Last updated on October 23rd, 2023 at 08:47 pm
The pests mainly target houseplants and can be recognized by their typical damage pattern – and can be successfully combated in time with these tips.
Fighting thrips – the most important things in a nutshell.
- Thrips are tiny, elongated insects that suck plant cells.
- The infestation can be recognized by whitish speckled leaves. The spots have a silvery sheen.
- If the infestation is severe, leaves turn yellow and fall off, and there is scabby growth on shoots and flowers.
- Small to medium sized plants can be drenched.
Neem helps as a natural insecticide.
They are small, but very annoying when they appear en masse: thrips (Thysanoptera), also known as fringe winged insects or blister feet, are insects that are one to three millimeters in size and feed on plant sap. To do this, the animals bore into the leaf surfaces with their mouthparts and suck out the cells.
Incidentally, the animals are called bladderfoots because they can literally inflate their feet in order to hold themselves better on smooth surfaces with the resulting enlarged surface. Therefore, the animals prefer the often smooth undersides of leaves as a place to stay. Colloquially, thrips are also called thunderbugs, but this also refers to other insects.
How can you recognize an infestation of thrips?
Since thrips are so tiny, they can hardly be seen with the naked eye, at most heavy infestations, when the elongated pests and their whitish-green larvae accumulate in larger groups.
One notices the infestation only when the leaves get whitish spots and speckles that have a conspicuous silvery shine. Since thrips and their larvae can only pierce the leaves with their short mouthparts close to the surface, the emptied cells or tissue fill with air and produce the silvery sheen.
Honeydew does not emerge, for which the pests would have to sting right into the phloem of the plants, where the sweet sap flows. Aphids, for example, can do this, and honeydew is one of their pests.
Leaves heavily sucked by fringed aphids turn yellow and fall off. In addition, dark brown feces can be seen in spots on the leaves. Plants react to heavy infestation with crippled shoots or flowers. Under ideal conditions, thrips can cause so much damage that the plants die.
Spider mites also cause bright leaf spots, but they do not have a silvery sheen. In contrast to the fringe-winged fungi, spider mites also cover the shoot tips with a fine web.
Which plants are attacked by thrips?
The heat-loving plant pests particularly target houseplants such as dieffenbachia, orchids, rubber trees, passion flowers or cyclamen. But even plants in greenhouses are not spared, where thrips like to infest cucumbers. Since thrips love dry warmth, an increased infestation is to be expected at the beginning of the heating period as well as in summer.
How can thrips be prevented?
Prevention is better than combat: Optimal site conditions for houseplants, avoid waterlogging and repot regularly: To protect plants preventively, they should be as vital as possible and the humidity should be sufficiently high during the heating period. This is because thrips hate high humidity and also like to attack weakened plants with soft tissue.
To raise the humidity, water-filled bowls on the windowsill near the heating system or, even better, an indoor fountain, which evaporates significantly more water, are sufficient.
Large saucers with water also work very well, but you should fill them with expanded clay so that the plants are not directly in the water. Means with neem you can also use preventively in case of thrips infestation that occurs according to experience.
Neem as a remedy against thrips
The basis of this natural insecticide is the neem tree (Azadirachta indica), which originates from India. The main active ingredient, azadirachtin, is extracted from the seeds and is effective against sucking and biting insects such as aphids, thrips, leaf miners and spider mites.
The agent penetrates through the leaves and is transported further within the plant over short distances. When thrips suck on the leaves, absorb the agent.
After that, the pests stop feeding and do not develop further. It is therefore normal if pests do not immediately fall dead from the plant. Even if the active ingredients are of natural origin, you should apply the agents with appropriate care. They are plant protection agents.
What can be used to combat thrips?
If you notice thrips on your houseplants, first isolate the plant so that the pests cannot spread further. Since thrips mainly pupate in the pot root ball, you should replace the soil after an infestation so that it doesn’t start all over again.
The best home remedy for controlling thrips is soft soap, which you spray on the plant for several weeks and then rinse off in the shower. Use 15 grams of soft soap for one liter of water.
Do not forget about the undersides of the leaves. To prevent soil from washing out of the root ball and clogging the drain, wrap the pot with plastic wrap beforehand. This also prevents the pests from simply being washed down into the soil by the soapy water and then crawling back up the plant.
For large plants, however, showering is a tedious method of controlling thrips. But there’s a home remedy for that, too: spray the plants twice a week with a solution of one quart of lukewarm water, two tablespoons of olive oil and a few drops of dishwashing liquid. If you spray the plants with this more often, the oil can clog the stomata of the leaves.
Many amateur gardeners swear by a decoction of garlic or onions against thrips, to which you should also add nettles. However, these are hard to get in the winter, so you are limited to the garlic.
Add 200 grams of freshly pressed garlic to 1.5 liters of water. The decoction is left overnight and then poured over the plant. Thrips can be controlled with the already mentioned neem oil.
Other insecticides exist, of course, and these also work, but should only be used in cases of heavy infestation. After all, who wants pure chemistry in the house or on their cucumbers in the greenhouse. There is another way.
Maybe you have ever wondered what the blue boards are supposed to be good for, which are available in the garden center next to the well-known yellow boards coated with glue.
They’re against the fringe winged insects that are attracted to the blue paint and then stick to the glue. Stick the blue boards into the pot of the plant you want to protect. However, not all thrips have wings, so blue boards are primarily useful for infestation reduction and monitoring.
Since fringed thrips mainly occur indoors, you can target beneficial insects such as lacewings and certain predatory mite species.
This is the gentlest method of control, as you completely avoid using any agents. The beneficial insects stay on the plants and do not spread in the apartment or infest people and pets. You order the beneficial insects in the garden center and receive them by mail in a substrate, which you tap out on the plants.