Basics for effective crop disease management

As the global population soars to reach nine billion people, emerging challenges of feeding this population is becoming more real than ever in the world.

Many countries in the world, Zambia included, now are under great stress to feed its people. Stories of people eating mangoes as the main meal in Lundazi are still fresh on our minds or busala in Southern Province and many other areas. On average, forty per cent of what is cultivated globally is lost due to crop diseases, pests and failure to manage weeds. Of this loss, diseases contribute in excess of fifteen per cent. For a country like Zambia which cultivates about two million hectares under maize, the loss due to disease accounts for about two million four hundred thousand tonnes of the potential yield annually, if we averaged the potential yield at eight tonnes per hectare. This is a great loss to the farmer as an individual and a country as a whole. In monetary value, this can be a huge boost to the treasury and the economy of the country. It is prudent therefore that farmers with the help of the extension officers and partners in the sector help to mitigate the losses due to diseases. The examples cited in this articled are focused on maize but are even worse with horticultural crops.

It is important to understand the types of diseases that affect crops and how they can be transmitted from one plant to the other. In maize production, some of the diseases that are important and of economic value are fungal and viral diseases; there are very few occurrences of bacterial diseases. From the onset, it should be borne in our minds that there is absolutely nothing we can do once our crop is affected by viral diseases. The common viral maize disease that is prevalent in Zambia is mosaic streak virus (MSV); just like human HIV, it has no cure once the crop is infected. There are no pesticides currently on the market that can be applied to cure it. However, it is a disease that we can easily manage, and many farmers, especially commercial farmers, have managed this disease so well. The disease is transmitted by grasshoppers as they suck sap from the crop. Therefore, managing to control such vectors, including aphids, will indirectly control the outbreak of this disease. It is therefore important that you protect your crop with a recommended insecticide as well as planting seed that is treated with an insecticide; preferably, a systemic insecticide. Always demand for seed that is treated when acquiring seed.

The other diseases that are so prominent and have affected so many fields in Zambia are fungal diseases. These are diseases like grey leaf spot and many others such as Fusarium. These are widely spread and affect each and every maize field grown in the country. To control them, one needs to understand the conditions which favour of the outbreak and proliferation of the disease. It is also important to note that there are thousands different strains of fungal diseases from the same family. Others may affect maize, rice, wheat and other crops in the same family. There are a few that can exhibit cross infection. It is important to also know that the soil is the largest carrier of spores that cause crop diseases. For instance, there are millions of Fusarium spores every square metre of soil. These spores can remain inactive in the soil for a long time until when the right crop is planted – this might sound scary to you but you don’t have to worry because science has advanced as well. Thanks to technology, some seed treatment pesticides are normally applied to the seed. This protects the plant as it is germinating; it is some form of ‘immunization’ that crop scientists have developed in their quest to lessen the outbreak of such diseases. A seed that is well treated should have an insecticide as well as a fungicide or two to protect the crop. This is similar to what happens in human life; when a child is just born, they are vaccinated against such serious diseases like polio, tuberculosis and tetanus. The child is so prone to so many diseases because its immune system is not well developed. This is the same thing that happens with our dear crop; when very young, it is prone to many risks. The technology that our Almighty Jehovah God used when He made human beings is similar to plants. He could have used the same manual (on a lighter note). What is important, therefore, is that farmers should only plant seed that is treated. How can a farmer know that the seed is treated? The farmer should buy seed only from genuine sources or seed companies and their appointed agro-dealers. Farmers should also inquire on the type of seed treatment that was used. Remember that I shared with you how some farmers have ended up losing money by buying seed that is perceived to be cheap when in actual fact it was fake. This is well documented in my book, ‘A Guide to Agribusiness in Zambia: Untapped Opportunities. We need to tap into these opportunities, time to gamble remained in 2019. Remember every time before retiring to bed as a farmer, you have the obligation to feed nine billion souls.

The author is an Agribusiness Development Consultant.


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