Fruit

Mummy Berry (Monilinia vaccinii-corymbosi): Mummy berry is an important disease in many parts of New England, and its severity varies from year to year. It is caused by a fungus that attacks new growth, blossoms, foliage and fruit, and it can cause extensive losses.

The fungus overwinters in mummified fruit on the ground. In spring, the mummies form cup-shaped structures called apothecia, typically around the time that forsythia are in bloom. Apothecia produce spores that infect young tissue and cause rapid wilting. This is called leaf and twig blight, or shoot blight. These symptoms are difficult to distinguish from frost injury or Botrytis shoot blight. These first infections form more spores, which are spread by rain, wind and bees to blossoms and other young tissue. The fungus then infects and invades developing fruit. Infected fruit becomes malformed and turn salmon-colored or grey by midsummer. By fall, these fruits drop to the ground, ready to produce apothecia the next spring.

Management: Cultural controls can be used to reduce inoculum levels. In very small plantings, infected fruit can be hand-picked or mummies can be raked up and removed. On a larger scale, mummies can be buried by covering with a new layer of mulch at least 2” thick. Combining cultivation between rows with an application of 50% urea prills in the spring can also destroy mummies. The cultivation should be done just as apothecia start to emerge in the spring, but not before blueberry bud-break. Urea should not be applied to areas where there is standing water, as this may cause fertilizer burn. Apply urea to drier parts of the field and go back to the wetter areas later.

Cultivars  differ in susceptibility to both phases of mummy berry infection: shoot blight and fruit infection. Those that are most resistant to the shoot blighting phase of the disease include Bluejay, Darrow, Duke, Elliot, and Toro. Cultivars that appear to be the most susceptible are Bluegold, Blueray, Coville, Legacy, Northblue, Northsky, Patriot, and Sierra. Cultivars that are consistently resistant to the fruit infection phase include Northsky, Reka, Northblue, Bluegold, Bluejay, Weymouth, and Patriot. Those that are highly susceptible include Berkley, Herbert, Lateblue, Bluehaven, Elliot and Elizabeth and Blueray. Resistance to fruit infection appears to be unrelated to resistance to shoot blight, and weather factors can also affect cultivar response to the disease.

Several fungicides are labeled for use against this disease. Labeled materials and state registrations change annually. See pest management schedule for recommended materials and timing.

Botrytis Blight/Gray Mold (Botrytis cinerea): As with other small fruits, Botrytis primarily affects blossoms and ripening fruit, although under certain circumstances the fungus can cause shoot blight as well. Infection occurs largely during bloom on flowers. The fungus survives the winter on dead twigs and on crop debris, and outside the field on other plants. It is present every year, but only causes severe damage during cool, wet periods lasting several days. The most critical period for infection is during bloom. Disease is most severe where excessive nitrogen has been used, where air circulation is poor, or where frost has injured blossoms. Infected berries typically have a gray cast of mycelium and spores which gives the disease its name. Stem symptoms are hard to distinguish from those caused by Phomopsis or frost. Consult your state university plant diagnostic lab for proper disease identification. Varieties possessing tight fruit clusters (for example, Weymouth, Blueray and Rancocas) are particularly susceptible to Botrytis.

Management: When weather or history indicates that Botrytis will be a problem, fungicides should be applied, starting at mid- bloom, with subsequent sprays at 7-10 day intervals through petal fall. See pest management schedule for recommended materials and timing.

Anthracnose (Colletotrichum acutatum): This fungus primarily damages fruit, but may also infect twigs and spurs. Infected fruit often exhibit a soft, sunken area near the calyx-end of the fruit. Salmon-colored spores spread to “good” fruit during and after harvest, causing significant post-harvest losses. The disease is especially prevalent during hot muggy weather and frequently occurs post-harvest.

Anthracnose overwinters in dead or diseased twigs, fruit spurs, and cankers. Spores are released in spring, and are spread by rain and wind. Blossoms, mature fruit and succulent tissue are infected, and spores may be spread from these infections. Infected blossom clusters turn brown or black. Infected fruit show salmon-colored spore masses at the blossom end. Stem cankers are rare, but are about 1/8” in diameter, with raised purple margins when they are present. Young girdled stems die back, resulting in a brown withering of leaves. Bluecrop, Bluetta, Chanticleer and Spartan are particularly susceptible to anthracnose. Elliot and Weymouth appear to have good resistance.

Management: Anthracnose is controlled primarily with fungicide applications, though pruning for optimal air circulation and clean harvesting are beneficial. Old canes and small twiggy wood should be cleared out in order to increase air circulation around the fruit clusters. See pest management schedule for recommended materials and timing.

Stems and Foliage

Fusicoccum Canker or Godronia Canker (Godronia cassandrae): Fusicoccum canker is caused by a fungus that infects blueberry stems causing dieback and plant decline. Losses from this disease can be serious. The fungus overwinters as mycelium in cankers on living plants. In Massachusetts, spores are released from March to mid-July, and new infections can occur throughout the growing season. Spores are disseminated by rainwater. New infections occur following rains when tender new tissue is present and temperatures are 50-72˚ F. Cold stress may play a part in increasing disease damage. Leaves turn reddish-chocolate colored and often hang on late into the fall.

