Why Do My Raspberries Have White Spots?

The white spots on your raspberries are almost certainly white drupelet disorder, a cosmetic condition where individual drupelets lose their color after exposure to intense sunlight and heat. Each raspberry is a cluster of tiny bead-like drupelets, and when some of those drupelets turn pale white or tan while the rest stay red, you are seeing cellular damage from sun and environmental stress rather than disease. Less commonly, a white powdery coating across the fruit surface points to powdery mildew, a fungal infection with a distinctly different look and cause.

What White Drupelet Disorder Actually Is

White drupelet disorder (often abbreviated WDD) is the single most common reason home gardeners notice white patches on otherwise ripe raspberries. The affected drupelets do not rot or go mushy. They simply bleach out, turning white, cream, or pale tan, while the rest of the berry ripens normally. The discoloration is caused by damage to the cells in those individual drupelets, most often from a combination of ultraviolet radiation and heat. If you pick the berry and look closely, the white drupelets are typically on the side of the fruit that faced the sky or was most exposed to direct afternoon sun.

The condition is not a disease organism invading your plant. It is a physiological response to environmental stress, closer to a sunburn than an infection. This is why WDD tends to appear in waves during hot spells, particularly when a stretch of cool, cloudy weather is suddenly followed by bright, high-temperature days. Berries that were developing under cloud cover have not built up the pigment defenses to handle a sudden blast of UV, and the exposed drupelets get damaged before they can adapt.

What Triggers It

Temperature and solar radiation are the two biggest drivers, but the picture is more complex than just “hot sunny day.” Research on white drupelet disorder has identified several interacting environmental factors, including temperature, radiation, low humidity, rainfall, and wind.¹ Low humidity is a factor that surprises some growers. When the air is dry, evaporative cooling from the fruit surface speeds up, which can create a temperature differential between the sun-facing and shaded sides of the berry. Wind compounds this by stripping moisture away even faster. The combination of high heat, strong UV, dry air, and wind creates the worst conditions for WDD, even if no single factor alone seems extreme.

Rainfall matters too, but in the opposite direction. A berry that ripens during a stretch of overcast, rainy weather rarely develops white drupelets. The trouble comes when that rainy stretch breaks and a heat wave follows. Growers in regions with highly variable summer weather tend to see more WDD than those in climates with consistently sunny, warm conditions, because the berries in stable environments develop pigment and waxy cuticle gradually as they ripen.

Some raspberry cultivars are far more susceptible than others. Varieties with lighter natural coloring or thinner skin tend to show WDD more readily. Commercial growers are increasingly selecting cultivars bred for resistance to the disorder, but many popular home-garden varieties remain vulnerable. If you grow a cultivar that reliably develops white drupelets every summer, the variety itself may be part of the problem.

How to Tell WDD Apart From Powdery Mildew

Powdery mildew on raspberries looks quite different from white drupelet disorder, though both involve “white stuff on my berries.” Where WDD turns individual drupelets white from the inside, powdery mildew deposits a dusty white or grayish coating on the surface of the fruit, leaves, and cane tips. If you rub a powdery mildew-affected berry gently, the white layer smears or comes off on your finger. A WDD-affected drupelet, by contrast, is white all the way through and cannot be rubbed clean.

Powdery mildew on raspberries is caused by fungi in the genus Podosphaera. Recent taxonomic work has clarified that the species infecting raspberries is distinct from the one attacking strawberries, with researchers proposing the name Podosphaera ruborum specifically for the powdery mildew on Rubus species.² This matters because control strategies that work for strawberry powdery mildew do not always translate directly to raspberries.

Powdery mildew thrives in warm, dry weather with cool nights, which is a slightly different sweet spot than WDD. You will see it show up when daytime temperatures are moderate, humidity is low during the day but high overnight, and air circulation around the plants is poor. Crowded canes in a thick, unpruned patch are the classic setup. If your white spots are accompanied by curling leaf edges and a faint white dusting on the undersides of leaves, powdery mildew is the likely culprit.

When Insects Leave White or Damaged Spots

Certain insect pests can cause discoloration on raspberry drupelets that gets mistaken for WDD or disease. Stink bugs are among the more common offenders. Their feeding punctures individual drupelets, leaving small holes between the drupelets and sometimes depositing excretions that further mar the fruit surface.³ The damage from stink bugs looks less like uniform pale drupelets and more like irregular puncture marks, sometimes with a sunken or slightly dried-out appearance around the feeding site.

Thrips are another group of tiny insects that colonize raspberry flowers and developing fruit. Their presence in raspberry flowers has been documented, but specific information about the damage they cause and how to manage them on raspberry remains limited, making identification tricky for growers.⁴ Thrips feeding on developing drupelets can cause silvery or whitish scarring on the fruit surface, which is easy to confuse with early-stage WDD. The clue is timing and pattern: thrips damage shows up on drupelets that were exposed during the flower stage, often on random drupelets across the berry rather than clustered on the sun-facing side.

If you suspect insects, look at the flowers and developing green fruit, not just the ripe berries. Stink bugs are large enough to spot with the naked eye. Thrips are tiny and require gently tapping a flower over a white piece of paper to see the slender, fast-moving insects fall out.

Grey Mould and Other Fungal Fruit Rots

Grey mould, caused by the fungus Botrytis cinerea, is another common raspberry problem, though it produces grey or brownish fuzzy growth rather than the clean white of WDD. It thrives in cool, humid conditions and can infect flowers, leaves, and developing fruit, ultimately causing fruit rot and quality breakdown.⁵ The fungus overwinters in dead plant material and produces enormous quantities of spores that spread on wind and rain splash.

