Garden Detective

Garden Detective: Fungus may be causing nectarine woes

Brown rot can attack stone fruit including peaches, nectarines and apricots. This fungal infection can often start on the tree.
Brown rot can attack stone fruit including peaches, nectarines and apricots. This fungal infection can often start on the tree. Bigstock

Experts tackle readers’ garden questions.

Q: My nectarine tree is several years old, pruned annually, sprayed with a dormant spray twice a year and never shows problems of leaf curl. However, each year the fruit is strangely distorted, lumpy, misshapen, and every fruit has damage on the blossom end that looks just like apple scab. I can see no evidence of trunk or branch canker, a few shot-hole feedings in the leaves, but no webs, nor anything else. Any ideas?

Jack Seedman,


Master gardener Carol Rogala: Your nectarine tree may have brown rot. Caused by Monilinia fungi, brown rot is a very serious disease in stone fruit. Brown rot pathogens blight blossoms and young shoots, rot ripening fruit, and may attack very young green fruit. (This is also known as green fruit rot or jacket rot.)

Brown rot is most severe in years when mild wet weather occurs during bloom. Blossoms on plants infected with Monilinia brown and wither.

Dead blossoms often cling to twigs for a long time. Sunken, brown areas may develop around twigs at the base of infected flowers, causing leaves at the tips of twigs to shrivel up. Brown, sticky droplets of gum may exude from the base of dead flowers and the bark of infected twigs. Velvety gray or tan tufts of spores are formed on diseased blossoms or twig cankers.

The fruit rot first appears as small dark spots on the fruit surface. Brown or tan spots spread rapidly over the fruit surface and produce spores. Fruit infection is most common during the last few weeks before harvest.

Good sanitation in the garden helps reduce the spread of brown rot. Prompt removal and destruction of fruit “mummies” (old fruit that clings to the tree) and diseased plant parts prevents the build-up of brown rot inoculum and helps keep rot below damaging levels.

Prune trees to allow good ventilation. Clean up all dropped fruit on the ground. Furrow irrigate or use low-angle sprinklers to avoid wetting blossoms, foliage, and fruit.

If you have had problems in the past, applications of fungicides such as myclobutanil at pink bud stage can help avoid serious losses.

Additional applications when fruit starts to color may be needed if rainy weather persists.

Carol Rogala is a UC Cooperative Extension master gardener in Sacramento County.

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