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When heat is on, spider mites attack

Web-spinning pest loves hot, dry conditions

Spider mite webs with debris
Spider mite webs catch all kinds of tree debris. (Photos: Debbie Arrington)

Some pests LOVE this heat. The hotter, drier, dustier the conditions, the more they thrive. Topping that heat-loving list: Spider mites.

Where are they? Just look for the fine webs.

Right now, several of my shrubs look like they’ve been web-bombed. Leaves of my Christmas camellias are so coated, they pick up all sorts of garden debris – anything dropping from nearby trees or blown into the webbing by gusts of wind.

Spider mites don’t mind. These itty-bitty arachnids thrive in hot, dry, dusty conditions. Their favorite food? Water-stressed plants. During this record heat, just about any plant can fall into that category.

If it seems like spider mites and their telltale webs came out of nowhere, they almost did. According to the UC Cooperative Extension master gardeners, spider mites can multiply rapidly during these conditions.

“If the temperature and food supplies are favorable, a generation can be completed in less than a week,” say the master gardeners’ pest notes.

No bigger than a pinpoint, a spider mite is a teeny-tiny arachnid, the same eight-legged class that includes spiders and ticks.

Spider mites spin fine-textured webs, which are much more noticeable than the tiny creatures. They attack just about any plant from strawberries to full-size trees, sucking out moisture.

Spider mite webs on camellia leaves
This camellia has several spider mite webs on the leaves.

Beneficial insects usually can outnumber the spider mites and keep them under control. But when the weather turns unusually hot and dry (like right now), predators retreat, allowing the spider mite populations to explode.

What’s the best cure for spider mites? Water. Take the hose and spray dust (and bugs) off leaves, making sure to get the undersides of foliage, too. A strong shower disrupts spider mite paradise and holds them at bay until the real rains come (hopefully) in fall. It also gives those natural predators a chance to catch up with their mite munching.

To keep spider mites away all summer, regularly water your landscape. Irrigation is key to spider mite control; this pest prefers life hot and dry. Whether you see webs or not, occasionally wash off foliage, especially of large shrubs such as camellias or roses. Your plants will be happier and healthier – only the spider mites will be gone.

For more on spider mites:


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Dig In: Garden checklist for week of Oct. 2

Plan to make the most of the mild weather in your garden.

* October is the best month to plant trees and shrubs.

* October also is the best time to plant perennials in our area. Add a little well-aged compost and bone meal to planting holes or beds, but hold off on other fertilizers until spring. Keep the transplants well-watered (but not wet) for the first month as they become settled.

* Now is the time to plant seeds for many flowers directly into the garden, including cornflower, nasturtium, nigella, poppy, portulaca, sweet pea and stock.

* Plant seeds for radishes, bok choy, mustard, spinach and peas.

* Plant garlic and onions.

* Set out cool-weather bedding plants, including calendula, pansy, snapdragon, primrose and viola.

* Reseed and feed the lawn. Work on bare spots.

* Dig up corms and tubers of gladioluses, dahlias and tuberous begonias after the foliage dies. Clean and store in a cool, dry place.

* Treat azaleas, gardenias and camellias with chelated iron if leaves are yellowing between the veins.

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