Zinc - o - Facts

Fall applied foliar zinc - sounds like a great idea! It gives you a jump on next season's crop with promises of improving fruit set and increasing leaf zinc. Well, don't get too excited. The research to support these benefits just isn't there.

It's there but it ain't movin'

During the growing season, zinc appears to be relatively immobile. Deficiency symptoms show up in younger leaves. This shows limited zinc movement from older to younger leaves. But in the fall, it seems to be a more mobile. Like nitrogen, phosphorus and potassium, it moves out of the leaves. So in one way, fall foliar applications make sense. But past research has shown that fall foliar zinc applications are fruitless.

Applying radioactive zinc isotopes, several researchers have looked at how zinc moves out of leaves. From these studies, it appears that most of the applied zinc stays in the leaf. In one case, only 2.1% of the zinc was transported out of the leaves twenty days after application. Zinc was also fall applied to trees or vines during leaf abscission or without leaves. In both cases there was no increase in leaf zinc concentrations or fruit set the following year. Zinc applied after harvest stays in those leaves. It doesn't get moved to dormant or developing fruit buds. So, applying zinc to abscising leaves just adds zinc to the soil.

Wrong time of the year

Several studies have compared fall, dormant and spring zinc applications. The best time for application seems to be about 1 to 2 weeks before full bloom. In extreme zinc deficiency cases, continuing applications through bloom to fruit set seemed to be beneficial. Post bloom applications had inconsistent responses.

When would it be a plus?

Before applying any foliar or soil zinc, invest your time and dollars in soil and leaf or petiole analysis to confirm that a zinc deficiency exists. Generally there will be a response to applications if there is an established need.

| Top of Page |