Thresholds ? knowing when to act
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CTA. 2008. Thresholds ? knowing when to act. Rural Radio Resource Pack 08/2. Wageningen, The Netherlands: CTA.
Permanent link to this item: http://hdl.handle.net/10568/57375
To control pests, farmers must learn to identify and count them
Thresholds ? knowing when to act Cue: For farmers, chemical pesticides are a valuable weapon in the fight against damaging insects. But chemicals can be expensive, and if used incorrectly they can not only damage the environment but lead to problems of resistance in the insects they are intended to control. Effective use of chemicals depends on farmers knowing at what point they should be used. For example, there may be insects in the field, but are they pest species, and are there enough of them to justify using a chemical spray? The point at which spraying becomes a good idea is known as a threshold. To find out more about these thresholds, and why they are so important, Adu Domfeh visited the Kwame Nkrumah University of Science and Technology in Kumasi, Ghana, and spoke to Senior Lecturer Dr Jakpasu Afun. Dr Afun began by explaining that not all insects should be seen as enemies. IN: ?All the insects we see are not pests? OUT: ?will also be able to apply this threshold.? DUR?N: 5?21? BACK ANNOUNCEMENT: Dr Jakpasu Afun, explaining to Adu Domfeh why farmers need accurate information on exactly when to take action against pest species, the point known as the action threshold. The interview comes from a resource pack produced by CTA. Transcript Afun All the insects we see are not pests. A whole lot of them are beneficial to the farmer and it is not every quantity or amount of pests that warrant a control. Domfeh So specifically, how does the farmer know there is a problem or likely problem of pest infestation or damage? Afun The farmers themselves, not until they are trained, they find it difficult to determine which is the pest and which is not a pest. So we take them through a whole season of planting, right from land preparation through to harvest, pointing out to them which of them are the pests, what numbers they should expect before taking action, what quantity of damage those things should do before they should take any action. This is where we are coming to this word of ?threshold?. And we have two forms of threshold: one we call the ?action threshold?. That is where you see some given amount of damage before you go in to do your control. And another which we call the ?economic injury level?. That is the level beyond which, if there should be damage beyond that level then there is no justification because even if you try to do some remedial action you might not break even. It will lead to a loss to the farmer, loss of income. So you realise we are dealing with two thresholds, the action threshold is below the economic injury level. So the pest that the farmer is concerned about is the quantity of pest or damage between these two levels. If the farmer can take care of the pest within these two threshold levels then the farmer is in good business. Domfeh And in these instances what basic scouting methods can the farmers adopt or use when they want to take action against destructive pests? Afun We teach them to do site counting. So they go in, they look out for the pest on the crop. Then they count, because they see and count and then they look at some distance. Ok, if I see for example one or two pests within maybe two steps then I need to control. Or they can do what we call ?sweeping?, and then they look at the number of pests within what you have collected and you look at the number and compare with the scale. And what we do, what we call a scale ranges from zero to nine. Zero means where you do not have any pest problem at all, where nine means there is almost total damage. So on that scale, we call a point three on the scale. That point of three on that scale of nine is what we are calling the action threshold now. So if your damage is below that score of three on the scale of nine then you do not have any trouble, but if it is at the three or beyond then you need to take some action. Domfeh Are there some examples of the action they could take to control these pests? Afun If, for example, we look at the crop like cowpea which takes a lot of insecticide, almost all farmers will apply all sorts of chemicals onto their cowpea crop. We have four main pests that attack the crop right from seedling to maturity and even in store. So we teach them for example if you go into your field and you see what we call aphids or what we call plant lice, if you see them scattered in your crop - because these insects can be very prolific they can produce between five and fifteen children, let me call them children, in a day. So if you go and you see a cluster of say three or four scattered among your crop then you need to take action immediately because if you did not by the time you go back the next day that has increased into a very large colony. Then there is another one called ?maruka?. That one is very devastating because it will destroy the flower, it will destroy the pod. So we teach them to open these flowers to the centre of it. If they see the pest or the seed is damaged then that flower is considered as damaged. So if they count, they take twenty and maybe out of that twenty, five of them show damage symptoms then quickly you need to spray that very day. You do not wait until the next day. So these are some of the specific things we teach them to do. Domfeh How then do we get the threshold right? Afun It is all education. The problem is even now we have the threshold for a few pests on a few crops. So the first thing is that we researchers will have to double up. We need support to be able to determine these thresholds which we can then communicate to the farmers. Then they will also be able to apply this threshold. End of track