I have two small boxwood hedges in my garden which I have trained over the years by cutting into the form of a cuboid. One hedge is in a shady and wet place, one is fully exposed to the sun, south oriented.

They are two different kind of boxwoods, of which I don't know the species. One, I'd say, is the classical one, round leaf variety, one has slightly triangular leaves. Both show the same symptoms.

Last year, I don't know why, I cut the hedges in October only. Even though I'm aware that it should be done in late/middle-summer. I think I thought, what the heck.

Right after cutting I noticed that the some leaves started getting (or already had been gotten) dry and became white-greyish. I thought, ok it was too late, but it won't kill them, they will recover.

At the same time people in the village reported a box-infection of some kind of insect (I forget the name).

Then winter came, we had colds going down to -5 °C and I thought if it is insects, they are dead now.

Now in spring I'm fearing the worst, 50% of the hedges show grey leaves, there is barely new growth.

Today I noticed that there some kind of webs inside (might be normal) and some crumbs, which could be sediments of something, or simply birch pollen. (There are birches nearby).

Here are some pictures I took. I'd like to know what it is and if there is anything I can to do prevent further damage.

Typical gray leaf Overview Crumbs Damages

  • These insects don't die during winter, because eggs are lay deep in the earth, on the roots. And it has no specific enemy. We're kind of doomed with our boxwoods. – J. Chomel Apr 24 '17 at 9:36
up vote 3 down vote accepted

If there's webbing amongst the leaves, my money's on box tree caterpillar, although its odd you've not actually noticed the caterpillars themselves yet. Of all the problems Box gets (and its an ever increasing list) the only one that goes with webbing is the caterpillar. The caterpillar is the larval stage of a moth and was first found in mainland Europe in 2007, so it's been around for a while, not quite so long in the UK as over there. Eggs are often present under the leaves if the caterpillars are not hatched yet, so check beneath.

This link lists various problems from which Box suffers - you can click on each one for more information to see for yourself what you think.If it is Box caterpillar, picking them off by hand is useful, but spraying may be required. Note the spray has to be pretty forceful in order to penetrate the webbing. Pesticide products recommended in the link may not be available under the same names where you are, but there should be products using the same active ingredients.

Not sure what those deposits are on the leaves in the bottom left picture, but I do know that other evidence of Box Tree Caterpillar/Moth is frass deposits and residues of moult such as 'black head capsules of different sizes'. Sounds charming - got that from this link here: Plantwise Knowledge Bank which has information that may be more pertinent to mainland Europe.

  • 1
    There are multiple problems with this boxwood...but I think you are correct for the largest problem. – stormy Apr 22 '17 at 21:24
  • And the completely white leaves? Which seems to be sucked empty? Is this also the caterpillar? In the linked list of problems they are talking about the box sucker. Could this be damage created by the sucker in the first place? – Patrick B. Apr 22 '17 at 22:09
  • 1
    This page rhs.org.uk/advice/profile?PID=851 shows a possibility of a leaf miner and Macrophoma leaf spot. I will check in more details tomorrow. Right now I think I have a blight and the caterpillar. What strikes me with the blight is that the triangular leaf-shaped one is affected as well. I thought this variant is resistant. – Patrick B. Apr 22 '17 at 22:14
  • If it proves to be blight later on, don't cut for a year, feed regularly throughout the growing season and it may recover, but I don't suspect blight at this stage - the moth infestation can cause all this damage on its own. – Bamboo Apr 22 '17 at 22:38

After Bamboo's answer I checked again and collected around 20 caterpillars just on one plant (50x50cm) and I'm sure I missed some of them.

enter image description here

I checked again for the alert I received from a fellow gardener of the village last year, and it is exactly what I found on mine: Pyrales du buis: Cydalima perspectalis, the box tree moth.

I will try the treatment based on the bacillius thuringiensis.

  • That's it! I have the same, here in France it's horrible how quick all our buxus get killed one after the other... hope you save your trees. – J. Chomel Apr 24 '17 at 9:14
  • I also heard pheromone trap worked well... But they are so many and keep coming back. Because the issue with thuringiensis is it also attacks a broad range of insects – J. Chomel Apr 24 '17 at 9:16
  • Pheromone trap would be for the moth to prevent it from laying eggs. It won't help against the caterpillars. – Patrick B. Apr 24 '17 at 9:17
  • Yes of course! the eggs are the problem, because they are put on the roots. This is the most concerning issue. If you shake your buxus from time to time, the caterpillars are not that a big issue compared to the eggs. – J. Chomel Apr 24 '17 at 9:19
  • Yes, it surely attacks other insects. I'm pondering between doing nothing and removing the boxwood or trying thuringiensis. No way I will use a chemical insecticide. I leave that to the professional farmers around the village ;-( – Patrick B. Apr 24 '17 at 9:19

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