Why Are the Blackberries Turning White?

From the garden e-mail bag, Teri asks: "What is wrong with my blackberries?"

Dewey & Ann write: "What is causing this problem with my Chester blackberries? This is on the majority of them.  I had it last year too. I checked with the local Hmongs and they also had it and said it was the 111 degrees we had in Oroville. We are at 2500 feet and 10 degrees cooler, but it wasn’t this hot last year. My Black Satin Blackberries were forming and doing well and I thought the problem was only with the Chester. Well, pretty soon I see it on them also. Am I missing something in our soil? It’s not on every one of them. It’s a dried seed eventually, but goes from a pink to beige and then worse if you don’t pick them. I would like to get to bottom of this. Can you help me?"

Your local Hmong are wise gardeners. The recent week of very sunny 100+ temperatures, along with a couple of triple digit scorchers in the first week of June, could very well be the culprit.

Usually when we think of heat stressed plants, the cool season ones that tend to croak when it gets hot come to mind...

 

Such as lettuce...


















Or sweet peas.

 
Even warm season vegetables that like sunlight, especially tomatoes, can be adversely effected by too much high intensity sun. Abiotic disorders such as cracking, solar yellowing or green shoulders are common this time of year on young tomato crops.

Solar Yellowing

Cracking

One remedy for that: don't prune off any of the leaf canopy of tomato plants; or, cover with a lightweight row cover to provide some more shade.






















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 this year. The problem is known as White Drupelet.

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. In the Monterey Bay area, white drupelet typically occurs when temperatures that are fairly steady around 70 degrees suddenly go above 90 degrees, and there is an absence of fog.

While white drupelets may seem to be directly caused by weather, they are actually caused by ultra-violet (UV) radiation. 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.

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. 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.

While some varieties, such as Apache blackberry, Kiowa blackberry, and Caroline red raspberry tend to get white drupelets more frequently than others, almost all caneberry varieties are susceptible to white drupelet to some degree."

Hey, blame it on the weather.
 

Early Summer Tomato Troubles

The cool, damp spring is still with us....even though it's 90 degrees, dry and officially summer. The harbinger of that recent past? The backyard tomato crop. Take a close look at those ripening red orbs that you planted during a drizzly April and early May.

Do they look like this?

Fruit Cracking

Or this? 

Or like this?

Solar Yellowing

Soon... they may look like this!

Blossom End Rot

The first two conditions, fruit cracking  and bacterial speck, you can blame on the cool, wet spring weather. 

That third condition, solar yellowing, is just what the name implies: too much hot sun, too soon.

That fourth ugly example, blossom end rot? A combination of weather, irregular watering, and lack of calcium uptake.


Another weather related malady: lack of tomato fruit set.

FRUIT CRACKS are tomatoes with deep ridges, radiating from the stem. When a wet spring suddenly turns to summer, those hot, sunny days may deplete more soil moisture than you anticipated. Radial cracking can occur during alternate rainy and sunny periods, such as what we had in May. Fruit exposed to the sun may also develop cracks. Maintain a uniform water supply. Mulches can help maintain that uniformity. A full leaf canopy will also help protect fruit from the sun and reduce cracking.

BACTERIAL SPECK: Hits during rain or overhead irrigation early in the season, during cool weather. Retards growth, reduces yields up to 25%, fruit spots, leaf spots. Leaf spots are near the edge of the leaf, dark brown with a yellow ring. Can spread throughout the leaf margin area. Common in cool coastal areas of CA. Solution: plant later in the season; avoid overhead watering.

Blossom end rot. According to the University of California, Tomato plants with blossom end rot show small, light brown spots at the blossom end of immature fruit. The affected area gradually expands into a sunken, leathery, brown or black lesion as the fruit ripens. Hard, brown areas may develop inside the fruit, either with or without external symptoms. Blossom end rot results from a low level of calcium in the fruit and water balance in the plant. It is aggravated by high soil salt content or low soil moisture and is more common on sandier soils.  Too much nitrogen fertilizer can also be a factor. Improper soil pH may play a role; tomatoes prefer a pH range of 6.0-7.0. To reduce incidences of blossom end rot, make sure that the root zone neither dries out nor remains saturated. Follow recommended rates for fertilizers. Some varieties are more affected than others. The disease is not caused by a pathogen. Although UC says there are no pesticide solutions, some gardeners believe that calcium sprays intended for this purpose offer some relief. My solution: avoid varieties that have betrayed you in the past, especially paste tomatoes.

SOLAR YELLOWING. According to the  UC Davis, Vegetable Research and Information Center , the reason for the yellow or yellow-orange color, rather than the normal red, is that the red pigment (lycopene) fails to form above 86 degrees (F). This phenomenon was first described by researchers in 1952 and was later confirmed by others. When lycopene fails to form, only carotenes remain for fruit color. An orangey-red color results. In production areas where temperatures do not exceed 85 degrees (F), much higher red color develops.

Failure to Set Blossoms. If you're lucky, your tomato plant has more to it than this picture right now. Among the reasons your tomato plant may look healthy, but lack fruit and blossoms:

Night temperatures are too low (below 55);

Day temperatures are too high (above 90);

Tomatoes were planted too early in the season; 

(late April-mid-May is best tomato planting time here in the valleys, foothills and Bay Area of Northern CA);

Smog;

Too much nitrogen fertilizer;

Plants are in too much shade;

Tomato variety isn't adapted to California's hot summers;

Early season blossoms are not good fruit setters.

What's an impatient gardener to do about a lack of tomatoes?

Hormone sprays, designed to help deter blossom drop on tomatoes, is more effective at improving fruit set if the reason is low nighttime temperatures. According to the University of California, those sprays will not help in high temperatures. 

Another strategy: hand pollinate your tomatoes. When you see open tomato blossoms, gently shake or tap stems during mid-morning, three times a week. This can help fruit set during the late spring and early summer.

To avoid too much nitrogen fertilizer, choose a vegetable or tomato fertilizer that has relatively low amounts of nitrogen, phosphorus and potassium (as represented by the three prominent numbers on the front of most fertilizer containers). Choosing an organic fertilizer for tomatoes and vegetables, such as a 5-7-3, is a safe bet. Read and follow all label directions, no matter which fertilizer you choose.

More tomato growing info for the home gardener: UC Davis, Vegetable Research and Information Center