Did you wonder, like me, if the frigid temperatures of early January were going to wipe out our insect problems this year?
Unfortunately, the cold appears to have had no adverse affect on insect populations. I was hopeful that the sub-20 temperatures would knock out annoying critters like fire ants, aphids, mealy bugs, lace bugs, thrips, spider mites and scale. However, based on e-mails I'm getting and plant samples I'm seeing, it seems like some of these populations have rebounded quite well.
This week, I've chosen to focus on thrips (chilli thrips) and spider mites. Thrips will cause premature bud drop on roses, hibiscus, and many other plants. They basically ravage the rose bud as it attempts to open and give the bud petals a burnt and often gnarled look. This has been the #1 problem showing up at all my recent live appearances.
Both spider mites and thrips are, in most cases, imperceptible to the naked eye. So, for treatment purposes, 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. 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.
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. Once a month 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 and fungicides mixed together, like Bonide Rose RX, and feeding added to other products like Ortho's Three-In-One. 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 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 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. Most people opt for the systemic approach.
The systemic solutions 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, much of the same treatments can be applied for their bud drop as well. In fact, I wrote about thrips and midges-affected hibiscus in THIS previous e-mail tip.