Can copper and sulfur be mixed for fumigation?

One of the main drawbacks of foliar applications is that they represent an additional cost and effort compared to fertigation treatments, added to the time, the cost of machines (gasoline), protective equipment, etc.

However, for the control of certain pests and diseases, in many cases it is even mandatory to carry out these foliar applications, which is why we try as much as possible, mix several products in the same treatment broth.

The key question en: can copper and sulfur be mixed for fumigation and foliar application?

Both products are widely used in conventional and organic agriculture, and their mixture is interesting for prevent or cure disease known in most cultures as powdery mildew, mildew, botrytis, bacteria, etc.

Compatibility to mix copper and sulfur

For most crops, can you mix copper and sulfur. It is still a raw material widely used in agriculture, as copper sulfate.

However, when we solubilize the copper sulphate, at the maximum concentration, we will obtain a proportion of 6.5% w/w copper and 8.0% w/w sulfur.

Many farmers looking for a higher concentration of copper and sulfur resort to mixing more concentrated forms of copper and sulfur, such as copper oxychloride, copper hydroxide, 80% wettable or powdered sulphur, with concentrations of 98% w/w.

In most cases, for horticultural crops, olive groves, vineyards and most fruit trees, the mixture at the recommended dose of each product, it is compatible.

Tips for Avoiding Phytotoxicity with the Mixture of Copper and Sulfur

Copper, in high doses, is phytotoxic to plants. Usually, even though the concentrations of this element found in many products are high, only a very small part (parts per million) penetrates inside the plant and at the cellular level.

For this reason, it is increasingly common to use nutritional coppers such as copper gluconate, a complexed form of copper with gluconic acid, which makes copper more assimilable by the plant and reduces its phytotoxicity.

Besides that, there are also some additional recommendations for avoid problems when mixing copper and sulfur in foliar application:

  • Avoid applying copper and sulfur to cold, damp areas as much as possible.
  • In stone and pome fruit trees, avoid application during the vegetative period, use a lower rate or carry out a small compatibility test (1 or 2 trees).
  • Do not apply the copper-sulphur mixture during flowering in all crops.
  • In melon and watermelon, use a lower dose of copper or use organically complexed copper, of lower concentration.

Maximum dose of copper

The new 2019 regulations limit the use of copper, where the quantity and frequency of application have been abused, particularly in viticulture.

There is currently a 7 year extension from 2019, with use limited to 4 kg/ha per year.

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