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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Food in My Back Yard Series
March 18: Time to give vegetable seedlings some more space
March 11: Ways to win the fight against weeds
March 4: Potatoes from the garden
Feb. 25: Plant a fruit tree now -- for later
Feb. 18: How to squeeze more food into less space
Feb. 11: When to plant? Consider staggering your transplants
Feb. 4: Starting in seed starting
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Garden Checklist for week of March 16
Make the most of dry breaks between showers. Your garden is in high-growth mode.
* Pull weeds now! Don’t let them get started. Take a hoe and whack them as soon as they sprout.
* Prepare 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.
* Feed roses with a balanced fertilizer (such as 10-10-10, the ratio of nitrogen, phosphorus and potassium available in that product).
* Prune and fertilize spring-flowering shrubs and trees after they bloom. Try using well-composted manure, spread 1-inch-thick under the tree (but avoid piling it up around the trunk). This serves as both fertilizer and mulch, retaining moisture while cutting down on weeds.
* Cut back and fertilize perennial herbs to encourage new growth.
* In the vegetable garden, transplant lettuce and cole family plants, such as cauliflower, broccoli, collards and kale.
* Seed chard and beets directly into the ground. (To speed germination, soak beet seeds overnight in room-temperature water before planting.)
* Before the mercury starts inching upward, this is your last chance to plant such annuals as pansies, violas and primroses.
* 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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