http://ssfruit.cas.psu.edu/chapter9/chapter9a.htm

Several blueberry species are indigenous to the United States. These include the lowbush blueberry (Vaccinium angustifolium), which is of commercial importance in Maine and Canada; the rabbit eye blueberry (V. ashei), which is grown commercially in the southern United States; and the highbush blueberry (V. corymbosum), which is the commercial blueberry of importance in Pennsylvania and in the mid-Atlantic and midwestern regions of the United States. The information that follows pertains solely to highbush blueberry production.

The highbush blueberry plant is indigenous to North America, but its value as a commercial fruit crop has been exploited only in the past 60 years or so. Original breeding work and research was conducted by Mrs. Elizabeth White and Dr. Frederick Coville, beginning shortly after the turn of the century.

The blueberry plant is a perennial, consisting of a shallow root system and woody canes that originate from the crown of the plant. The root system is very fibrous but devoid of root hairs. (Root hairs in most plants function by increasing the surface area of the root for water and nutrient uptake.) This characteristic makes the blueberry plant very sensitive to changing soil water conditions.

A mature cultivated blueberry usually has 15 to 18 canes. Its growth habit varies among cultivars, with some bushes growing very upright and others having a more spreading growth habit. The fruit is borne on buds that are formed the previous growing season.

Cold Hardiness

Blueberries generally will tolerate temperatures to -20°F, although cultivars vary somewhat. Most require 750 hours of chilling below 45°F. In Pennsylvania, this requirement is met usually by no later than early February. After the chilling requirement is met, the plant loses its dormancy and thus its cold hardiness with each warm period, making it increasingly susceptible to cold injury as the season progresses.

Soils

The best soils for blueberries are moist, porous, and acid. The soil pH should be between 4.5 and 5.0. A lower pH can result in manganese or aluminum toxicity, while a higher pH results in the unavailability of certain nutrients, most notably iron. In southern New Jersey, blueberries are grown on very sandy soils in areas where the water table is very shallow, so they can be canal irrigated when needed. Many parts of Pennsylvania do not have these very light soils, so soils usually need to be amended.

Preparation

In the year before planting, eliminate all noxious weeds, increase soil organic matter by manure application and/or cover crops, and test the soil. Soil test kits are available from county extension offices. Amend the soil according to test recommendations. The effects of sulfur (to lower the soil pH) and phosphorus (if needed) require time, so these materials should be added in the fall before planting. Potassium can be added either in the fall or when nitrogen is applied in the spring. Do not plant blueberry plants in high-pH soils without amending them first! Because sulfur does not move readily through the soil, surface sulfur applications after the plants are in place are ineffective in lowering the pH, and the plants will not thrive.

Irrigation and Mulch

Because the blueberry plant is very sensitive to fluctuating soil moisture, mulch and irrigation are essential for a healthy planting and consistent yields. Blueberry plants require at least 1 inch of water per week. Hardwood bark mulch (such as that used for landscaping), rotted sawdust, and chopped corncobs are good mulches. They should be applied to a depth of 4 inches and replenished whenever necessary. Avoid mulches with high pHs such as mushroom compost or noncomposted leaves, which may be high in natural toxins.

Although either overhead or trickle irrigation can be used on blueberries, trickle irrigation both conserves moisture and supplies the plant with adequate water. The trickle line can be placed under the mulch so it is out of the way and, in some cases, semipermanent. Because the small emitter holes in trickle irrigation components clog easily, the water must be from a very clean source (such as municipal water, a well, or a clean spring), or filtered through a 'sand' filter. Overhead irrigation has the advantage of cooling the plants and the berries during extremely high temperatures.

I heard about this a while ago. Among foods, many fruits have health benefits in the form of antioxidants, but blueberries appear to be especially potent. Here is an article:

http://www.ushbc.org/health.htm

Eating blueberries may help you remember where you placed your car keys-important findings if you’d like to keep Alzheimer’s and heart disease at bay.
The research was presented Monday, August 19, at the ACS national meeting in Boston.

