Rose chafer
Macrodactylus subspinosus
A long-legged tan beetle that appears in numbers on sandy ground for a few weeks in June, skeletonizing roses and grapes and then vanishing.
How to know it
A slender, ungainly beetle 10–12 mm long, tan to reddish-brown with a greenish tinge and disproportionately long spiny orange legs. They cluster in groups on flowers and shoot tips and are sluggish and easy to catch. The grubs are small white C-shaped larvae in sandy soil.
What you'll see
- Groups of long-legged tan beetles feeding openly on rose blooms and grape leaves in June.
- Flowers chewed to tatters, especially white and pale ones.
- Leaves skeletonized between the veins into a lace.
- Damage appearing suddenly in late May or June and finished by early July.
- Gardens on sandy or gravelly soil hit hard and heavy-soil gardens nearby hardly at all.
Where it comes from
One generation a year. Adults emerge from sandy ground in late spring and feed for four to six weeks, then lay eggs in that same light soil. The grubs feed on grass roots through the autumn, overwinter deep, and pupate in spring. They are strongly tied to sandy, sparse, grassy ground for laying — which is why the problem is so local.
Sandy and gravelly soils in the northeast and midwest, especially gardens next to sandy pasture, dunes or old fields. Numbers vary hugely from year to year and from garden to garden a mile apart.
Dealing with it
- Knock the beetles into soapy water first thing in the morning; they are slow and gather in groups, so this works well.
- Cover roses, grapes and small fruit with fine netting for the four weeks of the flight.
- Pick and remove badly chewed blooms so the groups have less to gather on.
- Do not hang traps; as with Japanese beetle they draw more in than they catch.
- Keep poultry away from the beetles — rose chafers are genuinely toxic to chickens and other birds.
Keeping it out
- Net the plants that matter before the flight starts, in mid-May.
- Keep the lawn and any sandy ground nearby thick and well grassed rather than sparse, which discourages laying.
- Plant the most attractive plants — pale roses, peonies, grapes — away from the sandy boundary.
- Apply beneficial nematodes to sandy turf in late summer where the grubs are breeding.
- Expect it for a month and plan around it rather than fighting it all season.
What it goes for
Roses, grapes, peonies, apples, raspberries, hollyhocks and elderberry above all.
Who hunts it for you
- Beneficial nematodesSteinernema & Heterorhabditis spp. Microscopic worms watered onto damp soil that hunt down soil-dwelling grubs and release a bacterium that kills them within days. Timing is the whole thing: warm, damp soil and a small target grub, which means late summer for most of what they are used against.
- Garden birdsPasseriformes Both things are true: birds strip your currants and a brood of blue tits takes several thousand caterpillars out of one fruit tree in a fortnight. Net what you must and welcome them everywhere else — a nest box near the apples is worth more than a spray. Grow to recruit it: Echinacea,Elderberry,English holly,Goldenrod,Rudbeckia,Sunflower
See also
The Cottage Garden Companion — the gardener's bestiary at cottagegardencompanion.com