Hello!

From what you are describing, it sounds like your raspberries are experiencing crumbly fruit. The possible causes are viruses, poor pollination, tarnished plant bugs, two spotted spider mites, boron deficiency, and sometimes Botrytis. I doubt that poor pollination or boron deficiency is the problem because only a small section of your plants are affected.

Have you seen any bugs on the affected plants? Tarnished plant bugs, a subset of Lygus bugs, are described here: Blackberry and Raspberry-Lygus bug | Pacific Northwest Pest Management Handbooks. Two spotted spider mites are described here: Blackberry and Raspberry-Spider mite | Pacific Northwest Pest Management Handbooks. The spider mites do not fly, the damage they do starts from the bottom of the plant and moves upwards. They must crawl between plants, so the damage pattern could match what you are seeing.

If you had a Botrytis problem, I think you would see more issues than just malformed berries.

The remaining cause is viruses. The possible viruses are Raspberry bushy dwarf virus (RBDV), Raspberry leaf mottle virus (RLMV), Raspberry latent virus (RpLV), and/or Black raspberry necrosis virus (BRNV). If virus(es) are the cause, it is typical for the plant to be affected by a combination of these viruses, rather than just one. Unfortunately, it’s difficult to diagnose viruses without a lab test.

Raspberry (Rubus spp.)-Crumbly Fruit | Pacific Northwest Pest Management Handbooks

Some more resources:

Crumbly raspberry disorder being seen across Michigan - MSU Extension

Raspberries: Fruits is small, deformed, or crumbly | Berry Diagnostic Tool

Raspberry viruses | Berry Diagnostic Tool

I hope this is helpful!

Regards,

Leo Sherry

OSU Extension Master Gardener Volunteer

Hello!

The closest analytical lab that can diagnose plant disease is the OSU Plant Clinic in Corvallis. It looks like samples can also be mailed to them.

College of Agricultural Sciences OSU Plant Clinic

I also found this list for analytical laboratories, but they are farther away than OSU.

Analytical Laboratories Serving Oregon | OSU Extension Catalog

Blackberries are generally less affected by the viruses, so hopefully you will be okay there. If they are infected with only one of them, they may be completely symptomless. If it is a virus problem, it is possible they were a source. (The paragraph above the cultural control section in here describes it: Raspberry (Rubus spp.)-Crumbly Fruit | Pacific Northwest Pest Management Handbooks, same resource as my previous email.)

If it is a virus spread by aphids, controlling aphid population can help slow the transmission if removal of the plant is not a good option. If it is a virus spread by pollinators, removing the plant would be the best move, unfortunately.

Regards,

Leo Sherry

OSU Extension Master Gardener Volunteer