Black crud at stem end of peaches

Question:

My peaches are delicious, but they have developed black crud around the stem end. I cut it off, but I lose 1/4 to 1/3 of the peach. The rest of the peach tastes fine. Is there anything I can do to prevent the black crud?
Carol P.

Answer:

Although I haven't seen your peaches, I suspect that the problem is sooty mold that has developed on the outside of the peach at the stem end. Sooty mold should not create a problem with the flesh of the peach. Although the sooty mold itself may not harm the flesh inside, it may indicate a condition that can cause problems by damaging the flesh.

The sooty mold grows on sugary sap that is lost from the peach. The probable cause of this sap loss is the rain. As a peach matures, the skin hardens. If rain occurs after the peach skin hardens, the peach may absorb water through the skin of the fruit or through its roots. This may cause the fruit to expand, but the hardened skin resists this expansion. If there is sufficient water, the skin may split. (This is common in tomato fruits and sometimes occurs in peaches and other fruits.) If the skin doesn't split, another weak area is the point at which the fruit attaches to the stem. If the skin of the fruit pulls away from the stem at this point, the sap can ooze out. This sugary sap on the surface of the fruit provides a good environment for growth of sooty mold. This is especially true when the air is humid, as it has been this monsoon season in much of New Mexico.

The opening through the skin (whether by cracking or separating at the stem) allows sap out, and it can also allow disease organisms inside. This is why the sooty mold may be indicating a problem. If the flesh near the stem end is discolored or mushy, there is a possibility that decay organisms have entered and damaged the flesh. Some people are reluctant to eat the fruit if there is evidence of damage to even part of the flesh. This is because the fungal hyphae (thread-like filaments) extend farther into the fruit than the damaged flesh reveals.

It is difficult to prevent this type of damage, and it is impossible to cure once the skin has broken. Irrigation during early fruit development may help to keep the skin from hardening too soon, but in our dry air this is often not possible. If the flesh inside the fruit shows no sign of decay, then the only problem is the sooty mold on the surface, which can be cut away by peeling the peach.

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Marisa Y. Thompson, PhD, is the Extension Horticulture Specialist, in the Department of Extension Plant Sciences at the New Mexico State University Los Lunas Agricultural Science Center, email: desertblooms@nmsu.edu, office: 505-865-7340, ext. 113.

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