How to Identify and Manage Thrips
Many of the most destructive insects are also the smallest, and thrips are no exception. Thrips (“thrips” is used for both the singular and the plural) are capable of causing damage to many plant species. One of the most destructive species of thrips is the western flower thrips, Frankliniella occidentalis.
Luckily this is not a common interior pest; it’s more of a greenhouse pest. The species can be a real issue on the interior is the chilli thrips, Scirtothrips dorsalis. This is a newer species to the US and is often misidentified because its damage can look like broad mite damage. It also feeds on many of the tropical foliage plants.
Why Are Thrips So Destructive?
Thrips like to feed on new plant growth that is emerging from the growing tips. A thrips infestation can stunt the growth of a plant and harm its buds, resulting in aesthetic damage to the plants. Thrips can also vector plant viruses. Luckily most of these viruses are isolated to vegetable and flower crops and do not really affect the plants used on the interior landscape.
How to Identify Thrips
If you suspect a thrips infestation, take a hand lens with you, as these insects are very small. Depending on species, they can be several different colors. Chilli thrips are extremely small, pale in color and about 0.5 – 1.2 mm long. Western flower thrips are a bit darker and about 1.0 – 1.5 mm long. You can also identify chilli thrips by their feeding damage. It causes new growth to be curled and distorted. The foliage can also turn silvery to black.
The Life Cycle of Thrips
For chilli thrips it takes 2-3 week weeks to complete its life cycle. Temperature and host plant will influence the duration. Female thrips make cuts into leaves and insert their eggs into the tissue, where they will hatch. The newly hatched nymphs will feed on the plant until they pupate. Chilli thrips pupa can be found on the foliage of the plant, some in the soil, or tucked in blooms. It’s best to try and target their control on the plant and not in the soil like you do with western flower thrips.
Do You Have a Thrips Infestation?
- Tiny black specks on leaves and buds, leaf stippling. There are other insects that leave black specs on plants, so use a magnifying glass to confirm that your pest is a thrips.
- An easy way to look for thrips is to bang a branch or leaves over a sheet of white paper. The thrips will fall on the paper, making them easy to see.
- Blue or yellow sticky cards are another tool. Thrips are attracted to these colors, so the cards will let you know if they are in the area.
It’s Time to Take Back Control
How will you get rid of thrips? As with other pests there is always the option of plant removal. Another control option is through biological control. Luckily there is a predatory mite that does an excellent job of controlling chilli thrips, Amblyseius swirskii. This tiny cream colored mite will feed on the early life stages on chilli thrips (but not the eggs, nothing will control thrips eggs biologically or chemically). When used properly, A. swirskii will provide control of chilli thrips
on tropical foliage plants in the interior landscape. Treating chilli thrips on the interior landscape with pesticides can be challenging. This is why using biological control for this pest is so appealing. Often when talking about control of thrips, beneficial nematodes are brought up. Nematodes work great for larger thrips species like western flower thrips but they will not control chilli thrips because of the chilli thrips small body size.
Preventing Thrips Infestations
Always check plants on arrival. Use blue or yellow sticky cards in the holding area to detect if there is an issue.
Battling other common indoor plant pests? Check out my Professional’s Field Guide to Plant Pest Control for information on Spider Mites, Whiteflies, Fungus Gnats, Mealybugs, Aphids, and Scale insects.
Western Flower Thrips featured image by Lyle Buss