Symptoms of Fusicoccum canker are similar to Phomopsis canker on blueberry. The most unique symptom is a red-maroon-brown lesion centered around a leaf scar. A bullseye pattern often results. As the lesion enlarges, the margin remains red and the center turns gray and dies. On young (1-2 year old) stems, extensive stem infections quickly lead to flagging and dieback of the entire stem. On warm, dry days shoots will suddenly wilt and die due to the stem girdling.

Management: Sanitation is essential. A fungicide program should be used where the incidence of disease is high. Apply at 2-week intervals from late dormancy to petal fall. Varieties differ in their resistance to this disease. See pest management schedule for recommended materials and timing.

Phomopsis Twig Blight (Phomopsis vaccinii): This disease may be the most prevalent of the canker diseases. The fungus, Phomopsis, causes stem damage similar to that caused by Fusicoccum.

Spores from old cankers are released in spring and, to a limited extent, in summer. Most spores are released from bud swell to petal fall, and none are released after September 1. Rain is necessary for spore release, and temperatures from 70-80˚F encourage infections. The disease is most severe after winters in which mild spells are interspersed with cold weather. Periods of hot, dry weather during the growing season probably also predispose plants to a certain degree. The fungus overwinters in infected plant parts.

Symptoms first appear on smaller twigs and spread into larger branches and may affect the crown. It is possible for Phomopsis to spread downward in injured canes to the crown and then progress upward on new canes. This rarely occurs, usually only where the crown itself has been injured after a particularly severe winter, or in highly susceptible varieties. Younger tissue may show no symptoms at first, and then exhibit rapid wilting and dieback. Stem lesions are similar to those caused by Fusicoccum but generally lack the bullseye pattern. The disease also causes premature ripening of berries. Leaf spots have  been observed where disease is particularly severe, and the fungus may also cause fruit rot, although this is rarely observed in New England. Most commercial cultivars are susceptible to Phomopsis canker.

Management: Since mechanical damage and cold stress seem to be necessary for Phomopsis infection, avoid unnecessary cultivating, and do not fertilize after July 1st. Prune weakest canes to the ground. Avoid drought stress by keeping plants well-watered through prolonged periods of dry weather in summer. The cultivars Bluetta, Elliot, and Rancocas have been reported to have partial resistance to Phomopsis. Fungicide applications may also be beneficial. See the pest management schedule in this chapter for recommended materials and timing.

Coryneum Canker (Coryneum microstictum): This canker disease appears to be uniquely situated in the southeast part of New England. No estimates of loss from the disease are available; it does not occur regularly and is often found with other canker fungi.

The symptoms are similar to other canker diseases. The cankers are commonly seen on sun-scalded or cold-stressed bushes where the fungus produces spores. Wounds are apparently necessary for infection.

Management: Cultural practices that maintain vigorous growth without stimulating too much succulent growth are recommended for this canker disease as well as the others. (See the Phomopsis section). No chemical controls are specifically recommended.

Powdery Mildew (Microsphaera vaccinii): This disease affects the leaves primarily and is uncommon in New England, although localized outbreaks of the disease occur occasionally. Symptoms include a white fungal growth on upper leaf surfaces, puckering of leaves, and reddish leaf spots. When severe infection occurs, defoliation may occur.

Management: Some cultivars are more resistant than other cultivars. Well-timed fungicides will also control the disease, but are probably not necessary in New England.

Witches’ Broom: Witches’ broom is a relatively minor disease of highbush and lowbush blueberries and other Vaccinium spp. in North America and is caused by the fungus Pucciniastrum goeppertianum. Diseased blueberry plants have broom-like masses of swollen, spongy shoots with shortened internodes and small leaves. Brooms usually begin to develop during the year following infection and then persist for many years, producing infected new growth each spring. Young stems on broom are initially reddish or yellow, but as the season progresses become brown and shiny, then dull, and eventually dry and cracked. Although heavily infected plants produce no fruit, disease incidence is usually so low that crop losses are negligible. Nearly 100% of blueberry plants may be infected in fields located near fir (Abies spp.) trees, the alternate host of the rust fungus that causes witches’ broom.

Management: Because the pathogen is perennial and systemic in blueberry crowns and rhizomes, pruning does not eliminate witches’ broom. The best control strategy is to eradicate fir trees within 1200 feet of blueberry plants, though this may not be practical. Infected bushes should be rogued out.

Blueberry Leaf Rust: Is a minor disease of blueberries caused by the rust fungus, Pucciniastrum vaccinia. In early spring to summer, spores from hemlocks (alternate host) are dispersed by wind and infect young blueberry leaves. The disease first appears as small yellow (chlorotic) spots on the upper surface of young blueberry leaves. As the infection progresses spots turn a reddish-purple color with a discrete yellow halo. On the underside of leaves, spots have a distinct brown edge with pustules of yellow-orange spores in the center. These spores can cause new infections throughout the growing season. 

Management: Plant disease resistant plants. Bluecrop, Burlington, Collins, and Weymouth are very resistant to leaf rust. Fungicides are generally not needed to manage leaf rust, but if symptoms appear early in the season consider applying a fungicide to suppress additional infections. See pesticide table for fungicide recommendations.

