IN this era, mechanised agriculture is being promoted as a means to enhance sustainable food production and poverty alleviation in many African countries including Zambia.
In some African countries and Zambia in particular, some farmers now use tractors, mounted boom sprayers and manually operated knapsack sprayer to spray chemicals such as herbicides for the control of weeds on farms in agricultural production.
In Zambia, it is quite obvious that the use of herbicides is likely to increase beyond levels the country is at now and this give yield to the aspect of herbicide resistance.
In helping farmers understand this critical aspect of crop production, we will first try to define herbicide, weeds and herbicides resistance.
We will also look at the economic importance of the herbicides before exploring the causes of herbicide resistance then conclude by highlighting practices of managing herbicide resistance.
Herbicides can be defined as crop-protecting chemicals used to kill weedy plants or interrupt normal plant growth while providing a convenient, economical, and effective way to help manage weeds.
The application of herbicides for instance, is done through the use of boom sprayers which are mounted on agricultural equipment to control weeds in prospective farm estates.
With emphasis to diversify in agriculture to livestock, poultry and fish production, pasture and commercial crop production like soya beans, wheat, maize and cereals is still likely to increase for the purpose of stock feed production.
This increase will also result in the demand on the use of herbicides which makes it a fact that the dream of agriculture diversification will be actualised.
One may not undermine the research that’s going on in agriculture which is ensuring adequate preparations for the challenges that comes with diversification.
Furthermore, in the world where the use of new technologies and use of herbicide is taking lead in weed management , it is ideal to put control management measures of herbicide resistance mostly for small scale farmers.
In some cases herbicide resistance does not come with costs, however, the farmers’ ignorance about certain plant weeds having herbicide resistance to certain herbicides lead to high costs.
It’s possible to be purchasing wrong herbicides for a wrong weed population.
Resistance may happen because of not considering the warning on the use of the  particular herbicide for certain weeds and lack of knowledge about the class or group codes of the herbicides.
In addition, exclusively use of a particular herbicide repeatedly in the same field for many years can develop the resistance.
According to University of California, division of agriculture and natural resources publication 8012 on herbicide resistance, definitions and management strategies, herbicide resistance was first reported in the 1970s.
Herbicides classes 16 in number were reported to have  developed  resistance to biotypes of 172 weed species; however, there has not been official statement of herbicide resistance in Zambia.
According to the journal, resistance in plants was not as early as in insects and fungus due to the life cycle fundamental differences and genetics.
Probably the current scenario in Zambia where cases of herbicides resistance are not common could be attributed to the same.
Delay in the appearance of resistance weeds is generally attributed to slower generation time of plants, incomplete selection pressure from most herbicides, soil seed reserves and plasticity of weedy plants, all of which keep susceptible individuals in a population and thus delay the evolution of resistance.
In defining  weed plants, we can say weeds are plants whose economic value has not been discovered, or extremely noxious, useless or poisonous plants growing where something else must grow or nothing must grow, out of place, growing voluntarily where not needed, and has potential for causing harm than good.
It is good to note that in as much as herbicides are poisonous; they are not harmful to humans and animals when used according to instructions.
On my way to the Copperbelt Province from Lusaka last week, I was taking a serious glance on the commercial crops grown on farms on the Great North Road.
It is amazing to see how best use of herbicides could eradicate existence of weed foliage in soya beans fields, for instance.
Herbicides plays a significant role in the suppression of weeds in crop fields and, therefore, attacks huge share in crop management budget to lessen extra costs that result from using wrong herbicides in achieving higher yields and increases farm incomes.
Costs incurred as a result of using herbicides depend on different factors which include using non calibrated equipment’s, wrong walk speed  during spraying , using  wrong measurement rates, using expired products, not spraying at the recommended weed size, applying when there is no moisture for some herbicides.
Moreover, wrong use of herbicides reduces effectiveness of herbicides resulting into the weed plants surviving even after being exposed to different types of herbicides.
Herbicide resistance can be defined as  the inherited ability of a weed plant to survive and reproduce after exposure to a dose of herbicide that would certainly be deadly or lethal to that weed type in plants occurring naturally, or through genetic engineering, or random and infrequent mutations.
This can be noted in fields where a population of individual weed dominates other weed species.
In this vein, information on herbicide resistance warning is clearly stated in some herbicide labels by the manufacturers of the herbicides to alert the use of those herbicides of chances for any weed population having individual weed plants that are naturally resistance to the herbicide.
Farmers need to know an herbicide which is able to kill a particular weed species, and know exactly which herbicide to purchase and use to kill the identified weed type.
The assessments on the performance of the herbicide to the weed in which the herbicide is lethal can be done and monitored to ascertain the possibility of weeds showing  herbicide resistance to particular classes of herbicides.
It’s possible to perceive and assume weed plants have developed herbicide resistance.
It is therefore important to use a correct herbicide in line with what is recommended by the manufacturer and then conclude that, a particular weed has developed herbicide resistance to those classes of herbicides.
There was no evidence that demonstrated herbicide-induced mutation, which is basically a process in which the genetics materials of a plant structure passed on to seed, results in change of physical characteristics and response to herbicides in particular.
Look out for part two of this article next week.
For comment: +260954206601 or e-mail: dansinkamba@yahoo.com.
The Author is an agricultural consultant at Malangwa Agricultural Innovative Services, with 18 years experience, as farm manager, extension officer and sales agronomist.