Pests and Diseases – Part Two – Disease Treatments

I knew that when I started this series that it was going to be a daunting task, and it is proving me right. But we are on the right track. I got some positive feedback on the last article, so we are forging ahead. The trick to the whole subject is tackling the relationship between three main factors; specific plant species, different pests and diseases that might occur on them, and the myriad of treatments available and their efficacy. I could make a nice chart, but I don’t have a way to make a three dimensional version. I can only relate two things at once. With that in mind, I decided to talk about treatments so that you can have that information in hand. Later on, I will talk about specific pests and diseases, so this subject will drag on for few months. We are going to cover disease treatments this month, then move on from there. But first, we need to go over some of the fundamentals.  

Forgive me if I repeat some things as we go through the series. If I do, it’s for your benefit, to remind you of safe practices, both for you and your plants. Just like the medical profession, our first objective should be to do no harm, to either tree or self. Be sure to check out any chemical you plan to use thoroughly. Read the instructions. Many of the chemicals listed will affect humans in some way, but in the doses and exposures we receive while handling them in the specified manner, they have been deemed to be insignificant.  

However, if we deviate from the specs, things can change dramatically. Some chemicals are safe when applied in certain ways, and not safe by other means. Certain chemicals are only approved for commercial applications, but are not regulated by sale to you. Many chemicals can be absorbed directly through your skin. Others may drift in the wind while you spray, getting in eyes or lungs.  

If you search online, all of the chemicals will have a bulletin available which goes through all the specific details of what it affects and how. Go to to find these bulletins. You can also download the actual labels as a PDF, which I find infinitely easier to read than the fine print on the bottle. Another thing to keep in mind is that these chemicals have been tested on certain species of plants, which are listed on the labels.  

Our bonsai are quite varied by species and variety and it is not possible to test all formulations for all of the variations. So if your plant is not listed, the chemical may still work, but it may also have unwanted results. Best to test it first. Also, some chemicals are too strong to use on tender new growth. Keep that in mind. There is the occasion that chemicals will also work for something that it was not directly intended. Boon turned me onto a spray call Bifin that was originally designed as termiticide for professional pest control, but he uses it for those pesky spider mites. More on that next time.  

For now, we are going to talk about treatments for disease. The best defense is a good offense – healthy, vigorous trees. We tend to overall slow the growth of trees and put them in an unfamiliar environment, both of which present challenges to keeping trees strong, but we also give them extra care that hopefully more than makes up for that.   

Even so, we may run into problems with diseases. These diseases come in two general categories, and so do their treatments. Some diseases are surface born, and we see the effects directly on the leaves or needles. We will see these as rust, mildews, smuts, needle casts, blights, etc…. Other diseases are systemic – they affect the vascular system of the plant. These tend to be cankers and rots – things that have fruiting bodies like mushrooms or conks, and that eat away at the woody tissue.  

Keep these in mind as we talk about different chemicals and how they work. Most chemicals for diseases work prophylactically, meaning they are designed to prevent disease, not cure it. That means that we need to remove any sign of the disease, whether dead foliage, branches, or cankers, then spray to prevent re-infection. Any damaged tissue will remain so. No problem for deciduous trees which lose their leaves each year, but conifers will hold onto those damaged needles for few years unless we remove them.  

At the end of this article, you’ll find a chart to summarize each of the chemicals and their characteristics. As I mentioned in the last article, finding these online is probably going to be much easier than heading to your local garden center. You can find Daconil and Mancozeb fairly easily, but the rest are more specific and commercially oriented. Be sure to look for chemical itself, as some chemicals are marketed under different trade names. Ok, let’s dive in.

One of my tried and true, go-to fungicides. If you have pine trees, you are going to need it. It’s the third most popular fungicide in the U.S., behind Sulfur and Copper. It is a broad spectrum, non-systemic fungicide that works on needle blights (pines), rusts and mildews. Daconil is a wettable powder, which means that the powder is suspended in a liquid form and easily settles into the bottom of whatever container it’s in. So this automatically means frequent shaking or stirring while spraying. It also means that it leaves a very visible, powdery residue on the leaves. Don’t worry, the rain easily washes it away after awhile, which means of course, respraying. It is also used on some crops.

This is my other tried and true fungicide. Mancozeb is a combination Maneb and Zineb in a wettable powder, just like Danconil. All the same spraying issues. It’s used on a lot of edible crops and is very broad spectrum. It simply treats a lot of stuff, so I tend to use it on both conifers and deciduous trees as a general treatment. It is relatively inexpensive and easier to find than anything discussed here, save Daconil. It is in my regular rotation to combat Phomopsis in junipers. I have had great, measurable results there.  

This fungicide is also broad spectrum, but I use it mainly against Phomopsis. You’ll notice that I am using two to three different formulations in rotation for tough diseases like Phomopsis. This is to make sure I can stay on top of any variants and stay ahead of the disease. Heritage is very expensive, though I think the very small bottle will last me many years. It comes as tiny granules with it’s own measuring and dispensing system. Each spray bottle takes about the amount of pencil eraser. A little goes a long way, but the initial investment is steep. Maybe you can share with others.  

Cleary’s 3336
This chemical is rather new in my rotation. Another great, broad spectrum chemical. This one is systemic and one of the few that can be curative – able to actually get rid of the disease after it appears. You can use it as a spray, dip, or drench. If I could only have one, I would seriously look at 3336. It works on many diseases, including Anthracnose, snow mold, rust, smut, Phomopsis, Katbatina, and needle casts.

Banner Maxx
I have used this a bit, but with unsubstantiated results. The base chemical, propiconazole is available under many names, and with different concentrations and thus different instructions, so beware! We thought it would work great on Phomopsis but has proved less effective than hoped.

I am still gathering information on other fungicides like Aliette, Subdue Maxx, and Agri-Phos. My challenge here is identifying the actual disease that I am fighting, more than anything.  

Many formulations of copper have been around for a long time and many are safer than their more modern counterparts. Unfortunately, I have very little experience with these formulations to comment on them. Generally, they have not been strong enough to go after the tough diseases that I am encountering.

So why don’t I have things like Safari, Imidacloprid, Malathion, Orthene, etc…. on this list? It might not be obvious, but those guys all deal with bugs, and that will be another, upcoming article. There are many, many more treatments out there. Most are designed for very specific situations and diseases. Many use special techniques, like direct injection into the bark. I have tried to winnow down my knowledge and experience into something that is helpful to you and will save you lots of time and testing. See you next month.  


Table of chemical treatments

Table of chemical treatments