Peach and Nectarine Inking Update

by Dr. Carlos Crisosto, University of California-Davis

Inking symptoms appear as discolored brown and black sports and/or longitudinal stripes, and are restricted to the skin. Although inking affects only the fruit's cosmetic appearance, this disorder causes considerable losses to the peach and nectarine industry each year. Foliar nutrient, fungicide, and insecticide preharvest sprays can act as sources of contamination for inking development depending on the type of chemical preharvest application interval. Last season, there were cases in which inking was induced by the fruit (wax) additives during the packaging operation. Additionally, there was some over waxing that caused inking and pitting symptoms-especially on nectarines.

The inking research was completed by analyzing several pesticides for presence and amount of heavy metals, fruit additives, and foliar nutrient sprays currently used in the tree fruit industry. Several chemicals such as insecticides, fungicides, foliar nutrients and fruit waxing coatings had inking activity. Bases on their iron concentration, these selected products were classified into groups based on their potential for inducing inking development. It is important to point out tat this potential inking activity-screening test can vary according to product lots and years, and as such, it is important to send chemical samples for iron and copper analysis to a local laboratory if there is a suspicion that they may be contributing to inking development. Based on the research work the following recommendations are suggested to help growers reduce inking problems in yellow/white flesh cultivars.

Recommendations:

  • Handle fruit gently.
  • Avoid long hauling distances.
  • Keep harvest containers free of dirt.
  • Morning picking is better than late picking.

Reduce contamination of fruit:

  • Keep harvesting equipment clean.
  • Avoid dust contamination on fruit.
  • Check spray water quality for heavy metal (Iron and Copper) contaminants.
  • Do not spray foliar nutrients containing heavy metals within 21 days before harvest.
  • Check for potential heavy metal contaminants in insecticides, fungicides and foliar nutrient sprays.
  • Check for potential heavy metal contaminants in your packing operation such as washer water, hydrocooling water; fruit coatings, waxes, etc.
  • Keep water pH below 8.0 during your packing operation.

In the case of a possible inking situation with peach and/or nectarine, delay packaging for 48 hours to detect fruit inking damage during grading. It takes at least 24 hours for inking damage to develop to maximum expression.

These same recommendations are also valid for white flesh peaches and nectarines. For these white flesh cultivars, it is essential, if fruit are wet, to maintain high levels of 100-ppm active chlorine (HOCL) and pH 7-8 during the washing and hydrocooling processes.

(Assisting were: Kevin Day, Harry Andris, Bob Beebe & Jim Adaskaveg.)


  1. Rutgers
  2. Executive Dean of Agriculture and Natural Resources
  3. School of Environmental and Biological Sciences