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Home / Smart Harvest

Step by step guide on disease, weeds and pest control

Sodom apple weed. [Olivia Murithi, Standard]

Any seasoned farmer knows that crop interferences brought about by plant pests, diseases and weeds can wipe out their hard work and cause significant crop loss if not 100 per cent loss.

The advancement in agriculture over the past century has brought about new cases of transboundary organisms such as pests, disease agents or weeds that are novel and cost farmers heavy crop losses.

The agrarian revolution highly advocated for the controlled growth of crops in monoculture where environmental biodiversity is lost leading to lower resiliency of the cropping system.

The resultant conventional agriculture was a system that has a great potential for food security but easily threatened by invasions of harmful species.

Africa and Kenya in particular, has had our fair share of these new crop pests, diseases and weeds over the past two or three decades. This calls for a robust crop protection strategy.

But what is crop protection?

Crop protection is defined as science and practice of managing plant diseases, weeds and pests that cause damage to the crops. Crop pests include vertebrae (birds, rats, moles, monkeys, elephants) and invertebrates led by the insect group.

Invasive alien species

According to the Convention on Biological Diversity, invasive alien species include animals, plants, fungi and microbes introduced accidentally or deliberately outside their natural habitats or countries of origin.

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For a species to become invasive, it must successfully out-compete native organisms, spread through its new environment, increase in population density and harm ecosystems in its introduced range.

Studies by Kenya Plant Health Inspectorate Service (Kephis) show that Kenya has been invaded by 34 species - eleven arthropods, 10 microorganisms, nine plant species and four vertebrates. Some of the invasive species introduced in Kenya include: weeds like Striga weed (Striga hermonthica), Devils hair (Cuscuta campestris) a parasitic weed with great economic importance in cash crops like tea, pests like Tuta absoluta, fall armyworm, locusts and diseases such as Maize Lethal Necrosis Disease and tomato spotted wilt virus.

They are introduced into the country via boundary towns like Busia, Namanga, Taveta and Mombasa.

Vincent Onyango at his farm in Dunga Beach, Kisumu county, on March 25, 2017. [Collins Oduor, Standard]

Additionally, crop protection is a complex of instruments, products and strategies used to defend crops against weeds, pests, viruses, plant diseases and other harmful factors. Management strategies include quarantine measures for unintentional and intentional introductions, eradication, containment and control, monitoring and research, regional cooperation and public awareness.

So how do you manage these intruders?

To manage the pests, diseases and weeds the first requirement for a farmer is to correctly identify them. This is done through crop monitoring. If one cannot identify a new pest or weed or disease symptoms, consult an expert or your local agronomist or county extension officer.

Crop-monitoring is a powerful tool for achieving sustainable crop production. It helps promote agro-ecological knowledge and practice to develop a resilient farming system. This approach averts the negative factors, thus reducing the potential costs needed in case of problem manifestation.

So, what are the main methods of crop threat prevention?

Agrochemical Control Method

This involves the use of natural or synthetic chemicals that cause the death, repulsion or attraction of pest. Such chemicals are called pesticides. These pesticides are classified according to the type of pest they control. Insecticides are used to control insects, herbicides to control weeds, fungicide to control fungi, nematicides to control nematodes, rodenticides to control rodents, acaricides for mites and avicides for birds. The most important factors that a farmer needs to understand when using agrochemicals to control pests, weeds and diseases in their farm include:

1.      Recommended dosage and frequency

This refers to the amount of chemical to be used to control the damaging species. For example, when using a synthetic pesticide whose use has a broad coverage and can be used to kill aphids, mites, white flies, consider the amount needed to kill each. This helps to avoid the build-up of resistance to the pesticide in the harmful organism.

If it is recommended that one uses 10 grammes for control of aphids per knapsack sprayer, DO NOT exceed the 10 grammes as it will be harmful in the long run. Farmers are also advised to avoid the repletion of the same product over and over. Product labels clearly state the timeline between applications.

