Fungal Diseases

Kisetsu-en Shohin Bonsai Europe FORUM Bonsai Fungal Diseases

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    Oliver Wohlfarth

      Hello everyone. I have some problems with fungal diseases here in my garden. I hope someone can help me and if not I hope one day this will help you maybe.
      The winter from 2020 to 2021 was very warm and wet here in the middle of Germany. Then later extreme cold and then warm and wet again. The first tree with some fungal leave sights was my lovely grab apple (which I got from my girlsfriends grandmother and no matter what I will costs me I don‘t can loose it!) 5A023D05-7C17-456C-AAFC-7ADBB853412A0F7077DF-5709-40EF-AC1D-B5556480537C

      I sprayed with lime sulfur & water 1:10 know he has almost no leaves left but I saw today new buds so I hope the best. Today I saw my new trident maple with black spots under the leaves


      So 1. it is not only on 1 tree says to me it is my fault or something with my area/weather/water etc.

      1. it is not coming from my tools (i desinfect them after every use and also between different trees)
      2. it have nothing to do with the water I use, because everything else is good and I do not water over the leaves



      So what should I do? Less water/fertilese the trees?More sun or no sun? Should I remove the last leaves on the Apple? Please help. Every leave I loss is too much.

      Geoff Hobson

        Oliver have you checked for insects? I expect you have but possible otherwise I don’t know. The third picture look as if had been eaten on the edge. Has the Crab Apple  flowered this year?


        Oliver Wohlfarth

          Hello Geoff. Yes, I have checked for insects. There was some aphids on the apple and on my azalea I have sprayed it. The apple was full of flowers but I have removed all apples. In a day or two the apple will have no leaves left. 😢

          Geoff Hobson

            I don’t know Oliver, maybe Morten can help. I will be on the Zoom Thursday night, hope to see you there and you could ask him.



              that doesn’t look good, what about the roots, if all the leaves are falling in such a short time, it sounds like the roots to me, maybe too wet, maybe after all with the almost minus 20 degrees at night that we experience almost had, and then he drove out of the reserves, but can no longer manage the rest, is very weakened, and is now being given the rest by mushrooms?

              Geoff Hobson


                are these the only trees affected or more? I would have them in the sun and if they are wet let them dry a bit. Does the water drain well when you water? You could drop it out of the pot and see if the roots look ok. One thought, if you take it out look for Vine Weevils in the soil.


                  This is a yearly spring issue and can have several different causes.

                  First of all. Small prickles or dots appearing at leaves often is caused by aphids. Other bugs will eat the edges of a leaf.

                  Aphids and bugs in general likes tender new shoots and spring growth is a feast after winter dormancy. Leaves are tasty as the sugars are building up fast. Beech for example have tasty leaves, and you can eat them in a salad the first weeks after they open. Thereafter they turn bitter and insects will not like them. As you won’t.

                  As temperatures, rice bugs will reproduce rapidly. Look for them at the underside of leaves where they can hide.

                  This spring has been very cold and therefore bonsai also are weaker than normal, even if fed well last season. The awful cold unstable spring has set them back and make them more vulnerable to attacks.

                  Insecticides are one way to treat the attacks, and another method is flushing the leaves with water daily. Also from beneath to annoy and wash the insects away.

                  The advantage of the cold spring is that there will be fewer insects to attack our bonsai than normally. For the environment, this is worse, but that’s another story. On the other hand, fungus loves it.

                  The other part of the issue raised here is about fungus. This also thrives in this cold spring with a lot of humidity after several periods of rain.

                  Here treatment is trusted on fungicides. The only way to get that down when an attack is present. If it is powdery mildew low-fat milk sprayed daily will cure the mildew within two weeks or so. The milk makes the mildew break down and can be brushed off gently. Depending on the weather changes or not; else you have to continue the treatment as new attacks might occur. A very environmental friendly cure.

                  Or you can find products online or at garden centres. Other fungal diseases can be cured with Limesulphur diluted 1:10 with water and sprayed on the attacked areas. Avoid it going into soil and roots by covering the surface when spraying.


                  To avoid both types of attacks, aphids and fungal diseases, we have to look at how we grow our trees. How we arrange them in the garden or elsewhere.

                  Healthy trees are less vulnerable to any attacks. A bad spring like this year will set back some trees health anyway though. But else, it is important to keep trees strong growing and healthy. This will lower the attack rate. Some species are more prone to attacks of aphids than others though. So watch out especially for those trees.

                  Many trees have a natural defence mechanism build in. Healthy trees will react to attacks changing their sugars that are extra tasty in the spring, so they are less tasty when experiencing an attack. But bonsai are not as strong growing as trees in nature, so they are more likely to be attacked and their ability to withstand attacks is not as good as big trees. Just the small amount of foliage makes them vulnerable because only a small group of insects can rip off the leaves and fungus will quickly spread over a small area.

                  Therefore we need to protect the best possible. One way is placing bonsai where they receive optimal light so they grow strong. Next is to place the bonsai where it is a little windy. Not that they should blow off the shelves of course, but if the air is not moving humidity will be high and fungus will love it. So will bugs. Some air circulation is necessary for a healthy bonsai environment. Maybe the most important aspect of placing your trees is having some air circulation. Both to protect against insects and fungal attacks.

                  So the answer is all of this and better weather. 🙂 Hope this helps a little. good luck with the trees.

                  Regards, Morten

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