The Cultivator and Country Gentleman
Albany, NY
April 14, 1881
Vol. XLVI, No. 1472
Oiling Fruit Trees.
Please state what is the proper time in this latitude for painting apple trees with linseed oil, to destroy lice. Also whether it should be raw, or boiled oil.
A Montreal Subscriber
It is safest to apply it before the buds of spring begin to swell, and as much before that time as practicable, or late in winter. It would probably be safe at any time on hardened bark and with drying oil. We should regard it as accompanied with danger if applied to the tender bark of young trees while in a growing state, unless the oil is well prepared by boiling or otherwise for drying soon.
Wow! Linseed oil is a renewable resource! It comes from the seed of flax (Linum usitatissimum), the same plant that our ancestors grew and processed to create long silvery strands of fiber. This material was then woven into linen. Could I have stumbled on a forgotten formula for an organic, renewable horticultural oil? Perhaps…Let’s see what this oiling-fruit-trees thing is all about.
There are several destructive insects that are particularly frustrating to orchardists. Among these are mites and scale (not lice, but we’ll give A Montreal Subscriber a break on that one). These insects are small, with a hard exoskeleton that protects them from the elements, as well as some pesticides. Just like you and I, insects require some method of drawing oxygen from the air in order to survive. We breathe with lungs, and insects “breathe” through spiracles, a series of “holes” (if you will) along the sides of their abdomens. So, the method by which oil kills insects is simple. It clogs up the spiracles. The insects can’t get oxygen, and they die. Yahoo! (Entomologists will tell you there are also some insects that have a protective waxy coating that gets dissolved by the oil, which then kills them…but for my benefit, I’ve got to keep this simple).
So, linseed oil should goop-up those spiracles, wouldn’t you think? It should kill those nasty bugs. Sure, but let’s look at the tree before we start slathering the stuff all over the orchard.
As we know, trees have to “breathe” too. Of course, trees don’t call it breathing, they call it “transpiration.” But the point is that trees need to exchange gasses too, and like insects, they do this through little “holes.” Trees call their holes “stomata.” So, here’s the problem: If linseed oil can goop-up the spiracles of an insect (thereby leading to its demise), well then, it can goop-up a tree’s stomata too. So, what can you do to solve this problem?
You change the volatility of the oil. You mix up different batches with some special stuff that leaves the oil thick (Dormant Oil) or thin (Horticultural Oil). You conduct trials with your mixture, and you figure out that generally…and I stress generally…the tree can tolerate a longer period of having its “holes” clogged, than the insects can. This is particularly true in the winter season, when your trees aren’t doing a lot of transpiring. The idea is to devise a formula that allows the oil to stay around long enough to kill the bugs, but not so long as to kill the tree. A thick oil works better during the winter season, when the tree is dormant. Hence, it’s a “Dormant Oil.” Thinner, more volatile oils can be used during the growing season.
So now we come back to linseed oil. Will it work? It just may! But just like A Montreal Subscriber, we don’t know how volatile linseed oil is. Therefore, we don’t know the best time to apply it to the tree (and the information given by the Cultivator isn’t any good. In fact, it stinks.) All dormant oils should be applied before the tree’s buds have broken. But I don’t want to test linseed oil on my trees. I’ll let someone else test it on their trees.
Flit about the internet, and you’ll find some home recipes for oil sprays made with vegetable oil. But I wouldn’t recommend them. I think we’d be better off with products that have been through trials, and come with specific instructions. MasterGardening.com has a good one. But hurry up, because the dormant season is ending soon.
