Aphids

Garden pest · Aphidoidea

Description

Aphids are small, soft-bodied insects that feed by piercing plants and drawing out sap. The group includes many species, commonly green, black, yellow, or pink. Most gather in colonies on tender shoots, buds, and the undersides of young leaves. Feeding can curl or distort new growth and, when populations are large, weaken plants. Aphids also excrete a sugary liquid called honeydew. It leaves foliage sticky and can support the growth of black sooty mold; ants may visit to collect it. Some aphid species transmit plant viruses as they feed, so even a brief infestation can matter on susceptible crops. Colonies can grow quickly because many species reproduce without mating during the growing season. Winged adults may appear when colonies become crowded or plants decline, allowing aphids to move to new hosts. Damage varies widely with the aphid species, the plant, and the size of the colony.

Symptoms

• Yellowing leaves
• Sticky residue on leaves
• Black sooty coating
• Curled or cupped leaves
• Distorted new growth
• Stunted growth
• Leaves dropping
• Insects visible on the plant

How to Identify

Inspect tender shoots, flower buds, and leaf undersides for clusters of small, pear-shaped insects. Many aphids have two short, tube-like projections, called cornicles, near the rear of the body. You may see pale shed skins among the insects, sticky honeydew below them, or ants moving through the colony. Unlike spider mites, aphids are readily visible without magnification and do not produce fine webbing. Whiteflies fly up when disturbed; aphids usually remain clustered, although some adults have wings. Sooty mold is a consequence of honeydew rather than an aphid itself, so check for the insects before choosing a treatment.

Prevention

Check new plants before bringing them into the garden, and inspect tender growth regularly so colonies are found while small. Give plants appropriate light, water, and spacing to keep them growing steadily. Avoid excessive nitrogen fertilizer, which encourages the lush, soft growth many aphids favor. Grow a variety of flowering plants to support predators and parasitoid wasps, and avoid unnecessary broad-spectrum insecticides that kill these natural enemies. If ants are tending aphids, manage the ants where practical; they may protect colonies from predators. Remove heavily infested weeds near susceptible plants, but check them first for beneficial insects. In greenhouses, screen openings where feasible and inspect incoming plants carefully. These measures reduce infestations but cannot guarantee that winged aphids will not arrive.

Treatment

Start by checking whether predators, such as lady beetle larvae or lacewing larvae, are already controlling the colony. For small infestations, rub aphids off by hand or prune out a few badly infested shoot tips. A firm spray of water can dislodge aphids from sturdy plants; direct it at leaf undersides and repeat as needed. If colonies persist, use an insecticidal soap or horticultural oil labeled for the plant, following its directions. Cover the aphids thoroughly, since these products work mainly on contact, and repeat only as the label permits. Test a small area first because some plants are sensitive; avoid spraying in hot sun or when pollinators are visiting flowers. Manage ants if they are protecting the colony. Reserve stronger, plant-labeled insecticides for serious infestations after less toxic methods fail, and follow all label precautions. If aphids have transmitted a virus, killing them will not cure the infected plant.