Roots

Phytophthora Root Rot (Phytophthora cinnamomi): This disease is usually associated with poorly drained areas in a field. Symptoms are noted on the roots and on the above-ground portions of the plant. The very fine absorbing roots turn brown to black; larger diameter roots may also be discolored. In severely infected bushes, the entire root system is reduced in stature and is totally black. Above-ground symptoms include chlorosis and reddening of the leaves, smaller leaves, defoliation, death of branches or entire canes, stunting, and death of the entire bush. The disease may be present in a few infected plants scattered throughout the planting or localized in groups of plants in low-lying areas. The disease is worst where plants are growing in heavy clay soils.

Phytophthora cinnamomi, in addition to attacking blueberry, attacks several other Ericaceous hosts, including rhododendron, azalea, and cranberry. Lowbush blueberry appears to be immune. This species of Phytophthora is not an important pathogen on any other small fruit covered in this guide. The fungus thrives in wet soils and can survive for long periods of time.

Management: The disease is best avoided through careful site selection. Heavy soil that becomes waterlogged or suffers from a high water table should be avoided. If a wet site is unavoidable, water drainage should be improved. Plant growth may be improved by growing on raised beds. Most varieties are susceptible to the disease, although some varieties may better tolerate infections. Bluecrop and Weymouth are two varieties that have shown promise. Mefenoxam (Ridomil Gold) can be used at planting if problems with Phytophthora root rot are anticipated. It can also be applied as a drench to established plantings. If needed, Mefenoxam should be applied twice per growing season. However, the best strategy is to plant on well drained sites or improve soil drainage.

Armillaria Root Rot (Armillaria mellea and A. ostoyae): Although this disease is uncommon, it can cause serious injury to plants in fields where the fungus is present in the soil. To date, the disease has only been found in fields that were originally pine/oak forests. The fungus survives in soil on root pieces of susceptible hosts (pine, oak, etc.). The fungus can infect bushes through root grafts and can survive on wood chip mulches. Mulches should be carefully selected so that fungal inoculum is not introduced into the field.

Infected bushes usually decline over several growing seasons, and their symptoms can be confused with those caused by winter injury, Phomopsis twig blight, or a nutritional imbalance. Affected plants are chlorotic, have smaller-than-usual leaves, and are more susceptible to other stresses than healthy plants. Branches may suddenly wilt, followed by plant mortality in some instances. The disease may be found throughout an entire field, or it may be confined to one or a few areas. The most important diagnostic characteristic is the presence of the fungus: white mycelial fans underneath the outer bark or the crown of the plant, black rhizomorphs (resembling shoestrings) attached to the roots or the trunk, and yellowish-brown mushrooms produced at the base of the plant in late summer or early autumn.

Management: The disease is best avoided by thoroughly discing soil where blueberries are to be planted, and by removing as many root fragments as is possible. If possible, leave the field fallow three years after trees have been removed. Soil sterilants or fumigants are effective at killing the fungal inoculum. The disease is very difficult to control once it is present in a field. Dead or dying plants should be removed, and adjacent plants should be inspected at the soil-line for mycelial fans or rhizomorphs. Remove any plants that have signs of the pathogen. Wood chip mulch should be removed from infection “hot spots.” Although spot fumigation might be effective, chemical controls are usually not feasible in fields where the disease is present. Most varieties are probably susceptible to the disease.

Viruses and Mycoplasma-like Organisms (MLO)

Blueberry Shoestring Disease: This viral disease was originally described in New Jersey. In Michigan, the disease has been found in 0.5% of the bushes; an assessment has not been done for potential losses due to the virus. Blueberry shoestring disease is aphid-transmitted.

The most common symptom is an elongated reddish streak along the new stems. The leaves may also show red banding or a red-purple oak-leaf pattern. Diseased leaves are narrow, wavy and somewhat sickle-shaped. Flowers may be red-streaked, and berries turn purple prematurely. Within a few years, berry production drops dramatically.

Management: Other than buying disease-free plants, destroying wild plants near the planting, and removing diseased plants, controls do not exist. As with most virus diseases, the best controls are preventing disease introduction, and detecting the disease early. The virus has been observed most often in Jersey, Blueray, Burlington, Cabot, Earliblue, Elliott, Jersey, June, Rancocas, Rubel, Spartan and Weymouth. Bluecrop and Atlantic are resistant to the disease. Varieties with moderate resistance include Draper, Aurora, Liberty, Legacy and Brigitta. Aphid control is most important in fields containing varieties that are susceptible to shoestring virus. If fields of these varieties contain symptoms of shoestring, aphid control should be a priority during the season and infected bushes showing symptoms should be tagged and removed in the late fall once aphids are not able to be spread through the field during removal.

Blueberry Stunt: This disease was originally thought to be caused by a virus but it is now known to be caused by a mycoplasma-like organism or phytoplasma. The only known carrier is the sharp-nosed leafhopper, though other vectors probably exist.

Symptoms vary with the stage of growth, time of year, age of infection, and variety. Symptoms are most noticeable during mid-June and late September. Affected plants are dwarfed with shortened internodes, are excessively branched, and are low in vigor with small downward cupped leaves which turn yellow along the margins and between the lateral veins, giving a green and yellow mottled appearance. These mottled areas will turn brilliant red prematurely in late summer, although the midrib remains a dark bluish-green. Fruits on infected bushes are small, hard, lack flavor, ripen late if at all, and remain attached to infected plants much longer than they would on healthy plants.

