Caterpillar defoliator: how I take care of my boxwood

My box hedge one year after the first attack of the defoliator caterpillar

If yours box hedge is attacked by the caterpillar defoliator do not panic and above all do not lose hope. The damage is not irreparable and the plant can return to the way it was before. But you have to act soon because this moth that feeds on boxwood leaves (and only those) is very resistant and does not go alone.

Personally with thecydalima perspectalis, or box borer, or more commonly boxwood defoliator caterpillar (but there are still other sinominiums) I have been fighting with it for over a year (since early summer 2013) and I periodically update IdeeGreen on the progress of my battle, which had a favorable outcome but which has not ended because I have verified that 'relapses' are possible.

Imagining that the reader has problems with the boxwood caterpillar and I'm looking for some tips, I get to the point and immediately say the products I used to successfully eradicate the infestation. As a contrast, on the initial advice of a phytopathologist, I used a product based on deltamethrin (there are some on the market, of which I do not mention the brands) and as a support a nitrogen-based fertilizer.

In my case, the infestation of caterpillar defoliator it concerned in a 'heavy' way an ancient hedge (we are in the province of Verbania at 900 meters above sea level) perfectly healthy before the attack and quite extended in linear meters. For this reason, also panicked, I asked a gardener for emergency assistance. From the second treatment onwards I made do on my own with the store bought deltamethrin and a common sprayer, following the instructions and all the necessary precautions for my health as well (when working with insecticides you have to be careful!). Here is by points what I checked and did in person:

  • One treatment is not enough. Fifteen days after the first intervention with deltramethrin performed by the gardener (August 2013) the caterpillar defoliator was still there. The typical cobwebs had 'almost' disappeared but in the hedge (I mean the non-defoliated part) I still found some active larvae.
  • I personally performed a second surgery 15 days after the first and a third one month after the second, always respecting the recommended doses and never exaggerating. Only at this point did I notice that the hedge was completely 'free', even if completely defoliated in some places.
  • During the pest control I supported the box hedge with a nitrogen-rich fertilizer to aid leaf regeneration. Frankly, I don't know if this tonic help has served and how much ('tonic' is a word invented by marketing) but given the result it was probably useful.
  • In the following months, autumn and winter, mine box hedge showed signs of recovery. The defoliator caterpillar eats the leaves but does not damage the roots and does not infect the lymphatic system. The plant can certainly die but only if it remains too long without leaves. In practice, it is a death from asphyxiation-lack of air. Timeliness of treatment is essential.
  • Between the end of winter and the beginning of spring 2014 (March) the caterpillar defoliator it reappeared and was already starting to defoliate. Everything as before: visible cocoons and black-green larvae well present. The only difference is that this time I noticed it earlier.
  • I believe that the mild winter 2013-2014 has favored the box borer, the fact is that I restarted the treatments with deltamethrin. One a month until June, always with caution and protecting myself. I admit that the last treatment, that of June, was mostly precautionary and on a hedge that seemed already free, but until May I found traces of larvae.
  • There box hedge she recovered well and during the spring-summer 2014 she became lush again, even without the support of nitrogen fertilizer. In some places where the attack was more ferocious, consistent traces remained in dry areas (I'm talking about a year later!) That I am slowly trying to eliminate with pruning.
  • I have the impression that I have won the battle against boxwood defoliator caterpillar because the hedge was saved and returned healthy, but what an effort! I believe that the success factor of the therapy was constant attention-monitoring and prompt intervention at the first sign of relapse.
  • The guard must remain high because I'm sure the caterpillar defoliator it can also be repeated on previously treated hedges. From the news I read this summer 2014 there have been massive attacks especially in Veneto and Emilia Romagna. The first case of infestation reported in Italy dates back to 2011 on Lake Como, after which the most affected areas were Lombardy and Piedmont, in particular in the lakes areas.

I am not a fan of synthetic insecticides, on the contrary I really hate them and I never use them preferring natural systems. But when I saw my hedge dry, I had no alternative for 'first aid' and I believe that if I hadn't used deltamethrin (or cypermethrin which is similar) I would have lost it. Now, having overcome the fear and better framing the threat, I am moving towards natural remedies for the boxwood defoliator caterpillar.

I have had confirmation that Bacillus Thuringiensis can be used in the biological control of box borer, in the Kurstaki and Aizawai varieties (better the latter). Bacillus Thuringiensis, which is a spore-forming bacterium naturally inhabiting the soil, has been known and used for some time in organic farming. It is found in specialized shops (there are different varieties and formulations) and is applied by spraying on the leaves. It defeats moths such as the caterpillar defoliator (but also dipterans) paralyzing their digestive system, but does not bother bees and other insects.

Bacillus thuringiensis Aizawai from 500 gr

For an updated and in-depth knowledge of Bacillus Thuringiensis I recommend the downloadable text in Kindle format Bacillus thuringiensis Biotechnology (the paper volume is bookable but will only be available on Amazon from October 2014).

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Video: Boxwood Winter Kill Issues (October 2021).