Plants Affected

Abelia, Adzuki Bean, Alder, Amaranth, Amaryllis, American Basswood, American Beech, American Elm, American Hornbeam, American Sycamore, Apple, Artichoke, Arugula, Ash, Asparagus, Aspen, Banana, Barberry, Barley, Basil, Basswood, Beech, Beet, Bell Pepper, Birch, Bitter Melon, Black Bean, Black Cottonwood, Black Rice, Black Walnut, Black-eyed Pea, Black-eyed Susan, Bluebonnet, Bok Choy, Borage, Bottle Gourd, Bougainvillea, Broccoflower, Broccoli, Broccolini, Broom, Brown Rice, Brussels Sprouts, Burdock Root, Butterfly Bush, Cabbage, California Poppy, Camellia, Cannellini Bean, Caragana, Carnation, Carrot, Cauliflower, Ceanothus, Cedar, Celeriac, Celery, Chaenomeles, Chayote, Cherry, Cherry Blossom, Chervil, Chickpea, Chinese Broccoli, Chinese Cabbage, Chives, Chokeberry, Chokecherry, Chrysanthemum, Cilantro, Clematis, Collard Greens, Coneflower, Coreopsis, Coriander, Cork Elm, Cork Spruce, Cornus, Cosmos, Cotoneaster, Crabapple, Cranberry Bean, Cucumber, Cumin, Cypress, Daffodil, Daikon, Daisy, Dandelion Greens, Daphne, Daylily, Delphinium, Desert Rose, Deutzia, Dill, Drumstick, Eastern Cottonwood, Echeveria, Edamame, Eggplant, Elderberry, Elm, Endive, European Beech, European Hornbeam, Fava Bean, Fennel, Fenugreek, Fir, Forget-me-not, Forsythia, Freesia, Geranium, Gerbera Daisy, Goldenrod, Great Northern Bean, Green Bean, Guar Bean, Hamamelis, Hibiscus, Honeysuckle, Hornbeam, Horse Gram, Horseradish, Hyacinth, Hyacinth Bean, Hydrangea, Hypericum, Impatiens, Iris, Ivory Gourd, Jacaranda, Jack Bean, Japanese Maple, Jasmine, Jerusalem Artichoke, Jicama, Kabocha Squash, Kaffir Lime Leaf, Kale, Kidney Bean, Kohlrabi, Kolkwitzia, Komatsuna, Lablab Bean, Lambsquarters, Larch, Lavender, Lentil, Lettuce, Ligustrum, Lily, Lima Bean, Lisianthus, Littleleaf Linden, London Plane, Lonicera, Lotus, Lotus Root, Lovage, Lupine, Malanga, Maple, Marigold, Marjoram, Milkweed, Millet, Mint, Mizuna, Morning Glory, Moth Bean, Mountain Ash, Mulberry, Mung Bean, Mustard Greens, Napa Cabbage, Nasturtium, Navy Bean, Ninebark, Norway Maple, Oats, Okra, Oleander, Orange, Oregano, Paeonia, Pansy, Paper Birch, Parrot Flower, Parsley, Parsley Root, Parsnip, Passionflower, Pea, Peach, Pecan, Peony, Petunia, Philadelphus, Photinia, Physocarpus, Pickerelweed, Pinto Bean, Pittosporum, Plantain, Poncirus, Poplar, Poppy, Potato, Privet, Purslane, Quaking Aspen, Queen Anne’s Lace, Quince, Quinoa, Radicchio, Radish, Rapini, Red Cabbage, Red Maple, Red Twig Dogwood, Rhamnus, Ribes, Rice Bean, Ridge Gourd, River Birch, Rock Elm, Romanesco, Rosa, Rose, Rose of Sharon, Rutabaga, Rye, Sage, Salix, Salsify, Sambucus, Sand Cherry, Savory, Savoy Cabbage, Scarlet Runner Bean, Shasta Daisy, Silver Maple, Snake Gourd, Snap Pea, Snapdragon, Snow Pea, Snowberry, Sorghum, Sorrel, Soybean, Spinach, Spirea, Spruce, St. John's Wort, Statice, Sumac, Sunchoke, Sunflower, Sweet Pea, Swiss Chard, Sword Bean, Sycamore, Sycamore Maple, Symphoricarpos, Tamarix, Taro, Tarragon, Tatsoi, Tepary Bean, Thyme, Trumpet Vine, Tulip, Tulip Poplar, Tulip Tree, Turnip, Ube, Ulex, Urad Bean, Velvet Bean, Viburnum, Walnut, Water Hyacinth, Water Lily, Watercress, Watermelon, Wehani Rice, Weigela, Wheat, White Bean, White Birch, Willow, Winged Bean, Winter Melon, Wisteria, Witch Hazel, Yardlong Bean, Yellow Birch, Yellow Poplar, Zanthoxylum, Zelkova, Zinnia, Ziziphus

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