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Plum tree blossoms turn brown. #392650
Asked April 08, 2017, 11:08 PM EDT
Linn County Oregon
Expert Response
From your description it sounds like brown rot. This is the information on brown rot - a fungus.
Brown rot blossom blight is a common and destructive disease of all stone fruits including flowering cherry and plum as well as their fruit bearing relatives.
Flowering and weeping cherry, flowering plum, fruit trees; apricot, cherry, peach, and plum.
The brown rot fungus can attack blossoms, fruit, leaves, twigs and branches. Disease symptoms appear in the spring after the blossoms open. Diseased flowers wilt, turn brown and are covered with masses of spores. The disease spreads into twigs causing small branch dieback. Profuse gumming may appear on infected branches. Fruit infections appear as soft brown spots and can engulf the whole fruit. Infected fruit and flowers shrink into "mummies" and may persist on the tree until next year.
Brown rot is caused by a fungus that over winters on infected plant parts. In the spring during wet weather masses of spores are produced that can infect the blossoms and young shoots. The disease will continue infection cycles during wet periods in the spring.
A combination of cultural methods and treatments are needed to control this disease in our wet rainy northwest climate.
Sanitation is very important. Remove and destroy all infected twigs and branches. Remove all rotted fruit. (Look at your other plums to see if they have ever looked like the plum fruit picture below). Prune back the limb about 4 inches from the brown rot. Always keep a 10% (1 part bleach to 9 parts water) bleach solution or isopropyl alcohol with you to clean your pruners. Do not prune one tree then go to another for pruning without cleaning your pruners, you will transfer the disease.
Remove wild or neglected stone fruit trees that serve as disease reservoirs. This is highly contagious and will eventually infect all your plums.
Avoid wounding fruit during harvest.
Use wettable sulfur or lime sulfur (find it at Wilco) during periods of wet weather. Follow the instructions for both solution strength and when and how to use it during the year.
Apply three to four treatments of an approved fungicide (some are systemic) starting at bud break in the early spring and continue at regular intervals during the spring until dry weather. Thoroughly treat all leaf and twig surfaces. Treatments during blossoming are essential for good control. (You will not get any fruit this year). The wetter and rainier the spring, the worse the disease problem is. Also apply a dormant oil treatment before fall rains.
I spray during the fall once a month through January if possible. You need about 40 degrees, dry (for 8 hours) and windless day to spray. Usually in January there are a couple of warm weeks. If possible, weather cooperating, I spray dormant oil (winter) and lime sulfur separately. If the weather stays nice for spraying, a week later I use Neem oil (- use concentrated and follow the instructions. Alternate between lime sulfur and Neem oil. DO NOT USE NEEM when the bees are out during blossom time - it will kill them.
Here is a link to images of brown rot. https://www.bing.com/images/search?q=brown+rot+on+plum+blossoms&FORM=HDRSC2
I hope this helps you. Please contact Ask an Expert if you have other questions.