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13 March 2016

Pesticide Shmesticide

Note from RollingEyeballs: The following post was written by a particularly prolific and evidence-driven member of the GardenWeb Cacti and Succulents Forum, known in that circle as ewwmayo (he does hate mayonnaise, something I vehemently disagree with---I eat my fries with mayo and although I also like "ketchup", I spell it "catsup"). I am sharing it with you (with permission, of course) because it is one of those things I wish I had the wit and patience to write down, but didn't. Having no desire or inclination to reinvent this particular wheel, I am just posting this in toto, with minor typo corrections. This post was followed by a lively discussion which you can check out here. The rest, I give you ewwmayo, to wit:

Insecticide/Pesticide Insights

Not everyone is an enemy. Hemaris thysbe, commonly known as the hummingbird clearwing, is a moth of the Sphingidae (hawkmoth) family.
While wrapping up my red spider mite battle, I wanted to share a few helpful things I've learned about many insecticides and their usage. I am not an expert on the subject, but have done a lot of research and wading through the misinformation online. Hopefully it'll help or at least tell you something new.
I think most of us have run into pest issues and I'd rather share my findings than pretend I live in some kind of Canadian pest-free universe. =)

Are my pests really a problem?
  • Proper identification and evaluation is the most important. Mealybugs and spider mites start slow, but their populations explode quickly. A minor problem festering for a few months can suddenly turn into a major problem in just a couple days.
  • You need to know what exactly you are dealing with because insecticides and pesticides are target at different vermin in specific ways. Pick the wrong one and it will be ineffective and you risk damaging your plant.
  • The toughest part is noticing the early stages, pests are often hard to find and if you never dealt with a specific one before, it is easily overlooked.
Why is spraying recommended at dusk?
  • Less pollinators are out and many pests may come out as the sun goes down. Insecticide droplets and magnifying the sun's rays, causing leaf damage appears to be a myth.
  • However, putting a plant out in the sun after it has been sprayed with insecticide is a still bad idea. Many insecticides (Pyrethroids in particular) break down quickly under bright sunlight and high temperatures, wihch renders them ineffective in just several hours.

How should I prevent contact?
  • Nitrile disposable or rubber gloves are recommended. Wear long sleeved clothes for spraying. Respirator recommended.
Why do you need to shake well?
  • One of the biggest problems with insecticides is that many are not water soluble (only emulsifiable). Which means most companies are using solvents or emulsion agents to suspend the particles.
  • So shake as much as possible for use to ensure good mixing otherwise your dose could be too weak or too strong. Just think that a fraction of a percent of the total volume is actually insecticide and the rest is just some liquid to facilitate delivery of those tiny particles.
What active ingredients does your insecticide have?
  • It is important to know what your pesticides contain to ensure they will kill your pest, optimize their effectiveness, and for human health safety. Here are many common ones and my comments for each.
Why does insecticide smell bad? Why is a respirator recommended?
  • As mentioned above, many are not water-soluble so solvents are used. They emit VOCs (volatile organic compounds) which are bad for your health.
  • If spraying in an enclosed area or putting plants there, your respirator cartridge should be rated for filtering out VOCs. It should be fitted properly and you should not be able to smell anything in your mask.
Why does insecticide damage plant leaves?
  • It can be two-fold, the active ingredient is damaging and/or the solvent is damaging. Neem Oil can damage sensitive plants, as can some insecticidal soaps and other oils. The solvent could be oxygenated such as alcohol/esters or hydrocarbons, such as Xylene (previously used).
  • Dumping a ton of alcohol or paint thinner would be presumably bad for a plant, so be careful in your application. This is why they recommend testing on a leaf first instead of the whole plant.
  • It is important to know that phytotoxicity may not show immediately, but a few days after application. So take care not to stress the plant further (put it in a mild environment) and watch for damage. If your plant survives, then good! If not, then you will know not to reapply or to apply more carefully next time (and consider if death or further damage is worth the risk).

