Thrips are Microscopic Insects but Big Problems

Thrip on a flower

I never knew thrips existed until I started growing African violets. I don't have a picture of them on violets, but most likely if you've ever bought an African violet at a grocery store or big box, you've seen the signs of them. Their larvae love to eat the pollen of the violets, and when they do it falls onto the petals, making it obvious. It is always noticed more on dark colored violets, as the yellow shows up best against the dark color. If you see pollen on the petals, do not buy the violet. You are bringing home trouble. When I come home from an African violet show, if I've purchased plants, the first thing I do is take all the flowers off the plant. This is not an easy thing to do. Heartbreaking, in fact. It is necessary, though to get rid of any pests, such as thrips that may be lurking in the flowers. I also quarantine my plants for a few weeks to make sure they don't have any other insects or diseases.

The pollen sacs are the yellow in the middle of the flower

 Thrips are very small insects, almost impossible to see with the naked eye. The most common on greenhouse plants are the Western Flower Thrip, Frankliniella occidentalis. These pictures are enlarged quite a bit. If you breathe on flowers that you suspect have thrips, you can see them run, if you have good eyesight. Thrips have piercing, sucking mouth parts. The biggest problem that thrips cause is damaged areas that disease can then enter. They are vectors for virus to enter the plant. You will notice the damage before you see the microscopic insect. On flowers the damage may appear as streaked or discolored areas, on leaves they will be dried out and have a silvery appearance. They attack plants inside and out, but we are going to deal with indoor plants, of course.

The best way to deal with thrips is to not allow them to enter your plant area. They are so small, they can fly through most window screens. They can also come in on cut flowers, either from the florist or from your own yard. I know people who would never open a window in their plant room.

If you have them, how do you remove them? Systemic insecticides may not work well, as the systemic does not easily pass into the flowers of the plant where the thrips are feeding. Also, thrips feed on cell content, not the xylem or phloem where the systemic is contained. The amount that does go into the flowers may not be enough to kill the thrips. Also, flowers do not last as long as leaves, so there is less time for the insecticide to accumulate. Spinosad and neem oil also work on thrips and are less toxic than other chemicals. Removing the flowers is a good way to rid yourselves of thrips, especially if growing African violets. Keep the flowers removed for quite some time. Using sticky traps to monitor thrips works, but use blue sticky traps instead of the usual yellow.

Thrip on a streptocarpus flower

If you want to rid yourselves of these pests with biological controls, there is more than one that will work. Predatory nematodes, Steinernema carpocapsae help control thrips, as well as Steinernema feltiae, Orius insidiosis, the pirate bug, and the thrip  predatory mite, Amblyseius cucumeris. These are all biological controls that could be used to eat the larvae and/or adults. Once again, I'm listing these biological controls, knowing that it may not be practical  for many people to use them. That being said, I wanted to list all the ways that one could control thrips. 

Once again, I can't stress enough, that a healthy plant is the best way to deter pests. Check your plants every time you water for pests and disease. Keep your plants well watered, fertilized and in the correct light to keep them healthy and happy.