Thrips
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What are thrips?
If your plant gets infected with thrips, you need to act fast! These little insects multiply quickly and can do a lot of damage to your houseplants. Thrips are a very problematic plant pest. Thrips can be resistant to pesticides. The combination of all of these factors makes it very difficult to manage and treat them effectively.
Symptoms
Paperlike marks
Silvery or bronze discoloration
Browning or yellowing leaves
Black specks
Drooping leaves
Partially dead leaves
Deformed and stunted growth
What to do now
Isolate the plant - thrips spread really fast!
Examine all your other plants in the household
Place the plant in the shower and rinse the leaves thoroughly with a jet of lukewarm water
On sturdier plants you can use masking tape or a lint roller and clean off all the thrip
Kill the thrips with pesticide, neem oil or thrips predators
Repeat treating your plant about once a week for the upcoming 4-6 weeks. Then repeat it about once a month for a couple of months. After that you can repeat the treatment if necessary.
Continue to remove any visible thrips on your plant between the treatments to speed up the process. You can squash them with your fingers, shower the plant with a jet of water or using masking tape or lint roller.
Put up sticky traps around infested plants to help catching adult thrips. White and blue traps can be more effective than yellow traps when treating against thrips.
Pesticide, neem oil and thrips predators
With pesticide
There are several different types of pesticides that can help you kill and manage thrips. They are unfortunately resistant to many types of pesticides so be sure the check the label of the product you're purchasing. Note that some plants can react badly to pesticides or soaps so test it on a smaller area of the plant first. Always avoid direct sunlight after application as it can burn the plant.
With neem oil
Neem oil has a very strong smell, which many find unpleasant. The smell will fade as soon as the oil is dry.
Mix 1 quart of lukewarm water, 1 tsp neem oil, 1/2 tsp liquid soap and a few drops of rubbing alcohol. Shake until all the neem oil is diluted into the mix (neem oil mixes more easily with warm water)
Spray the entire plant with the solution and pour any excess down into the soil
With predators
Biological control can help to reduce an infestation but should be used in combination with other treatments for the best effect. Note that these beneficial insects will also be harmed by pesticides used on the plant. Add them when you're done with the repeated initial weekly treatments or you think the thrips are mostly gone on the plant.
Neoseiulus cucumeris - prey on the eggs and nymphs
Minute pirate bug (Orius insidiosus), and other Orius bugs - eat both eggs, nymphs and adult thrips
There are several different predatory insects and mites on the market and it can vary depending on where you live.
The idea of releasing MORE insects in your home may not feel very pleasant, however, this is an effective way to prevent pests on newly acquired plants and to help removing thrips between the treatments.
Common questions
How big are they?
Thrips are small, slender insects not larger than about 1/25-inch (1 mm) long. There are thousands of different species so they can vary in color and size. Usually adult thrips are black, brown, beige or yellow while the larvae are creamy white, pale green or yellowish in color.
What do they eat?
The kinds of thrips that damage your house plants feed mostly on plant sap and the pollen from flowers. They feed on the sap by puncturing the surface of the leaf and sucking up the content of the cells. This is why you often find silvery or bronze-colored scars on leaves where the thrips have been.
Where did they come from?
Most thrips are brought home with newly acquired plants that are already infested. In rare cases, they can hitch a ride in on cut flowers, fruits or vegetables. Bringing outdoor plants indoors, open windows or being outside can also risk bringing in thrips to your house plants as well. You'll usually not notice thrips on outdoor plants as they're kept under control from natural predators.
Can they fly?
They do fly, but not very far. They have feathery wings which aren't suitable for conventional flights.
How long do they live?
It depends on what species and environmental factors. During beneficial conditions it takes around 2 weeks for an egg to turn into a fully adult thrips. And the adult thrips can live for about 30-60 days. There may be as many as 12-15 thrips generations per year.
Why are they difficult to get rid off?
The reason for them being difficult to manage is due to their life-cycle and their mobility. Some species lay their eggs in the plants tissue where they are protected from pesticides and predators. Some species also spend their pupae stage down in the soil, in crevices of the plant or other protected spots where they too are protected from pesticides and predators.
How can I prevent this in the future?
You can stop a major infestation by carefully checking and quarantining new plants that come into your home.
Put all new houseplants in quarantine before introducing them to the rest of your plants
Do regular check-ups on your plants
If your worried you can also try to keep fresh fruits, herbs, vegetables and cut flowers away from your plants