Answer: It sounds like your patch is suffering from the aptly named crumbly berry virus, or perhaps another similar virus. Raspberries are especially prone to viral diseases, which is why it is very important to purchase certified virus-free stock when planting a new patch.
Crumbly berry disease is caused by the tomato ringspot virus and spread by the dagger nematode. Plants may appear normal but will produce small fruit that falls apart when picked. This is a result of the failure of some of the drupelets in the berry to develop. This virus has a wide host range including many weeds, such as dandelion.
Unlike some viruses, the organism can live for years in dead plant material, so when you remove the infected canes, get as much of the roots, crown, and canes as you can and burn or bury them. The virus is spread by aphids, so if you noticed these pests on your healthy canes last year, be aware that they may have infected more of your patch. As a safeguard, you can order new, disease-free stock this year and plant it at least 200 yards from your current patch, so you won't have a break in harvest if your current patch is affected this year.
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