Horticultural Oils
Horticultural oils, such as Golden Pest Spray Oil, when used at the rate of 1.2 to 2% volume to volume, applied after green fruit or first pink fruit stage in four consecutive applications spaced 2 or 3 weeks apart give significant control of redberry mite, while causing less harm to fruit yield than sulfur sprays.

I start now with Golden Pest Spray Oil.
Lime Sulfur in dead winter only if have winter freeze so go dormant.

Forget about UV damage on blackberries its meth are BS sun only damage druplet by skin braking and drying to Brown drulet bust by over compaction from other druplets and turn Brown.

Here is a link that might be useful: half ripe berries

If you mean 50% of each affected berry is black and red, and the red part remains very hard, that is the classical symptom of the red berry mite damage. Those mites are tiny but can be seen scurrying around if you get your eye about 3" from the plant.

For UV damage, the berries will start to have bleeding, white or pale drupelets in the red phase. During the black phase, the pale drupelets become most obvious. Eventually they do dry out, becoming crunchy and brown, as gator mentioned above.

The image you linked to, from the gardener in Greece, did have UV damage; the whole berry was soft.

I had about 40 to 50% good fruit (all black), and the remaining 50% are bad, either all red and very hard, or 50% of the berry is black and 50% of it is red and hard.

As I mentioned, I had the same thing last year on this thornless blackberry bush. I cut all those canes away and threw them out. Did the mites hang around since 8 months ago & hide on the primocanes of the new growth and then wait for the berries to start growing and infect them?

I have a thorn black berry bush against the wall in a different part of my yard and none of those fruit were affected.

I noticed Golden Pest Spray oil's active ingredient is 98% soybean oil. I was at a nursery today and they suggested

http://www.arbico-organics.com/fullsize/1172/23

which active ingredient was 98% mineral oil. Is there a difference, or is Golden Pest Spray superior?

Thanks

Thanks for clarifying the affected berries. Some berries can remain all red where mites have damaged all the drupelets.

Thorny versus thornless has nothing to do with it.

Yes, mites hang out in tight places in new growth and overwinter. They emerge during "bud break" and oil is recommended when new growth is an inch or two long with tiny leaves. Then perhaps a second application some weeks later.
No sense in waiting until major growth occurs, then it is too hard to oil all the surfaces.

I don't know about the two oils mentioned above.

Larry_Gene, major growth has already occurred on the Primocanes that will have fruit next year. i have 4 of them that are at least 7 feet long. There's still 5 old canes right now with some good fruit and the majority of redmite infected fruit which I'll be cutting away in the next week. So if these mites are hiding in the new canes already, I have to spray all these canes with oil to kill them off?

I was reading some of the active ingredients in these horticultural oils and one said 98% soybean oil and a different one had 98% canola oil. Dumb question, but can you just use 100% canola oil that you use for cooking, or what's the difference?

Anyway, is it too late to attack the problem, i don't want the same thing happening again next year :(

Your primocanes are leafed out, and perhaps in California hold their leaves all winter, but the fruiting spurs for next year have not emerged. So late next winter or early spring, when the new growth restarts, oil then.

You could try applying some oil when you have rescued all of this year's fruit and cut out the fruiting canes, and then again next year. I don't know the comparative effectiveness of horticultural oil versus cooking oil.

but can you just use 100% canola oil that you use for cooking, or what's the difference?
Here the differences.

Essentially all commercially available horticultural oils (e.g., SunsprayR, ScalecideR, VolckR) are refined petroleum products also known as mineral oils. Impurities in the oil that are associated with plant injury, such as aromatic compounds and compounds containing sulfur, nitrogen or oxygen, are removed. Filtration, distillation and dewaxing complete the production of the finished base oil. Final formulations of horticultural oils are normally combined with an emulsifying agent that allows the oil to mix with water. This mixture usually is used at about a 2 percent dilution.

Vegetable oils also can be used as insecticides, although the type of oil can greatly affect its activity. Cottonseed oil is generally considered the most insecticidal of the vegetable oils. Soybean oil, the most commonly available vegetable oil used in cooking, has often provided fair to good control of some insects and mites.

You mix 1.5 to 2% oil with water your cooking oil may not mix with water.