Grey mould occasionally confuses gardeners because it can start as small, pale, water-soaked patches on individual drupelets before the characteristic fuzzy grey sporulation appears. At that very early stage, a berry with Botrytis might look like it has a few off-color drupelets. Within a day or two, though, the telltale grey fuzz develops and the berry softens noticeably. If your white spots progress to fuzz and the berry turns mushy, Botrytis is your answer. If the white drupelets stay firm and the berry never develops fuzz, you are back to WDD.

Are They Safe to Eat

Berries with white drupelet disorder are safe to eat. The affected drupelets may taste slightly bland or lack the sweetness and acidity of fully pigmented ones, but they are not toxic or spoiled. Many commercial berry operations sort out WDD-affected fruit because it looks unappealing rather than because it poses any food safety concern. For home gardeners, a berry with a few white drupelets mixed among red ones is perfectly fine for fresh eating, smoothies, jams, and baking. You will not notice the flavor difference once the berry is mixed with other ingredients.

Berries with powdery mildew are a different story. While consuming a small amount of powdery mildew is not dangerous for most people, heavily infected fruit tastes off and the texture is unpleasant. Washing removes some of the surface fungus but not the damage underneath. Most gardeners prefer to discard visibly affected berries and use the clean ones.

Berries showing grey mould should not be eaten. Botrytis-infected fruit is actively decaying, and the fungus can produce mycotoxins at levels that are not worth risking, especially if the rot has spread beyond the visible fuzz into the fruit tissue. Toss any berry that feels soft and shows grey or brown fuzzy patches.

Preventing White Drupelets in Your Patch

Since WDD is driven by sun and heat exposure, the most effective prevention strategies involve managing how much direct sunlight hits ripening fruit. Research on caneberries has shown that trellis and cane training systems can minimize the exposure of fruit to direct sunlight in summer, and that selecting cultivars and manipulating the canopy help ensure maximum yield under local environmental conditions.⁶ For home gardeners, this translates into a few practical steps.

Training your canes onto a trellis so they arch outward creates a natural canopy of leaves above the fruiting zone. The leaves shade the berries from direct overhead sun while still allowing air to circulate through the patch. If your canes grow upright with fruit exposed at the tips, you will see more WDD than if the fruiting laterals hang down underneath a leaf canopy. Some growers in hot climates use shade cloth draped over the trellis during peak summer, reducing UV exposure by roughly 30 to 50 percent depending on the cloth density.

Keeping the soil consistently moist helps too. Well-watered plants maintain better turgor in the fruit, which makes the drupelets slightly more resistant to heat stress. Mulching around the base of canes with straw or wood chips reduces soil temperature and retains moisture. In arid regions, drip irrigation run during the hottest part of the afternoon can lower the air temperature right around the fruit zone.

For powdery mildew prevention, the priorities are different: open up the canopy for airflow rather than closing it for shade. Thin out weak or crowded canes in late winter so that each remaining cane has space and gets good air movement. Remove and destroy any canes that showed heavy mildew the previous year, since the fungus can overwinter on plant debris. Avoid overhead watering late in the day, because wet leaves going into a cool night is the ideal trigger for mildew germination. The tension between shading fruit for WDD and opening the canopy for mildew control is real, and most home gardeners end up prioritizing whichever problem is worse in their specific climate.

When Cultivar Choice Matters More Than Management

If you do everything right with trellising, irrigation, and pruning and still see white drupelets every year, the cultivar may be inherently prone to WDD. Raspberry breeding programs have observed significant variation in WDD susceptibility among varieties, and some widely grown cultivars are simply more vulnerable. Unfortunately, most nursery catalogs do not list WDD resistance as a trait, so you may need to consult extension service recommendations for your region.

Primocane-bearing (fall-bearing) varieties present a particular wrinkle. They fruit later in the season when day length is shorter and sun angles are lower, which in theory should reduce WDD. But in warm climates, primocane varieties often start fruiting in late summer when temperatures are still extreme, and the fruit can be hit by WDD just as hard as summer-bearing types. In cooler northern regions, primocane varieties tend to escape the worst of it simply because their fruit ripens during milder weather.

If you are choosing new plants and WDD has been a recurring frustration, ask local growers or your county extension office which cultivars perform well in your area. The answer varies enormously by climate zone. A variety that produces beautiful, unblemished fruit in the Pacific Northwest may bleach badly in the heat of the mid-Atlantic or the interior valleys of California.

Why the Problem Seems to Be Getting Worse

Many experienced raspberry growers report seeing more WDD now than they did a decade or two ago. Climate researchers studying the disorder have linked its increasing prevalence to changing weather patterns, including more frequent heat waves, wider temperature swings, and shifts in precipitation timing.¹ The disorder has become a significant quality concern for commercial raspberry operations in South America, where production regions have seen measurable increases in peak summer temperatures and UV intensity.

For home gardeners, the practical takeaway is that WDD is not something you are doing wrong. A patch that produced perfect berries for years can start showing white drupelets simply because summers have become hotter and more erratic. The same environmental factors that drive WDD, including high temperatures, intense solar radiation, low humidity, and wind, are all projected to intensify in many growing regions. Growers who relied on a moderately sunny spot and no shade cloth a generation ago may now need to adjust their setup.

The silver lining is that WDD remains a cosmetic issue. The berries are still good food. If you are growing for your own kitchen rather than a market, a certain percentage of white-flecked berries is the cost of doing business with a warming climate, and the fruit still makes excellent jam.