In one study, Jim Joseph, director of the neuroscience laboratory in the USDA Human Nutrition Center (HNRCA), fed blueberry extractions-the equivalent of a human eating one cup of blueberries a day-to mice and then ran them through a series of motor skills tests.

He found that the blueberry-fed mice performed better than their control group counterparts in motor behavioral learning and memory, and he noticed an increase in exploratory behavior. When he examined their brains, he found a marked decrease in oxidative stress in two regions of the brain and better retention of signal-transmitting neurons compared with the control mice.

The chemical that appears responsible for this neuron protection, anthocyanin also gives blueberries their color and might be the key component of the blueberry’s antioxidant and anti-inflammatory properties.

I love blueberries. When I lived in Minnesota I remember hearing about how blueberries were being cultivated in that state. Apparently the species planted had to be selected to survive the cold winters-there can be stretches where the temperature struggles to get above -20F.

I love blueberries. When I lived in Minnesota I remember hearing about how blueberries were being cultivated in that state. Apparently the species planted had to be selected to survive the cold winters-there can be stretches where the temperature struggles to get above -20F.

Blueberries grow wild here in Manitoba, in the coniferous forests (there are times when the winter temperatures struggle to stay above -30).  I would imagine it is the same species that grows in Minnesota.

I could see that.  Wild blueberries don't grow as large nor as many on a bush as farmed varieties.

Oh and about the temperatures. It always amused me that Minnesotans when talking about the weather would talk about the coldness of their state-International Falls is the "icebox" and they would treat Manitoba to the North like it didn't exist. I'd watch the weather forecasts on WCCO or KARE and the maps would have the temperatures plotted over the state. Over the Canadian border-nothing, a complete blank!

The weather forecasts on the local stations here do the same to the US.  Minnesota and North Dakota are the grey areas to the south.   

The information on pests seems much worse that it actually is.  This is my second year with blueberries, and the pests do not seem too bad.  I started with three plants, and they are managable.  I check them daily in the moring and evening.  In the winter time, I don't worry about pests - it's too cold, so that leaves spring through fall.  Late spring to early fall are the times for vigilance, but with few plants, one can usaully control pests.  I practice organic gardening - i.e. I do not use pesticides.  Instead I manually remove any harmful insects.

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Continuation of PSU information ( http://ssfruit.cas.psu.edu/chapter9/chapter9j.htm ) - This information seems to be more directed to commercial growers with hundreds or thousand of plants.

Plum Curculio

The plum curculio, Conotrachelus nenuphar (Herbst), is a weevil, a type of beetle. It is dark brown, 1/4 inch long, and has four humps on its back and a long (one-third of the body length) snout projecting forward and downward from its head. The beetles overwinter as adults under debris in the woods or field margins and migrate into the fields at about petal fall. They migrate more heavily when temperatures exceed 75°F, and are slowed significantly when the weather is damp and cool (below 70°F). Plum curculio usually is more prevalent on plants adjacent to woods, fence rows, and trashy fields.

Females lay eggs in shallow pits excavated on the surface of green berries. Usually a single egg is laid in each berry, and a crescent-shaped scar develops on the surface at this site. Upon hatching, larvae burrow into the fruit where they feed on the pulp for about 2 weeks, many times causing the fruit to drop. Infested berries sometimes remain on the plant, however, and can contaminate harvested flats. Fully grown larvae leave the fruit, burrow into the soil, and pupate within an earthen chamber. The adults emerge about 4 weeks later. Most of these adults enter diapause after several weeks of feeding, but if green berries are still present, a few will mate and produce a second generation.

Infestations of plum curculio usually can be detected by examining green berries for the typical oviposition scar. These berries are usually the first to turn blue. Adult curculio are secretive and nocturnal, but they can be found early in the morning or late in the evening by shaking the branches of a bush over a white cloth that has been placed on the ground. Adults disturbed in this manner drop onto the sheet and feign death, folding their legs tightly against their body, remaining motionless. They can be mistaken easily for debris.

Because the weevil spends much of its life cycle on the ground under the bushes, frequent cultivation can facilitate its control. Effective control can be obtained by postpollination applications of insecticides. Make sure flowers have dropped from treated blocks so bees will not be killed.

