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As temperatures warm, watch out for aphids

Hungry pests can devour tender new growth

Aphids on green rose bud
Aphids are munching away on this tender rosebud. Don't let them get ahead of you, or they will destroy all the almost-spring growth. (Photo: Kathy Morrison)

Spring arrived early in Sacramento. So did aphid season.

Warmer temperatures bring an explosion of green growth in our gardens – and possibly masses of hungry aphids, too. These voracious insects love temperatures in the 65- to 80-degree range, and our current forecast is for several days in the high 60s and low 70s.

Just as your favorite spring flowers are opening, aphids seem to burst on the scene to spoil the show. They can overwhelm new shoots and buds on rose bushes and other plants now pushing out spring growth. They can eat up your whole cabbage patch as well as attack almost everything in the vegetable garden from beans to potatoes. They’re particularly destructive to seedlings and tender shoots. (They like fruit trees, too.)

Aphids can seem to come out of nowhere, in part because they never really go away. Our winter temperatures are mild enough that aphids can survive our cold months. Then, when temperatures start to rise, they “reappear.”

Their numbers can rise so rapidly because the adult females can produce a dozen live offspring a day without mating. And they’re ready to start birthing in about a week.

“When the weather is warm, many species of aphids can develop from newborn nymph to reproducing adult in seven to eight days,” explains the UC Cooperative Extension pest notes. “Because each adult aphid can produce up to 80 offspring in a matter of a week, aphid populations can increase with great speed.”

What can a gardener do to stop this onslaught? Get out the hose.

On sturdy plants, a strong blast of water can knock off aphids. They can’t fly and their soft bodies can’t survive the fall to the ground.

“Using water sprays early in the day allows plants to dry off rapidly in the sun and be less susceptible to fungal diseases,” advise the master gardeners.

For more tender plants, try adding a teaspoon or two of liquid soap to a quart of water and spray the aphids directly. Or use insecticidal soap, specifically made for this purpose.

Use of insecticides is not recommended; chemical sprays will wipe out the beneficial insects (and there are many species of these) that prey on aphids and help keep them under control.

Instead, monitor for aphids regularly, checking the underside of leaves as well as shoots. Also, remove weeds (especially mustard) that can serve as aphid nurseries.

To cut down on aphid problems, watch how much you feed your plants. Too much nitrogen (which prompts rapid growth) can invite an aphid army.

“High levels of nitrogen fertilizer favor aphid reproduction, so never use more nitrogen than necessary. Instead, use a less soluble form of nitrogen and apply it in small portions throughout the season rather than all at once,” say the master gardeners. “Slow-release fertilizers such as organic fertilizers or urea-based time-release formulations are best.”

Sometimes the best solution is to cover tender seedlings.

“Because many vegetables are susceptible to serious aphid damage primarily during the seedling stage, reduce losses by growing seedlings under
protective covers in the garden, in a greenhouse, or inside and then transplanting them when the seedlings are older and more tolerant of aphid feeding,” added the master gardeners. “Protective covers will also prevent transmission of aphid-borne viruses.”

And don’t forget lady beetles, especially the nymphs. They LOVE aphids. But the adults usually leave your garden after they’ve had their fill.

For more on aphids and possible controls:


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Dig In: Garden checklist for week of Feb. 5

Make the most of sunny days and get winter tasks done:

* This is the last chance to spray fruit trees before they bloom. Treat peach and nectarine trees with copper-based fungicide. Spray apricot trees at bud swell to prevent brown rot. Apply horticultural oil to control scale, mites and aphids on fruit trees soon after a rain. But remember: Oils need at least 24 hours to dry to be effective. Don’t spray during foggy weather or when rain is forecast.

* Feed spring-blooming shrubs and fall-planted perennials with slow-release fertilizer. Feed mature trees and shrubs after spring growth starts.

* Finish pruning roses and deciduous trees.

* Remove aphids from blooming bulbs with a strong spray of water or insecticidal soap.

* Fertilize strawberries and asparagus.

* Transplant or direct-seed several flowers, including snapdragon, candytuft, lilies, astilbe, larkspur, Shasta and painted daisies, stocks, bleeding heart and coral bells.

* In the vegetable garden, plant Jerusalem artichoke tubers, and strawberry and rhubarb roots.

* Transplant cabbage and its close cousins – broccoli, kale and Brussels sprouts – as well as lettuce (both loose leaf and head).

* Plant artichokes, asparagus and horseradish from root divisions.

* Plant potatoes from tubers and onions from sets (small bulbs). The onions will sprout quickly and can be used as green onions in March.

* From seed, plant beets, chard, lettuce, mustard, peas, radishes and turnips.

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