What's Rotting My Nectarines...and Peaches!

Advice from the Help Desk of the
UC Master Gardener Program of Contra Costa

Client:  I have 5 different varieties of nectarine and peach trees in my Central CCC backyard. I treat the trees in late winter for peach leaf curl using an organic - approved spray. That works great.

My problem is that last year the fruit on one of my nectarine trees started rotting on the tree. The tree is about 6 years old. The fruit rots to a dark brown color. None of the other nectarine or peach trees have the same problem.

What do you think the problem is? What is the cure? I prefer to use organic methods.

Advice from the MGCC's Help Desk: Thanks for contacting the MGCC Program's Help Desk. From your description, the problem with your nectarine fruit appears to be caused by the “brown rot fungus”, monilinia fruiticola. Peaches can be attacked by Brown Rot as well.

Brown rot fungus is tough and can survive over the winter:

• in infected twigs
• inside dead blighted blossoms that remain on the tree
• dry mummified fruit that has been left on the tree from the previous year
• dry mummified fruit left on the ground from the previous year

Brown rot infection and disease development can take place over a wide temperature range and flowers can be infected from the time buds open until petals fall. Water must be present on the flower surface for infection to occur. Spores produced on the tree parts described above in spring are carried through the air by wind and splashing water to infect flowers of the new year's crop.

Prompt removal and destruction of fruit mummies and diseased plant parts prevents the buildup of brown rot inoculum and helps keep rot below damaging levels. Pruning trees to allow good air movement will also help. Good air circulation through the tree facilitates rapid drying of the foliage and flowers after rain or overhead irrigation (not recommended). Some varieties of nectarine are more susceptible to brown rot than others, as you have seen in your own garden!

Appropriate applications of fungicide is the usual preventive measure to prevent brown rot, especially if you've had it occur before. However, fungicides can only prevent brown rot; they will not cure brown rot so timely application is important. Organic fungicides do not appear to be readily available for home gardeners. Recommended applications of copper-containing fungicides or synthetic fungicides such as myclobutanil at pink bud stage - just before the buds open can help avoid serious fruit losses. Rainy periods will require more spray. Additional applications when fruit starts to color may be needed if rainy weather persists. Do not apply copper compounds after bloom.

More specific information can be found by following the links below:

http://www.ipm.ucdavis.edu/PMG/GARDEN/FRUIT/DISEASE/aprbrownrot.html

and

http://www.ipm.ucdavis.edu/PMG/GARDEN/FRUIT/nectarines.html

Good luck this year with your nectarines. Hopefully, pruning, sanitation, cultural care, and a timely application of a fungicide will minimize brown rot.

Please let us know if you have any further questions we can help you with, and thank you for contacting our program!

Help Desk of the UC Master Gardener Program of Contra Costa (JMA)

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Note: The  UC Master Gardeners of Contra Costa's Help Desk is available year-round to answer your gardening questions.  Except for a few holidays, we're open every week, Monday through Thursday for walk-ins from 9:00 am to Noon at 75 Santa Barbara Road, 2d Floor, Pleasant Hill, CA  94523. We can also be reached via telephone:  (925) 646-6586, email: ccmg@ucanr.edu, or on the web at http://ccmg.ucanr.edu/Ask_Us/ MGCC Blogs can be found at http://ccmg.ucanr.edu/HortCoCo/ You can also subscribe to the Blog  (//ucanr.edu/blogs/CCMGBlog/).