Apache Blackberries and White Drupelets?
About half of our Apache blackberries (which are otherwise healthy) have white drupelets.
They look - just - like the photos of white drupelets on Apaches that I see on the net.
I do not see a lot of stinkbugs in the garden.
The row of three Apaches is planted north to south.
The row does get full sun after about 11 am.
It is not an especially windy spot, being bordered by a tall hedge on one side and a tall garage on another.
They get water from a drip line twice a day.
Is there anything that I can do?
Sean (near Portland)
Overhead watering of blackberries may help on the very hot days, as explained in this article from University of California IPM about caneberries white drupelet: http://www.ipm.ucdavis.edu/PMG/r71800111.html
The article does mention Apache being prone to white drupelet, and the Willamette Valley growers specifically because of our temperature swings. The current forecast is for cooling weather, so perhaps the damage that has been done will not continue.
Overhead watering is not practical for us. Could a shade fabric cloth be draped over the plants on hot, dry days? I see one on amazon that makes 50% shade, and has a few stars: "Agfabric 50% Sunblock Shade Cloth, Cut Edge Uv Resistant Shade Fabric, Tarp Cloth, 12*20ft" Would this help? I think we would just use it on days above 85 degrees. Thanks.
I am not finding research indicating anything about shade cloth for white drupelet: useful or not. It wouldn't be viable for commercial growers so research wouldn't focus on the shade cloth ideas, I suppose. One gardening advice page mentions it, though not too close to the plants because the cloth can hold heat against the leaves. I can't really recommend it because of the lack of research, but I also don't have information that it doesn't work.
I will attach a couple of links to university extension service articles you may find helpful. One mentions that white drupelet doesn't hurt the flavor and usefulness of the berries, and usually is an early-season problem resolving as the crop continues. Another says that the UV rays can penetrate the leaf canopy, so damage can occur even on shaded berries. Also the sudden 100 degree days are used as the example, rather than repeating hot days being a concern.
NC State University "White Drupelets?" http://rubus.ces.ncsu.edu/2015/06/white-drupelets/
Purdue University "White Drupelets on Raspberries and Blackberries" https://www.ppdl.purdue.edu/PPDL/weeklypics/9-6-10.html