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Some pests love hot, dry weather

Spider mites, tomato hornworms spiking now

Sacramento Digs Gardening
BY Debbie Arrington PUBLISHED AUG 31, 2020

Spider mites love hot, dry conditions. Ash and fallen leaves cling to spider mite webs covering a camellia. (Photos: Debbie Arrington)

Some of the biggest and smallest pests to attack our gardens are enjoying these last days of summer – much to our dismay. While many critters retreat in high heat, these invaders actually spike in numbers and activity as the mercury rises.

Recent dusty, hot and smoky weather has been terrible for people. Spider mites think it’s heaven. They don’t mind the ash clinging to their webs.

These itty-bitty arachnids thrive in hot, dry, dusty conditions, attacking water-stressed plants.

According to the UC Cooperative Extension master gardeners, spider mites can multiply especially 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 minute arachnid, the same eight-legged class that includes spiders and ticks.

Spider mites spin telltale 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.

Beneficial insects usually can outnumber the spider mites and keep them under control. But when the weather turns unusually hot, dry and smoky as it has been, the predators tend to retreat, allowing the spider mites to take hold.

The solution? Water. Take the hose and spray dust and ash 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.

To keep them away, keep the garden well watered. Irrigation is key to spider mite control. They don’t like it wet.

Tomato hornworms will munch on leaves, stems and fruit (both

unripe and ripe) of tomato plants.

Meanwhile, the heat also brought out a late-summer surge of one of the biggest bugs in the vegetable garden: The tomato hornworm.

Natural enemies usually keep their populations under control. But hornworm numbers can spike in late summer with high heat.

Fat as a finger and just as long, hornworms rank as Sacramento’s largest caterpillars. They eat big bites out of their favorite food: Ripe tomatoes. They’ll also eat green tomatoes, leaves and stems.

Their stripes let them hide in plain sight. They blend in so well with their surroundings, they can seem impossible to spot.

If you suspect hornworms, look for their poop. They leave large black or green droppings on or around the plant. If you see those droppings, carefully inspect the plant’s leaves and stems. When you find it, pick off the hornworm and dispose of it.

If the hornworm escapes capture, it burrows into the soil and pupates into a moth of equally gigantic proportion: The hawk moth. Emerging in spring, this brown and gray moth has a 5-inch wingspan.

Rototilling the tomato bed after harvest prevents those moths from ever developing – and laying eggs next spring.

For more on spider mites: http://ipm.ucanr.edu/PMG/PESTNOTES/pn7405.html

For more on tomato hornworms: http://ipm.ucanr.edu/PMG/GARDEN/VEGES/PESTS/hornworm.ht ml

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Keywords:

UCCE master gardeners Sacramento pests heat wave heat stress heat pest gardening integrated pest management vegetables heat summer vegetables garden pests vegetable gardening

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Garden Checklist for week of May 5

Survey your garden after the May 4 rainstorm. Heavy rain and gusty winds can break the neck of large flowers such as roses. Also:

* Keep an eye on new transplants or seedlings; they could take a pounding from the rain.

* Watch out for powdery mildew. Warmth following moist conditions can cause this fungal disease to “bloom,” too. If you see a leaf that looks like it’s dusted with powdered sugar, snip it off.

* After the storm, start setting out tomato transplants, but wait on the peppers and eggplants (they want warmer nights). Pinch off any flowers on new transplants to make them concentrate on establishing roots instead of setting premature fruit.

* Trim dead flowers but not leaves from spring-flowering bulbs such as daffodils and tulips. Those leaves gather energy to create next year's flowers. Also, give the bulbs a fertilizer boost after bloom.

* Pinch chrysanthemums back to 12 inches for fall flowers. Cut old stems to the ground.

* Mulch around plants to conserve moisture and control weeds.

* From seed, plant beans, beets, cantaloupes, carrots, corn, cucumbers, melons, pumpkins, radishes and squash.

* Plant onion sets.

* In the flower garden, plant seeds for asters, cosmos, celosia, marigolds, salvia, sunflowers and zinnias. Transplant petunias, zinnias, geraniums and other summer bloomers.

* Plant perennials and dahlia tubers for summer bloom.

* Don’t wait; plant summer bulbs, such as gladiolus and tuberous begonias.

* Harvest cabbage, lettuce, peas and green onions.

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