This answer came from Pavel and me (Olga Makarova/Francheska). Pavel Enikeev is an expert on different plant infections and the way to fight them with different chemicals. Now, however, I will not talk about it. Quite to the contrary I will talk about why I think we should not use any chemicals as a prophylactic measure against plant pathogens.
Here are the few reasons for that.
What is the most important thing we have? I think it is our lives: life of our loved one, our life, life of the people who we give or sell our plants. Of course, plant life is also important, especially for us plants lovers. However, if we got sick there will be no plant life in our house.
1. We should not take the effect of chemical agents (pesticides for example) on human health too lightly. All pesticides (including majority of natural ones) are harmful for humans. Toxicity symptoms are often subtle but with a time can bring irreversible damage to our bodies. They affect practically all human organs and functions. It will be difficult to list all adverse effects. Cancer, hormonal imbalance, neurological damage, weakening of immune systems, cognitive impairment just to name a few.
2. Practice shows that most of the time pesticides are not applied according to the label. Indeed sometimes it is difficult to follow the manufacturers’ instructions.
When we apply too much, or don’t use precautions (wearing gloves, respirators etc) it is even worse for our health.
There is an article in the May-June 2015 African Violet magazine by Gail Elmore named “Urgent Concern”. She also mentioned that she saw many handouts that have very vague statement about using the pesticide Marathon.
She recently treated plants she got from somebody that were infected with soil mealy bug. However, when she treated them with Marathon it didn’t seem to do much, if anything.
She wrote that previously Marathon had a strong effect and quickly killed the bugs.
Let’s talk about Marathon (not the worst pesticide in terms of effect on humans), which is widely used as a prophylactic measure by the growers who use watering methods like wick, or mat or Oyama pots. These growers are reasoning that constant moisture and cross-contamination may warrant using some chemicals as a preventive measure.
Let’s look at the Marathon label:
PRECAUTIONARY STATEMENTS HAZARDS TO HUMANS AND DOMESTIC ANIMALS CAUTION: Harmful if swallowed or absorbed through skin. Avoid contact with skin, eyes, or clothing. Wash thoroughly with soap and water after handling. Keep children or pets off treated area until spray is dry. Personal Protective Equipment (PPE) Applicators and other handlers must wear: Applicators and other handlers must wear: • Long-sleeved shirt and long pants • Chemical-resistant gloves made of any waterproof material such as barrier laminate, butyl rubber, nitrile rubber, neoprene rubber, natural rubber, polyethylene, polyvinylchloride (PVC) or viton • Shoes plus socks Follow manufacturer’s instructions for cleaning/maintaining PPE. If no such instructions for washables, use detergent and hot water. Keep and wash PPE separately from other laundry
I have a question. What percentage of people really read
that label? Probably some people did read it and followed the
Instructions to wear gloves for example. Now, who noticed
that gloves should be special - not the plastic ones we use
everywhere, but chemical-resistant gloves? Marathon
can penetrate through regular gloves and then through our skin.
Even if we do everything right, what about other growers who get
our plants and don’t know that soil has pesticide in it. Marathon is
very stable and stays in soil for months and years!!
3. Suppose we still decided to use pesticides prophylactically. The problem is that we need to apply not only different pesticides to different insects, but also fungicides. By the way, fungi are notorious for developing resistance very quickly. And how about mites? More chemicals?
4. I think we have talked enough about effects of pesticide on humans. But what about our beloved plants?
We talk before about difficulties applying the right concentration of chemicals. If we apply too little we can run into another problem. Microorganism we are trying to fight may overcome the toxins and become resistant to the pesticide. (It is also happens with the right dose of chemicals!) now we need to increase concentration or add another chemical. It is exactly what happens with overuse of antibiotics. Now infections are responsible for thousands death due to spread of antibiotic-resistant bugs.
5. The original question was whether or not to use chemical during re-potting. Some people mix their own (usually soilless mix), some, including me, use commercial soilless mix. These soils do not have harmful microorganisms!
6. Another thought. Your prophylactic chemical, as I said before may not completely kill infectious agent. The strongest microorganisms do not die, but remain dormant, not propagating (or propagation very slowly) and not doing any visible harm to your plant. It means that if we get infection we might not notice it right away infectious agent slowly spread through your entire collection.
7. Another scenario. We give our plant to a person who does not use pesticide and now the “liberated” bugs can quickly eliminate somebody’s whole collection.
10 It is obvious that by using systemic pesticide or fungicides we are killing beneficial organisms.
For example, by applying fungicide we also kill important fungi that are very necessary for growing healthy root system and plant in general. It was also mentioned in the article by Gail Elmore.
11 Finally practically all chemicals (I am not talking about fertilizer) have weakening effect on plant.
In conclusion I want to say that other, non-chemical prophylactic measures are very important.
I only get my plants from a few trusted people. I know that these people do not use any chemical that may mask infectious agents.
If you not certain the plants that you bring to your house are clean, (which you probably never are) then a 3-6 month quarantine is necessary. Plants or leaves should be in another room, or at least on another shelf.
Sometimes when I get a leaf I treat it with 10% bleach for 5-10 minutes. It will kill everything on the leaf surface. However, if you get a leaf that has thrips infection, even bleach will not kill it because thrips can easily survive inside the leaf.
It is also good practice to change your clothing if you come to your plant room after working in the garden.
This short article is not meant to be comprehensive and I am making some generalizations. I am sure that someone can find some exceptions.