What should you do if the insecticide has been over-applied?
  • If you go overboard, note that insecticide is not necessarily washed off easily with water!! Most are not water-soluble, so spraying with water may get rid of some excess, but the rest will probably run into the soil/roots and cause further damage there. Better to be careful and not panic than do something rash.
  • One of my strategies is to spray and then put my plants in a small bathroom with the exhaust fan running and an air circulation fan. The circulation fan is intended to evaporate off any solvents to reduce their pytotoxicity, leaving just the active pesticide ingredients to work. Fumes are contained and safely vented outdoors (sorry to the environment, but it's the best option for me).
Common insecticide/pesticide active ingredients:
  1. Imidiacloplorid - Systemic that kills a large range of pests, but not mites. Will kill pollinators, so be careful to keep flowering plants indoors up to six months after treatment. Included in Bayer Tree and Shrub and 3-in-1. Not available in Canada unless you have a special license.
  2. Pryrethroids/Pyrethrin - Kills a large range of pests, including mites. Only kills on contact and breaks down quickly with UV light and high temperatures. Included in Bayer 3-in-1 to kill mites (tau-fluvalinate), as well as Schultz Houseplant and Garden Insecticide 709.
  3. Alcohol - Included in many insecticides to help kill mealybugs and other pests. Similar/same stuff to isopropyl (rubbing alcohol).
  4. Neem Oil - Kills many pests by hormone interference. The oil can also suffocate insects. Don't douse your soil because oil and roots are not a good combination. Can by phytotoxic (toxic to plants)
  5. Canola Oil - Often put in some commercial pesticides. Functions to smother the breathing holes of insects. Oils like this are commonly used to kill wasps by suffocaton.
  6. Potassium salts of fatty acids - Also called insecticidal soaps. They penetrate soft bodied insects and disrupt cell membranes. Can be phytotoxic.
  7. Sulfur - Used as a fungicide in many pesticides, such as Safer's Fungicide.
  8. Tebuconazole - Used as a fungicide in Bayer 3-in-1. Not very good for your health, so avoid contact.
  9. BTK - Bacillus thuringiensis var. kurstaki is a bacteria toxic to larvae. Good against fungus gnats, caterpillars, etc. Can take several treatments and is found in many dried or liquid forms (Bt bottles or mosquito dunks).
It's hard to say what solvents are actually in pesticides because manufacturers are not required to specify, even in the MSDS.

Succulents plants I've treated and sensitivities (if any were observed):
Please do not take this list as a guarantee. This is just my experience so far and I take no responsibility for plant damage!

  • Adromischus maculatus (Imidacloplorid and Pyrethrin)
  • Crassula aborescens (Imidacloplorid)
  • Crassula gollum (Imidacloplorid)
  • Crassula 'Morgan's Beauty' (Imidacloplorid)
  • Crassula 'Tricolor' (Imidacloplorid, Pyrethrin caused a few leaves to be damaged)
  • Echeveria elegans (Imidacloplorid, Pyrethrin caused some leaves to be dropped)
  • Aloinopsis schooneesii (Imidacloplorid, Pyrethrin)
  • Faucaria felina (Imidacloplorid, Pyrethrin)
  • Neohenricia sibbettii (Imidacloplorid, Pyrethrin)
  • Stomatium mustellinum (Imidacloplorid, Pyrethrin)
  • Anacampseros rufescens (Imidacloplorid)
  • Huernia zebrina (Pyrethrin major plant damage, but could have been my fault)
  • Stapelia giganta (Pyrethrin major plant damage, but could have been my fault)
  • Schlumbergera truncata (BTK)
  • Schlumbergera x buckleyi (BTK)
If you have any of your own experiences and information, please feel free to share below. I prefer to keep this discussion about commercial insecticides/pesticides and not home/DIY concoctions.

Credit: Text and photos by ewwmayo

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