Control of pests, weeds and diseases in Tsubo-en

Our definition of pest control and weed control may be somewhat less formal than the Wikipedia one, the work involved is regarded of utmost importance to have our garden survive all the attacks and even get it full-grown.
Weed control is the botanical component of pest control and as such we include it here.

Although vermin can be regarded as pests or at least as nuisance, we do not further address it here. Most animals that we do not like to see in our garden are listed in the maintenance chapter under Uninvited visitors.
Pest control is a must when you have a garden.
How do Buddhists and Zennist remain faithful to their principles and beliefs of "live and let live" ?
We do not know and this is something we have never understood. We have been unable to find anything on the subject in the context of the Japanese garden, neither on the Internet nor in any book. How is this possible and why ?
We can only imagine that this is a great taboo, and that well kept secret-procedures must be in place for pest control even in gardens on Japanese soil.

Mea culpa: Although for sure totally out of line with the Buddhist spirit, with over thirty years of garden experience, twenty-five of which with Japanese gardening, we have chosen to use preventive and offensive methods based mostly on proven insecticides, chemicals and herbicides. We say sorry to all those opposed, but until we have better means to control our garden, this is what we (need to) do.

Be cautious with pesticides and insecticides. As said environment friendly insecticides and pesticides are recommended but did not always give us the desired result. Some pest control products are harmful to the plants. Some contain harmful components when inhaled or touched. Some require you to use a specially designed filter unit with your pesticide to filter out certain materials that could be present in the water.

It is important to use the proper repellent correctly and at the right time. Timing is extremely important. Timing with regard to the growth and season and timing related to weather-conditions and forecast.

To prevent mistakes due to mix up of liquids, containers or sprayers, we have a number of well marked pressure-sprayers for different purposes.
Not all insect are enemies. Some pollinate, some break down organic matter, and others are beneficial predators that feed on your real enemies. You want to be able to discriminate the good from the bad and ugly, and then encourage the friends and frustrate the foes. This is however partly theoretical. In many situations you will not be able to be selective. You should at least try to optimise such discrimination by using appropriate technologies, such as physical barriers, special traps, and specific agents, biological or chemical.

Protecting your garden and at the same time maintain a safe, harmonious natural environment is not an easy task at all. Hopefully this page will just offer some of the help you are looking for.

As we do not want to promote any specific brand we name the active substance of the agent that we use for a specific "threat".

Harmfull insects on planting (external agent)

The most used insecticide in our garden is based on the active substance Deltamethrin. It is very effective and also used for crop protection. Deltamethrin is one of the safest classes of pesticides or synthetic pyrethroids. It is highly toxic to aquatic life, particularly fish so be careful. It proved ideal for a karesansui garden. Since deltamethrin is a neurotoxin, it attacks the nervous system and penetrates the body via (skin) contact.
Our application:
  • Spiders.
    This is not about spiders in the garden but about spiders in and around the house. Although we are honestly fond of spiders, not controlling them has proved a horror. They love the overhanging roofs (Integration of house and garden). Even when we removed the spider-webs on a daily basis we still got overtaken by them. At that point we decided to use pest control. The first results with environment friendly insecticides where poor. Then we found this chemical one, that also proved multi-purpose.
  • Ant
    Despite of the fact that ants belong to the social insects they do not at all behave as such in our garden. Although the damage may look limited initially it is always just the beginning. Eventually their urge for expansion may kill plants and take over or undermine any garden object, component or construct. Although true for most vermin, in particular ants are not aware of any natural boundaries nor do they have an off-switch.
  • Harmfull insects on planting like aphids, psyllids (leafhoppers or jumping plant lice), beetles, sawflies, spittlebugs, moths, weevil, scale and the rest.
    On planting we use this insecticide on an ad-hoc basis if and when required. If we encounter (potentionally) harmfull insects that eat, suck, nibble, roles-up or otherwise damages plants, then we spray it (when not in bloom: read the usage directions).
    This will not always work for insects that have already built nests that protect them against being sprayed or coming in contact with the substance in any other way. For this we use a different approach based on an "internal agent".

Harmfull insects on planting (internal agent)

An effective more or less preventive agent is based on the active substance Imidacloprid. Although most used on our Karikomi and hako-zukuri based Buxus, it is broadly used on many trees, evergreen and deciduous and on shrubs and even on (parts of) hedgerows.