Cranberry Fruitworm

Found throughout the eastern United States wherever wild blueberries grow, the cranberry fruitworm, Acrobasis vaccinii (Riley), affects cultivated blueberries that are poorly maintained. This pest overwinters as a fully grown larva in the litter near the soil surface under the bushes. The small, brown, adult moths emerge when the berries of early varieties begin to form, and they begin inserting eggs along the rim of the calyx cup. After hatching from the egg, the larva enters the berry. It eventually webs together several berries with silk, feeding inside as many as four. One generation hatches each year. The cranberry fruitworm infestation is characterized by masses of brown frass (excrement) and silk.

Cranberry fruitworm infestations can be difficult to detect early. Look for a pin-sized entry hole near the stem of any small shrunken berries that have turned blue, and then open adjacent berries to find the larva. The distinctive frass and webbing do not appear until later in the larva’s lifetime when it begins to move between berries. One method of control for this pest (and for cherry fruitworm) is to pick and destroy infested berry clusters showing evidence of webbing. Repeated disking to eliminate weeds and trash also helps in its control. Pesticides used for plum curculio also usually result in control of cranberry fruitworm.

Cherry Fruitworm

The cherry fruitworm, Grapholitha packardi (Zeller), overwinters as large larvae in cavities usually made in the dead wood on the bush. The small, dark grey moths with brown banded wings emerge in the late spring. The green-white flattened eggs are laid on the undersurfaces of leaves and on the fruit. After hatching, the larvae enter the berries. The 3/8-inch pink and red larvae usually feed on one berry at a time and then penetrate and feed on another. Unlike cranberry fruitworms, the cherry fruitworms seal entrance holes with silk so that frass is not visible outside the berries, and an infestation is evidenced only by prematurely blue, shrunken berries webbed together by silk.

Both fruitworms can be controlled with two insecticide sprays. Apply the first at petal fall on a variety-by-variety basis to avoid poisoning bees. It is important to remove bee hives from the area before any insecticide spraying takes place. Spray again about 10 days later.

Blueberry Maggot

The blueberry maggot, Rhagoletis mendax (Curran), is the major pest of blueberries in many parts of the Northeast; however, blueberry plantings in Pennsylvania have not been heavily attacked to date. The presence of infested fruit at harvest can result in the condemnation of whole fields of harvested fruit. Moreover, the control of the insect is complicated by its long emergence period, its migration tendencies, and the fact that it usually does not attack fruit until after harvest has begun.

The female fly is about 3/16 inch long. The abdomen is pointed and black with white cross bands. The wings are clear and marked with heavy black bands in the shape of an upside-down “W.” Several other species of fruit flies can be confused with blueberry maggot if they are not inspected carefully.

Overwintering as pupae buried anywhere from just beneath the leaf litter to 6 inches deep in the soil, the blueberry maggots emerge from the soil as flies in June or July. After emerging, the flies, which live for about 30 days, spend the first 2 weeks resting and feeding on nectar, dew, and honeydew. Mating takes place near the end of this resting period, and females seek large, ripened berries in which to lay eggs. The female pierces the skin of the fruit with her egg-laying apparatus and deposits a single egg in each berry. Each fly may lay up to 100 eggs in a 2- to 3-week period. Upon leaving the berry, the female deposits a chemical that deters other flies from laying eggs in that berry. The egg hatches in about 5 days, and the larva burrows into the berry and feeds on the pulp for about 2 weeks. The mature larva leaves the berry and drops to the soil to pupate and remain until the next summer. Only one generation hatches each year, but a few pupae may remain in the soil for 2 to 3 years.

The potential for infestations of blueberry maggots can be assessed by trapping adults before their numbers reach damaging levels. The traps are yellow, sticky boards placed near the planting at least a week before the first flies are expected to emerge (early June). These boards are baited with a feeding attractant, either ammonium acetate or protein hydrolysates. Baited traps can be purchased or made. Trapping should continue through harvest, and the traps should be replaced every 3 weeks or when they become clogged with insects. The flies on each trap should be counted and removed each week. Insecticides should be applied when three adults per trap per week or five adults per field per week are found. NOTE: Several other fly species will be trapped on the boards (along with other insects). Make sure that only blueberry maggot flies are counted. If species identification is a problem, consult your county extension agent.

