Q: Why is boron toxicity so vilified by conventional agronomy?
When soil biology does not provide enough calcium during rapid vegetative growth stages, cell division continues imperfectly, resulting in “zippers” on corn leaves and other grass crops. The location of the zipper can also indicate whether boron is inadequate. When the zippering effect occurs at the edge of the leaf, it may indicate there is not enough boron present to move calcium to the leaf edge. When zippering occurs in the middle of the leaf, boron may be adequate, but calcium remains low.
A: In mainstream contemporary agronomy, there is perhaps no element that is more vilified than boron. But I’ve probably only observed boron toxicity a dozen times in my life.
The physiological symptoms of boron toxicity and of calcium deficiency overlap about 90 percent — they’re almost exactly the same — and you can easily mitigate and reverse boron toxicity by adding calcium.
I witnessed one extreme example where a grower was growing strawberries in pots in a greenhouse, and someone applied boron at one hundred times the recommended rate. A tissue analysis (this was before sap analysis) showed 2,000 ppm boron, and the plants showed it. We put on a very high rate of calcium, as a foliar spray and in the irrigation system. Within a week, the boron toxicity symptoms completely disappeared — not just on the new growth, but also on the old growth that had shown the symptoms. The fascinating thing was that on the tissue analysis, the boron concentration was still 2,000 parts per million, but the toxicity symptoms were gone — simply because we had added enough calcium to buffer out the boron toxicity.
In the ’40s, ’50s and ’60s, one of the most widely recommended treatments for insect control was foliar applications of Borax. Boron was understood to be a very effective insecticide. They didn’t understand the mechanisms; I still don’t understand the mechanisms today. This is not boron as an insecticide; this is boron as a nutrient. When you get boron into the crop in high enough concentrations, your insect pressure declines to next to nothing.
