the help of Dr. Phd. S. mushekwa.
School of Science and Technology
Department of Agriculture Science
RUSANGU UNIVERSITY, Monze, Southern Part of Zambia.
This paper covers the following;
(1) The various methods used in weed control under biotechnology
How effective the method are?
(3) Shortfalls or failures of using biotechnology?
The various methods used in weed control;
Biotechnology involves new methods of weed control system to try to control and manage weeds that have now become resistance to chemicals and herbicides. The first method under biotechnology control is known as;
1 GENETIC CONTROL
Genetic control method is a way of introducing specific genetic controls that could change and ultimately eliminate the population of weeds. It involves the use of genetic modification techniques to change the sex ratio- the ratio of females to males- in various weed populations for example waterhemp, and palmer amaranth. Theoletically with the right genetic manipulation, every mating would result in only male offspring. If this occurred cover multiple generations, every individual in these populations would eventually be male. Reproduction would cease and population would crash. The concept is similar to a controversial strategy being tested for mosquito control. In that case when genetically modified males are released and mate with normal females, the offspring die before maturity. The strategy could reduce the incidence of zika, malaria, and other mosquito born diseases. A similar strategy in waterhemp and palmer amaranth could avoid major crop losses as the herbicide resistant weeds become less and less responsive to existing control strategies.
2 USE OF TRANSGENIC CROPS
Genetically modified crops are plants used in agriculture, the DNA of which has been modified using genetic engineering methods. In most cases, the aim is to introduce a new trait to the plant which does not occure naturally in the species. Examples in food crops include;.
This technique involves the transfer of genes that will modify the crops and enable to suppress weeds and become better competitors against weeds For example early shooting emergency, rapid early growth, fast canopy closure. When this happens crops are able to become better competitors for various crop growth requirements that is, nutrients, water, sunlight and enough room space will be created for crops. One of the most important aspect is that weeds will die in the process and therefore crops will grow without any interference.
crops that are resistant to weeds.
The transfer of allelopathic chemicals to nonallelopathic crops. These crops with allelopathic properties give off substances that are toxic to other plants. These toxin inhabit growth or keep seeds from germinating. These substances either vaporize and settle to earth or are washed there by rains. They can all be released through the roots or as the allelopathi plant decomposes. Plants and seeds susceptible to the compounds will be stunted, will fail to germinate, and in extreme cases, wither and die. Here are the examples of plants that carry allelopathic properties; asters to control ragweed, barley, wheat and sorghum to control pigweed, foxtail and purslane; cucumber to control mustard and Bermuda grass.
that Contribute to weediness.
A plants perennial growth habit, seed dormancy and allelopathy. There are three physiological mechanisms for natural or induced tolerance or resistance to an herbicide.
 Reduced sensitivity at a molecular site of action.
 Increased metabolic degradation.
 Avoidance of uptake or sequestration [hiding] after uptake.
Each of these has potential use in development of resistance in crops.
TYPES OF MODIFICATIONS
Transgenic plants have genes inserted into them that are derived from another species. The inserted genes can come from species within the same kingdom or between kingdoms for example, bacteria to plants. In many cases the inserted DNA has to be modified slightly in order to correctly and efficiently express in the host organism. Transgenic plants are used to express protein like and carry toxins from herbicide resistant genes.
Cisgenic plants are made using genes found within the same species or a closely related one, where conversional plant breeding can occur. Some breeders and scientists argue that cisgenic modification is useful for plants that difficult to crossbreed by convertional means such as potatoes, and that plant in the cisgenic category should not require the same regulatory scruting as transgenics.
These plants are genetically modified and can also be developed using gene knockdown or gene knockout to alter the genetic makeup of a plant without incorporating genes from other plants.
3 USE OF COVER CROPS
These are plants planted primarily to manage weeds. Thick cover crops stands often compete well with weds during the cover crop growth period, and can prevent most germinated weed seeds from completing their life cycle and reproducing. If the cover crop is left on the surface rather than incorporated into the soil as a green manure after its growth is terminated, it can form a nearly impenetrable mat. This drastically reduces light transmittance to weed seeds, which in many cases reduce seed germination rates. They also prevent soil, improve soil fertility, soil quality, water, pests, diseases, and biodiversity on a farm. These cover crops will
self-destruct after they have suppressed weeds but before they begin to competing with the crops.
How effective the methods are
 The technology has the potential to shift herbicide development away from initial screening for activity and environmental acceptability to the letter occurring first. Resistance to herbicides that environmentally favourable but lack adequate selectivity in any crops or in a major crop so their development will be profitable could be engineered and the hrbicides use fullness could be expanded greatly.
 Extended life cycle.
GMO crops last longer. This decreases the amount of wasted crops and foods. The first genetically modified crop approved for sale in the U.S. was the Flavrsavr tomato, which had a longer shelf life.
 Improved photosynthesis
Plants use non photochemical quenching to protect them from excessive amounts of sunlight. Plants can switch on the quenching mechanism almost instantaneously but it takes longer for it to switch again. During the time that it is switched off, the amount of energy that is wasted increases. A genetic modification in three genes allows to correct this. Another improvement that can be made on the photosynthesis process with c3 pathway plants is on photorespiration. By inserting the c4 pathway into c3 plants, production may increase by as much as 50 per cent for cereal crops such as rice.
 Improved nutritional value [edible oils] Some GM soybeans offer improved oil profles for processing. Camelina sativa has been modified to produce plants that accumulate high levels of oils similar to fish oil.
 Vitamin enrichment
Golden rice, developed by the international research institute, provides greater amount of vitamin A targeted at reducing vitamin A deficiency. As of January 2016 golden rice has not been grown by commercially in any country.
 Toxin reduction
A genetically modified cassava under development offers lower cyanogen glucosides and enhanced protein and other nutrients called biocassava.
 Biotechnology methods has made crops better competitors with weeds through improving competitive traits or making the crops more allelopathic.
 Biotechnology methods enable herbicide resistance crops providing solutions to intractable weed problems in some crops. For example glyphosate resistace has been created in several crops. It is an environmentally favourable herbicide, and therefore it is better to use it in lieu of other herbicides that are not environmentally favourable.
The shortfalls or failures of using biotechnology
 Transfer of genes from one population to another may lead to unwanted effects for weed management and the environment. Over flow may enable the resistant gene to move between HR and non HR varieties and thus pollute a crop which is considered GM free or HR genes may be stacked from years of pollination of HRCs, which may result in problems for the farmer in controlling volunteer crops in the field.
 Resistant gene flow to sexually compatible plants. This is acknowledged as a potential risk of introducing any genetically engineered variety. The risk is transfer of desired herbicide from the the crop to a weed where undesired resistance persist by a natural selection. The risk may be especially high where the crop and weed are closely related and can inetrbreed.
 Cost of food production and food cost to the consumer will rise.
 Biotechnology methods will only favour large farms and lead to loss of small scale farmers because loss of the ability to save seed may drive these farmers out of farming.
 Herbicide resistance among weeds may become more widespread because of continued use of an herbicide to which a crop is resistant.
 Biotechnology approaches are expensive to execute, takes considerably long time to succeed and may to increased chemical loads in the environment.
 Genetic traits that have a higher potential of enabling truly sustainable agricultural systems have not been developed and this will cause this new technology to fail.
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