Why do blackberries develop white parts?

According to the UC Integrated Pest Management Guidelines for Caneberries:
"White drupelet is a tan-to-white discoloration of one to many drupelets on the fruit. Most often, white drupelets will appear when there has been an abrupt increase in temperature accompanied by a drop in humidity; it is especially pronounced when there is wind. ...

“While white drupelets may seem to be directly caused by weather, they are actually caused by ultra-violet (UV) radiation,” note the UC experts. “Weather conditions modulate this by the effect they have on penetration of UV radiation into the fruit. Cool, humid air scatters and absorbs UV radiation, while hot dry air has the opposite effect and allows more direct UV rays to reach the fruit.

“The movement of humidity away from the canopy by wind only heightens the effect of hot dry air. Additionally, as humidity is moved away from the plant canopy, more UV rays penetrate the canopy and damage fruit that may not even have been exposed to the sun. Fruit inside of the canopy is not acclimatized to UV radiation and is subsequently more susceptible when it reaches them.”

How do you combat WDD? Make your own fog.

“Some growers of caneberries in the Willamette Valley of Oregon, where rapid changes from a normally mild climate to temperatures up to and above 100 degrees occur through the summer, use overhead irrigation to minimize fruit loss to white drupelet,” say the researchers. “This is not merely to mist the fruit; instead, large amounts of water are applied to thoroughly wet the canopy and maintain cool temperatures and high canopy humidity for as long as possible. Sprinkling is not done too late in the evening to allow fruit to dry before nightfall.”

Learn more here: https://ipm.ucanr.edu/agriculture/caneberries/white-drupelet/#gsc.tab=0

Hoffman also cited other university researchers. As other berry-growing regions get hotter and drier, WDD will only become a bigger problem.

Meanwhile, Hoffman offered tips for berry success in his “Beyond the Garden Basics” segment, plus reasons why taking time to smell the roses (and other aromatic plants) really is good for you in his Friday podcast, “Stressed? Your Garden Can Help.” (And who isn't this summer?)

Find Hoffman’s podcasts and more here: https://gardenbasics.net/.