Thrips & Spider Mites – Summer Damage Suspects

Thrips on rose
Photo Credit: Randy Lemmon
Thrips Damage Rose & Hibiscus Blooms Every Summer 

In the heat wave here in Texas during the summer of 2022, many insect populations blew up thanks to the heat and frankly the avoidance of homeowners to get out and truly checking for insect outbreaks.  Obviously, it’s easy to see insects like aphids and lace bugs and the damage left in their wake.  But there’s way more damage being done by two insects that are normally imperceptible to the naked eye – Spider Mites & Chili Thrips.  These are not usually instantly diagnosed by the average homeowner.

Both spider mites and thrips, in most cases, simply can’t be seen by most humans, until you do some deep inspection and a couple of physical protocols so you can actually see them in action. Which is why we say they are imperceptible to the naked eye.  But for treatment purposes, you must first make sure this is what you have.

Take an infected-looking rose bud and tap it onto a sheet of white paper. Thrips are microscopic critters 1/25 to 1/8 inch long, and they range in color from white to brown to yellow to orange to black. Consider them microscopic worms, that love to live in everything from hibiscus to rose blooms.

Spider mites are essentially microscopic spiders, smaller than a tip of needle. If you have either, you’ll see them scattering and crawling on the paper.
For clarification purposes, thrips mostly devour flowering buds from the inside.  Roses and hibiscus are a favorite target.  You often don’t even know you have them until you realize that all your potential flowering buds look gnarled and brown before they can fully open up!  Spider mites can do such damage on potential buds too, but they are even more well-known for sucking the life out of evergreens like Cypress and Juniper-related plants.
To control thrips and spider mites organically, you’ll have to keep up a persistent spray regimen using neem oil once a week, or at least every two weeks. There are some Spinosad-based organic sprays that have some positive effects in controlling these two critters as well. However, a once-a-month treatment is simply not frequent enough to control these ravaging insects. The ultimate organic control, of course, is to have truly healthy soils and truly healthy plants. But if thrips and mites attack, and neem oil doesn’t do the trick, it’s time to pull out the chemicals.
Systemic controls have long been the norm for controlling these pests, and there are a couple of ways to do it – with roses in particular. You have heard of systemic rose food, haven’t you? There are also systemic insecticides/fungicides, like Bonide Rose RX, and other products like Ortho’s Three-In-One, that can be added to liquid fertilizers.

But to make it simpler, there are really only two readily available systemic products for thrips and spider mites: Imidacloprid and Acephate.  Imidacloprid is also marketed as Merit, and it’s the active systemic in every Bayer Advanced product. Many other products also have Imidacloprid as the active ingredient. Just look at the product label.
Acephate was once called Liquid Orthene. While it’s not on the market by that name today, there are plenty of Acephate-based systemics available.  For roses and hibiscus buds in particular, there is another critically important step to take when controlling thrips – spray the buds with a liquid pyrethroid like Permethrin, Resmethrin, Cypermethrin or Lambda-Cyhalothrin.

Spider mites normally turn plants like cypress, junipers and arborvitaes brown. If yours seem to brown or rust from the inside out, that’s almost always caused by the dreaded spider mite. While neem oil is the accepted organic control, it must be used rather religiously to get total control.  There is a newer product on the market known as Neem Max which has been shown to be way more effective at first treatment than just regular Neem.

Most people opt for the systemic approach.  The systemic solutions described above apply here as well.  However, you don’t want to use systemic rose foods on evergreen plants such as a juniper.  Rather, if you can find one, a systemic azalea food can be applied to shrubs such as cypress, arborvitaes and junipers.

Acephate-based systemics are usually a contact control and a systemic control combined. So, if you’re convinced your juniper has spider mites, the simple answer is Acephate because you won’t have to treat anything else separately.  As for hibiscus, many of the same treatments can be applied for their bud drop as well.