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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 Jan. 29

Bundle up and get work done!

* Prune, prune, prune. Now is the time to cut back most deciduous trees and shrubs. The exceptions are spring-flowering shrubs such as lilacs.

* Now is the time to prune fruit trees, except apricot and cherry trees. Clean up leaves and debris around the trees to prevent the spread of disease.

* Prune roses, even if they’re still trying to bloom or sprouting new growth. Strip off any remaining leaves, so the bush will be able to put out new growth in early spring.

* Prune Christmas camellias (Camellia sasanqua), the early-flowering varieties, after their bloom. They don’t need much, but selective pruning can promote bushiness, upright growth and more bloom next winter. Feed with an acid-type fertilizer. But don’t feed your Japonica camellias until after they finish blooming next month. Feeding while camellias are in bloom may cause them to drop unopened buds.

* Clean up leaves and debris around your newly pruned roses and shrubs. Put down fresh mulch or bark to keep roots cozy.

* Apply horticultural oil to fruit trees to control scale, mites and aphids. Oils need 24 hours of dry weather after application to be effective.

* This is also the time to spray a copper-based oil to peach and nectarine trees to fight leaf curl. Avoid spraying on windy days.

* Divide daylilies, Shasta daisies and other perennials.

* Cut back and divide chrysanthemums.

* Plant bare-root roses, trees and shrubs.

* Transplant pansies, violas, calendulas, English daisies, snapdragons and fairy primroses.

* In the vegetable garden, plant fava beans, head lettuce, mustard, onion sets, radicchio and radishes.

* Plant bare-root asparagus and root divisions of rhubarb.

* In the bulb department, plant callas, anemones, ranunculus and gladiolus for bloom from late spring into summer.

* Plant blooming azaleas, camellias and rhododendrons. If you’re shopping for these beautiful landscape plants, you can now find them in full flower at local nurseries.

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