Strawberry Aphids

Biology

Aphids are small (1-3 mm long), soft-bodied, pear-shaped insects that suck plant juices. Winged or wingless, they may be green yellow, pink, white, bronze, dark-brown or black. Sometimes, the wingless form is green and the winged form of the same species is black. The antennae are usually quite long. Aphids can be distinguished from similar insects by examining their "tail" ends. Aphids have a pair of tubes at the tip of their abdomens that resemble tiny exhaust pipes. Also, aphids tend to move very slowly compared to insects that are similar in appearance.

Several species may attack strawberries in southern Manitoba. Often, aphids occur on strawberries when the fields are weedy, suggesting that they may be "spillovers" from other host plants.

Symptoms Of Damage

Aphids suck plant sap, removing nutrients, reducing yields, and, in some cases, causing disease. Symptoms of damage include leaf discolouration, a flattened appearance, bent, white or distorted heads, and dying or dead patches (large bronzy or brown areas) in the field.

Honeydew deposits or sooty mould on the fruit and the white skins shed by aphid nymphs when they moult are clues to the presence of these insects. When aphid numbers are high, strawberries may appear wilted.

Monitoring

Look for symptoms of aphid damage throughout your fields on a weekly basis. Severe infestations are often easily visible from the edge of the field. Later in the season, infested patches may appear as thin stands. In younger plants, aphids may cluster near the base of the plant, on the upper sides of the leaves. In older plants, check inside the leaf whorls for the aphids. Keep your hand lens with you in the field so you can see the aphids clearly. If specimens are required for identification, collect infested plants by cutting the roots below the crown. Keep the specimen cool until it can be examined by an expert.

Economic Thresholds

Aphid control should begin as soon as aphids are found on several strawberry plants. Given their enormous reproductive potential and the damage that they can do, immediate action may be necessary. Consider the aphid density, the current weather conditions, the presence and abundance of natural enemies, the value of the crop, the stage of the crop being attacked, and the time to harvest before making a decision to apply an insecticide. In California, an economic threshold of 30 aphids per plant is used. A similar threshold would work in Manitoba.

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