If control is necessary, a relatively nontoxic, short residual insecticide should be used so that it does not interfere with harvest. If ripe berries are present, they should be harvested before the spray is applied. Tank mixing the insecticide with protein hydrolysate will increase the treatment efficacy. Once spraying has begun, it should be continued with an application every 7 to 10 days until all unharvested fruit has dropped.

Scales, Including Putnam Scale and Terrapin Scale

These insects may be common in blueberry plantings, especially if pruning has been neglected for several years and the scales’ parasites and predators have been destroyed by insecticide sprays. Scales spend most of their lives as legless, sedentary individuals, usually clustered with other scale insects to form what appears to be a crust, in the case of Putnam scale, Aspidiotus ancylus (Putnam); or shiny brown hemispheres, in the case of terrapin scale, Lecanium nigrofasciatum (Pergande); on the wood surface. Some scales also reside on leaves and fruit.

Males are produced in late summer, and after they mate, the females settle on the wood to overwinter. Live offspring issue forth in the spring to early summer in the form of “crawlers,” thereby effecting the spread of these insects. Scales feed by removing sap from the plant, and can reduce vigor, decrease yield, and even cause the decline of the plant. Some scales also produce large quantities of honeydew, a sugary liquid that coats the leaves and fruit and promotes the growth of sooty mold, which can decrease berry quality.

Good scale control is accomplished first by good pruning practices. Removing and destroying old wood during pruning often does much to reduce scale populations. The second approach is the use of dormant oils to smother the overwintering scales. Cover sprays during the growing season usually are ineffective because the scales are protected by their secreted “shell;” however, sprays timed to coincide with crawler emergence can be effective.

Shoestring Disease

Shoestring disease is probably the most well-known virus disease, occurring primarily in Michigan and New Jersey. It has been seen in North Carolina and Washington, but is not important in these two states. In Michigan, bush and yield losses were over $3 million in 1981.

The most prominent symptoms are elongated reddish streaks about 1/8 inch wide by 1/2 to 3/4 inch long on current-year and 1-year-old stems, especially on the side exposed to the sun. During blossoming, flowers of infected bushes exhibit pinkish to reddish petals. (Note that Blueray has naturally reddish petals.) Infected leaves often are straplike, hence the name “shoestring.” Many leaves on a bush might appear this way, although in some cases just a few clumps near the crown will show this symptom. A few leaves may show red vein-banding or reddish streaking along the midrib of the leaf. In some cases, an “oak leaf” pattern will show on the leaf blade. Other leaves may be crescent-shaped and partially or totally reddened. Infected stems may appear crooked, especially the tip-end half.

Shoestring disease spreads “down the row,” or from bush to bush. This is because the virus is spread by the blueberry aphid. The aphid picks up the virus as it feeds on an infected bush and then, when it moves to the next bush in the row to feed (the bushes usually are touching), it passes the virus to the next bush. There is a 4-year latent period; that is, it takes 4 years from the time of first infection until the symptoms begin to develop. Shoestring-infected wild blueberries also have been found in the wooded areas surrounding commercial plantings.

Diseased propagation wood has been an important factor in the spread of shoestring disease from one field to another.

In fields having infected bushes, aphicides provide the best control. The first insecticide application should begin when the first aphids appear on the terminals of the stems, usually by late May or early June. Two or three sprays may be required throughout the growing season to keep aphid levels low. Infected bushes should be killed or removed. Growers who use mechanical harvesters must wash them to remove aphids; it has been shown that aphids can be carried from a source bush to bushes 60 or more spaces down the row.

Shoestring disease has been seen in the field in Jersey, Rubel, and Blueray cultivars. Elliott and Spartan have been susceptible in experiments. In the field, Bluecrop seems to be resistant.

Blueberry Leaf Mottle Disease

Leaf mottle disease currently is found only in Michigan, but it could appear in other states at any time. This disease is potentially devastating because it is caused by a pollen-borne virus spread by honeybees. Controlling the disease may mean reducing pollination. Within a few years after the onset of symptoms, leaf mottle disease kills back the stems of the bush and greatly reduces the bearing surface. Eventually the bush dies.

