Topic: Potato juice as an insect destroyer

[Jesse]

As an insect destroyer the juice of the potato plant is said to be of great value; the leaves and stems are well boiled in water, and when the liquid is cold it is sprinkled over plants attacked with insects, when it at once destroys caterpillars, black and green flies, gnats, and other enemies to vegetables, and in no way impairs the growth of the plants. A peculiar odor remains, and prevents insects from coming again for a long time.

The Farm and Household Cyclopedia - circa 1888

Has anyone heard of this before or tried it? I wonder if it works.

[john_miller]

Given that the Victorians were familiar with using coffee grounds to deter slugs, obviuosly preceeding the research done recently at the University of Hawaii, this could be another technique that got lost in the age of chemicals. Worth trying on that basis, just make sure you grow first earlies!
It really says gnats are plant enemies? They must be omnivores!

[Multiveg]

That sounds interesting... We would have to say it is a foliar feed!

[Jesse]

Yes, it does say gnats! I have some salad potatoes chitting so when I've harvested them I'm going to make up a brew and keep it handy for when the bugs invade. I will be particularly interested to see if it does in fact destroy caterpillars, last year my cabbages got destroyed by them and there were so many of them I gave up picking them off.

[aquilegia]

My concern would be that it might harm our insect friends (ladybirds, hoverflies, bees, etc)?

[Jesse]

Good point Aqui, I wouldn't want to harm the friendlies.

[john_miller]

I wonder if the 'destroy' is just Victorian hyperbole? Some of the claims made for products in those times were so outlandish that now they seem laughable to many.
A search on google came up with this:
http://www.uky.edu/Agriculture/Entomology/entfacts/struct/ef632.htm
which confirms what I have always been led to believe about gnats. Their science, or hyperbole, seems to have let them down on that point.
While the active ingredient in potato foliage may cause death of feeding insects in the very short term (like any organic control it will suffer photodegradation) I would suspect the 'peculiar odor' may confuse 'enemies of vegetables' (many respond to scent) later on and deter them. I don't think it would harm beneficials or other non feeders but, just in case, apply at dusk? One reason I don't use milk to control powdery mildew is the issue of odor later on. I wonder how persistent the smell of rotting potatoes is, even to our poor sense of smell?