University of California Agriculture and Natural Resources released guidance on Mar. 23 for managing aphids as their populations increase with the arrival of spring. The organization described how aphids, which come in various colors and thrive between 65 and 80 degrees, can rapidly infest plants such as roses during this season.
Aphid outbreaks matter to gardeners because these insects not only feed on plant fluids but can also transmit viruses that affect both ornamental plants and vegetable crops like squash and tomatoes. While some damage from aphids is tolerable, heavy infestations can lead to honeydew buildup, attracting sooty mold that may weaken plants by limiting photosynthesis.
The organization advised against immediately using broad-spectrum insecticides since these products harm beneficial insects such as ladybugs, lacewings, damsel bugs, and hoverfly larvae—natural predators that help control aphid populations. Instead, it recommended monitoring plants daily during periods of rapid growth, removing aphids with strong water sprays or pruning infested parts, controlling ant populations to allow beneficial insects to thrive, avoiding over-fertilization in springtime, and choosing less toxic alternatives like insecticidal soaps or neem oils when necessary.
The release explained that systemic products should be a last resort for severe cases on ornamental plants like roses—not for use on vegetables or fruit trees—and must be applied strictly according to label instructions. “So remember when considering different control tactics for aphids, choose the methods that moderate aphid populations and do not disrupt the natural population of beneficial insects. You’re in for a constant battle with bugs if you do,” the statement said.
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