Talkback: Bug hunt and rosemary leaf beetle

Gardeners' World Web User

Although the others you describe are probably the harlequin ladybird, Harmonia axyridis, your metallic stripy 'ladybird' is almost certainly a rosemary leaf beetle, Chrysolina americana. Look out for the pale grey grubs, up to 10 mm long, sitting hard up to the stems, nibbling the edges of the leaves. The beetle rarely does much damage and it is such a wonderful looking insect.

Gardeners' World Web User

I have just discovered a multitude of rosemary beetle on my rosemary. Is it the cause of frothy collections at the base of some of the sprouting shoots?

Gardeners' World Web User

You say these plants are resilient,but our small rosemary bush was almost destroyed last year, and this year,with only a tiny amount of greenery visible, once again is covered in them. It has no chance!

Gardeners' World Web User

I think that sophie's frothiness at the base of the plant's stems is probably cuckoo spit which is made by the froghopper, nymph of the broad-headed bugs (red and black backed).

Gardeners' World Web User

Claire is right you have cuckoo spit. Which of course is a terrible slight on cuckoos, which I am sure never expectorate in public. The froth is made by the nymph of a plant hopper, Philaenus spumarius (from the latin for spume/ froth). It sucks plant sap and whips up its watery excrement into a protective coating of bubbles. They keep it warm when it is cold, cool when it is hot, hide it from predators and parasites and are a useful byproduct from its liquid diet. Many sap-suckers have the problem of sucking so much food to get enough protein to grow that they have to find some way of getting rid of the copious liquid that must pass through their bodies. Aphids give off honeydew to ants to solve the problem. The adult 'froghopper', 3.5 to 5.0 mm long has a wide variety of patterns from pale beige, mottled grey/ brown to black and is very common. I'd like to say that it never causes any problems, but I said that about rosemary beetles and as you can see felix says different. All I can say is that they are not pests unless they reach pest proportions.

Gardeners' World Web User

I have just been trying to establish what was on my rosemary then I saw this blog entry. Can I easily get rid of them and can I still eat the rosemary?

Gardeners' World Web User

As with lily beetles, the best way to get rid of rosemary leaf beetles is to hand pick them. Also look out for the C-shaped grey grubs which are the main leaf-eating culprits. The rosemary is still edible.

Gardeners' World Web User

My sage, thyme and rosemary are covered in these pretty beetles. I can't spot the grubs, but the sage in particular is being demolished. Very annoying!

Gardeners' World Web User

Last year my three year old rosemary bush got some kind of disease and it killed the entire plant. I dug up the plant, put down new soil. This spring I plant two new rosemary plant, not in same spot and it now is getting the same disease. There is a frothy looking substance on every branch, sticky. The plant was getting so full and beautiful. I cut back the plant to about eight or ten inches but they now have all the frothy stuff on them. I cannot find out what it is, nor how to get rid of it.

Gardeners' World Web User

Reply to Lynn. It sounds like you have the spittle bug, Philaenus spumarius, also called cuckoo spit bug. The nymphs make froth blobs to hide in whilst they suck sap. Pippa recently put up a note about them. They are usually more or less harmless to plants, but can cause problems if too numerous.

Gardeners' World Web User

Thanks, i was trying to find out what this bug was - now i know. It first appeared all over our lavender bush 2 years ago, and now the bush is not dead but is only ever bare, which is a shame as we never see the bees anymore. It is all over the rosemary too but there's a lot more of that to get through.