Rubel shows the most severe symptoms. Bushes that have been infected for 5 or 6 years develop a severe dieback of older stems, leaving only stunted and deformed new growth emanating from the crown area. Leaves show a mottling pattern, sometimes with yellow, roughly circular “windows” that are apparent if the leaf is held up to light. In the most severe cases, leaf malformations and leaf strapping occur. On Jersey, symptoms are much milder; stem dieback is less prevalent, as are stunting and growth reduction. The terminal leaves, especially in the crown area, are rosetted due to the shortening of internodes. The color of these rosetted terminals is a yellowish pale green. In general, the leaves of infected bushes are smaller than normal.

Leaf mottle spreads through virus-infected pollen moved by honeybees. Honeybees and hives are an integral part of blueberry culture, but they carry virus-infected pollen in their pollen sacs. Bees also transfer virus-infected pollen from one individual to another in the hive. Honeybees have been tagged at a hive and found in other hives 660 yards away. Tagged honeybees from a given hive also have been observed foraging in blueberries up to a mile away from the hive. Leaf mottle in one 20-acre commercial field in Michigan spread from a few infected bushes to more than 50 percent of the bushes in less than 10 years. Diseased propagation wood could be a second factor in the spread of this disease from one planting to another.

The best control is to kill and remove all infected bushes from the field. Symptoms of the disease are not always distinct, and the first symptoms often do not appear until 4 years after infection.

Placement of beehives is important. If, for example, a grower’s field does not have the disease, but a neighbor’s does, the grower should place hives as far as possible from the neighbor’s field. If a grower has one block with disease and another nearby block without disease, again, the hives should be placed such that the distance between the virus source in one block and the hives in the other block is as large as possible. Hives should be used only once in a field during the blossom season.

Necrotic Ringspot Disease and Tomato Ringspot Virus Disease

Necrotic ringspot and tomato ringspot are discussed together here because of the similarity of their symptoms. Necrotic ringspot disease, caused by tobacco ringspot virus, is by far the more important of the two diseases in terms of frequency. Both of these diseases cause a general decline of the bush.

Necrotic ringspot disease has been reported in Arkansas, Connecticut, Oregon, Illinois, Michigan, Pennsylvania, and New Jersey. It is common in the varieties Pemberton, Stanley, Rubel, Concord, Collins, and Earliblue. Tomato ringspot virus disease has been reported in Michigan, Oregon, Pennsylvania, and Washington. In the field, it has been observed in Earliblue. Both causal viruses are very common in fruit crops and in woody ornamental plants. In addition, both viruses are found in many weeds that occur in fruit plantings.

Necrotic ringspot disease: Varieties such as Pemberton and Earliblue exhibit stem dieback and bush stunting. Leaves are deformed and somewhat thickened. Leaves may become yellow and show blackish spots 1/16 to 1/8 inch in diameter. These spots may fall out, leaving a shothole effect. On other susceptible varieties (for example, Concord and Stanley), symptoms usually are expressed as short internodes on stem terminals and small straplike leaves. The twigs may show brownish, necrotic spots 1/16 to 1/8 inch in diameter. Fruit production often is greatly reduced.

Tomato ringspot virus disease: In Earliblue, leaves are often malformed and have circular chlorotic spots on them, 1/16 to 1/8 inch in diameter. In addition, stems, twigs, and branches may exhibit circular, brownish necrotic spots of similar size. Younger terminal leaves tend to be strap-shaped and have a mottled pattern (alternating yellowish to greenish stippling). Fruit production may be reduced.


Both diseases are spread by the dagger nematode and through diseased propagation wood. One indication that the disease is spread by the dagger nematode is that symptoms spread slowly in a circular pattern at a rate of about 3 feet per year in all directions.

The best control for these diseases is prevention. Plant only virus-tested clean stock and test soils for the presence of nematodes.

If infection is found in an established field, control becomes more complicated. Infected bushes must be identified by inspection. Once the areas of infection have been identified in a field, remove all infected bushes along with major roots and the crown. Thoroughly fumigate the soil with a liquid fumigant. After a 2-week aeration period, replant with virus-tested clean stock.

