Problems with green gage plum tree

Asked September 29, 2018, 10:16 AM EDT

I live in Portland and have a green gage plum tree that is about 5 years old. The tree has many flowers in the spring, and many of them develop into fruit. However, most of the small plums fall off, and those that remain all have some sort of pest, because each plum has one or more drops of amber fluid that is visible on the skin. In the end, none of the plums successfully ripen. Currently, the only thing I do with the tree is to trim it in the winter; no chemical applications are sprayed onto the tree and I have not fertilized it. As an organic gardener, I don't want to use toxic chemicals on the tree. What can I do to help allow the fruit to mature successfully? The tree gets full sun only a few hours each day. The tree growth is strong in terms of branches. Thank you!

Multnomah County Oregon plum trees

15 Responses

Thanks for your question. We need to start with the amber fluid that you're observing. Can you take a photo and attach it to a response? There are several pesticides that are organic, but it is difficult to recommend one unless we can see what you're describing. I'll get back to you once I have more information. Thanks!

Unfortunately I don't have a photo of the problem. This year's plums dropped off months ago. But I have found a photo on the Internet that looks similar to what I see. Usually there are only a couple of drops of the exuded fluid. I have never looked for bite holes, so can't tell you if they exist. The plums fall off before reaching maturity. I hope this helps.

Unfortunately I don't have a photo of the problem. This year's plums dropped off months ago. But I have found a photo on the Internet that looks similar to what I see. Usually there are only a couple of drops of the exuded fluid. I have never looked for bite holes, so can't tell you if they exist. The plums fall off before reaching maturity. I hope this helps.

Unfortunately I don't have a photo of the problem. This year's plums dropped off months ago. But I have found a photo on the Internet that looks similar to what I see. Usually there are only a couple of drops of the exuded fluid. I have never looked for bite holes, so can't tell you if they exist. The plums fall off before reaching maturity. I hope this helps.

Thank you for the photo. Unfortunately, the fact that it "looks similar to" the pictures off the Internet doesn't effectively identify exactly what your plant has. In order to utilize the most effective treatment methods, we first have to identify the problem. Rather than try to revisit last season, I suggest you read the following Extension article, and follow the instructions to keep the tree from having the same problem(s) next year: http://cru.cahe.wsu.edu/cepublications/em066e/em066e.pdf

I have read through the extension article, but I don't find anything in it that sounds like my problem. The closest thing might be the coddling moth, but I am far from certain about that. So should I try using spinosad next year and see what happens?

We cannot recommend a solution without first having identified the problem, which brings us back to the first issue. Some orchardists apply every treatment in the book, wasting money and pesticides. The best that I can add to prior input is that the problem needs to be identified while it is happening. Perhaps we’ll have better success next year!

Thinking that my problem might be caused by codling moths, I applied a solution of Capitan Jack's Deadbug (spinosad) to my green gage plum tree just after the last flower petals fell from the tree. I think the solution was too strong, because some leaves and tiny plums withered and died subsequently. But a goodly number of plums survived. Because of these results, I have not reapplied the spinosad again. Most of the surviving plums continue to do well, but I just noticed one that had a dead bug attached to it and some clear liquid leaking from the skin at another location. (A second plum had the same type of insect attached to it, but the bug was dead and the hole was just skin deep. I assume that the residual spinosad killed both insects before they could do much harm.)

Attached are three photos of the plum and insect. Does it seem likely that this is the bug that has caused me so many problems in the past? I cannot determine if the place where the clear liquid is leaking was caused by a bug bite. But the liquid is the same as what I have observed in the past.

Attached are three photos of the one plum.

The insect you’re seeing is a lady beetle, a beneficial insect that eats harmful insects. Using insecticides when beneficial insects (including bees, wasps and other pollinating insects) are present decreases their already disappearing populations. You could well have coddling moths, which cause this type of damage. You can see similar issues, as well as prevention and treatment strategies in this article: https://catalog.extension.oregonstate.edu/ec631/html

Thank you for your response. I am surprised to learn that the lady beetle is beneficial, in that both examples I have found on my plums were biting into the fruit, which doesn't seem beneficial to them.
I looked at the information on the page specified in your reply and am not sure how to proceed. The chart for plums doesn't mention codling moths at all, and lists no symptoms similar to what I observe on my plums. Table 1 on that page mentions codling moths, with Cyd-X and Ortho Max listed as treatments. I'm not so sure I want to use either of these treatments.Table 2 lists a number of moth treatments, including spinosad.
I did use a pheromone trap during the bloom cycle and did not find any codling moths in it.
What do you recommend that I do next year?

The lady beetles are consuming insects that are attracted to the fruit ‘juice’ in the fruit surface (http://treefruit.wsu.edu/crop-protection/opm/lady-beetles/). We need to determine the pest before getting to sprays. The other two possibilities are that your fruit have brown rot, discussed and treatment controls here: https://catalog.extension.oregonstate.edu/ec631/html or they have been infested by the brown marmorated stink bug, for which there is as yet no effective treatment: https://www.oregon.gov/ODA/shared/Documents/Publications/IPPM/BrownMarmoratedStinkBugPestAlert.pdf

I looked at the brown rot article, and I don't think that is the problem. The photograph in the article illustrating brown rot does not resemble even faintly anything that I have seen on my plums, as there is no general mold inside them even at a late stage. The plums retain the hard drops of clear fluid and there are localized areas of bad fruit inside. These areas somewhat resemble what a different photo in the article shows for codling moth. I have seen a couple of stink bugs in the back yard, where the plum tree is located, over the years, but I don't think they are the brown marmorated type. I will keep an eye out for stink bugs in the future. Other than that, what can I do to determine the pest? Thanks very much!

Using monitoring traps is the cheapest and most environmentally friendly method. But you need to start right after dormancy ends.

Yes, I did that for codling moths, and didn't find any. I see that there are traps for stink bugs, and will try that. Is there any trap for brown rot?