Fungicide is sprayed on a tree one of two times: right when disease symptoms first appear, treating an active infection directly, or ahead of symptoms on a preventive schedule tied to the tree's growth stage rather than the calendar.

When Should I Spray Fungicide for an Active Infection?

Once a tree shows disease symptoms, spraying starts immediately and repeats on a fixed interval rather than a single application. Liquid Copper Fungicide Spray, for example, is applied at the first sign of disease and reapplied every 7 to 14 days, with the interval shortened during frequent rain, since new spores keep forming as long as wet, humid conditions continue.

When Should I Spray Fungicide as Prevention, Before Symptoms Appear?

Preventive spraying is timed to a tree's growth stage instead of a set date, since that's when new, unprotected tissue is most exposed to infection. Cedar-apple rust prevention, for example, calls for one application when the tree flowers, a second once about 75 percent of the petals have dropped, and a third 10 to 14 days later, covering the tree through the window when it's most vulnerable.

Frequently Asked Questions

Can a tree be sprayed even if it isn't showing symptoms yet?

Yes. For diseases like cedar-apple rust that spread between two host trees, every tree in the area gets sprayed, including ones without visible symptoms, since spores can travel by wind before symptoms show up.

Is it possible to treat a tree once an infection has already taken hold?

Not fully. Once a disease has established itself in a tree's tissue, spraying limits how far it spreads rather than reversing the infection already present.

Does fungicide need to cover the whole tree, or just the affected areas?

The whole tree. Spraying is done until foliage is thoroughly wet to the point of runoff, covering all plant surfaces rather than just the spots already showing symptoms.

Can the same fungicide product be used for both preventive and active-infection spraying?

Yes. Liquid Copper Fungicide Spray, for instance, works both ways: as a preventive spray starting when new leaves emerge in spring, and as a reactive treatment once symptoms are already visible, at the same 7- to 14-day interval either way.