Management: Diseased bushes cannot be cured; these must be removed from the field as soon as a diagnosis has been made. Removing diseased plants may spread the disease by dislodging leafhoppers, causing them to hop to neighboring healthy bushes. Infected bushes should be sprayed with an appropriate insecticide before infected bushes are removed. Using virus indexed plants is also helpful. Bluetta, Jersey, and Weymouth are particularly susceptible, whereas Rancocas is resistant.

Blueberry Red Ringspot: This is the most widespread viral disease in New Jersey at the present time. The symptoms are very distinctive, including red spots, rings and oak-leaf patterns which usually appear on the older leaves in late June or July. Fruit production is seriously reduced and berries become pockmarked and unattractive. Blueray, Bluetta, Burlington, Cabot, Coville, Darrow, Earliblue, and Rubel are susceptible to the disease, whereas Bluecrop and Jersey are resistant or tolerant. Infected bushes must be rogued out.

Blueberry Mosaic: Like some of the previously described viruses, this virus is probably indigenous in wild blueberry plants. Infected plants become unproductive. Leaves are brilliantly mottled with yellow, yellow-green and pink areas. Not all leaves show symptoms and some branches on an affected bush may be symptomless. It may take several years for a bush to show symptoms. The disease appears most commonly in Herbert and Stanley; most varieties appear to have field resistance to the virus. Infected bushes cannot be cured and must be removed promptly.

Blueberry Scorch (formerly Sheep Pen Hill Disease): This disease has recently been found in fields in Massachusetts and Connecticut. It is a serious problem in fields in New Jersey (it was originally found in a field in the Sheep Pen Hill area). Symptoms fluctuate greatly from year to year, and symptoms are worst during excessively wet years.

The disease is characterized by dieback of blossoms and young vegetative shoots in the spring followed by a flush of growth in summer and development of a necrotic line pattern in fall foliage. Roots suffer injury, and fruit production can be greatly impacted. In New Jersey, blueberry scorch virus has been shown to cause severe symptoms on all varieties except Jersey.

Management: The causal agent is a flexuous rod-shaped virus and is vectored by aphids. The sole control strategy is to remove affected bushes, though control of aphids is also important in managing any spread of this disease. Effective aphicides should be applied before removing infected bushes, to reduce further spread caused by aphids moving to healthy bushes.

Bacteria

Crown Gall (Agrobacterium tumefaciens): Crown gall is the only bacterial disease which is a significant problem in the Northeast at present: crown gall. The disease is caused by the bacterium Agrobacterium tumefaciens. Since blueberries are grown on acidic soils, and the crown gall bacterium does not grow well in acidic soils, the disease occurs infrequently.

Globose, pea-size to large woody galls occur on low branches, twigs, and at the base of canes near the ground. Injured tissue is more likely to produce galls.

Management: Sanitation, purchasing healthy nursery plants and maintaining proper soil conditions are the most reliable controls.

Post-Harvest Diseases

As with most soft fruit, blueberries have particular post-harvest disease problems. There are three fungi which can cause major post-harvest losses: Colletotrichum acutatum (anthracnose), Botrytis cinerea (gray mold), and Alternaria spp. The diseases can cause up to 30% rot within 7 days of harvest even when fruit are refrigerated. Without refrigeration, berries can show 15% rot in 3 days.

Management: In New England, where virtually all highbush blueberries are sold fresh, well-ventilated containers and refrigeration should be combined with careful picking and handling.

Fruit Damaging Insects

Spotted Wing Drosophila (SWD) (Drosophila suzukii): SWD are invasive vinegar flies (fruit flies) that can attack unripen fruit. Female SWD cut into intact fruit with a serrated ovipositor to deposit eggs under the skin. This allows SWD larvae to be present during ripening, leading to a risk of detection in ripe fruit after harvest. During egg-laying and larval feeding, sour rot and fungal diseases can be introduced, further affecting fruit quality. There is a much greater risk of fruit contamination at harvest from SWD compared with native species that lay eggs only in already-damaged and rotting fruit.

Management: Monitoring for the annual arrival of SWD is particulatly important for blueberry. Pest pressure is often low for most of of the blueberry season and it is likely that early-ripening varieties may not need to be protected from SWD infestation. Homemade traps for the flies can be made by drilling 1/8” holes in plastic containers or cups (red or black color is most attractive). The cups should be baited with apple cider vinegar or sugar water with a pinch of yeast. Commercial traps (from Scentry or Trece) contain similar attractive odors as homemade recipes and may be more convienient. Check the traps regularly for flies. The males can be identified by a single small black spot near the top of each wing. The females have no spots. Once adult SWD are trapped and blueberries begin to turn blue, apply insecticides weekly through harvest, rotating between insecticide classes. Choose insecticides based on efficacy and preharvest interval. Good pruning is also an important part of SWD management as open canopies are less hospitable to egg-laying.

