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In a sunny, well-drained spot evening primroses are among the least troubled plants in the garden. Diseases are rare. The one pest that turns up reliably is the flea beetle, and the one condition that kills plants outright is soil that stays wet around the crown.
| Problem | When to watch | What you see |
|---|---|---|
| Flea beetles (adults) | Spring to autumn | Tiny shiny dark beetles that jump; small round holes in leaves |
| Flea beetle larvae | Spring to autumn | Leaves chewed and skeletonized, especially new growth |
| Crown and root rot | Wet winters; heavy soil | Plant yellows, wilts and collapses from the base |
| Powdery mildew | Humid late summer, crowded plants | White dusty film on older leaves |
| Aphids | Spring, on soft growth | Clusters on shoot tips and buds |
Flea beetles
Evening primrose flea beetles are about 1/8 in (3 mm) long, shiny and dark, often with a metallic blue or green sheen. The easiest way to recognize them is that they jump when disturbed, like fleas. Adults pepper the leaves with small holes, and the larvae feed on the foliage too, sometimes stripping young shoots and buds. Damage can show any time from spring to autumn.
Because they jump, the trick is to catch them as they fall. Hold a shallow dish of soapy water, or a sheet of cardboard smeared with something sticky, under the leaves and tap the stem; the beetles drop or leap straight into it. Do this in the cool of the morning when they are sluggish, and repeat every few days during an outbreak. Pick off leaves carrying larvae.
Healthy, established plants usually outgrow flea beetle damage. Protect seedlings and young plants most, since they have the least leaf to spare.
Rot and other problems
Crown and root rot are almost always a drainage problem. A taproot sitting in cold, waterlogged soil over winter goes soft and the plant collapses in spring. Raise the bed, add grit to clay, keep mulch away from the crown and, for the small alpine kinds, give them a sheet of glass or a cloche over winter to keep off the rain. There is no cure once the crown has rotted; remove the plant and improve the soil before replanting.
Powdery mildew sometimes appears on older leaves in muggy late summer, mostly on crowded plants. Thin them, water at the base and remove the worst leaves. Aphids on soft spring growth can be rubbed off or hosed away, and are rarely a problem on plants that are not overfed.