Problem with mealybugs and malathion with Phals
 

I had a problem with mealybugs and I had to throw away two orchids! So I decided to protect the rest of my orchids and treated them with half the recommended dose of this insecticide. After about two weeks some orchids got yellow leaves that fell off. The remaining leaves are going soft but still green. The weird thing is that there are orchids which are perfectly fine with the same treatment. Could it be that the ones that had mealybugs are the ones that are suffering?
I didn't treat the orchids with flowers. Any advice out there?

First thing, malathion now is only authorised in France for building disinsectisation, there's no phyto use.

Plus malathion is very bad for your health, not only those of plants and bugs…

First thing to do with mealies is to remove them as much as possible with mechanical means (toothpic, surgical cotton with alcohol, earpics with alcohol, or a shower (I don't recommend this last in winter). If you are invaded, not just a few on phals, it'd be good to repot with new barks to get rid of a lot of the hidden bugs/eggs.

You can kill on sight with an alcohol/soap/water spray (3 tsp/1 tsp/1 liter).

As a mild insect killer (it's not killing, just making things untasty for bug) I use nettle water (purin d'orties in French), you can find it in gardencenters. I recommend the Naturendie trademark, to use in spray and when watering, at 5% at most. I've found it effective at 1-2%. It will NOT work on huge invasions.

On the organic side still: emulsified neem oil, you can buy at Neem and Neem oil products as organic pesticide and insecticide. Buy neem products directly from Nature Neem, producers & exporters of neem products from India., it's fresh, rightly emulsified neem oil for gardening and no issue for orchids (tested and approved on Paphiopedilum)

For more serious issues, use calypso™ (thiaclopride) based insecticides or Acetamipride based ones with the proper protections at the level indicated for tomatoes or roses, neither more nor less please.

The dose may have been too strong for the plants? We use Malathion for our fruit trees but I have never used it on anything else. For my house plants, I spray them with olive oil in the evening, let them sit overnight and then wash the leaves well with soapy water. It tends to take care of the problem quite effectively (as well as spidermite, scale, and aphids).

I have used Malathion on my orchids and never seen any adverse effects. Maybe the dose was too strong, or the leaves were left wet in the crowns after it was sprayed.

Or it was too old… Chemicals get old and the effects can be weird. the trial of an old bug killer (way too old) brought malformed leaves to an african violet. You can't predict the result of oxidised/left to mute chemicals.

I have no idea of the concentration of the product authorised for disinfestation (and it's in no way a base for a use on plants), plus there may be additives that can be armful if it's the product used. The generic molecule is usually never alone in the bottle .

What's the point to use it when for the chemical way there's effective killers available and there's the organic means too?

It's not a reproach, we have to act logically:

- What's the issue?
- How far has gone the invasion?
- What are the options?
- Act in proportion.
- Watch out for backslide.

For the options:
- Does a mechanical cleaning will help?
- Does a repotting will help?
- Organic or chemical? Or a mix?
- In what steps from action one?
- Calendar

(I think it shows I'm preparing a conference…)

Thank you for your messages.
I am a newbie but this does not mean that the default pathway of newbies is to act illogically!

To answer your questions:
What's the issue?
The issue is in the subject of my question: mealybugs and the loss of now 5 orchids.
- How far has gone the invasion?
The invasion has gone very far
- What are the options?
I tried the mechanical method, for days under a magnifying glass and forceps, soap etc and it didn't work.
- Act in proportion.
I am acting in proportion
- Watch out for backslide.
I am watching out for the backslide

For the options:
- Does a mechanical cleaning will help?
No, it didn't!
- Does a repotting will help?
I did a repotting and it didn't help.
- Organic or chemical? Or a mix?
Organic didn't help, so chemical.
- In what steps from action one?
- Calendar
December.
I think that the problem was suggested here. I sprayed the orchids but didn't dry the crown, so crown rot got established. This is just a guess but this is the only thing I can think as a hypothesis. I read somewhere that people had used this product successfully against mealybugs but at a lower dose than the one suggested. I used at half the dose of the one suggested for roses.

There's no Malathion sold in France for roses. It's not even authorised for professionals. And I guess it's forbidden in all Europe given its chemical class.

Mechanical cleaning always help (all right, if you have thousands of orchids, it won't be practical), because you eliminate visible adults, nymphs, batches of eggs and too tiny to see larvae. But save if you do it when the first bug dives in, it won't suffice.

I forgot to mention alcohol baths, but I think that if you have: an invasion, and crown rot, the first thing is to deal with the rot first hand. And move to a proper systemic with alternate treatments and proper protection for you. Thiaclopride and acetamipride are just that, at the recommended dose (no guess, follow the directions for roses/tomatoes), and in the timely manner (it's about every 10-15 days). they are translaminar products so it will go inside by the leaves.

One important thing to do is to watch out for any other source of bugs you may have at home or outside. Some plants are true home for pests (hoyas, ornamental laurels…) and you'll have issues regularly if it's not cared about.

Note that there's competent orchid forums in France with people ready to help out in case. Good ones for beginners are Orchidouxdingues • Page d and Orchidees.Fr : Informations sur les orchidées, leur culture, encyclopdie photo, boutiques en ligne (for the last, the actual forum has moved, I don't have the new URL in mind right now).

Excellent advice, and so easily overlooked! I used to have a citrus house plant, started from seed, that occasionally had spider mites. They were usually cleared up promptly with tea tree oil and some alcohol, and I didn't even consider them spreading to my orchids since they were far apart. Then, one day I discovered multiple orchids, some cacti and another houseplant fully engulfed in the webbing. Terrible shock.

I first tossed out the old citrus plant, root and branch, and treated the others infested with the tea tree oil and alcohol. Next day I washed them all down with a very mild, warm detergent spray and removed all visible webbing by hand. After that, I repotted everything in fresh medium, scrubbing all the pots carefully in vinegar, then bleach water, then rinsed in plain water. Washed down all the shelves, tools and other containers in the same way.

One reason to use the vinegar first is to remove salts deposits that could hide insect eggs, etc.

What a job. But it has been three years now with zero signs of spider mites, or any other insect pest.

I think this process might be good for any other massive invasion, but the best is not to ignore any insects and especially not to think that they can't migrate from one plant to another easily. I think citrus would not be a good plant to have in the same room or greenhouse with orchids, as citrus seems to be especially vulnerable to the mites and scale. There may be others as well, of course.