Find it before you spray it
Something is eating the leaves off my roses. I do not yet know what, and that is the whole of this post, because the first mistake with a rose being eaten is reaching for a bottle before you know what you are aiming at. Three of the things that strip a rose bare are never sprayed — two of them are mammals and one is a bee you want — and of the insects that are, one is immune to the spray most people reach for first. Find it before you spray it. The damage names the eater, and the eater names the treatment.
Read the damage
Go out in the morning with a cup of soapy water and a flashlight if it is still dark, and look — at the leaves, under the leaves, at the stems, and at the ground beneath. The pattern tells you most of it before you find anything alive.
| What you see | Who | When, here | How to be sure |
|---|---|---|---|
| Leaves eaten to a lace of veins, flowers chewed too; it happens in daylight | Japanese beetle | Late June to mid-August | You will see them; metallic green and copper, often in pairs |
| Pale "windowpanes" on the leaf where one surface was eaten, then holes; damage from the underside | Rose slug (sawfly larvae) | May–June, and the bristly kind in waves into October | Turn a leaf over: small green larvae, slug-like, some bristly, flush against the vein |
| Neat semicircles cut from the leaf edge, nothing else touched | Leafcutter bee | June to August | No insect on the plant; the cuts are too tidy to be anything else |
| Ragged holes in the middle of leaves; rolled or webbed leaves; frass (black specks) on leaves below | Caterpillars | July to September | Open a rolled leaf; look for the droppings |
| Ragged holes from the edges, late in the season, on a hot dry year | Grasshoppers | August–September | They jump when you walk the bed |
| Whole leaves and soft stem tips gone, ends torn and ragged, damage from knee height up, overnight | Deer | All year; worst October to March | Tracks, droppings, a browse line at the same height on everything nearby |
| Stems cut clean at 45°, low on the plant, bark gnawed at the base in winter | Rabbits | All year; worst in winter and on spring growth | Round pellets under the plant; the cut looks made with secateurs |
| Leaves yellowing with black spots and dropping, from the bottom up; the leaves are on the ground, not eaten | Not a pest — black spot | Any wet month | Look at the fallen leaves; nothing ate them |
Deer are worth a second sentence, because in a Kentucky fall they are the commonest answer and the one people least expect in a suburb. A deer has no upper front teeth, so it cannot bite cleanly; it grips and tears, and the torn stem end is the signature. A rabbit, which does bite cleanly, leaves a cut so neat it looks like pruning, and it cannot reach above two feet. If the damage is high and ragged it is deer; low and clean it is rabbits; and if it is both, you live where I do.
Who eats when
The month narrows the list before you have looked at a leaf. In July everything on the chart is possible and the beetles are the loud ones. In October the insects are mostly done — a last generation of bristly rose slugs, a caterpillar or two — and the leaves are going to the deer and the rabbits, who are starting the season in which a rose is the greenest thing in the yard.
The treatments, least harm first
Japanese beetles. Hand-pick them into the cup of soapy water, early in the morning when they are sluggish, every day for the six weeks they are here; it is tedious and it is the most effective thing anyone does. Beyond that, neem oil or a pyrethrin spray on the foliage, applied in the evening when the bees are home, knocks the numbers down and needs repeating after rain. Do not hang a beetle trap. The lure draws beetles from a quarter mile and the bag catches a fraction of them; a trap in your yard is an advertisement, and the research on this is unusually clear. Treating the lawn for grubs in late summer helps next year's neighbourhood a little and this year's roses not at all.
Rose slugs. They are sawfly larvae, not caterpillars, and that matters: Bt, the caterpillar bacterium, does nothing to them. A hard spray of water from the hose knocks them off and most do not climb back. Insecticidal soap or spinosad, sprayed on the undersides of the leaves where they feed, finishes the rest; either is gone in days and spares the bees if sprayed at dusk. Check again in two weeks for the next wave.
Caterpillars. Pick off what you find, open the rolled leaves, and if there are many, this is what Bt (Bacillus thuringiensis) is for — it kills only caterpillars, only when they eat it, and nothing else in the garden notices. Spinosad also works. Grasshoppers are not worth spraying for on a rose; they are passing through, and a row cover over a prized plant for the three bad weeks of a dry September does more than any bottle.
Leafcutter bees. Nothing. They take a few semicircles to line their nests, the plant does not care, and they are among the best pollinators you have. A rose with leafcutter marks is a rose in a healthy garden.
Deer. The only thing that works always is a fence a deer will not jump, which is eight feet, or a short double fence; everything else works sometimes. Repellents — the egg-and-garlic sprays, the predator-urine granules — work for a few weeks each and then the deer learn, so the method is to rotate two or three and re-apply after rain. Netting over a bed through the winter works and is ugly. Motion sprinklers work until they freeze. A dog works. What does not work is anything the deer can get used to, which is a single repellent, a radio, and hope.
Rabbits. A two-foot cylinder of hardware cloth around each plant, or a low fence of it around the bed, buried a few inches, and the problem is over for the price of a roll. Repellents with capsaicin help in the meantime. In winter, when they gnaw bark at the base, the cylinder is the only answer, and a girdled cane is a dead cane.
What not to do
Three things, all common. Spray without looking. A broad-spectrum insecticide on a flowering rose kills the bees on the flowers and the predators under the leaves, and if the eater was a deer it kills nothing you wanted dead. Reach for a systemic. The soil-drench products — imidacloprid and its relatives — move into the pollen and nectar, and on a plant whose whole point is flowers that is a decision about every bee in the neighbourhood; the label on most of them now says not to use them on flowering plants, and the label is the law, as it was in the scale post. Treat a disease as a pest. Leaves on the ground with black spots were not eaten, and no insecticide ever cured a fungus; that one is a different post, and a fungicide, and mostly a cleanup.
Will it come back
Almost certainly. A rose can lose every leaf in August and push new ones in three weeks; it has done this for millions of years against things with more legs than you. A rose stripped in October is in better shape still, because it was about to drop those leaves anyway and the energy for next year is already in the roots and canes. Do not feed it to "help it recover" — nitrogen now is the one thing that will hurt it going into winter — and do not prune the bare canes; a bare cane is not a dead cane, and the leaves will tell you in April which is which. Water it if the fall is dry, clean up what is on the ground, deal with whatever you found, and then put it to bed exactly as if nothing had happened: the mound keeps the rose cold, eaten or not.