Winter Moth (Operophtera brumata): This is an important pest of blueberries and other deciduous plants, especially in Southeastern New England. Moths emerge from the soil in late November and may be active into January. Male moths are light brown to tan in color and attracted to lights at night. Females are gray, almost wingless and cannot fly, and may be found on tree trunks. After mating, females deposit tiny eggs in bark crevices or among lichens which overwinter. Eggs begin hatching in late March or early April after the first warm days of spring, generally around 20 Growing Degree Days (GDD) (base 50˚F) or about 200 GDD (base 40˚F). Egg hatch coincides with bud break of McIntosh apple trees. After hatching, larvae wriggle into swelling buds of blueberries and many deciduous tree, and begin feeding. Caterpillars continue feeding on leaves and flowers until late May when they drop to the ground to pupate. Destruction of flower buds can greatly reduce yield.

Winter moth larvae are pale green caterpillars with white longitudinal stripes running down both sides of the body. They are “loopers” or “inchworms” and have just 2 pairs of prolegs. Mature caterpillars are approximately one inch long.

Management: A dormant oil spray to trunks and branches of bushes may be helpful by killing overwintering eggs before hatching. However, some eggs are under bark flaps and loose lichen and may be protected from oil sprays. Caterpillars may also invade blueberries by blowing into plantings from nearby trees. Bacillus thuringiensis (B.t. kurstaki), manages winter moth caterpillars well once caterpillars are feeding on exposed foliage. B.t. and other insecticides are not effective when caterpillars are feeding inside closed buds. Spinosad is another biorational compound that works well against winter moth caterpillars. Finally, tebufenozide (e.g. Confirm) is an insect growth regulator (IGR) that works well on most lepidopteran caterpillars.

Blueberry Maggot (Rhagoletis mendax): The adult is a black fly about 1/5” long with a pattern of dark and clear bands on its wings. The maggots are white, legless, and about 1/4” long when full grown. Flies alight on fruit to lay eggs under the fruit skin just as fruit begins to turn blue. Maggots are later found in ripening and harvested fruit, making fruit unmarketable since berries become soft and mushy. Undetected infested berries contaminate pack-out.

Management: Red sticky spheres or yellow sticky rectangle traps (available from suppliers listed in appendix) can be used to monitor blueberry maggot populations in plantings. In large bushes, sticky traps should be hung in upper half of the canopy, suspended from wires and about 1-1/2 feet from outer foliage. All fruit and foliage within 8 inches of trap should be cleared away, and all traps positioned so that there is as much foliage and fruit surrounding them as possible. In small plantings, it may be possible to trap out this insect with a sufficient number of traps. Consult with your state’s regional fruit specialist for further information. Spray recommendations are found in the blueberry pest management schedule.

Brown Marmorated Stink bug (BMSB) (Halyomorpha halys): Adult BMSB are approximately 3/4 inch long and are shades of brown on both the upper and lower body surfaces. They are the typical “shield” shape of other stink bugs, almost as wide as they are long. To distinguish them from other stink bugs, look for lighter bands on the antennae and darker bands on the membranous, overlapping part at the rear of the front pair of wings. Masses of 20-30 eggs are deposited on underside of leaves. The 5 nymphal stages range in size from 1/8 - 1/2 inch. Nymphs and adult BMSB feed on many hosts including small fruits, tree fruits, vegetables, ornamentals, and seeded crops such as corn and soybeans. BMSB feeds by puncturing fruit with piercing/sucking mouthparts. Fruit tissue dies at the point of entry and just below into the flesh, and the rest of the fruit grows around it. This leaves sunken areas on the skin and browning, dead tissue in the flesh.

BMSB has become a serious insect pest in mid-Atlantic states, southern New York, Connecticut, and possibly other New England states. It is unknown at this time whether there is one or two generations per year in New England.

Management: BMSB cannot be controlled with many common fruit insecticides, including Imidan and Sevin. Spray recommendations are found in the blueberry pest management schedule.

Plum Curculio (Conotrachelus nenuphar): This dark brown snout beetle is about 1/4” long with 4 humps on its wing covers. It feeds on developing flower buds and developing berries. Females lay eggs on the fruit, and after hatching, light colored larvae develop inside the fruit (one larva per fruit). Larval feeding causes fruit to ripen prematurely and drop off bushes.

Management: Plum curculio are more abundant where blueberries are located near fruit trees. Spray applications made at petal fall to manage cranberry or cherry fruitworm may also manage plum curculio.

Cranberry Fruitworm (Acrobasis vaccinii): Cranberry fruitworm larva (caterpillar) is green with some brownish-red coloration on its top surface, measuring 1/2” at maturity. It is found within developing and ripening berries. Feeding reduces yield and spoils marketability of berries. Eggs are laid in the calyx cup (blossom end) of unripe fruit. Hatched larvae move to the stem end of fruit, enter, and feed inside berries. Larvae consume 3-6 berries, filling berry skins with brown frass and tying berries together with silk.

Management: When damage is severe, treat the following year with insecticide. See pest management schedule for recommended materials. In small plantings, cranberry fruitworms may be managed by picking off infested berries, which are easily detected due to webbing and early ripening. Eliminating weeds around plants reduces overwintering protection for cocoons.

Cherry Fruitworm (Grapholita packardi): At maturity, cherry fruitworm larvae are orange-red and about 1/4-1/2” long and found within developing and ripening berries. Feeding reduces yield and spoils marketability of berries. Soon after petal fall, hatching larvae bore into the calyx cup (blossom end) of berries, feed until about half-grown, and then move to a second fruit. (This is distinct from the cranberry fruitworm described above.) The two infested berries are usually joined by silk.

