Oleander aphids
Bright yellow-orange aphids (Aphis nerii) with black legs, 2 mm long, packed shoulder-to-shoulder along stems and on the underside of upper leaves. They specialize in the milkweed family and almost no other plants. Clusters can cover 6 inches of stem in mid-summer.
Dense yellow-orange masses are alarming to look at but milkweed shrugs them off. A sticky shiny film coats lower leaves and the soil below. New growth may twist slightly. The plant rarely declines, even with heavy clusters, because milkweed has deep taproots and tough mature foliage.
Strong water blast every few days
Hold a hose nozzle 12 inches from the affected stems and spray at high pressure. Most aphids dislodge and don't make it back. Repeat every 2 to 3 days until clusters thin out. This is the only treatment most milkweed gardeners should use because it doesn't harm monarch eggs or caterpillars on the same plant.
Squish by hand or wipe with a wet cloth
Pull on a glove and run your fingers up the stem to crush clusters in place, or wipe with a damp cloth. Slow but completely safe for monarch eggs and caterpillars on adjacent leaves. Check the plant first for caterpillars before squishing anything.
Tolerate them and let predators catch up
Aphid populations crash on their own once ladybugs, lacewings, and parasitic wasps find the cluster (usually 1 to 2 weeks). The aphids are unsightly but rarely kill milkweed. If you can sit with the visual, doing nothing is a real option, especially mid-season when monarchs are using the plant.
Spray insecticidal soap or neem oil to kill the aphids fast.
Both kill monarch eggs and young caterpillars on contact, even the organic versions. Sprays don't distinguish between aphids and the monarch larvae you planted milkweed to support. On milkweed, water blasts and tolerance are the only sane choices. Skip every spray, organic or not.
