Markus Kobelt, the founder and breeder of the Swiss fruit tree nursery Lubera, talks about how you can see the difference between the BigandEarly and the Summerlong.
I've trialed a lot of thornless blackberry cultivars and the best/most promising is the Navaho Summerlong as stated on this great site which knows its stuff.
The Summerlong is superior to the other Navaho types which I found to be quite late in ripening, prone to chlorosis, and flowers can be damaged by heavy showers or fail to open due to aborted pollination. Both the Navahos Bigandearly/Original can suffer badly from white drupelets from sun scorch. The canes in Bigandearly can break off from the base easily whilst the original suckers all over the place. Only ever seen this brittleness in Waldo previously.
The blackberry Navaho Summerlong suffers none of these problems(apart from the odd white druplet now and again which happens in just a few early ripening berries after rain shower then a sunny period.
It is very disease resistant and is the most compact season ripening blackberry I've ever seen- mid July to mid Sept or sooner and it is done whatever weather conditions. Best I've seen to date.
I purchased the modern blackberry Navaho Summerlong early last year after grubbing out all my other thornless blackberries which ripened in late Aug.
The large white flowers were pretty to see and a bee magnet. It proved to be an excellent cropper of sweet firm berries of a good size in mid July onwards. It put out 3 more canes in mid summer. Now it is growing nicely with lots of shoots opening on the canes. Expecting a big crop of blackberries!