Thrips in French beans, how to deal with them
Last week we examined how to use various crop protection products to control pests and diseases affecting French beans.
So far, Farmer Irene has been scouting the crop regularly to identify if there are any pests and diseases. One of the major pests affecting the crop is thrips.
Thrips are small black or silvery slender insects that suck the juices from the fruits. When disturbed, the pest usually flies or leaps for a short distance.
They also affect the leaves and flowers, resulting in flower abortions. Thrips normally attack a wide variety of fruits, vegetables and flowers. The injuries caused by the insects normally become entry points for other pathogens, resulting in diseases.
The insects also carry pathogens using their mouth parts as they attack one plant to the next spreading diseases. It is thus important to ensure thrips are well-controlled before they damage the plants.
While scouting for the pest, check for thrip damage at the growing tips of the plants before the flowering stage. Farmer Irene has been checking the crop early in the morning since they tend to hide inside the flowers or underneath the leaves when temperatures rise.
You can check the presence of thrips by shaking the plant on a white paper. Adult insects will fall on the paper.
It’s important to monitor the crops to detect when the thrips start infesting them and determine the population levels. This helps in identification of the appropriate and cost-effective method of control.
The thrips infestation in French beans begins on the flowers by sucking the sap. High infestations cause poor pod set, stunted plant growth and the leaves and flowers wilt.
On the flowers, thrips attack usually results in abortion, which reduces the overall crop yields. When the thrips feed on the cell sap, they interfere with the transportation of foliar nutrients.
Thrips should be controlled at the early stages by ensuring the farm’s hygiene is well-maintained. Other methods of controlling them before planting include deep ploughing, as a well-prepared fertile seedbed promotes crop vigour.
Planting barriers of Mexican marigold attracts thrips from beans. The farmer should also consider planting tolerant varieties.
Avoid planting onions next to French beans as they act as hosts to thrips.
Chemicals can be used to control thrips. Good spray coverage is important as thrips hide underneath the flowers and leaves.
While using insecticides, consider systemic chemicals since they are sucking insects, hence sucking the chemicals in the sap.
The insecticide rates should be appropriately used and the chemicals should be administered in an alternating manner to prevent resistance.
The chemicals should have different active ingredients, what helps to prevent the pest from developing resistance.
The chemicals should be applied early in the morning or late in the evening. One should avoid spraying during sunny weather to prevent chemical evaporation. The chemical pre-harvest interval should be observed as indicated on the product label.
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