Last week, I worked a shift in the Spokane County Master Gardener plant clinic. That's where we identify plant diseases or insects, or make plant suggestions for specific settings, and so on.
Two clients came in with the same problem and it was something I've noticed on my own raspberry plants so had planned to research it.
Do you see how parts of the berries in each photo are white or tan, rather than red?
That is "White Drupelet Disorder." It is caused by exposure to ultra-violet rays which occurs during periods of hot weather. And if you live in the Inland Northwest, you know we've been having a heat wave over the past 5 weeks or so.
In case you're wondering what in the world a drupelet is, that's what each "bump" on a raspberry is called, which surrounds a seed.
After doing some research on how to resolve this problem, I learned there are two main things:
1. If possible, cover your raspberry patch with a lightweight shade cloth.
2. Water your plants overhead twice a day for about 15 minutes at a time. This will cool down the plants. If one of those times is in the evening, be sure to do it early so the plants and berries have the chance to dry off before night sets in.
According to what I read, most caneberries are susceptible to this so both raspberries and blackberries can develop White Drupelet Disorder.
My raspberry patch is just about done bearing for the season, so I plan to try the above two steps on my blackberry patch. I remember having problems on them last summer so it's worth a try!