Plum Trees


Since I received such good help from my questions on my pear trees, I need to ask a few things about my plum trees.
I planted two plum trees five years ago I’d bought from Tractor Supply. They didn’t look very healthy and they were inexpensive. Over the next five years, they grew and produced some fruit.
Although the fruit grows large, it often falls from the tree before it ripens. It’s very easy to tell when a plum is ripe, it goes from a deep green color to a purple one. In the last two years, the limbs sprouted a lot of green fruit, but they fell from the tree before turning purple.
Also, fungus. Black smuck. I’m not sure what it should be called. Both trees were infected with this black fungus every year. I trimmed most of the limbs from one tree since they were all infected. It seems to be growing back. The other tree I was able to remove the infected limbs and it’s producing fruit.
Both trees I washed with a mix of detergent and oil that you can buy from garden stores (can’t remember the brand). I also sprayed them down with fungicide. The black smuck seems to be at bay, atlthough it’s still spring.
Again, any advice would be appreciated.


Pictures would be helpful.

In my experience, trees from chain stores like TSC, HD, Lowes, seem to be cheap and not good quality. Usually they are too advanced for the season, such as leafed out and blossomed before the grass even begins to green. They usually arent trimmed well, if at all, and usually neglected. One usually gets what they pay for when buying trees from those places. P


My plum trees dropped almost all its fruit when they were still green because of the bug bite, plum curculio. Did you dissect the dropped fruit to see whether there are worm inside? This year, I am spraying Insecticide triazicide vigilantly since petal fall. So far so good, I haven’t seen any bite mark yet. Hopefully, I will have a good crop this year.

I don’t know what the black smuck is. If you post a picture, other members may be able to identify.


Agree with @Sara_in_philly, premature dropped plums usually because they are damaged by insects such as plum curculios or Oriental fruit moths. They will have entry holes, some are small or hit near the stem ends that you may not notice. Picked up all dropped fruit and throw them out with trash. Do not compost them. If you do, you recycle their life cycle.

The black smuck is likely black knot. Please look up “black knot on plums” . Plums are susceptible to this disease. It’s hard to control. Strong fungicide spray may reduce its severity. Some plum varieties are more susceptible to it.


I picked an unripe plum. I dissected it and couldn’t find any infection. This year I treated the plum tree with Daconil fungicide and washed them with Bonide Insecticidal Soap.


I looked up Black Knot Fungus. From the pictures on-line, this is the disease that infested my trees. So far, no fungus. Fingers crossed and fungicide on standby.


There isn’t really any fungicide for black knot, you just need to cut it out. I am just starting to get some knots in my orchard and cut out several today.

For the plums falling, look for plums with small marks on the bottoms, a small smile. That is the plum curculio scar. They are likely the cause of the fruits falling and they are very hard to control. I have done maybe 3-4 Surround sprays for them so far this year. Or you can spray a poison like triazicide.


Since yoir tree is at least 5 years old. (It may be a 2 year old tree when you bought it). So, your tree is mature enough to hold on to its fruit (immature trees can drop their fruit).

My next guess is that your plum tree does not get adequate pollination. What is the variety of your plum tree?

Black knot usually started last year, overwintered and continue to develop into those ugly fungus this year.


Agree with @mamuang on pollination being a possible issue. I have a Satsuma plum tree I planted in late 2018. In 2019, I hand-pollinated with Santa Rosa (couple of blooms from a teeny graft) pollen and it produced massively. This year, I wanted to test how it does without hand-pollination. It set massive amount of fruits again but all of them dropped early.


Here is a picture of the unripe plum fruit.
Unripe plum


Those were plum curculio bite marks.


Agree with @mamuang, those are plum curculio bite marks. Here are a couple of pictures of my plum with the bite mark:
43FF00B7-0967-46B1-859B-6C19153D2E9A 12F29301-25E8-4C62-90C1-E402226E83D5


Yup… it is probably too late for this year but figure out your curculio control program for next year. I use Surround which works well and is not a poison, or you can use a poison like triazicide.


Ack! Sorry your plums got hit by plum curculio.

Me too. About 2/3 of my dozen or so Toka plums that made it through the freeze have plum curculio bites and egg laying scars.

I know better, but still slacked because I figured with our freeze earlier this month that I’d have no fruit hanging on. I also sort of incorrectly figured since we are on the edge of a new sub-division in a open field no PC would find me. Well that was wrong. Better luck next year, I guess. I cut out the scars hoping to get the eggs on the plums that had them (some folks do this) and sprayed tonight to protect the rest that are left.