By Alice Marty, Mobile Master Gardener | CoastalAlabamaGardening@gmail.com
The old saying “the dog days of August” usually refers to the long, hot, dry days when our gardens — as well as ourselves — are waiting out summer and hoping for an early fall. My definition of “dog days” is when the spider mites show up in my garden.
Spider mites, unlike other living things, love the long, hot, dry days of summer, and this year they showed up in my garden early after the hot, dry May weather. My battle with the nasty little mites has gone on for several years. I can’t say I’ve ever actually won the summer battle, but I’m becoming craftier each summer, so a draw feels almost like a win.
Spider mites are related to spiders, not insects, but will attack several types of plants and can be a major problem for agricultural crops. They look like tiny white spiders on plants but can also appear to be tan, red or black. Since they are so small, spider mites aren’t noticeable until their population explodes — and their damage becomes noticeable.
Spider mites multiply very quickly and, in the right conditions, can double their population every couple of weeks. In a few weeks an adult female can lay hundreds of eggs. When those eggs start to hatch, the result is an exponential population growth in a very short time. They become fully grown about a week after they hatch.
All mites have needle-like piercing-sucking mouthparts. They feed primarily on the underside of leaves by penetrating the plant tissue with these mouthparts. They spin fine strands of webbing on the host plant — hence their name.
Mite feeding causes a stippled-bleached effect, and later the leaves turn yellow, gray or bronze. New leaves may look deformed. Complete defoliation may occur if the mites aren’t controlled. Some of their favorite edibles are hydrangea, brugmansia and hibiscus, as well as many annuals and perennials.
To detect spider mites, examine the undersides of the leaves closely for mites and webbing. A more efficient technique is to place a sheet of white typing paper beneath the leaves and tap the foliage sharply. The mites will fall onto the paper and can be more easily observed and identified than on the green foliage. Brush the paper lightly with your hand; if the paper smears reddish yellow, it is probably spider mites.
Spider mite remedies
Now that you have identified the problem, what can you do about it? If you are a veteran gardener with previous spider mite experience, perhaps you have started control before the mites showed up this year. That would be the best practice. But many gardeners (including some Master Gardeners) will have been busy planting, weeding and enjoying their garden and react only when problems present themselves.
One method used to control spider mites and other garden pests is releasing beneficial insects. The larval or adult stages of these prey on other insects. Their eggs can be purchased in large numbers to place in your garden. Lady bugs are one of the more well-known species for that use. Other insects for natural control are predatory spider mites, minute pirate bugs, six-spotted thrips, lacewings and lady beetles. This is a solution that is most effective earlier in the season when the spider mite population is small.
The hot weather the mites love is problematic when it comes to remedies. Almost all pesticide sprays suggest not using in hot temperatures because spraying during hot temperatures will burn plant leaves.
Insecticidal soaps and oils such as Neem should be considered first when a pesticide is required. They are effective against mites and the least toxic to people, other nontarget organisms and the environment. Some oils can be used in any season.
They still should be used carefully during hot weather by confining your spraying to late evening or early morning, when temperatures lessen a bit. This timing also will help protect pollinators like bees and butterflies.
A few plants react badly to certain chemicals, even the ones considered somewhat mild, like insecticidal soap. Try a small, inconspicuous test area to see how it will react before covering your entire plant.
There are chemical pesticides that are specifically designed for mites, but spider mites may develop resistance to them after a few applications. Synthetic pyrethroids fall into that category. Pyrethrins are naturally occurring compounds extracted from chrysanthemum plants and used to make pesticides.
Pyrethroids have the same basic chemical makeup as pyrethrins but are not naturally occurring. Pyrethroids are man-made products that are also used as pesticides. The similarity of these two names is frequently confusing.
Alternating methods or chemicals used each time you treat for mites will help keep resistance from becoming a problem. Whatever method you choose will need to be repeated to keep up with the hatching of new spider mite life cycles for a few weeks.
Using a broad-spectrum insecticide will kill all insects, even the beneficial varieties. When choosing a pesticide, read all instructions on the label. You will learn what chemicals are used, what insects it will affect and what plants or wildlife it may damage.
It is also imperative that you know all first aid needed if a chemical accident occurs. One of the more important lessons taught about IPM (Integrated Pest Management) in Master Gardener classes is “Read the label! Read the label! Read the label!” Not a misprint — it’s that important!
For more information about spider mites and other garden pests, contact either the Mobile or Baldwin county offices of the Alabama Cooperative Extension System. These folks have a wealth of knowledge about plants and will be happy to share it with you.
GARDENERS, CHECK THIS OUT
What: Market in the Square (look for the Master Gardener tent for gardening information)
Find: Local produce, homemade bread, jams, preserves, honey, crafts, music
Where: Cathedral Square, Mobile
When: Saturdays through July 28, 7:30 a.m. to noon
MBG: Mobilebotanicalgardens.org for information on fall classes and events.
Master Gardener Helpline: 1-877-252-4769 or send your gardening questions to firstname.lastname@example.org.