THRIPS – A MAJOR HEADACHE FOR PEPPER FARMERS!

Year in year out, many pepper farmers around the world have to battle the tiny insects called thrips. The insect may originate from previous crops, nearby farms / fields / bushes or weeds. It can cause damage to over 50% – 80%, or even an entire farm depending on how early it is detected and control measures put in place. Interestingly, it is not visible to many farmers and aids such as magnifying glasses may have to be used. Their damage however, cannot be invisible. If not carefully checked, damage begins from the young stages of the plant – even in nurseries, to mature flowering or fruiting stages.

It is revealing to note that a lot of infections are carried from nurseries to growing fields / greenhouses. This is why phyto sanitary measures are important in all nurseries. Attack of the tender seedling can be damaging as plant may not recover. Careful inspection of transplants, possibly through sampling, is important in averting the smooth transfer of pests to fields / greenhouses. Also, greenhouse dis-infestation is important especially for houses which had previous crops, as there may be hidden infections.

?Why pepper: Although thrips are a major challenge in many pepper fields, do not be surprised to see them in other crops like melons, cucumber, eggplants and rarely tomato. They are usually observed in the flowers of these plants. Thrips may feed on pollens present in the flowers. Once fruits form and flowers drop, activities of thrips are extended to the fruits. Where plants are young and flowering not started, the leaves host the pest. They suck up the sap in the leaves, and leave it nearly whitish, thus affecting photosynthesis. In order of crop preference, thrips have a bigger affinity for peppers, followed by cucumbers, melons and other crops. The damage caused by thrips is mainly through their feeding activities.

?Control measures

Checking presence: The yellow to brownish-black colour of thrips makes them clearly visible on a plain white background. The commonly used method of detecting thrips is to shake parts of the plant, especially the flowers onto a white sheet of paper. The insects then begin to move on the paper. Also, due to the whitish nature of pepper flowers, critical inspection, especially with a magnifying lens can detect the presence of thrips. The most obvious sign of thrips is shrinking of leaves of pepper plants. In other words, the broad leaves of the plant no longer expresses that broadness. In some cases of thrip presence on peppers, there may also be the presence of broad mites who may cause termination of growth points. The effects of a thrip’s rasping activity is clearly seen on the fruits as whitish “net looking” lines appear, sometimes just as the fruit begins to appear. This may also be noticed on bigger fruits and affects the market value of the produce.

Remove and Discard: Thrips transmit tomato spotted wilt virus (TSWV) to pepper plants. Once a plant is detected to have TSWV, it is advised to remove and discard that plant. This action is important because the infected plant will serve as a breeding source for thrips to transmit to other healthy plant. Heaviest thrip infections and breeding are usually found on plants infected with TSWV. In the activity of removing and discarding, care must be taken not to spread thrips to other plants. A disposal bin or polythene must be taken close to the infested plant and dumped immediately removed. Discard infested plants in pits, about 100m from cultivation area.

Spraying: Controlling thrips through spraying gives the quickest results, but it must be done properly to avoid resistance. Also, spraying must be targeted at specific stages of the thrips, especially the larval or adult forms. Spraying must also consider the stages of the crop because whilst a bigger pre-harvest interval may be acceptable in the early stages of the crop, the harvesting stage will not allow that room. It is important to have about three to four different active ingredients for efficient spraying. In targeting thrips, a farmer can assemble Chlorpyrifos, lambda-cyhalothrin, emamectin + acetamiprid, and an oil-based insecticide. A spraying schedule should be developed from these ingredients that avoids repetition.

Eradicating thrips from a pepper farm is an arduous activity. This can be done by leaving long fallow periods of about four seasons, without any crop for the pest to feed on. Fallow periods for a commercial farm may not be economical, thus the best approach is to manage the population of thrips in a farm. Keeping low population levels, through constant monitoring and taking remedial action will allow your crops to grow without much damage from thrips.

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Article by:

Prince K. Boakye

Academic Manager/Agronomist

Agritop Limited