Noticed this while I was weed whacking my yard today on a plum tree of mine. I removed the effected area just in case but is this the beginning of black knot? This would be my first experience with BK if so. 
Could it be an egg mass of some kind?
Hi Christina
You have very good perception to spot that! I am no expert but that growth does have the similar appearance of examples on the internet. Make sure to either burn it or completely remove it from your property. What plum variety is affected?
Dennis
Kent wa
Usually black knot starts with a brown bumpy area that turns black later.
Can you touch the area and see if it can be easily dislodged?
If it is black knot, it does not budge and needs to be removed by sharp knife.
After inspecting it, it did not appear to be one as far as I could tell it it’s possible.
Thank you! Yes, I removed the effected area and put it in straight in the trash. It was found on a beach plum branch.
Thank you for you help. The mass would not move and was stuck very firmly on to the tree
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From what I have read, If others in your area have experienced it, then it’s likely to return. Using dormant sprays can help prevent spores spreading. Your local ag extension agent would likely know if your climate is vulnerable and may know of more resistant varieties.
Good luck
Dennis
Kent, wa
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Looks like black knot to me. Watch out for new growth like that (note that it can be oval, or elongated) on this tree and any other plum trees that you have. I removed a dozen or more strikes from a bunch of my plum/pluot trees this spring.
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