Milkweed

Monarchs come first. If you grow milkweed for butterflies, do not spray it with insecticides. In University of Florida trials, imidacloprid, acetamiprid and flupyradifurone killed every monarch caterpillar fed on treated plants the day after application, and imidacloprid and flupyradifurone still killed most at two weeks. Another systemic, pymetrozine, was still killing caterpillars four weeks on, twice as long as it held the aphids down. Insecticidal soap did not kill caterpillars directly, but it never brought the aphids below the treatment threshold. UF/IFAS discourages pesticides on milkweed and says to expect some cosmetic damage through the season. Check for monarch eggs and small caterpillars before you squash, prune or hose anything.

The crowds of bright yellow, black-legged aphids on the shoot tips and flowers are oleander aphid. The damage is mostly honeydew and sooty mould, but it costs monarchs indirectly: in a Florida study, females laid three times as many eggs on aphid-free plants. UF/IFAS advises a blast of water from the hose instead of pesticides. Squash colonies or prune the worst tips, and let the hoverflies and parasitic wasps that follow them build up.

The orange-and-black bugs on the pods are milkweed bugs. The large milkweed bug, ½–1 inch long, feeds on the seeds, leaves and stems, and Missouri's field guide says it does not damage milkweed much unless numbers are exceptional. The small milkweed bug, about ½ inch with a red-orange X on its back, sips nectar and sap from milkweed seeds and also scavenges. Both store milkweed toxins, as monarchs do, and their black-and-orange colours warn predators off. Leave them alone. The caterpillars stripping the leaves may be the monarchs you planted it for: UF/IFAS says they can eat a plant's leaves quickly but do not usually damage it long-term.