Red drupelet disorder

Red drupelets in blackberry fruit harvested in the afternoon. Upper image is showing more than 15% red drupelets. Lower image is a mild case. Upper image PPV, lower image GF.

Now that we are reaching peak harvest and peak summer temperatures, red drupelet disorder is starting to appear in harvested fruit. After the fruit is harvested, individual black drupetlets will revert back to a red color. Red druplet disorder is also called reversion, reddening or red cell. Penny Perkins-Veazie has worked on this problem for several years. Here are some of her thoughts:

- Harvest before 10 am, get to cooler within an hour of harvest. 
- Remove heat quickly or delay field heat development.
- Forced air cool may need to be set 5 F higher than usual to avoid excess coldness at top of pallet.
-Semi truck loads tend to have more red drupe at front end (near rig) and at top due to air movement and nearness to cooling units.
-Least susceptible variety continues to be Navaho.  Those showing problems are Natchez, Tupi.  Ouachita can be problematic if rainfall has been high and harvest is going into afternoon.
-I'm not sure about PrimeArk 45 or Osage.  The new 'crispy' type does not seem to get red drupe, indicating a firmness/cell wall component in color reversion.
-A 15% red drupe (color reversion) in the load is considered the limit to avoid rejection.  
-Trellising or using E-W row orientation helps to keep fruit in shade longer, decreases exposure to light/heating.  (GF: our shift/RCA trellises seem to have less red and white druplets in general)
-We are not yet sure of production practice issues on red drupe although some reports with tunnel grown blackberries indicate keeping nitrogen rates lower and avoiding heat buildup help with the problem.
-Environmental possibilities for exacerbating the problem seem to be water stress (high rainfall within a few days of harvest, or high rainfall in spring followed by very hot temperatures), nitrogen imbalance, and possibly calcium/potassium availability.

Max Edgley, from the University of Tasmania, has an excellent slide show on this disorder. Max attended the Rubus and Ribes Symposium last year and has shared some of his findings here:

http://www.utas.edu.au/__data/assets/pdf_file/0003/792363/Red-drupelet-disorder-Presentation.pdf