The following question was sent to the P&PDL diagnosticians here at Purdue University:
Question: What is causing my blackberry plants to produce fruit that is ripening unevenly?
Answer: Several different causal agents have been implicated as causal agents of 'blond drupelets' (incomplete ripening).
Sunburn or sunscald from ultraviolet radiation and exposure to high temperatures may be responsible for the formation of 'blond drupelets', especially since this problem seems to be more common on the top (exposed part) of the berries.
Tarnished plant bug feeding is also thought to be a possible cause of 'blond drupelets'. In Pennsylvania, they caged fruit clusters with tarnished plant bugs and saw the symptoms.
If this is an Eastern Thornless Blackberry, it is important to note that they are late ripeners.
- Bruce Bordelon, small fruit extension horticulturalist
- Gail Ruhl, plant disease diagnostician