Management: When damage is severe, treat the following year with insecticide. See pest management schedule for recommended materials.

Leaf/Shoot Damaging Insects

Gypsy Moth or Spongy Moth (Lymantria dispar dispar): Young gypsy moth larvae (caterpillars) are hairy, dark brown to black in color and older caterpillars are marked with red and blue spots. They range in size, from 1/4 to 2” in length, depending on age. In outbreak years, larvae feed on leaves and buds, causing complete or partial defoliation and fruit loss.

Management: Remove egg masses present in plantings by early April. Small caterpillars can blow in from surrounding, infested trees in early May.  Bt insecticides effectively manage small, young caterpillars, but other insecticides are needed to manage large larvae. See pest management section for insecticide recommendations.

Blueberry Blossom Weevil; Cranberry Weevil (Anthonomus musculus): This is a dark reddish brown snout beetle, 1/8” long, with a curved snout. It emerges in spring, feeds and lays eggs in expanding flower and leaf buds. Weevils hide between clustered buds, and small infestations may be difficult to find. Damage results when punctured flowers do not open. Damaged leaf buds produce an abnormal cluster of dwarfed leaves. Adults of the second generation sometimes feed on blueberry leaves.

Management: No insecticides are labeled for this pest. Disking between rows and raking/hoeing under plants is helpful. Eradication of wild blueberries or other ericaceous plants in the vicinity of the blueberry planting may be beneficial.

Scale Insects; Putnum Scale and Lecanium Scale (Aspidiotus ancylus and Lecanium nigrofasciatum): These insects appear mound-shaped, of varied colors, and usually measuring 1/8” or less in length. They are found on rough, loose bark of older stems and sometimes on fruit. Infestations can result in reduced vigor and yield of bushes by feeding on plant sap. Fruit lecanium scale eggs hatch in early July (late June in southernmost New England) and first generation putnam scale crawlers emerge in early June.

Management: Good pruning is the first step in controlling scale insects. Prune out weakened canes. During dormancy, apply superior-type oil of 60- or 70-second viscosity at 3 gallons per 100 gallons of water. To avoid injury, apply when there is no danger of freezing temperatures for at least 24 hours after treatment.  See Insecticide Efficacy and Pest Management Tables in this chapter for other recommended materials and timing.

Blueberry Tip Borer (Hendecaneura shawiana): In June, before new growth has begun to harden, some blueberry shoots may begin to wilt, arch over, and become discolored, the leaves turning yellowish with red veins and stems turning purplish. This injury, which may be mistaken for primary mummyberry infection, is caused by blueberry tip borer. Newly hatched caterpillar, tiny and pink, enters soft stem and bores channels that may extend for 8 or 10” by autumn and result in the destruction of the stem’s fruit-production potential the following year.

Management: Prune out damaged tips when found and burn infected canes. A standard spray program used for other insect pests normally keeps this pest under control.

Blueberry Bud Mite (Acalitus vaccinii): Blueberry bud mites are whitish in color and tiny. Unlike other mites, they are elongate and conical, with 4 legs bunched near the head at the broad end of the mite. Heavily infested buds have a definite reddish coloration and characteristic rough bumps on outer bud scales. Eggs,  immatures, and adult mites are present throughout the year, generally confined to buds and blossoms. During fall and winter, many mites may be found between scales of a single fruit bud.

Bud mites feed on the surface of bud tissues and bud scales. Injured buds desiccate and usually produce distorted flowers. These flowers may fail to set fruit, or develop into fruit with rough skins. The potential for damage differs with variety.

Management: Plants should be inspected for bud mites in September, before new buds are well formed. Look for them under bud scales and between bud parts. Economic threshold levels have not been determined for bud mites. Thorough pruning of infested canes provides good control of bud mites. Limited chemical control measures are available. A new miticide, Magister SC, is registered for blueberry bud mite management and may be applied once per year after petal fall.

Blueberry Stem Gall Wasp (Hemadas nubilipennis): The adult blueberry stem gall wasp is a small (less than 1/8”) shiny black insect with delicate wings. It lays eggs in succulent shoots. Several grub-like larvae develop together inside the shoot, stimulating the shoot to grow abnormally and resulting in a pithy, kidney-shaped gall 3/4 to 1-1/4” long. Pupation occurs within larval chambers and new adults emerge from the galls during bloom, leaving exit holes. Early in the season galls are greenish and spongy to the touch. By fall the galls turn brownish-red and become hard. Shoot growth is reduced and the shoot may be diverted at severe angles.

Blueberry stem gall wasp can cause severe reduction in shoot growth and stem vigor. Hundreds of galls can develop on a single bush, reducing fruit production. Susceptibility to galls may depend on variety. This insect is rarely encountered in fields managed with standard chemical pesticide programs, but it can be a major pest of organically managed fields.

Management: Chemical treatments directed toward other pests are generally sufficient to keep stem gall in check. Removal and destruction of gall during normal pruning operations will also help manage this pest.

