As its name suggests, a fungicide is designed to be used against the various forms of fungi that attack plants. Fungicides come in liquid or powder form, and some of the latter are activated only when they are wetted. Although ‘broad-based’ fungicides are available, most are selective and target a specific fungus or group of fungi. Essentially, fungicides work in one of two ways:
Contact
Contact fungicides coat the plant with a protective barrier against possible fungal spores that may come from other plants, or when the soil is worked. Although many growers are inclined to use fungicides when the first signs of an infection are spotted, contact fungicides should be used before a disease is detected. Their purpose is to prevent and not cure a fungal infection. This is particularly important with plants known to be prone to fungal problems, such as soft fruits.
One of the downsides of contact fungicides is that they can be washed off by rain. They can also evaporate quickly, so reapplication may be necessary. It is important to ensure that the entire plant is covered with the fungicide, and not leave any part untreated. Bear in mind that if an infection is already present, it will continue to develop after the plant has been treated. This is because a contact fungicide cannot penetrate the plant in order to work inside it.
Systemic
A systemic fungicide is absorbed into the plant and it is therefore unnecessary to spray the entire plant for it to work effectively. It is not washed off by rain or watering, and gives long-term protection. Possibly the biggest advantage, though, is that a systemic fungicide provides both protection and remedial treatment.
Where fungicides with ‘greener’ environmentally better ingredients are used, it is important to give these applications a little more time to work. When used according to the instructions on the label, and applied at the right time, fungicides are an effective barrier against fungal outbreaks.
Paul Donovan is a Botswana-based zoologist.