Red Ringspot Disease

Red ringspot disease is an important virus disease in New Jersey. It also is present in Arkansas, Connecticut, Massachusetts, Michigan, New York, North Carolina, Pennsylvania, and Oregon. In Michigan, a test comparing 10 healthy bushes with 10 diseased bushes in the same planting revealed up to a 25 percent crop loss. The varieties that most commonly exhibit symptoms are Blueray, Bluetta, Burlington, Cabot, Coville, Darrow, Earliblue, and Rubel. Jersey and Bluecrop seem to be resistant or immune.

Stems at least 1 year old often exhibit reddish brown spots with green centers. The spots, 1/8 to 1/4 inch in diameter, also develop on the upper surfaces of older leaves in mid- to late summer. The powdery mildew fungus can cause similar symptoms on both sides of the leaf. Rancocas may have circular light areas of blotching on the fruit. Bluetta sometimes shows a red ringspot-like disorder.

Circumstantial evidence points to the mealybug as a vector in the spread of this disease. Other vectors may be involved as well. Virus-infected propagation stock is a means of introducing the disease into a new planting.

Because the vector has not yet been identified, the main form of control is prevention, by planting virus-tested clean planting stock. If diseased plants are seen in a planting, they should be rogued out and destroyed.

Mosaic Disease

Mosaic disease previously was thought to be a genetically caused variegation disorder. In 1957, it was shown to be of virus or virus-like origin. The disease has occurred in plantings of highbush blueberries throughout the eastern United States, Michigan, Indiana, Oregon, Washington, and British Columbia.

The disease has been observed on older varieties of highbush blueberry, such as Cabot, Concord, Earliblue, Pioneer, Rubel, and Stanley. Mosaic symptoms typically appear on a few basal shoots only. In some cases, the whole bush shows symptoms.

Symptoms include mild to brilliant mottle and mosaic patterns of chrome yellow, yellow, and yellow green on leaves. Sometimes the leaves show areas of pink. The distribution of symptoms on a bush can be spotty or ephemeral, showing in a given year and not showing the next year, and then reappearing a year later. On Coville, the mosaic pattern is less brilliant. Rather than a bright yellow mosaic, the pattern is a light green alternating with a deep green on the leaves.

Mosaic virus spreads in the field with the blueberry aphid as the vector. Diseased planting stock is responsible for the introduction of mosaic into plantings.

Insecticides applied for the control of the blueberry aphid should reduce the spread of mosaic disease. Plant virus-tested stock to prevent occurrence in new plantings.

Stunt

Stunt is caused by a mycoplasmalike organism, not a virus. Stunt is a very important disease of blueberry throughout the United States and eastern Canada. Most varieties of highbush blueberry are susceptible. Rancocas is the only variety with a high degree of resistance. Stunt is found in wild highbush and lowbush in the woods surrounding commercial plantings. No yield data are available on the losses caused by stunt, but symptomatic bushes usually are less than half the size of healthy bushes, and crop yields vary from very light to none.

Overall dwarfing of the bush is the primary symptom, hence the name “stunt.” Small leaves that are cupped downward or puckered are characteristic symptoms. Leaves of infected bushes are often yellow, with yellowing most pronounced along leaf margins and between lateral veins. Midribs and lateral veins usually retain normal green coloration. Yellow areas often turn a brilliant red in the late summer. Stem internodes become shortened, and growth of normally dormant buds causes twiggy branching.

Stunt is actively spread in the field by the sharp-nosed leafhopper. The pattern of stunt disease spread appears random. Leafhoppers are strong fliers and may come into a field from a great distance. Using diseased stock also is an important means of introducing the disease into a planting.

Insecticides applied on a timely basis to control the leafhopper help keep the disease in check. Research has shown that leafhopper populations start increasing at about the time of petal fall. Under Michigan conditions, one peak brood occurs in early July and a second in early September. Roguing and destroying symptomatic diseased plants is very important in controlling the disease. Use virus-tested planting stock when establishing a new field.