Plums are 'rotting' on the tree

[bswift]

Hi everyone,

this is my first time on this forum and I come with a problem. Hopefully, later I can help others with some of their gardening challenges.

I have a full size plum tree that's bearing fruit for the first time -- lots and lots of plums to start with. But now, many of them are turning purple (not a healthy plum type purple) with small particles on the skin, and falling off. Some of them shrivel first then fall off.

Can anyone give me an idea what is causing this and more importantly what to do about it. I'd hate to lose the who crop but that's the direction it's heading.

Thanks in advance for your input and suggestions.

[Kisal]

I'm not all that experienced with plum trees, but it sounds like a fungal infection to me. I did a quick search and came up with "brown rot of stone fruit." You can read about it and see pictures of it at this link:

https://www.nysaes.cornell.edu/pp/extension/tfabp/brstone.shtml

[hendi_alex]

I think that brown rot is on target. Here in S.C. my plums and cherries tend to get brown rot and sometimes a loaded tree will lose about all of its fruit. The condition is worse and spreads rapidly when lots of rainfall comes during the ripe or nearly ripe phase of fruiting. Warm temperatures could also be a contributor. Brown rot can be avoided or minimized with the proper spray regimen.

[cynthia_h]

Today I collected two 5-gallon buckets of plums from my MIL's neighbor (Sunset Zone 15, somewhat warmer than where I live).

For them, deep red or purple is good. But no brown spots.

I wonder if plums behave similarly to apples in that they set more fruit than they can properly support to maturity?

If so, thinning soon after fruit-set would help.

But, I gotta say, thinning the fruit on today's approx. 45-year-old tree would be a daunting task, even early in the season. It's probably *much* easier on a much smaller and younger tree...

Sorry about your crop!

Cynthia H.
USDA Zone 9, Sunset Zone 17

[Jess]

There is no chemical control available for brown rot.
It is a fungal disease spread mainly by insect damage. In the case of plums the main culprits are wasps (yellow jackets) Good housekeeping is the best way to control it.
Remove all damaged fruit. Prune out and dispose of (but not on the compost heap) dead shoots or spurs and any mummified fruits that remain on the tree, as the disease can overwinter on these.
Do you have other fruit trees nearby? (apples, pears) One tree can infect another.
Your plum tree will be best able to fight back if healthy.
Remove grass (if planted in a lawn) from around the base taking it back at least 3ft Apply a yearly organic mulch of well rotted manure to keep nitrogen levels up and moisture in for the summer. Plums hate dry conditions for growing. An addition of bonemeal to the soil in February is also helpful.
You may find that if you store the fruit brown rot may also develop. Check the fruit regularly and discard any that are infected.
I hope that information is of some help and that you do manage to get some plums this year.