Use of sulfur in agriculture

Sulfur is currently a widely used compound in agriculture . It is accepted in organic crops and acts as a miticide, fungicide and repellent. It is a cheap and relatively effective product, although it has some drawbacks that we are going to see in this article dedicated to sulfur, as well as its use to control some pests and diseases.

If we take a phytosanitary vademecum we see how there are many kinds of sulfur. In fact, as of the writing of this article, there are 18 records of products that contain sulfur in the magrama.

Its use is quite varied and is not only limited to preventing crops from pests and diseases , but also to correct soils with a basic pH (above 7). 1 kg of sulfur per square meter is capable of reducing the pH of a soil by 1 unit. If you do not know the pH of your soil you can do it through the following way .

In relation to pests and diseases, its use is accepted to treat powdery mildew / powdery mildew, spider mite, eriophids, mites, erinosis, etc.

Although the amount of product at the time of adding it to the crops varies with respect to its concentration, sulfur at 80% , for example, is usually applied at a rate of 20-30 kg / ha.

Its use is allowed as long as it is not mixed with oils or alkaline reaction products. When in doubt, check before “parda liarda”.


Like any phytosanitary product , sulfur also requires application standards and has certain requirements, which are discussed below:

  • Do not apply at high temperatures (we will see it in detail below).
  • As we have said, it should not be mixed with oils or alkaline reacting elements.
  • It does not apply to crops whose fruits are intended for canning.
  • It should not be applied on artichoke or sensitive fruit varieties (pear, apricot or apple tree, for example),

Being clear about these conditions, sulfur can be applied to our crops, whether they are organic or not.

However, it is not a very comfortable product to use, at least if it is in the solid phase (powder). We find it as powder to sprinkle, which means that if we are not very crafty, we will end up lost of sulfur, how careful, it can be irritating.

There are several ways to do it, and each teacher has his booklet, as they say. A sock, a jar with a small opening, etc. The point is to sprinkle it in a correct and balanced way on the crops.

In recent years, it has not enjoyed the same enthusiasm from farmers for this, its complicated way of applying on crops, since there are other fungicidal compounds on the market that are applied more comfortably and offer better results.


Apart from elemental sulfur, many commercial houses have specialized in producing mixtures of this element with other active materials that act as fungicides or insecticides, and increase its effectiveness. For example, sulfur with cypermethrin to combat powdery mildew, aphids, heliotis, thrips, etc., or sulfur with copper, to reinforce the antifungal power of the product, which is very effective against powdery mildew.

You will see that in the market there are a large number of products rich in powdered sulfur, as well as dusters and mixtures for the prevention and treatment of diseases.


If we go to annex 1 of  REGULATION (EC) no 889/2008  on production and labeling of organic products, we see how sulfur is accepted as a fertilizer and soil conditioner and as a pesticide or phytosanitary product (annex II) in point 6 Its action is acaricidal, fungicidal and repellent.

Of course, that it is ecological does not mean that it is free of problems or intoxications. Sulfur is an irritant and has a safety period before which the treated fruit can be collected, handled or ingested. For example, 80% sulfur in its composition has a safety period (PS) of between 3 and 5 days.

If it is done before and the recklessness of not respecting this period is run, it can affect the respiratory tract, irritate the skin or eyes and contaminate drinks or food.


One mistake that many farmers often (and quite often) make, out of ignorance, is applying sulfur to their crops when temperatures are high. Despite the technician’s recommendation not to do so, many decide to go ahead, with the risk it presents to their plants. Why?

To explain it, we are going to give a simple chemistry class:

The range of action of sulfur is very limited by temperature , especially as a fungicide. It works from 20 ºC and causes many problems when the thermometer exceeds 30 ºC.

When temperatures are very high, above 30-35 ºC, the sulfur dust (S)  turns into a gaseous state (especially since the dust is very fine (reaching one thousandth of a millimeter) and enters through the « pores »of the plant, known as stomata and found in the epidermis of plants (especially on the underside of leaves). Inside the plant it takes oxygen and passes into (SO 2 ) . sulfur dioxide.

Depending on the humidity conditions inside the plant, specifically in the stomata, this sulfur dioxide “takes” more oxygen (oxidizes) and passes into  (SO 3 ) , sulfur trioxide.

Sulfur trioxide is a corrosive substance considered a dangerous substance, and it is one of the compounds that cars and factories and others release into the atmosphere and produce acid rain.

Now, the farmer, oblivious to everything that is happening inside the plant, continues to water and assess “how well” the sulfur that he has incorporated in “midsummer” will do to his crops.

When the sulfur trioxide  found inside the plant captures moisture (water), a very interesting chemical modification occurs:

H2O + SO3 = H2SO4

Does it sound familiar to you? Is sulfuric acid ! A substance that is capable of taking away any organic tissue, be it plant or animal. We have just produced acid rain inside the plant, without knowing it.

The farmer, who happily wakes up, watches as an entire crop has literally been pulverized. Be very careful with applying powdered sulfur on crops at high temperatures.

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