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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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Garden Checklist for week of July 7

Take care of garden chores early in the morning, concentrating on watering. We’re still in survival mode until this heat wave breaks.

* Keep your vegetable garden watered, mulched and weeded. Water before 8 a.m. to conserve moisture.

* Prevent sunburn; provide temporary shade for tomatoes, peppers, eggplant, melons, squash and other crops with “sensitive” skin.

* Hold off on feeding plants until temperatures cool back down to “normal” range. That means daytime highs in the low to mid 90s.

* Don’t let tomatoes wilt or dry out completely. Give tomatoes a deep watering two to three times a week. Harvest vegetables promptly to encourage plants to produce more.

* Squash especially tends to grow rapidly in hot weather. Keep an eye on zucchini.

* Some weeds thrive in hot weather. Whack them before they go to seed.

* Pinch back chrysanthemums for bushy plants and more flowers in September.

* Harvest tomatoes, squash, peppers and eggplant. Prompt picking will help keep plants producing.

* Remove spent flowers from roses, daylilies and other bloomers as they finish flowering.

* Pinch off blooms from basil so the plant will grow more leaves.

* Cut back lavender after flowering to promote a second bloom.

* One good thing about hot days: Most lawns stop growing when temperatures top 95 degrees. Keep mower blades set on high.

* Once the weather cools down a little, it’s not too late to add a splash of color. Plant petunias, snapdragons, zinnias and marigolds.

* After the heat wave, plant corn, pumpkins, radishes, winter squash and sunflowers. Make sure the seeds stay hydrated.

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