White Grubs - Japanese Beetle (Popillia japonica), Rose Chafer (Macrodactylus subspinosus), Asiatic Garden Beetle (Maladera castanea), and others: White grubs are the larvae of a variety of beetle species some of which are listed above. White grub larvae are generally white or cream colored with brown heads and legs, and hold their bodies in a distinct hooked or C-shape. Stretched out, larger species may be over one inch in length. Many white grub species can be identified by distinctive patterns of stiff hairs located at the underside of abdomen tip. Most species overwinter as grubs deep in the soil and pupate in late spring before emerging as adult beetles. Some species feed on roots of plants for more than one year before completing development. Time of pupation and adult emergence varies with species.

Adults of white grubs are known generically as May Beetles, June bugs, chafers, or scarab beetles. The adults of some species feed on foliage, flowers and fruits of many plants. Japanese beetle and rose chafer adults can be significant pests of blueberry during harvest when they contaminate berries.

Recently white grubs have become serious pests in some fields, with populations as high as 30 grubs per bush. Grubs consume feeder roots and may also girdle or clip off larger roots. Infested plants may not show any outward signs of injury until a period of drought stress, when the reduced root system cannot provide enough water to the plant. Damaged bushes show low vigor and reduced production. Adults, especially Japanese beetle and rose chafer, sometimes become serious pests by consuming leaves and scarring berries.

Management: Unfortunately, sampling for white grubs damages roots of blueberry bushes. Growers should check new sites for white grubs before establishing a field, and take actions against grubs before planting. Admire Pro can be applied to soil to control white grubs. When applied correctly, it suppresses Asiatic garden beetle larvae and is effective against all other species of white grubs. There is great interest in the use of pathogenic nematodes as biological control agents for grubs. Adults are generally easy to control with foliar sprays, but timing is difficult since these are highly mobile insects that may suddenly appear in the field. Surround is a kaolin clay-based product that can deter adults from feeding on foliage. It may be of interest to organic growers, though removing Surround from fruit is difficult.

Yellow-necked Caterpillar (Dantana ministra): These hairy yellow caterpillars are usually found in large groups in mid- or late summer. If unnoticed, they can entirely strip foliage from a bush.

Management: Caterpillar strains of Bacillus thuringiensis (Bt) products are effective in managing larvae, especially when they are small. Chemical insecticides are also effective. Spraying the entire planting is not required.

Sharp-nosed leafhopper (Scaphytopius acutus): SNLH feeds and reproduce on blueberry, huckleberry, cranberry, and other related plants. SNLH feeding causes little direct damage but it transmits the phytoplasma that causes stunt disease in blueberries. They are small brown insects with a pointed head. SNLH picks up the disease while feeding on infested bushes and carries it to other plants in subsequent feedings. Usually only adults carry the disease from plant to plant, since nymphs are wingless and can’t fly. Adults are abundant in the woods and may move to commercial blueberry fields in the spring. Eggs overwinter inside fallen leaves and hatch in mid-May. Nymphs from the first generation reach adult stage in mid-June, while nymphs from the second generation reach adulthood in early August. Adults move back to the woods in the fall.

Management: First generation SNLH is often controlled with sprays targeted for plum curculio, aphids, and cranberry fruitworm. Treatment decisions for the 2nd generation should be based on individual population levels, as well as any history of stunt disease on your farm. Because adults migrate from woods, monitoring should concentrate on field perimeter. Insecticides are usually applied just prior to peak flight, generally late August to early September. It is also important to remove all plants that show symptoms of stunt disease. Removal of bushes should be done after insecticide treatment to avoid movement of leafhoppers from infested to healthy plants.

Blueberry aphid (Illinoia pepperi) is the vector of blueberry shoestring virus which can cause bush decline and significant yield reductions. It is also a potential vector of blueberry scorch virus. Because of the ability of aphids to serve as vectors of plant disease, they should be controlled to minimize virus spread in infected fields and in susceptible fields near to virus-infected fields.

Management: Blueberry aphids are most often found on the undersides of young leaves at the base of plants. Insecticides can be applied in June as aphid populations start to increase. Spray should be directed at base of plants and good coverage is essential for effective aphid control. This will be more challenging in weedy fields. See table 33 for insecticides effective against aphids.

Table 35. Highbush blueberry pest management table†.

Deer: White-tailed deer can cause extensive damage to blueberries by browsing top-growth in winter. Deer can also cause damage to other small fruit crops. For more information on controlling deer, please see Deer Control in the Appendices.

Birds: Birds are a major pest problem in highbush blueberries. Left unchecked, they can destroy enough of the crop to ruin profitability of a planting. The loss of chemical deterrents has made bird control a more difficult task in recent times, but effective means are still available.

Management: Netting is the most effective way to keep birds out of the planting. Although initial costs can be high, most netting will last for many years if cared for properly. Netting should be hung over some sort of support structure built around the planting. Usually posts are set nine feet above the ground around the perimeter of the planting, and wire is run from pole to pole to form a grid over the planting. The netting is hung over this grid when fruit begins to turn color. Some temporary nine foot poles may be placed within the planting at intersections of the grid to keep netting from drooping. Bury edges of the netting or anchor it to the ground to keep birds from crawling underneath. Remove netting when harvest is complete, and store in a cool, dry place.

Visual scare devices have variable effectiveness on birds. Scarecrows, balloons, kites, snakes or stuffed owls may work on certain bird species in certain areas, but none seem to have widespread dependability. When using visual scare devices, place in planting only when fruit begins to ripen, and move regularly, at least once a day. Six scare-eye balloons per acre are recommended. Remove from field as soon as harvest is over to reduce birds becoming accustomed to the devices. Kites and helium-filled balloons of hawks positioned high above the planting have provided good results in some areas.