The active substance gets absorbed via the leafs and then remains active in the plant for a couple of months. Active against eating and sucking insects, such as psyllids (or Homoptera), some of which that "dig themselves in".
The first time we encountered this problem it was too late and we missed at least one, but probably more, growth-seasons. The attacks can be massive. Spraying with a deltamethrin-based repellent will be too late as the insects will not get in contact with the substance.
The Internet shows that the boxwood leaf miner is the traditional and perennial pest of Boxwood. The good news is that this is something we never came across in our garden so far. Our "best" pest example is the Boxwood psyllid, Cacopsylla buxi (Dutch: topmijt of buxustopmijt en buxusbladvlo). This pest is the most serious pest of this evergreen plant in our garden. The insect starts building its home only in the freshest and newest buts and runners. It folds the leafs together to form a ball at the top and closes off its own small imperium. Cupped, distorted, stunted leaves are the result. Within this secured position it sucks the leafs to grow further. The branch of your buxus will not grow further and the plant will show a very irregular growth.


Snails and slugs

We use anti-slug pellets with Metaldehyde as active subtrate.

A quick removal of the leafs (March) under the buxus yields up a whole collection of slugs. This proves that it is necessary to take proper measures.

Moss and algae

There are also liquids we use in our homes that are effective natural and organic pest fighters. One example is (household) vinegar which is an effective herbicide. We use it to remove moss and lichen from walls and roofs and to remove moss and algae from the veranda and duckboards.

Spray it on a dry day when you expect more dry days. Then after a couple of days use a rough broom to sweep the algae left over.


At the start of this pages we stated:
How do Buddhists and Zennist remain faithful to their principles and beliefs of "live and let live" ?

Ants are in the top five of pests in our garden. As indicated above we do not have any idea about how this is controlled in Japanese gardens. There are many species of ant in Japan (see: Japanese Ant Image Database) so the problem must also exist in Japan.

In addition to the Deltamethrin-based agent we attack ants in the garden with powder, on basis of the active subtrate phoxim (Dutch: foxim), either scattered as powder or dissolved in water.
Although different ants may require a different attack-method, we donít make that difference. If we find out what or where they eat, like running up and down in a tree, we also spray or sprinkle there.
The above-mentioned insecticide Imidacloprid is also used in grains. The ants will carry them into their nest where it can be shared among the population. Thus it reaches places where other agents cannot penetrate.

However ... I am not sure if I have ever seen a positive result. Also after a night or so either dew or a rain shower will change the grains into a sticky and later solid and hard lump and the question if it works at all becomes even more obvious and unanswered.

Fungus infections

And then of course fungus and related infections.

Some types of fungi like "Black Mildew" (on our Pinus Densiflora) can be treated with
active subtrate sulpher, solved in water and sprayed over the foliage.

Important note:
Leaving old leafs and other debris in your garden is like putting out a welcome mat for pests and pathogens. Many insects over winter in such debris, and they will get an early start nibbling on your plants the following spring.


The active substance here is Glyphosate (Dutch: Glyfosaat) or Glufosinate-ammonium (DL-Phosphinotricin).
Be aware that this agent is a non-selective systemic herbicide, meaning it kills allmost every plant. So you have to apply it very selectively where correct timing can come to help.

The substance gets absorbed through the leaves, injected into the trunk, or applied to the stump of a tree. Then it ends up in the roots, where it seals them off and prevents absorption of water with as result that the plant dries-out.

The pipette (or chemical dropper) is used to selectively treat solitary and persistent weeds that can grow in groundcovers.

In the first years we have used Glyphosate (in a large sprayer) to structurally eliminate plants like reed and butterbur from the water front (back side) compartment.

Now the use is more ad-hoc, primarily to remove weeds that easily grow back when a piece of root is left behind.
An interesting application is to remove weeds but also unwanted mosses like Marchantia polymorpha (see: Mosses and lichen) from desired (wanted) mosses. This shows the application where the wanted moss is not affected.

Be aware that this is a non-selective herbicide. Selective Herbicides can be used for established annual and perennial weeds in lawns etc. The best herbicide to use depends upon the species of turfgrass.

We not only use (household) vinegar to remove moss, lichen and algae, we also use it to kill small weeds growing in joints e.g. in the drive way. As vinegar also kills mosses you should not apply it to joints where you want moss to grow. For this purpose we use a solution of 50% vinegar and 50% water. The day after the small weeds are dead already.

Unwanted mosses and lichen in ground covers

Moss and algae grow on the hardwood of the veranda and duckboards.
However, unwanted Mosses and lichen in ground covers are also regarded weeds.
The only save way we found so far was an extremely cumbersome, and little effective annual, manual job (see Bottom surface ). Use of an agent based on the active substrate of iron sulfate is under investigation, initially without encouraging results. As not only the moss Hygrohypnum luridum (Hygrohypnum Moss, Dutch: Gewoon spatwatermos) but also the groundcover turned black.
This photo was taken shortly after a pilot treatment.
To our surprise the above "damage" recovered more quickly than we expected, resulting in a great new tool.
Have a look at Unwanted moss removal in chapter Bottom surface maintenance, to see how this developed.

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