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Hot weather brings out spider mites, mosquitoes

spider mite webbing on spirea
Telltale webbing of spider mites covers this spirea. The cure? Water. (Photo: Debbie Arrington)

Watch out for sunburned plants, too

Recent blazing hot weather has brought out heat-related pest and garden issues – while making other problems disappear.

First the good news: Gone is powdery mildew. It can’t survive in this heat. We shouldn’t see another outbreak of this fungal disease until October or later.

Also unable to cope with triple-digit temperatures are immature brown marmorated stink bugs and leaf-footed bugs. This heat wave likely toasted a whole generation of these destructive pests. That also means fewer bad bugs in August.

But some pests like it hot.

Leaf with stippling
These tomato leaves show stippling by spider mites.
(Photo: Kathy Morrison)

With no rain for weeks, it’s also dry and dusty – perfect conditions for spider mites. If you see their telltale webs or stippling on leaves, get out the hose. Wash the plant down, removing the dust and likely many mites.

Spider mites attack a wide range of plants including roses, fruit trees, berries, grapevines, beans, squash, melons, tomatoes and more. Miticides are not recommended; they kill many beneficial insects in addition to the mites, which often manage to evade pesticide sprays.

For more advice, see the UC IPM pest notes on spider mites:

Also out in force now are mosquitoes, which are a threat to people and pets as well as wildlife. According to the state’s West Nile Virus website, five dead birds found in Sacramento County last week tested positive for WNV. That brings the 2020 county total to 12. Four more Sacramento County mosquito samples last week tested positive, too, bringing that total to six.

County officials urge residents to be alert for dead birds and report them to the WNV bird hotline, 1-877-WNV-BIRD (1-877-968-2473).

Protect yourself, too. Wear mosquito repellent when working outdoors. At dawn and dusk when mosquitoes are most active, wear long sleeves and long pants.

For more info and the latest WNV statistics, visit .

While most plants need full sun, too much sun (and heat) can cause problems, too.

Shaded plant
A plastic plant flat serves as shade for a Patio Yellow potted tomato plant.
(Photo: Kathy Morrison)
Just like people, plants can get sunburned. If you notice crispy edges to leaves or pale patches on ripening tomatoes and peppers, that plant may need some shade. Construct a temporary shade structure to give plants some relief. It can be as simple as cardboard pieces on top of a tomato cage or burlap loosely draped over stakes.

Sunburn also can damage bark, especially on young trees or shrubs, opening up the plant to wood-boring pests and premature death. It tends to be worse on the west- and south-facing sides of plants. Painting the trunk and exposed lower limbs with diluted interior white latex paint (1:1 dilution with water) can protect a young tree's bark.

Besides a little shade, consistent irrigation can help plants survive too much sun.

For more tips on helping your garden deal with sunburn, see the advice of UC Cooperative Extension experts at .


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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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