Black Knot
Hard black lumpy swellings wrapped around twigs and branches, looking like burnt charcoal or a lump of coal stuck on the wood. They start as a soft olive-green swelling in their first year and harden to the familiar black knot in the second, and nothing else on a plum or cherry produces that shape.
Disease checklist
Four things to look for. If most of them match what you are holding, you are in the right place.
What gets rid of it
Gentlest option first. For most backyard cases the first one is enough, so try these in order and stop as soon as it works. If you do spray something, the product label tells you how — please read the notice further down.
1Prune every knot out in late winter
Cut at least 4 inches below the swelling into clean wood while the tree is dormant, and get it done before the buds open.
pruning saw foldingTry this first2Get the prunings off the property
Burn or bin the cut knots before spring, since a knot lying on the ground still throws spores.
3Disinfect the saw between cuts
Wipe the blade with alcohol or a household disinfectant after each knot so you do not carry it to clean wood.
isopropyl alcohol spray bottle4Remove wild plums and cherries nearby
Volunteer wild plum and black cherry in a fencerow are usually the source that reinfects a garden tree.
brush cutter loppers5Plant resistant varieties
President and Shiro plums are less susceptible than Stanley and Damson, which are hit hardest.
black knot resistant plum tree6Protective sprays only alongside pruning
Fungicide applied from bud break through shoot growth can protect new wood, but it does nothing without the pruning first.
fruit tree fungicide spray
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Which plants get black knot
Every plant we cover that gets black knot, grouped by type — tap any one to open its page. A note beside a plant came from that plant’s own entry, because the same disease can be a minor nuisance on one plant and a serious problem on another. Plenty of plants we do not cover get it too.
trees4
Plant families hit hardest
Related plants often share the same problems, so if one plant in a family has it, check the others. The largest group here is Rosaceae, with 6 of the 6 affected plants.
- Rosaceae6 plants
When to treat
There is no spray that removes an existing knot, so the whole job is winter pruning: cut every knot out in late winter before the buds break, because the knots release spores in spring and get worse every year until the tree dies.
Timing only — the label is the law
This page tells you when to watch for black knot and when treating is worth considering. It is not a recommendation to apply any particular product. Read and follow the product label before you spray — under federal law the label is the legal instruction, and using a pesticide against it is illegal.
- Check the pre-harvest interval. Every product that’s cleared for an edible crop sets a minimum number of days between spraying and picking. Find it on the label before you spray anything you intend to eat.
- Check the re-entry interval before you or anyone else works in the treated area again, and use the protective equipment the label names.
- Confirm the product is registered for your crop in your state. This page groups many different crops together, and a product legal on one of them is not legal on all of them — state registrations differ too. Your state pesticide agency or local extension office can confirm both.
- Rates and mixing instructions come from the label, never from us. We don’t publish them because they differ by product and formulation.
Other problems on the same plants
If a plant gets black knot, these are the problems it most often gets as well, so they are worth checking for while you are out there. They tend to appear together; one does not cause another.