With the hot weather we recently had, you might be starting
to notice diseases or insects in your garden. One common garden pest during hot
dry conditions is the spider mite. The two-spotted spider mite is actually an
arachnid (not an insect), and is quite tiny being ¼ mm or less in length. These
tiny little arachnids have piercing mouthparts that puncture the cells of your
plants as they suck out the juices. This creates the “flecking” appearance on
leaves. They have a broad host range, and are capable of colonizing many common
garden plants including: eggplants, peppers, tomatoes, squashes, cucumbers,
corn, many houseplants, etc. Adult spider mites overwinter in the soil, and lay
their eggs on suitable host plants in the spring and summer. When weather conditions
are suitable, the eggs hatch and begin to feed on the plant. When conditions
are just right spider mite populations can bloom in no time. One day there are
a couple of leaves with spider mites and within a week you can have an entire
plant covered. Spider mites, as their name suggests, can spin disorganized webbing
over the plant when infestations are high. This is one way to easily identify
them.
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| The splotchy patches of yellowing leaves are a good symptom of spider mites. |
Symptoms and signs
Spider mite infestations are very easy to diagnose. If you
see leaves that are becoming flecked with patchy yellowing, or exhibit bronzing
then your plant is a good spider mite candidate host. Spider mites live on the
underside of the leaf, so to look for them you’ll need to flip the leaf over.
It is possible to see them with the naked eye, but a hand lens with at least
10x magnification is best for a good view. If you don’t have a hand lens, and
even if you do, you can take a piece of white paper and shake a leaf over it.
If you have spider mites, they should fall onto the paper and you should be
able to see them begin to slowly crawl.
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| Close up of infested leaf |
Management options
Not all mites are bad though. One of the top beneficial
insects for controlling spider mites is other mites! If you smear the mite on a
piece of white paper and it is green, it’s likely the parasite. If it’s orange
or yellow it is likely a beneficial. You can buy beneficial insects from
companies like Koppert that specialize in biological controls, encourage
beneficials through native plants or successive flowering plants. Or you can
raise your own mites using subset of the predatory mites and growing them in
bran. This can take a bit of time, but it very convenient for controlling mites
over multiple months in a large area. Other beneficial insects like lady bugs,
minute pirate bugs, and lacewings can also be used to control spider mite
infestations with varying degrees of effectiveness.
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| Turn an infested leaf over and you can see the grainy appearance of the spider mites, their dust, eggs and frass. If you look really closely you can see yellow spider mites with little red dots on their bums. |
If the infestation is light you can try to control mites
using insecticidal soaps, horticultural oils, miticide sprays, or common soaps
(Ivory and Murphy’s oil soap work well). If you’re using soaps or oils, don’t
apply while the weather is hot and sunny because these can damage your plants
if you’re not careful. With soaps in particular, you can typically apply with a
hand sprayer and rinse an hour after application. The soapy water creates a
film around the spider mite, suffocating it according to entomologist Dan
Hulbert. Adequate watering is important to help your plants deal with the added
stress of the spider mites. Some sources cite spraying water on the plants to
help control mild infestations of spider mites.
Sources contributing information to this post:
Virginia Tech Extension bulletin
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