Plant protection substances/active ingredients
Different active ingredients usually have distinct effects. Similarly to other protection measures, the use of natural inputs for plant protection requires competent advisory support to obtain satisfying results.
Sulphur (sulphur compounds, sulphur powder) and its application
Sulphur can be used to control powdery mildews, certain rusts, leaf blights and fruit rots. In contrary to copper (see below), it is not accumulated in the soil, but represents a risk for certain beneficial organisms. Like all pesticides, sulphur should only be used in view of a real threat to the crop, and not as a disease preventative strategy.
On-farm production of sulphur is not possible. Sulphur is only available as commercial products from international or national suppliers.
The product requires competent advice in the application to obtain optimal results. Practical research under local conditions is very useful to allow for competent advice.
Application against
Fungal diseases (anthracnose, leaf spot, rust, blight)
Mites
Mode of action
Under the influence of moisture, light and oxylling them from the inside.
Impact remarks
The higher the atmospheric temperature during and after application, the better the effect. At temperatures below 12 °C the effect is insufficient, at temperatures above 25 °C the effect is only short-lived due to the high evaporation rate (at 30 °C the sulphur is effective for approximately 4 to 5 days only). Under favourable conditions, the effect lasts 6 to 12 days.
Side effects
In fruits, for example, with increasing temperature and application rate, and depending on the sensitivity of the variety and the stage of development of the trees, toxic reactions to the plant can occur. High application rates also harm predatory mites.
Application
Do not mix with white oil or rapeseed oil.
In hot weather, carry out treatment in the early morning or in the evening.
Lime sulphur
Application against
Fungal diseases (anthracnose, leaf spot, rust, blight).
Mode of action
Lime sulphur is alkaline with a pH of around 10.5. This high pH destroys the cell membranes of the fungi and helps the active ingredient to enter into the fungal cells more easily. The higher permeation improves the absorption of the active ingredient.
When the active substance enters into the fungal cells, it interferes with the normal functions of these cells thereby killing the fungi.
Impact remarks
Lime sulphur is a contact fungicide with preventive, curative and non-specific effect.
Through contact with the atmosphere, the active ingredient degrades to sulphur and forms a preventive protective coating.
Side effects
The sulphur coating can cause sunburn at higher temperatures (>28 °C).
Application
Do not mix with other products.
Can be used as curative treatment after the onset of infection.
After treatment, rinse and wash all spray material well (corrosive effect).
Wait at least 15 days after treatment with paraffin oil.
Waiting period after application before harvest: 3 weeks for fruits
Copper (-hydroxide, -oxide, -oxychloride, -sulphate)
Copper has a different spectrum of action than sulphur. Copper is a very broadly effective fungicide, but has the disadvantage of being accumulated in the soil. Copper can be applied in several forms, e. g. as hydroxide, oxide, oxychloride or sulphate.
Copper sprays are primarily used to control fungal and more rarely bacterial diseases, e. g. leaf spots, blights, anthracnoses, downy mildews and cankers. Copper sprays are labelled for use on many organic vegetables, fruit and nut crops.
Theoretically, Bordeaux mixture (calcium hydroxide) could be produced on the farm from copper sulphate and hydrated lime. However, nowadays, copper oxychloride and copper hydroxide are more commonly used and are commercially available.
Copper fungicides are seen very critically by the organic sector, and should therefore not be promoted uncritically, but only as a last resort, if all other measures are insufficient. Optimum application (quantity, timing) of copper requires competent advice. For optimum advice, practical research under local conditions is very useful.
The EU organic legislation specifies maximum amounts of copper to be used per ha and year.
Application against
Fungal diseases (anthracnose, leaf spot, rust, blight).
Mode of action
The copper ions in solution block the enzyme system in the metabolism of the microorganisms.
Copper can also stimulate the plant’s own defence mechanisms (induced resistance through accumulation of phenols and phytoalexins, activation of enzymes).
Impact remarks
Works better than sulphur at lower temperatures.
The different copper formulations show hardly any differences in their effect.
Side effects
Accumulates as a heavy metal in the soil and (especially at low pH) can damage earthworms and inhibit microbial nitrogen mineralisation if heavily accumulated.
Very toxic to aquatic organisms with long lasting effects.
Application
Not miscible with sulphur lime, alumina preparations and potash soap.
Adding copper (e. g. to sulphur) makes sense (thanks to its better effect at lower temperatures).
Do not use during flowering.
In Europe, the maximum copper quantity allowed for crop protection purposes has been successively restricted over the last decades. Currently, the limit set by the European plant-protection legislation is at a maximum of 28 kg of pure copper per hectare over a period of 7 years (regulation (EU) 2018/1981). This corresponds in average to a maximum of 4 kg of copper per hectare per year. In a year with difficult growing conditions, the annual dose of 4 kg can be surpassed. However, the average dose over 7 years cannot be more than 4 kg. Some private standards have defined stricter limits. Farmers should know about these limitations in the use of copper products, especially in view of target markets.
Potassium bicarbonate
Potassium bicarbonate is made industrially from carbon dioxide gas and potassium hydroxide. The substance is harmless and non-toxic to humans and the environment. Potassium bicarbonate has a reduced spectrum of action and is effective against powdery mildews and other fungal diseases.
On-farm production of potassium bicarbonate is not possible. The input is available as commercial product from international or national suppliers.
Farmers could use baking powder (sodium bicarbonate) as substitute for potassium hydroxide. However, it must be purchased too and thus is not more reasonable than potassium bicarbonate. Application of this input requires competent advice for optimal application. As for other biopesticides too, practical research under local conditions is very useful to allow for contextual use.
Application against
Fungal diseases (anthracnose, leaf spot, rust, blight).
Mode of action
Causes the fungal hyphae to burst and delays the mycelium formation of the germinating spores due to its high pH value and water absorbing properties which cause drying to the fungus.
Impact remarks
Best effect when applied into wet foliage during the infection phase.
Side effects
Leaf burn possible with certain formulations and varieties if treated frequently without washing off.
Application
Not miscible with sulphur lime and alumina preparations.
Mixture with copper-containing products not advisable.
Treatments in combination with sulphur increase the effect.
Can also be used in higher concentrations for the regulation of hangings in fruit production.