2.      Active Ingredient

It is critical for farmers to understand the active ingredients of different chemicals. Why? Resistance is brought through continued use of the same active ingredient where the organisms naturally develop ways to overcome it.

This knowledge is critical since different companies sell the same active ingredient under different brand names and percentages. Just like the way we have different brands of soap-based on caustic soda, silicates, perfume among others as ingredients.

To keep track of this, farmers ought to maintain a record of all chemicals used in the farm for any protection measure. You can store the label itself or note down the active ingredients. According to the law, all chemicals must have their active ingredients clearly labelled including percentage by weight and total weight of product.

Record all chemicals used

The record comes in handy especially for exporters when a buyer demands for the same to meet market requirements. It also helps break pest resistance development. 

3.      Mode of action

Mode of action refers to how the chemical acts on the target organism for example contact insecticides, systemic or inhalation (fumigants). This impacts on the application method. For example, systemic pesticides are any chemicals that are applied on plants, absorbed by the plants and spread through the plant and will later kill any pest that consumes the said plant. This therefore means that one can apply them at any time of day even when the pests are not visible as their action will happen later through the plant system. When compared to contact insecticides the opposite is true. Since they kill the pests through contact, one must wait when the pests are visible before spraying otherwise it will not be effective.

4.      Post-Harvest Interval

This refers to the time needed to elapse before a sprayed crop is harvested.  Always allow the post-harvest interval to elapse as it allows the chemical to degrade to levels that are not harmful to human beings once consumed.

Biological Control

This is the use of living organisms as pest control agents. It takes advantage of the prey-predator relation between different organisms.  Biological control have the following advantages:

 i. Safe and no danger is involved during application.

 ii. It provides lasting control once the natural enemies have been established.

 iii. It is economical in the long run.

 iv. The pest is not likely to develop resistance.

Some of the most common biological control methods include use of domestic animals such as chicken to control insects, cats to control rodents and use of goats to consume weeds like lantana and Mathenge.

Cultural Control Method

This works through manipulation of the environment in such a manner that it would be unfavourable for the pest thereby adversely preventing the damage or at least limiting its severity. Cultural control practices include selection of a good site, use of clean planting materials, tillage, deep sowing, manipulation of planting and harvesting time, crop sanitation and rotation, intercropping, close season, planting of trap crop, mulching, irrigation, manipulation of crop spacing. Most of these cultural control methods are environment and cost-friendly.

Mechanical and physical control Method

Mechanical and physical controls kill a pest directly or make the environment unsuitable for it. For example, traps - for pest animals and insects; mulches - for weed management; steam sterilisation - for soil disease management; or barriers such as screens or fences to keep animals and insects out. This include physical removal of weeds through slashing, uprooting or use of jembes to mix them with soils.

Host Plant Resistance Method

This is the relative amount of heritable quality possessed by the plant which influences the ultimate damage done by the pest.

Host resistance to pest could be exhibited as Antixenosis (Anti-guest), Antibiosis for instance BT Maize and BT Cotton and Tolerance.

 Regulatory or Legal Control Method

This concerns government regulations to prevent the spread of pest from one country or region to another.

Legal control could be absolute prohibit, quarantine, post-entry quarantine services, restricted materials and closed season. This strategy ensures that pests, diseases and weeds do not move across countries, counties or even villages.

Integrated Pest Management (IPM)

This is a method of controlling pest in an economically efficient and ecologically sound manner. It uses all suitable techniques either to reduce pest population and maintain them at level below those causing economic injury or to manipulate the population so that they are prevented from causing injury. IPM strives to prevent the needless destruction of the environment and protects human health.

Weather data

After ensuring the you have protected your crop from pests, weeds and diseases, plan for weather-associated risks as they affect yield.

Farmers can get weather information from the media, government and county extension offices. This info helps to deduce the risks and plan in advance. Some control measures for weather risks include planning for irrigation when rain stops mid-season, planning for floods by constructing waterways in your farm away from the crops and use of plant support or wind breaks against strong winds. 

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