Noise deterrents, such as propane cannons, alarms and recorded distress calls seem to have the least effect on birds in blueberries, and may greatly annoy neighbors. A combination of noise and visuals may be effective, however. Several operations have hired people to regularly drive motorcycles and/or ATVs through plantings when fruit is ripe, and this seems to keep birds away quite well.

Bird Shield™, a repellent formulated from methyl anthranilate, is registered for use on blueberries, cherries, and grapes. Methyl anthranilate is commonly used as a grape flavoring in human food preparations. Bird avoidance is based on odor quality and irritation. To humans, this chemical has a grape-like or fruit odor and a slightly bitter, pungent taste. Unfortunately efficacy data does not support recommending the use of this material at this time.

Research using laser "scarecrows" is currently being conducted. Hopefully these devices will help deter birds in the near future.

Voles: Voles can be a serious problem in blueberry plantings. They feed on the bark of stems or on roots depending on which species of vole is present. In the Northeast, two species are found: the meadow vole (Microtus pennsylvanicus) and the pine vole (Microtus pinetorum). They may both be present in a blueberry planting. It is important to determine which species is present in order to make management decisions.

Size and appearance of the two species differ although it is somewhat rare to actually see them. The meadow vole has a long body (150-195 cm) and long tail, prominent eyes and ears, coarse fur, and is dull gray to chestnut in color with a gray belly. The pine vole has a short body (110-135 cm) and short tail, sunken eyes and ears, fine velvety fur, and is bright chestnut in color with a slate gray belly.

Evidence of their activity is more diagnostic. Meadow voles are active on the surface of the ground, feeding on the bark of the bushes and making shallow trails in the grass or mulch around the plants. Food caches and droppings can be found in these surface trails. Pine voles are active below ground, feeding on roots. Subsurface trails can be found by digging around the bushes. These trails come to the surface where mounds of dirt can be seen. Holes leading into these trails are about 1” in diameter.

Simply finding evidence of voles does not indicate a serious problem. To determine whether the voles are causing serious injury to the bushes, it is necessary to estimate the population of voles present. This requires some specialized sampling. It is best to contact your Extension Specialist for help with this sampling procedure.

Management: In some cases, removal of mulch material around bushes can help in reducing the meadow vole population. However, this is risky for bushes susceptible to drought stress. In those cases, choosing a mulch material that does not support tunneling (caves in easily), such as wood chips, is recommended. In some New England States, any application of toxicants or poisons for the purpose of killing any mammal or bird is prohibited. However, some toxicants may be allowed under certain situations with the proper permits. Call your Extension Specialist for recommendations.

The primary goal of weed management is to optimize yields by minimizing competition between the weeds and the crop. Weeds reduce yields by competing with the crop for water, space, light, and nutrients. Weeds also harbor insects and diseases and encourage vertebrate pests. Timely cultivation, wise use of herbicides, and never permitting weeds to go to seed are integral parts of a good weed management system. Many of the weeds found in crop fields are difficult-to-control perennial weeds that are not common in annual crop culture. New plantings usually have fewer perennial weed problems than older plantings. Annual and biennial weeds can also exist in these fields. Fields should be scouted at least twice a year (spring and fall) to determine specific weed problems. The selection of a weed management tool should be based on specific weeds present in each field.

The most important weed management strategy is employed prior to planting that is, eliminating all perennial weeds. Fields that have been dormant or have been in pasture may have perennial weeds that are well established. Fields that have been in cultivation are less likely to have established perennial weeds in them. Common perennial weeds include common dandelion, Canada thistle, stinging nettle, field bindweed, field horsetail, goldenrod, and quackgrass. Once these perennial weeds become established or remain established in a berry field, they are very difficult to remove. The most common way to remove perennial weeds is with Roundup (glyphosate) applied in the fall prior to planting. Perennial broadleaf weeds should be treated after flowering but prior to a killing frost. Perennial grasses can be treated late into November.

Weeds can develop resistance to herbicides. The Weed Science Society of America (WSSA) developed a grouping system based on the mode of action of different herbicides. WSSA Group numbers can be used as a tool to choose herbicides in different mode of action groups so mixtures or rotations of active ingredients can be planned to better manage weeds and reduce the potential for resistant species.

Cultural weed management in blueberry plantings includes mulching, cultivation, and soil pH management. Mulching is a major weed management tool in blueberry production. Mulches that are free of weed seeds and placed thickly enough can be very effective at reducing or eliminating most annual weeds from the crop row. They are seldom effective on perennial weeds, however. Use of cultivation is difficult and often is counter productive in blueberry plantings. It destroys surface feeding roots and does not work well where mulches are used. All cultivations should be timely and shallow to minimize crop root injury, to minimize loss of soil moisture, and to avoid repositioning new weed seeds to the soil surface. The low pH soil that blueberry plantings thrive in is not a good environment for most weed species. Keeping the soil pH at the right level will help to reduce weed pressure.

The areas between the crop row is usually maintained with a mowed cover of sod, clover, weeds, or a combination of these. This cover is used primarily for erosion control and to improve trafficability in the field.