Bonsai Tonight

Spider mites aren’t insects

Posted in Bonsai Development by Jonas Dupuich on December 19, 2014

Rather, they are members of the arachnid family. Here’s what they like:

  • Hot, dry and dusty conditions
  • Stressed trees
  • Selected pesticides – (see this article from UC’s IPM for details)

If possible, avoid these. Left unchecked, spider mite infestations can severely damage bonsai.

Although they are too tiny so see clearly without magnification, their damage is identifiable when you know what to look for.

Spider mite damage

Spider mite damage on black pine (photos from April 2012)

Checking for spider mites can be done with a white sheet of paper.

  1. Hold white paper below foliage suspected of infestation
  2. Tap the branch
  3. Check to see if any of the black dots are moving

Checking for spider mite

The paper catches debris and mites, if present

Checking for spider mite

If the dots move, you may have spider mites

Spider mites reproduce very quickly. If you’re not quick to catch them, they can overcome a garden of pines in a matter of days. And even if the infestation is stopped quickly, affected trees will show damage until next year’s needles mature.

The best defense against spider mites – as is the case with all infestations – is keeping trees healthy and well-hydrated, especially during the warmest months of summer.

Oils and insecticidal soaps are the typical first line of defense. If you have to resort to pesticides, look for miticides and check the instructions carefully to make sure they don’t exacerbate the problem.

Spider mites also provide good reason to spray lime sulfur or other dormant sprays in winter as they or their eggs can hang out during cold months under leaves or bark, patiently awaiting favorable conditions when the weather warms up.

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Posted in Bonsai Development by Jonas Dupuich on December 16, 2014

Have you ever seen moths or butterflies among your bonsai? Do you see them a lot? If so, there may be caterpillars nearby.

Caterpillars are among my least favorite garden pest. They can cause lots of damage quickly, especially on small, tender trees. You can find them on deciduous trees and on conifers.

Some are large, others are tiny. Many have mastered the art of camouflage.

Hinoki foliage and caterpillar

Hinoki foliage and a caterpillar that feeds on it
(Today’s photos will look familiar to readers of posts from a few years back)

With leafy trees, caterpillar damage is most often marked by holes in leaves, missing sections of leaves, or completely missing leaves. With conifers, caterpillars can eat soft growth tips or burrow inside tender shoots.

Worm in juniper foliage

Caterpillar in shimpaku foliage

It’s fairly easy to see damage caused by tip-eating caterpillars. When they burrow inside shoots, subtle dieback can occur.

Signs of a worm

Caterpillar damage on a Western juniper

Signs of a worm

What’s this – it’s still inside

Worm in juniper foliage

Creeping out into the light


The culprit

I’ve seen them on a variety of scale trees, from hinoki, to shimpaku, to Western juniper as well as Sierra juniper.

Signs of a worm

Tell-tale signs on Sierra juniper foliage

Worm in juniper foliage

Caterpillar in Sierra juniper foliage

Caterpillar control is most often accomplished with pesticides and a bacterium known as Bacillus thuringiensis – one of the more common active ingredients in caterpillar sprays. Bt must be sprayed when caterpillars are active as they have to eat it for it to be effective (it kills by destroying caterpillars’ guts). Spraying towards the end of the day, for example, is best for caterpillars that feed at night.

I tend to pinch away foliage with isolated caterpillar damage and save the sprays for more serious cases, but I’ve noticed that this can be a slippery slope. To really get ahead of serious caterpillar infestation, spraying at regular intervals and using multiple modes of attack – say neem oil and Bt – may be required.

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White spots on Western juniper

Posted in Bonsai Development by Jonas Dupuich on December 12, 2014

In the spirit of identifying white dots on bonsai these past few weeks, today’s subject is Western juniper.

Western juniper

Western juniper

For those unfamiliar with the variety, Western junipers are frequently covered with white dots, one per scale. On some occasions, the dots enlarge and merge together to form a sticky white mass.

Western juniper foliage

Sticky white substance on Western juniper foliage

Unlike the white dots caused by the various insects we’ve looked at recently, the white on Western juniper is a resin secreted by the foliage. Working on Western juniper can quickly lead to dirty, sticky fingers, but the resin is natural and not a sign of infestation.

Western juniper foliage

Resin build-up on Western juniper foliage

Sometimes this resin turns black. This can be either dust sticking to the white resin or a non-harmful fungus that grows on juniper foliage. As this fungus doesn’t do well where I live, I most often see it on newly collected junipers.

There’s nothing to do about the resin as it’s natural. I’ve come to appreciate it over time as one of the “charms” of the variety – a variety best known for great movement and deadwood.

So as not to turn completely away from bugs today, do read Michael Hagedorn’s recent post on wood-boring beetles if you haven’t – it’s a good read about a pernicious pest.

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Posted in Bonsai Development by Jonas Dupuich on December 9, 2014

Have you ever seen small white spots accumulate at the base of needles or buds on black pines? On other conifers? If so, you’ve likely seen adelgids.


See the small white spots just above the bud?

Adelgids are a cousin of sorts to aphids. They are also known as pine aphids or wooly conifer aphids as they occur on pine, spruce, fir and other conifers. I tend to first notice them at the base of pine needles and buds, but in the case of bad infestations, they can completely blanket needles, branches and bark along the trunk. The photos here show the very first signs of adelgid infestation – the best time to spray.


Signs of adelgids


Close up


Adelgids on immature pine growth

Treatment is similar to treatments for aphids or scale. The idea is to start with something mild like contact oils or soaps, then move to contact or systemic pesticides only if the need arises. Maybe because they take up residence in somewhat sheltered areas of the tree, I find that several applications may be required to eradicate adelgids from the garden. Better to keep trees healthy and to provide good ventilation and sunlight to make trees less susceptible to infestation.

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