2023-07-04 04:00:00
Jean, who contacted us via the orange Alert us button, is surprised by the presence of an insect pest on his potato plants. At the age of 75, Jean is surprised by the return of this unwanted child whom he thought had been missing for many years.
Jean, a pensioner, grows his own potatoes in Court-Saint-Étienne (in Walloon Brabant). For nearly 50 years, he has harvested between 50 and 70 kg of potatoes. But for the past few days, looking more closely at his plants, he notices that an intruder has entered the leaves.
After suffering the drought, his potatoes have now become the target of beetles. “I had the unpleasant surprise of discovering this insect in large numbers and in all its forms on most plants. I collected nearly 100 individuals and I will have to check every day to eliminate as many as possible”he exclaims.
Indeed, since this discovery, Jean scrutinizes his plantations. “It can be very prolific. It eats the leaves and reproduces in large numbers.” explains John. For this enthusiast, there is no question of chemical treatment. It is equipped with a glass jar that he goes in search of this little guest who can still do significant damage if he takes up residence for too long. “We know it’s sporadic so I take the trouble to visit the rows of potatoes and pick up the critters that we find”emphasizes John.
At 75, this pensioner speaks of a real surprise, because he thought that this insect had disappeared since his childhood. “When my grandparents were children, we gave the children time off to pick up the beetles”, he recalls. He therefore wonders about this sudden irruption of the beetles. “Why all of a sudden a larger outbreak when in some years you don’t see any. Is it due to global warming or hot winds bringing insects of all kinds?”, he wonders.
The Colorado potato beetle is an insect pest that comes from the United States. It arrived after the First World War, after the importation of potatoes. “At that time, it was really very problematic, because we had plots that no longer had a single leaf. It has faded a bit. But for the past fifteen years, we find them in crops , including vegetable gardens. They can sometimes manage to induce up to 50% of leaves which disappear. So there, it is very surprising”explains Frédéric Francis, professor at the Faculty of Agriculture in Gembloux.
The hotter it is, the greater the insect activity.
Only observation can detect the presence of the latter. “The hotter it is, the greater the activity of insects and therefore the more damage we will have. In addition, when we are faced with periods of drought, the plant has less opportunity to develop and produce new leaves. So if we find ourselves in dry periods, the phenomenon is more visible and has a greater impact on the citizen”says Frédéric Francis.
An observation shared by Louis Hautier, researcher at the Walloon Center for Agricultural Research. “It is estimated that above 30°C, the Colorado potato beetle completes its cycle (from egg to larva in the final stage) in 15 days”, he specifies.
The increase in the number of potato plots in Belgium also leads to more chances that the beetle can reproduce. In the 1990s, there were 50,000 hectares of potatoes. Today, that number is around 95,000.
It is an insect that hibernates in the ground.
For its part, the Fiwap (Walloon potato sector) is well aware of this upsurge. It thus makes producers aware of the damage that this insect pest can cause. It also works alongside the Walloon Center for Agricultural Research to monitor beetle populations and tell farmers whether or not chemical treatment is required. “It’s an insect that hibernates in the ground and will come out next year, especially on regrowth potatoes on other crops. So we have to manage to break this cycle from one year to the next. “explains Pierre Lebrun, coordinator of Fiwap.
Stemming the proliferation of beetles
Originally, beetle hunting was done manually. Insecticides were then developed and used on plots. “Sometimes you have to chemically treat the plot in order to stem the multiplication of beetles and try not to go further than the second generation on the way”says the coordinator.
The two professionals show us a plot attacked by beetles in Gembloux. Here, there is no possible doubt. From the larvae to the adult stage, insect pests are clearly visible. Pierre Lebrun explains to us that an experiment is underway in this area. A technique of mechanical control by brushing will thus be tested there. “The goal will be to try to drop the larvae and the adults in tanks mounted on a machine so as to get the beetles out of the plot without chemical intervention”he informs.
Before adding: “In the next few years, we can expect the technique to develop. First in the organic production sector where there are no synthetic insecticides that are used. And then certainly in cultivation conventional to further reduce the use of pesticides”.
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