Spider mites unseen pest of garden

I'm boring.

You see, I'm reading this fascinating book called "Death by Black Hole," kind of a humor-laced view of astrophysics. I only understand half of it, but I can't help relaying juicy tidbits to my kids.

For instance, did you know there are more stars in the universe than grains of sand on Earth? Did you know nothing in the universe travels faster than light? That a black hole is a star so dense that the gravity will not let light escape?

And you think the Lowcountry is hot: Because of an extreme greenhouse effect, Venus is 900 degrees. That melts lead, people. Lead.

By now you probably have the same bored look as my kids. The thing that amazes me is that astronomers figure half this stuff out without really seeing it. The same goes for one of horticulture's insect pests: spider mites.

Technically, spider mites are not insects. They're spiders, albeit really tiny ones. Mites are everywhere. They've killed bees and they live in your pillow. Creepy, huh?

Mites in sight

Certain species of spider mites feed on plants. They typically live on the underside of leaves and feed on plant cells with piercing-sucking mouthparts (sort of like a mosquito). The top of the leaf gets a stippled, bleached, sometimes bronzed appearance because the juice is getting sucked out from below.

It's sometimes difficult to see spider mites without magnification. They're about the size of pollen. If the infestation is severe, there may be evidence of webbing between the leaves and stems. The back of leaves could be covered with whitish scales that are the discarded exoskeletons of growing mites.

Horticulturists whip out their handy-dandy eye-magnifiers like a six-shooter to identify them, but that's because we're nerds. If magnification isn't handy, or you proudly don't own one, there's the simple branch-beating test. Smack an infested branch over a white piece of paper a few times and the mites are easy to see moving around on the paper.

There are many plant-infesting species of mites, but two of the most common in the Lowcountry are the two-spotted mite and Southern red mite.

They thrive in hot, dry conditions, such as indoors on foliage plants or greenhouses, but there's no shortage of them outdoors. I have seen them on fatsia, butterfly bush and sky pencil holly. In the past week, I noticed an outbreak of Southern red mites on Japanese holly. Today, I noticed an entire hedge of dwarf gardenia covered with clear spider mites, which could be newly hatched two-spotted mites.

Fight the mite

Horticultural oil and insecticidal soap will work, but good coverage is essential and reapplication may be necessary in a week or two. Some insecticides will work, but many horticulturists will use "miticides," such as Avid and Ovation, which are especially formulated to kill mites. As with any pesticide, read the label for directions. There are some products available to the homeowner that come in a granule and translocate systemically and kill mites as they feed.

Predatory spider mites and predatory thrips feed on parasitic mites. These can be purchased online from vendors such as www.hydroasis.com or www.growquest.com for about the price of a good miticide application. Predatory mites have been used with some success by strawberry growers and wholesale nurseries to suppress parasitic spider mites to acceptable levels. Releasing predatory mites is more effective for gardeners since they won't fly off like other insect predators.

Another solution is to get rid of the problem plant. One butterfly bush was particularly troublesome in my yard. After a few attempts to control the mites, I opted for a replacement. Problem solved. Never saw spider mites in the backyard again.

By the way, I learned our galaxy is on a collision course with the Andromeda galaxy in 3 billion years. If Earth survives, the sun will swallow the Earth 4.6 billions years later. Not even the spider mites will survive that.

Tony Bertauski is a horticulture instructor at Trident Technical College. To give feedback or request column topics, e-mail Tony at tony.bertauski@tridenttech.edu.