Blueberry Pests & Disease: Spotted Wing Drosophila and Mummy Berry

Spotted wing drosophila: why it's different

Most vinegar flies are a nuisance only on rotting fruit. Spotted wing drosophila (SWD) is different, and that's exactly what makes it dangerous: it attacks sound, ripening fruit. The female has a large, serrated ovipositor that saws through intact skin to lay one to three eggs inside each berry, where the larvae then develop — turning marketable fruit into mush.

The adult is tiny (2–3 mm) with red eyes, and the males carry the namesake dark spot near each wingtip. What makes it relentless is the math: a single female can lay several hundred eggs, with a new generation every 8–10 days in warm weather, and the larvae feed hidden inside the fruit. By the time you can see larvae, a large share of the crop is already infested — which is why the entire strategy is built around acting early.

Monitoring: trap before you see damage

Start monitoring as green berries begin to turn pink — not at harvest. Hang traps baited with apple cider vinegar (or a yeast-sugar bait) in a shaded spot on the field edge, at about chest height, and check them regularly.

You can also test fruit directly with a salt flotation test: crush a sample of ripe berries in a salt solution and wait about 30 minutes for any larvae to float free. But there's a catch — by the time larvae show up in fruit, it's usually too late to protect the crop. So adult trap catches, not larval counts, drive the decision. The trigger is simple: act on the first confirmed catch as fruit begins to color.

Managing SWD: the IPM stack

Extension IPM programs build SWD management in three layers — monitor, prevent, then treat. The preventative tools do most of the quiet work:

• Sanitation (your cheapest, best tool): pick and remove all cull and dropped fruit, which eliminates the egg-laying sites that fuel population growth. When infestation shows up, "re-set" the field by clean-picking everything ripe. Kill collected culls by sealing them in clear plastic bags in the sun (solarizing) or freezing them — don't just toss them at the field edge.
• Frequent, complete harvest so ripe fruit isn't sitting out, and prompt refrigeration, which slows or kills larvae in picked fruit.
• Canopy management: prune for airflow and spray penetration, and keep weeds down. Early-ripening varieties can escape the worst of peak pressure.
• Exclusion: for small or high-value plantings, fine netting (under 1 mm) over the bushes physically blocks egg-laying.

Mummy berry: know the cycle to break it

Mummy berry is the blueberry disease that does the most damage, caused by a fungus (Monilinia). Understanding its two-stage life cycle is what lets you interrupt it:

• Stage one — shoot strikes. Infected berries from last year shrivel into hard "mummies" and fall to the ground. In late winter and early spring, those mummies sprout tiny cup-shaped structures that release spores onto emerging shoots and flowers, blighting and browning the new growth.
• Stage two — fruit infection. Spores produced on those blighted shoots move to open blossoms and infect the developing fruit, which then shrivels into next year's mummies — reloading the soil and completing the loop.

The fungus thrives in cool, wet spring weather, so conditions during bloom largely set how bad a given year gets.

Managing mummy berry: bury the inoculum

Because the whole cycle starts from mummies on the ground, preventing that primary infection is the priority. The most effective cultural tactics all aim at the overwintering inoculum:

• Bury the mummies. Before bud break, a shallow cultivation (no deeper than an inch) under the bushes disrupts the spore cups — or cover the mummies with soil or a mulch layer at least 2 inches thick, which keeps them from emerging in the first place.
• Clean up dropped fruit after harvest to reduce how much inoculum overwinters.
• Keep flowers drier: improve drainage, and avoid wet sites and overhead irrigation through bloom, since the fungus needs moisture to infect.
• Choose resistant and late-blooming cultivars, which can sidestep the primary-infection window.

When pressure is high — spore cups showing on a meaningful share of bushes during warm, wet weather — fungicides applied from bud break through bloom protect the green tissue and flowers. As with insecticides, lean on your local extension's current recommendations for materials and timing. And note that no single sanitation step is sufficient on its own; it's the combination that works.

Other watch-outs

SWD and mummy berry dominate, but a few others are worth scouting for regionally. On the insect side: blueberry maggot, cherry and cranberry fruitworm, plum curculio, Japanese beetle, and scale. On the disease side: Botrytis (gray mold) at bloom, anthracnose (ripe rot) on the fruit, Phomopsis twig blight and stem canker, and Phytophthora root rot in poorly drained soils — a reminder that drainage is a disease-management tool, not just an agronomic one. The encouraging part: the same fundamentals handle most of them — monitoring, sanitation, airflow, drainage, and resistant cultivars, with targeted chemical control as backup.

Frequently asked questions