Nectarines (Prunus persica) turn brown because of rot. There are many different ways rot, called brown rot, can set into nectarines. The fruit, grown in U.S. Department of Agriculture plant hardiness zones 5 - 8, can develop brown rot while growing on trees. Frost, storage and handling is also a major factor in whether or not nectarines will turn brown.
Brown rot is caused by a fungus disease that can affect stone fruits while they are still growing on the trees. On the Pacific coast, the fungus is called Monilinia laxa, a European form of brown rot. The infected nectarines form brown spots that rapidly expand over the entire fruit, causing the nectarines to rot on the branches 1 to 3 weeks before they are ready to harvest.
Frost and Freezing
The whole fruit, whether it is on the tree or picked, is negatively affected by frost and freezing. Freezing occurs at temperatures below 32 F and causes the fruit’s skin and fibers to break down. After thawing, the overly soft to mushy nectarine will turn brown from rot.
Nectarines are highly perishable and will only last a few days to up to two weeks after they are picked. To prevent immediate rotting, store the fruit in perforated plastic bags in the refrigerator at temperatures of 32 F to 40 F. Immediately use fruit that is bruised or punctured because it will begin to rot while in storage.
Rough and careless handling can cause nectarines to bruise. Bruise spots on nectarines are highly susceptible to brown rot because the fruit’s skin is damaged and the fungus can more easily attack the fruit. Bruised fruit should be eaten immediately. If the fruit is far too bruised to eat, dispose of it immediately so that it does not infect any other nectarines.
Browning After Cutting
Many fruits including nectarines, begin to turn brown after being cut open. To prevent browning, eat the fruit immediately after cutting. If you are preparing nectarines for canning or freezing, drop the peeled, sliced fruit into a bowl containing 1 gallon water mixed with either one teaspoon ascorbic acid crystals or six crushed 500 milligram vitamin C tablets.