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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 Aug. 16

During this break in the heat, feed your garden. Make sure to water before and after applying fertilizer.

* In the garden, direct seed beets, carrots, leaf lettuce and turnips.

* Plant potatoes.

* Harvest tomatoes, beans, squash, pepper and eggplants to prompt plants to keep producing. Give your plants a deep watering twice a week, more if planted in containers. Also, give them a boost with phosphate-rich fertilizer to help fruiting.

* Watch out for caterpillars and hornworms in the vegetable garden. They can strip a plant bare in one day. Pick them off plants by hand in early morning or late afternoon.

* Feed citrus trees their last round of fertilizer for the year. This will give a boost to the fruit that’s still small.

* Mulch can be your garden’s best friend – it conserves moisture while blocking out weeds. But don't let mulch mound around stalks, stems or trunks. That can promote rot.

* Camellia leaves looking a little yellow? Give them some chelated iron. That goes for azaleas and gardenias, too.

* Pick up after your fruit trees. Clean up debris and dropped fruit; this cuts down on insects and prevents the spread of brown rot. Then feed fruit trees with slow-release fertilizer for better production for next year.

* To prolong bloom into fall, feed begonias, fuchsias and container plants. Always water before fertilizing.

* Fertilize fall-blooming perennials, too. Chrysanthemums can be fed until the buds start to open.

* Prepare for a fall full of flowers by paying a little extra attention to your garden. Cut off spent blooms from roses, annuals and perennials, then give them a boost of fertilizer. Make sure to water plants before feeding. Roses will rebloom about six to eight weeks after deadheading.

* Indoors, start seedlings for fall vegetable planting, including bunching onion, cabbage, broccoli, cauliflower, kale, radicchio and lettuce.

* Sow seeds of perennials in pots for fall planting including yarrow, coneflower and salvia.

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