Blueberry plants (Vaccinium) are susceptible to a wide range of insect pests that can cause major problems with your plants' health and fruit production. Blueberry bushes are also susceptible to several common diseases, such as mummy berry, stem canker, stem or twig blights, Botrytis blight and leaf spots. You'll need to study your blueberry plant's distinct symptoms and look for any insect activity around the plants to properly diagnose and treat the problem. Some insects that attack blueberry bushes may be microscopic or difficult to find, while others will be easy to detect.
Identify Blueberry Pests
Identify the blueberry maggot (Rhagoletis mendax) by looking for the white, legless maggots that are about ¼-inch long and are found feeding on the inside of the berries. The adult blueberry maggots are 1/5-inch-long flies that have clear wings with black markings on them and abdomens striped in black and white.
Detect the microscopic blueberry bud mite (Acalitus vaccinii) by its damage to your blueberry plant. This mite causes roughened blueberry skins from feeding and distorted or stunted flower buds.
Look for tiny, slender insects feeding on the leaves to spot blueberry thrips (Frankliniella vaccinii). The leaves will become rolled together beginning in early spring and throughout the summer.
Spot Putnam scales (Diaspidiotus ancylus) by looking for the tiny round insects feeding on the blueberries. You'll likely see more severe damage on older blueberry plants or on the older limbs of younger bushes.
Identify blueberry stem borers (Oberea myops) by their slender, ½-inch-long, light-brown bodies with black wings and eyes. The stem borer grubs bore into the stems of blueberry plants and often girdle the shoots. Blueberry tip borer (Hendecaneura shawiana) larvae also girdle and bore into shoots, but the adult is a tiny moth that lays eggs on the underside of younger leaves in June.
Look for dark-brown snout beetles that are about ¼-inch long and have two bumps on each wing cover to spot the plum curculio (Conotrachelus nenuphar). You'll find the plum curculio beetles feeding on the flowers and blueberries, the females making a crescent-shaped slice into the fruits to lay their eggs and the larvae burrowing into the blueberries to feed on the pulps.
Diagnose stem galls (Hemadus nubilipennis), which are created by the chalcid wasp larvae that feed on the blueberry plant's stems. The galls are ¾- to 1 ¼-inches wide and kidney-shaped.
Study the soil around the roots of your blueberry plant to detect white grubs, which can be the larvae of the oriental beetle (Anomala orientalis), Japanese beetle (Popillia japonica) or rose chafer (Macrodactylus subspinosus). These white grubs feed on the roots of blueberry plants and overwinter about 1 foot beneath the soil surface.
Diagnose blueberry plant problems due to infestations of the cranberry fruit worm (Acrobasis vaccinii) and the cherry fruit worm (Grapholita packardi) by looking for tiny worms feeding on the blueberries. These worms often burrow into the blueberries through the stem tips and cause the berries to ripen prematurely.
Identify the cranberry rootworm (Rhabdopterus picipes) by looking for small white grubs with brown heads and adults that are deep-brown and ¼-inch long. The larvae feed on the blueberry plant's roots, while the adult beetle eats the foliage in early summer.
Diagnose Blueberry Diseases
Diagnose mummy berry disease by looking for browning, wilting and dying new growth on the blueberry plant, as well as light tan or salmon-colored blueberries in midsummer that don't ripen and instead shrivel up and drop. The dropped berries mummify during the winter and perpetuate the fungus the following spring.
Look for red lesions on young shoots to diagnose stem canker in your blueberry plants. The best time to see the lesions is in fall or winter, after the leaves fall off.
Diagnose the fungal disease twig or stem blight by inspecting your blueberry plant for infected, dead twigs that rapidly die back up to 6 inches from the tip. Botrytis blight is a fungus that also attacks the shoots, but it also infects the blossoms and causes them to turn brown or become covered with gray, fuzzy mold.
Watch for leaf spots developing in midsummer, causing irregular discolored spots on the blueberry plant's leaves. This fungal disease causes the leaves to drop from the bottom of the bush upwards.