hard way – after planting and realising that the germination is below 30% they realise that it’s the after effects of the herbicides that affected germination.
While this may sound like a discouragement to use herbicides, it does not by any measure mean that this writer is against the new regime of chemicals that are available.
If anything, the use of pre-emergents herbicides is encouraged.
Then again, this goes back to the issue of proper planning as earlier mentioned.
Most farmers who do more than 600 hectares of open field farming apply their herbicides 30 days or more before planting whatever they want to plant.
But those who do small portions like 5 ha are encouraged to do mechanical weeding.
It is absolute and final.
When we are talking about mechanical weeding we mean using hoes or ox-drawn cultivars to weed off herbs.
The cost is usually the same; hiring labour and using post-emergent chemicals
You only need to do it twice: four weeks after germination and at the eighth week.
In fact, even farmers with huge portions of cultivated land use tractor-drawn cultivators to get rid of weeds.
It is the best way to do so.
Petruzzello (1984) describes a cultivator as a farm implement or machine designed to stir the soil around a crop as it matures to promote growth and destroy weeds.
Horse-drawn cultivators were introduced in the mid-19th century.
By 1870 a farmer with two horses could cultivate as much as 6 ha (15 acres) a day with a machine whose shovels (blades) straddled the crop rows.
In the 20th century, with tractor power substituting horses, the number of rows a single machine could cultivate grew to equal the capacity of multiple-row planters.
Accordingly, cultivators and weeders have evolved with time and currently there are many types of them.
Spring-tooth weeders have light spring teeth that flick out shallow-rooted weeds without injuring growing plants and can therefore be operated directly over planted rows in an early stage, ridding the field of many weeds as they emerge.
Rod weeders are used for weed control in open unplanted fields; their working element is a square-section rod that revolves a few inches below the soil surface.
Field cultivators, essentially light ploughs, are equipped with spring teeth, shovels, or sweeps.
It is against this background that farmers are reminded that while they are going with the flow of the green revolution it is important that they look back at some ways that have been effective in dealing with their most common problems.
It can be argued that once it starts raining it never gives you a chance to manually weed and hence the reason why most farmers prefer chemical weeding but at the earliest chance and opportunity going the traditional route may yield better results.
In some instances, farmers who use chemicals to weed their fields end up losing their own crops because they would have bought non-selective herbicides unknowingly because there are selective and non-selective herbicides.
Non-selective herbicides are typically more powerful, but they usually kill any plants they come into contact with, including grass and other blooms the farmer may want to keep safe.
There are also contact and non-contact herbicides.
In fact shopkeepers do not have time to explain to the farmers how to use the chemicals.
In addition farmers will buy the cheapest chemicals on the shelf without much consideration on the side effects of the chemicals.
Because of the huge demand for the herbicides during the rainy season shops run out of them quickly, opening a gap for criminals and unscrupulous dealers who then sell fake chemicals.
Some of the herbicides are actually diluted by the sellers so that they get huge volumes.
There are also chemicals that are harmful to animals like chicken, goats and cattle that are kept at the farm so buying them would disturb the ecosystem.
There are so many advantages such as that chemicals save on time and their disadvantages as already outlined above but the bottom line is mechanical weeding will give the farmer a better result than using chemicals especially if the herbicide is a post -emergent one.
By way of definition, post-emergent herbicides work on weeds that have already grown.
They utilise a mixture of chemicals to kill the weed and ensure that it does not grow back.
There are multiple types of post-emergent herbicides available to help eradicate different kinds of weeds in various environments.
On the other hand, pre-emergent weed killers are used before you see the weeds to prevent them from showing up.
This doesn’t mean the chemicals interfere with germination but rather they stop the formation of new root cells in baby weed plants.
Without roots, the seedlings cannot continue to feed and grow and they just die back.
This whole process happens at the soil level under the blades and thatch of the grass so you don’t ever have to see the sprouted weeds.
Timing, weather and the type of weeds that are problematic for the farmer will dictate the exact formula and application for using pre-emergents.
The chemicals in pre-emergent weed killers are not effective on vegetative buds that sprout from existing roots or rhizomes.
They also cannot be used on a prepared grass seedbed because their root stunting action in young plants will also affect sprouting grass.
What is clear about these herbicides is that they are scientific and require a certain level of intellect and knowledge to use at any particular time.
- Gwabanayi is a practising journalist and a farmer in his own right. — 0772 865 703 or email@example.com