Discolored berries are another example of crops affected by intense summer heat
This close-up on two blackberries shows the white-to-tan drupelets that can develop in hot, dry weather. Courtesy UC Integrated Pest Management
Add another crop to our list of heat victims this summer: Blackberries.
Throughout the Sacramento region, blackberries are developing odd white or tan discoloration. The little drupelets – the juicy sacs that make up the berry – turn white or tan. It’s not just cosmetic; they generally don’t taste so good either. Often, the discolored drupelet withers to nothing but a dried seed.
I noticed these weird drupelets on my own Baby Cakes blackberries as well as the wild blackberries that grow near our home. Was it the heat?
Thanks to Farmer Fred Hoffman (and UC research), we know why: Excess UV radiation. (And yes, that’s related to the heat.)
Hoffman, host of “Garden Basics with Farmer Fred” podcast, solved this mystery in response to an Oroville listener who saw her berries go from pink to tan to yuck.
In his column, Hoffman recapped heat-related problems with other crops such as tomatoes.
“And now, you can add blackberries to the list of crops that develop problems when it gets too sunny, too hot, dry and windy, especially because of extended heatwaves. The problem is known as White Drupelet Disorder (WDD),” Hoffman wrote.
It’s not just a matter of adding shade; the berry plants need humidity.
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/.
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Food in My Back Yard Series
June 10: Battling early-season tomato pests
June 3: Make your own compost
May 27: Where are the bees when you need them?
May 20: How to help tomatoes thrive on hot days
May 13: Your plants can tell you more than any calendar can
May 6: Maintain soil moisture with mulch for garden success
April 29: What's (already) wrong with my tomato plants?
April 22: Should you stock up on fertilizer? (Yes!)
April 15: Grow culinary herbs in containers
April 8: When to plant summer vegetables
April 1: Don't be fooled by these garden myths
March 25: Fertilizer tips: How to 'feed' your vegetables for healthy growth
March 18: Time to give vegetable seedlings some more space
March 11: Ways to win the fight against weeds
March 4: Potatoes from the garden
Feb. 25: Plant a fruit tree now -- for later
Feb. 18: How to squeeze more food into less space
Feb. 11: When to plant? Consider staggering your transplants
Feb. 4: Starting in seed starting
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Garden Checklist for week of June 15
Make the most of this “average” weather; your garden is growing fast! (So are the weeds!)
* Warm weather brings rapid growth in the vegetable garden, with tomatoes and squash enjoying the heat. Deep-water, then feed with a balanced fertilizer. Bone meal can spur the bloom cycle and help set fruit.
* Generally, tomatoes need deep watering two to three times a week, but don’t let them dry out completely. That can encourage blossom-end rot.
* From seed, plant corn, melons, pumpkins, radishes, squash and sunflowers.
* Plant basil to go with your tomatoes.
* Transplant summer annuals such as petunias, marigolds and zinnias. It’s also a good time to transplant perennial flowers including astilbe, columbine, coneflowers, coreopsis, dahlias, rudbeckia, salvia and verbena.
* Pull weeds before they go to seed.
* Let the grass grow longer. Set the mower blades high to reduce stress on your lawn during summer heat. To cut down on evaporation, water your lawn deeply during the wee hours of the morning, between 2 and 8 a.m.
* Tie up vines and stake tall plants such as gladiolus and lilies. That gives their heavy flowers some support.
* Dig and divide crowded bulbs after the tops have died down.
* Feed summer flowers with a slow-release fertilizer.
* Mulch, mulch, mulch! This “blanket” keeps moisture in the soil longer and helps your plants cope during hot weather. It also helps smother weeds.
* Thin grapes on the vine for bigger, better clusters later this summer.
* Cut back fruit-bearing canes on berries.
* Feed camellias, azaleas and other acid-loving plants. Mulch to conserve moisture and reduce heat stress.
* Cut back Shasta daisies after flowering to encourage a second bloom in the fall.
* Trim off dead flowers from rose bushes to keep them blooming through the summer. Roses also benefit from deep watering and feeding now. A top dressing of aged compost will keep them happy. It feeds as well as keeps roots moist.
* Pinch back chrysanthemums for bushier plants with many more flowers in September.
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