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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 Sept. 25

This week's warm break will revive summer crops such as peppers and tomatoes that may still be trying to produce fruit. Pumpkins and winter squash will add weight rapidly.

Be on the lookout for powdery mildew and other fungal diseases that may be enjoying this combination of warm air and moist soil.

* Late September is ideal for sowing a new lawn or re-seeding bare spots.

* Compost annuals and vegetable crops that have finished producing.

* Cultivate and add compost to the soil to replenish its nutrients for fall and winter vegetables and flowers.

* Plant for fall now. The warm soil will get cool-season veggies and flowers off to a fast start.

* Plant onions, lettuce, peas, radishes, turnips, beets, carrots, bok choy, spinach and potatoes directly into the vegetable beds.

* Transplant lettuce, cabbage, broccoli, kale, Brussels sprouts and cauliflower.

* Sow seeds of California poppies, clarkia and African daisies.

* Transplant cool-weather annuals such as pansies, violas, fairy primroses, calendulas, stocks and snapdragons.

* Divide and replant bulbs, rhizomes and perennials.

* Dig up and divide daylilies as they complete their bloom cycle.

* Divide and transplant peonies that have become overcrowded. Replant with "eyes" about an inch below the soil surface.

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