What type of plants are you growing and what are the chemicals you have been using? Spider mites are one of the toughest pests to control and one needs to spray both sides of all leaves several times over several days to get rid of them. Catching them early is the key whether you use organic or chemical methods of eradication.

Mostly rose bushes. Malathion, Bona, and BioAdvance.

But might try Castile soap. Found this on YouTube. https://youtu.be/LuDLgjp0KS8?si=70unHbhYTO84EOyG

Spider mites hate humidity so you can keep them under control by spraying or misting your plants with water daily. Also, standard insecticides will not work very effectively. You need a miticide....neem oil works very well for this purpose and is considered organic.

Thanks!

Thanks!

Hi Anno,

In order to dodge pesticide resistance issues, you might want to consider biocontrol (predators). I can't recommend a seller since we are not in the same country but these can rather easily be ordered online.

https://www.dragonfli.co.uk/blogs/news/which-predators-to-use-for-the-control-of-spider-mite-and-how-to-use-them

It is well documented that the use of malathion causes an increase in spider mite population by effectively killing off beneficial predatory insects and ’friendly’ mites. Other broad spectrum insecticides do this, too, but malathion long fell out of favor due to this problem.

rhizo, what you said about malathion might make sense, but could you give us a few links to all that documentation?

As for the spider mites I would put a short squirt of shampoo and 3 ounces of molasses into a quart spray bottle, fill with water, and spray that on the plants once a week. The molasses provides food for the microbes living on the surface of the plant. The shampoo is a 'sticker' that helps the molasses stick to the plant instead of beading up and rolling off.

Sodium laurel sulfate and sodium laureth sulfate are very effective surfactants used in shampoo and other cleaning products used to remove oily stains and residues. It's effectiveness on oil and grease also extends to the cuticular waxes in the leaf cuticle and periderm of plants. These ingredients are so effective at dissolving oil, grease, and wax they are the primary component of engine degreasers and industrial strength detergents. Let's not forget the perfumes, dyes, and a plethora of other phytotoxic ingredients in shampoos and cleaning products like dishsoaps are a multiformity of phytotoxic (poisonous to plants) ingredients; e.g., Dawn dishsoap contains no less than a dozen phytotoxic ingredients.

Dissolution of cuticular wax in the leaf cuticle (skin) leads to an increase in moisture loss through the cuticle, diminished ability of plants to resist entry of fungal and bacterial pathogens, diminished efficacy of cuticular wax as a barrier to insect herbivory, diminishment of the wax's ability to protect the plant against harmful UV rays, potential injury to the plants photosynthesizing machinery, and an increase in the rate of leaf senescence (aging).

Unfortunately, the logical fallacy (appeal to tradition) that 'having used it for x years without a problem' does not hold water. It's not a question of whether or not the SLS sisters cause damage to plants, rather, it's how bad will the damage be. Too, any discussion about specific surfactants and detergents should include the fact that initial damage often goes undiagnosed, or misdiagnosed, being attributed to some other cause long after the damage was done.

A relatively safe surfactant for use on most but not all plants would be a product based on long-chain fatty acids of potassium, the active ingredient in insecticidal soaps. They are specifically formulated to be as safe as possible for use on plants.

Al

tapla, as I asked rhizo, above, do you have links to the info you using? I'm not trying to turn this topic into a botany course, but I am personally interested in how plants do what they do. There's a Ph.d plant person out of Oregon who spews a lot of stuff, and some of her "evidence" is the total absence of scientific studies. She must think that the absence of science is science.

The shampoo I use for the garden does not have SLS or SLS, but modern chemistry marketing has a way of creating new names for old products to keep folks like us from staying current.

What is better about potassium based surfactants? As I recall shampoos used to have potassium based surfactants.

Dish soaps usually have antibacterial ingredients, so I would typically not suggest using those in the garden. Shampoos don't use that term.

Regarding your second paragraph (the meat of your post), I would suggest that different plants would have different levels of response to the surfactant used. Some waxy cuticles might wash away easily and some might be impenetrable with simple surfactants. Some may regenerate their cuticle quickly and some may take more time. The idea of the surfactant is to hurt the spider mites enough that they move on or die but not hurt the plant enough to damage it. The purpose of the molasses is to improve the health of the plant exterior, ideally making the plant "invisible," or not interesting, to spider mites.

"What is better about potassium based surfactants?" I already noted that soaps based on long-chain fatty acids of potassium which are formulated for their insecticidal properties are specifically designed to be easier on plants, but even these products can be harmful to cuticular waxes in some plants.

"I would suggest that different plants would have different levels of response to the surfactant used." That is possible, but has no bearing on the fact that most household products like shampoo and dishsoap have a number of phytotoxic ingredients. I have no problem if you use them as you wish. I'm just putting the information out there so others know there are far better strategies.

"Some waxy cuticles might wash away easily and some might be impenetrable with simple surfactants." Wishful thinking.

"Some may regenerate their cuticle quickly and some may take more time." That's a lot of 'suggesting', 'mights', and 'mays', which suggests you don't really understand how some surfactants and detergents affect the leaf cuticle. I might suggest that apples will start rising from the tree tomorrow instead of falling to the ground, but I think we'd both agree the suggestion doesn't merit equal time in a physics classroom. The fact is, most detergents, surfactants, and most of the ingredients used in their formulation are harmful to plants - to the cuticle and particularly to the root's lipid membrane should the surfactants make way into the soil.

"The idea of the surfactant is to hurt the spider mites enough that they move on or die but not hurt the plant enough to damage it." Wouldn't it be better to use insecticidal soap or a 2:1 or 1:1 solution of water and 70% unscented isopropyl (rubbing) alcohol? Both offer instant knockdown when applied and will easily keep might populations under control when applied by spraying/spritzing at 4 day intervals.

"The purpose of the molasses is to improve the health of the plant exterior, ideally making the plant "invisible," or not interesting, to spider mites." How can molasses make the "plant's exterior healthier"? I wouldn't use molasses on a plant anymore than I would use a solution of sugar or corn syrup and water. The reasons are several - sticky mess that attracts insects and clogs/inhibits pores that facilitate gas exchange (stomata/ lenticels) in plants. Collects dust on foliage and supports growth of sooty mold, both of which inhibits photosynthesis.

Al