Pruned black knot has to leave the area: infected branches are burned, buried, or otherwise disposed of, because cut branches left under the tree keep releasing spores that start new infections. Even with clean removal, new galls can still appear, so the tree is checked and pruned again each winter.

Why can black knot come back after pruning?

Because some infections are still hidden. The fungus grows inside a branch for several months with no outward sign, so a branch that looks clean at pruning time can produce a gall later, and nearby infected wild plums or cherries can bring spores back.

What should be done with cut black knot branches?

They are taken away from the tree, never left on the ground beneath it. Burning, burying, or otherwise disposing of the cut wood removes the spore source, since infected branches lying below the tree continue to release spores into its canopy.

When and how should black knot galls be pruned out?

In the dormant season, cutting at least 4 inches below each gall. Late winter cuts, made in February or March while temperatures are below freezing, keep spores from infecting the fresh wound. To reach galls high in a plum or cherry canopy without a ladder, the EZ Smart Pruning Saw With 16' Pole carries a 14 inch, two way cutting blade on a 16 foot pole.

Frequently Asked Questions

How long does a new black knot infection take to show?

About a year. Galls usually become visible about a year after infection and turn black about two years after.

Should nearby wild plums and cherries be removed?

Sometimes. Where only a few are infected, their galls are pruned out or the plants removed entirely, and where many grow nearby, new plums and cherries are best not planted.

What if a black knot gall is on the trunk?

An arborist check. A cracked, oozing gall on the trunk or a large branch calls for a certified arborist to judge whether the tree is still stable.

Why is winter the time to look for galls?

Bare branches. With the leaves gone, galls are easier to spot before buds break in spring.