Thrips Pests

A thrips (yes, thrips, with an “s” is the singular and plural versions of this pest’s name) is known not only for the direct plant tissue damage it causes but also for the serious plant diseases it vectors.

Adult thrips are also flyers. Their wings are more like feathers with fringes of hairs or setae and are very difficult to see, especially since they keep them close to their yellowish to dark green to brown-black elongate bodies when not in use. 

However, they do function well. Their wings carry them over great distances, and natural breezes make it critical to control thrips when they first appear.

Thrips have rasping and piercing-sucking mouthparts. They first rasp the cells, causing a “wound.” The “wound” oozes plant sap. 

The thrips then insert their straw-like style into the damaged cells and draw the juices. And if that isn’t enough, thrips are famed for their ability to transmit plant viruses, including impatiens necrotic spot virus (INSV) and tomato spotted wilt virus (TSWV).

We’ll give you information about these plant viruses, so read on. If you don’t want your plants to get these special tospoviruses, don’t let thrips into your facility, no matter how loudly they knock. 

If they do get in, control them as quickly as possible. Feeding damage can pale in comparison to what these viruses can do.

Thrips can lay a number of eggs. Their thrips pupae life cycle can be fairly short, dependent upon the temperature. If it’s cool, it can take over a month from egg to adult; if hot, it can take as little as fourteen days. Needless to say, thrips populations are more problematic in the hottest months of summer.

The various larval stages — of which there are two — and the adult stages are typically well-placed in their host plants. They can often be found deep within the plant’s flowers. Moreover, they will also hide in closed buds, making their control, especially with chemical insecticides, difficult at best.

Fortunately, some biocontrol agents available to thwart them will go in after them and drag ’em out screaming. Many growers who use chemical pesticides to control them will be suited to the hottest part of the day.

This is when the thrips are most active, often venturing freely all over the plant instead of only hiding within its tight places.

In a nutshell, they will fall off the plant and drop to the ground. The good news is that with the right tools, they can easily be controlled down under. Right tools like the beneficial insects or predatory mites, Stratiolaelaps scimitus.

Not all thrips species, mind you, do this, but the majority of which growers will be concerned with do. Some common species are flower thrips, echinothrips, greenhouse thrips, onion thrips and, by far the most prevalent, the western flower thrips. Cuban laurel thrips is another species of interest to growers.

Thrips, especially the thrips larvae, are, however, more difficult to count on blue traps. A proper scouting regimen will also utilize single plant inspections. For thrips monitoring, use some plants which will bear a steady supply of flowers. 

These flowers may be tapped or lightly shaken over a white sheet of paper — a dropcloth if you will — to facilitate easy detection. Like spraying, this should be done at high noon, but we encourage midday scouting anyway. You may also lightly blow into open flower petals, as this will generally lure them out.

One of the best ways to deal with thrips is to practice exclusion using an extremely fine insect screen and to carefully inspect incoming plant material, especially if it’s budding or flowering. 

Screening sounds pretty straightforward, but it entails planning because the material is so tightly woven that it will significantly reduce airflow. Looser meshed (anti-virus) screens are probably the way to go, as they keep most thrips outside where they belong without such a dramatic airflow reduction.

Using a trap crop is also a great idea for thrips. Blue flowers, like asters, work well. So do many other flowering plants. You may also choose to incorporate plants such as petunias and fava beans. 

These are especially important as they can indicate thrips and the viruses they vector. Symptoms such as leaf spots, brown, oozing patches, necrotic leaves, concentric rings of various colors, and others can all tell you a story about your local thrips-even if you don’t see the critters themselves.

If you see some of the symptoms described, seek the help of a book containing color photos of these diseases on the varieties of plants you’re growing for a side-by-side comparison. 

Also, don’t be afraid to do this. Seek the assistance of professionals who are well-versed in identifying these problems. Start with your area university’s cooperative extension office.

Aside from seeking the thrips themselves or looking for the disease symptoms they can cause, feeding damage may also be revealing. Silvery striations along the leaves or the leaf surface are indicative of feeding. 

They feed on leaves like a person would mow a lawn: back and forth or round and round, forming a pattern. The silvery patches are groups of individual, spent plant cells.

Other symptoms of feeding may include deformed leaves, buds and flowers. Some vegetables, such as peppers and cucumbers, and some fruits may suffer abortion. 

The last sign is the presence of fecal matter. The feces show themselves as tiny black specks. Please bear in mind that if you see these signs of thrips feeding damage, you have many of these nasty pests — at least locally on the plant(s) on which the symptoms appear.

If you notice evidence of a thrips infestation on one or more indoor plants, removing infested plants may stop the rampant spread altogether. Prompt action to control thrips is critical to protect nearby crops.

However, if you’re using biocontrols, your actions should be preventive and aggressive. It doesn’t have to cost very much money, but it must be preventive and aggressive for the best results! There are several biocontrol agents which are very effective against thrips. 

Some kill the larval stages, some the prepupal and pupal stages, others the adults. You may want to use them all. Two in particular, Neoseiulus cucumeris (for the larvae) and S. scimitus (as previously mentioned, for the in-ground pupal stages), when used in concert, preventively and aggressively, have proven themselves repeatedly — in interiorscapes and greenhouses.

Want something more? Here’s a new tip that you may find useful in your war with thrips.