Water Staining, Juice Blotch, and Sooty Mold of Fruit

Staining includes three types of fruit skin discoloration: water staining, juice blotch, and sooty mold stains. All of these stains are only cosmetic blemishes that can be removed.

Water staining

Leaf and vine wetness from heavy dew, rainfall, or irrigation leaches tannins and minerals from dead organic material in the canopy and then drips onto the fruit, causing a brownish discoloration on the fruit surface. Stains can appear as teardrops, large darkened areas, or blotches that cover significant portions of the fruit surface. Water staining can also occur when harvested fruit gets wet during the handling and packing process.

Juice blotch

Lots can contain soft fruit that are crushed during handling and packaging operations, leaking juice that contaminates the surface of sound fruit. Juice on unblemished fruit placed in high humidity environments (room or inside box liner) may discolor the fruit.

Sooty mold stains

Juice on fruit may support the growth of molds. Often in storage, molds such as Cladosporium and Alternaria species may develop on the juice-blotch stained areas, causing additional discoloration such as dark spots or lines on the fruit surface. The darkened areas may appear sooty or moldy.

Staining can occur on kiwifruit wherever they are grown. Water staining more frequently occurs when fruit is harvested late and exposed to fall rainfall. Sooty mold stains commonly develop in cold storage.

Management of staining in the field includes pruning dead tissue from the canopy and the application of citric acid or other agricultural acids prior to harvest. Use of soft water and high volume applications are needed to provide adequate coverage. Allow fruit to completely dry before harvesting. Citric acid sprays or postharvest dips remove field staining, but only for a short period of time. Under long cold storage conditions, sooty mold will grow on citric acid-treated fruit.

If fruit becomes wet during postharvest handling or after postharvest application of fungicides, be sure to remove excess water by brushing and allow time for air-drying before placing fruit into boxes with liners.