As the name implies, these are substances that either kill or inhibit the growth of fungi. The ones used on plants are generally called protectants. This means that they are preventative and protect the plant from infection. Therefore, they must be on the plant BEFORE the fungal spores land and germinate. Only a few fungicides used primarily in fruit production have any "back action" where they have the ability to impact fungi that have started to grow in the previous few days prior to application.

Most of the fungicides used on landscape plants are not systemic since they do not penetrate into the plants. They stay on the surface and intercept the fungal sports. This means that they are exposed to ultraviolet light, rain and irrigation water which will remove them or diminish their effectiveness over time. That is why timing of application is very important when using fungicides.

There are a few fungicides that are systemic. These must be absorbed by the roots or injected into the trunk of trees. Then, they move through the water transport system of the tree to be spread throughout the canopy. Systemic fungicide treatments tend to be expensive and somewhat invasive since holes have to be drilled into the bark in order to deliver the product to the vascular system.

As with most types of pesticides, some fungicides are narrow spectrum which control a limited number of fungal species while others are broad spectrum and kill most any type of fungi they encounter. Of course, it is usually better to use a product that is as specific as possible.


In general, fungicides have a rather low toxicity level to other types of organisms.


Organic vs Synthetic

There are many synthetic fungicides available at most garden centers and plant nurseries. Most of the systemic fungicides must be applied by an arborist since they take special training to apply properly.

One of the first fungicides used was a mixture of copper, sulfur and hydrated lime called Bordeaux mixture because it was sprayed for fungal diseases of grapes in that region of France. It is still available today and is sold commercially in some places. Other copper based, organic fungicides are also available.

Generally, the organic alternatives are less effective than the synthetics although if managed properly, they can be good enough. The key problem is the potential for damaging the foliage if they are not applied in the proper concentration at the correct time.

Note: We have provided some general information and observations on this topic aimed at the home gardener. Before you take any serious action in your landscape, check with your state's land grant university's Cooperative Extension Service for the most current, appropriate, localized recommendations.

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