Tiny pests thrive during hot, dry, dusty conditions
This squash plant has a bad case of spider mites. Notice the stippling and the delicate webbing along the edge of the leaf in front. Kathy Morrison
Notice lots of fine webs around your garden? Our recent hot, dry, dusty weather has caused an explosion in spider mites.
Although we humans have a tough time dealing with triple-digit heat, this July has been spider mite paradise. The itty-bitty arachnids seem to be spinning their webs over everything: Tomatoes, roses, camellias, berries, fruit trees, you name it.
Shrubs in my backyard are draped with gossamer webbing, layered in tiers from the top leaves down to the ground. The webbing seemed to appear almost overnight; I don’t know for sure. (It was too hot to go outside and check.)
A cousin of spiders, spider mites have built up massive populations in local community gardens as well as backyards. Usually, natural enemies can keep these voracious critters under control. But right now, spider mites are having a baby boom.
Spider mites can produce a whole generation in five to 10 days. Each mama mite can lay 100 eggs. No wonder their numbers can overwhelm a plant in a short time.
Spider mites are so tiny – smaller than the period at the end of this sentence – gardeners usually don’t notice them until they’re mature; that’s when they start spinning their telltale webs.
As they grow, they tend to hide out on the underside of foliage, practically invisible to even the most observant gardeners. Spider mite feeding may cause polka-dot stippling to appear on leaves.
According to the UC Cooperative Extension master gardeners, spider mites attack many fruit trees, shrubs, vines, berries, vegetables and other ornamental plants. Besides tomatoes and roses, they also love beans, grapevines, squash and melons.
The damage at first looks a little like peach leaf curl with foliage developing stipples and turning yellow or red before falling off. Then the webs start appearing, coating leaves and stems.
If left undisturbed, spider mites can overwhelm plants. They’re especially bad during drought conditions or intensely hot and dry weather; they can do the most harm to water-stressed plants.
Spider mites can’t be controlled by insecticides – they’re not an insect, they’re a mite. But miticides are not recommended either, since they kill many beneficial insects in addition to the mites, which often manage to evade pesticide sprays.
Neem oil applied in the early stages of an infestation may smother the mites, but also kills beneficial insects including those that eat mites. In addition, neem oil sprayed on hot days can cook the plant’s foliage – eliminating any benefit.
Instead of neem oil or miticides, grab a hose and make it “rain.” Spider mites are proliferating because of lack of rain and resulting dusty, dry conditions on plants. Washing down foliage mimics a summer storm and disrupts the mites’ happy homes.
Insecticidal soap also can be helpful if applied at the first signs of trouble. Make sure to spray the underside of leaves, too.
The good news? Spider mites usually die out in late summer when their natural enemies can keep their numbers in check. Until then, keep giving plants a gentle morning shower as needed to wash dust and mites away.
For more advice, see the UC IPM pest notes on spider mites: http://ipm.ucanr.edu/PMG/PESTNOTES/pn7405.html
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Garden Checklist for week of Nov. 3
November still offers good weather for fall planting:
* If you haven't already, it's time to clean up the remains of summer. Pull faded annuals and vegetables. Prune dead or broken branches from trees.
* Now is the best time to plant most trees and shrubs. This gives them plenty of time for root development before spring growth. They also benefit from fall and winter rains.
* Set out cool-weather annuals such as pansies and snapdragons.
* Lettuce, cabbage and broccoli also can be planted now.
* Plant garlic and onions.
* Keep planting bulbs to spread out your spring bloom. Some possible suggestions: daffodils, crocuses, hyacinths, tulips, anemones and scillas.
* This is also a good time to seed wildflowers and plant such spring bloomers as sweet pea, sweet alyssum and bachelor buttons.
* Rake and compost leaves, but dispose of any diseased plant material. For example, if peach and nectarine trees showed signs of leaf curl this year, clean up under trees and dispose of those leaves instead of composting.
* Save dry stalks and seedpods from poppies and coneflowers for fall bouquets and holiday decorating.
* For holiday blooms indoors, plant paperwhite narcissus bulbs now. Fill a shallow bowl or dish with 2 inches of rocks or pebbles. Place bulbs in the dish with the root end nestled in the rocks. Add water until it just touches the bottom of the bulbs. Place the dish in a sunny window. Add water as needed.
* Give your azaleas, gardenias and camellias a boost with chelated iron.
* For larger blooms, pinch off some camellia buds.
* Prune non-flowering trees and shrubs while dormant.
* To help prevent leaf curl, apply a copper fungicide spray to peach and nectarine trees after they lose their leaves this month. Leaf curl, which shows up in the spring, is caused by a fungus that winters as spores on the limbs and around the tree in fallen leaves. Sprays are most effective now.
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