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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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Dig In: Garden Checklist

For week of March 26:

Sacramento can expect another inch of rain from this latest storm. Leave the sprinklers off at least another week. Temps will dip down into the low 30s early in the week, so avoid planting tender seedlings (such as tomatoes). Concentrate on these tasks before or after this week’s rain:

* Fertilize roses, annual flowers and berries as spring growth begins to appear.

* Knock off aphids with a strong blast of water or some bug soap as soon as they appear.

* Pull weeds now! Don’t let them get started. Take a hoe and whack them as soon as they sprout.

* Prepare summer vegetable beds. Spade in compost and other amendments.

* Prune and fertilize spring-flowering shrubs after bloom.

* Feed camellias at the end of their bloom cycle. Pick up browned and fallen flowers to help corral blossom blight.

* Feed citrus trees, which are now in bloom and setting fruit.

To prevent sunburn and borer problems on young trees, paint the exposed portion of the trunk with diluted white latex (water-based) interior paint. Dilute the paint with an equal amount of cold water before application.

* Cut back and fertilize perennial herbs to encourage new growth.

* Seed and renovate the lawn (if you still have one). Feed cool-season grasses such as bent, blue, rye and fescue with a slow-release fertilizer. Check the irrigation system and perform maintenance. Make sure sprinkler heads are turned toward the lawn, not the sidewalk.

* In the vegetable garden, transplant lettuce and kale.

* Seed chard and beets directly into the ground.

* Plant summer bulbs, including gladiolus, tuberous begonias and callas. Also plant dahlia tubers.

* Shop for perennials. Many varieties are available in local nurseries and at plant events. They can be transplanted now while the weather remains relatively cool.

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