Expert advice

Influence of temperature on the activity of fungicides

The effectiveness of fungicide treatment is influenced by many factors, of which one doubtless is the temperature at the time of application and for a short while afterwards. Hence, in case of any selected substance, one can differentiate between three very important temperature thresholds indicating the possibility of its use and influencing the effectiveness of treatment.

For a specific group of active ingredients one can distinguish a certain minimum temperature, below which the application of products containing a specific active ingredient is not recommended, and a maximum temperature, above which the application of a specific plant protection product is not recommended. The temperature limits are related both to the properties of the active ingredient, the environmental conditions under specific temperatures, as well as the physiology of plants and agriphages. In practice, for most plant protection products, one assumes that the maximum temperature, up to which they may be used, is 25 °C, which is related to the possibility of quick harm to the treated crops and very quick evaporation of the spray liquid.

In case of plant protection products, important is the so-called optimum temperature range, a range, in which active substances exhibit the best effectiveness against a broad spectrum of agriphages. For fungicides, irrespective of the chemical group, it is assumed that this is temperature between 15 and 20 °C. The example temperature ranges for selected active substances were presented below.

Active ingredient Chemical group Minimum temperature [ᵒC] Optimum temperature [ᵒC]
Azoxystrobin Strobilurins 7 10-25
Proquinazid Quinazolines 5 8-25
Mancozeb Dithiocarbamates 7 10-25
Tebuconazole Triazoles 10 12-25
Prochloraz Imidiazoles 5 10-25
Fenpropidin Morpholines 5 10-25
Propiconazole Triazoles 14 15-21

The table data is only for orientation purposes, because the products, despite the fact that they contain the same active ingredient, may differ in terms of effectiveness in the lower temperature ranges, e. g. due to the selection of the additives of the products, used during the formation of the product and facilitating the speed of uptake or movement within the plant.

In order to limit the negative influence of low temperatures on the effectiveness of fungicides in formulae or in practical recommendations, advised is the use of active ingredients having varied minimum temperatures. This is of particular importance in case of the first fungicidal treatment in the spring.