Fungi Max Multi-Purpose Fungicide is the fungicide TreeHelp's own black knot guidance recommends, applied in spring at two or three sprays spaced seven to ten days apart to slow the fungus before new galls form.

What Causes Black Knot on Plum and Cherry Trees?

Black knot first appears as soft, greenish knots or elongated swellings on twigs and branches, which darken and harden into black galls as the infection matures. The galls girdle the branch they form on, cutting off water and nutrient flow to the growth beyond that point, which is why untreated infections gradually kill off entire limbs.

What's the Best Fungicide for Treating Black Knot?

TreeHelp's own black knot guidance recommends Fungi Max Multi-Purpose Fungicide, a broad-spectrum fungicide built around the active ingredient myclobutanil, applied as two or three sprays during spring at seven-to-ten-day intervals. Spraying on that schedule protects new growth while the fungus is spreading, rather than treating galls that have already formed.

Does Pruning Help Control Black Knot Without Fungicide?

Pruning out infected twigs and branches during fall and winter removes the fungus before it releases spores the following spring. Cuts should fall at least four inches below any visible knot, since the fungus grows further into the wood than the gall itself shows. For larger knots on main branches that can't be removed entirely, cutting out the infected tissue to a depth of at least half an inch beyond the visible infection limits how much fungus is left behind.

Why Does Tool Sanitation Matter When Removing Black Knot Galls?

Pruning tools can carry fungal spores from an infected cut to the next healthy branch, so sanitizing blades between cuts with a solution of one part bleach to six parts water keeps a pruning session from spreading the disease it's meant to control. This step matters most during dormant-season pruning, when several cuts are typically made across the same tree in one visit.

Frequently Asked Questions

How many times should black knot fungicide be sprayed each spring?

Two or three times. Spraying Fungi Max Multi-Purpose Fungicide at seven-to-ten-day intervals through spring keeps new growth protected while the fungus is actively spreading.

How far below a black knot gall should an infected branch be cut?

At least four inches. The fungus extends further into the wood than the visible knot shows, so a shorter cut risks leaving infected tissue behind.

Why does pruning tool sanitation matter when removing black knot galls?

Because unsanitized blades can carry spores from an infected cut to the next healthy branch. A solution of one part bleach to six parts water between cuts prevents that spread.

Is fall or winter the better time to prune out black knot galls?

Either works. Removing infected wood during the dormant season, before spring spore release begins, is what matters most, not the specific month within that window.