The 2011 North Carolina blueberry crop was of excellent quality due to the combination of a dry harvest season and good labor availability, which allowed growers to harvest top-quality fruit in a timely fashion. Most growers began harvesting around 16 May, with the bulk of the crop a few days early overall. Total volume was slightly reduced compared to the previous year, due to weather. The primary weather-related causes of loss were poor pollination in late March/early April, and drought during June and July.
In southeastern NC, cool, wet weather for an eight-day period (25 Mar to 1 Apr) decreased bee activity and thus pollination success of flowers that were blooming during that time, and reduced the volume of fruit on ‘Croatan’ and other cultivars in the same flowering period. In late April, small, unexpanded berries that had not been adequately pollinated were falling off the bushes at many locations. Not all fields were affected to the same degree, because bloom times vary by location and cultivar.
A drought from late May through July resulted in some shriveled fruit and loss of berry size, which accounts in part for the slight reduction in overall yield for the state. The drought was a real challenge -- most growers have irrigation, and with near-constant watering were able to keep fields from getting too dry; however fields without irrigation were severely affected and some bushes were lost.
Price and volume data were obtained from eight major shippers in the 2011 season. The first price reported for flats of 12-1 pint cups with lids was on May 17. Prices ranged mostly $20.50-$22.00. The last f.o.b. price report was issued on July 08 at $16.00. Approximately 29 million pounds, an equivalent of 3.2 million 12 1-pint flats, were shipped for fresh market. There was also an additional 7.7 million pounds processed (frozen). This total (fresh + processed) of 36.7 million pounds represents a record volume of berries harvested for fresh sales, a reduced volume of processed berries (frozen), and a slight reduction in overall pounds for the state.
Price and volume data provided by Karrie Gonzalez, NC Market News
Friday, December 2, 2011
Wednesday, November 30, 2011
10th International Vaccinium Symposium
On behalf of the Vaccinium Species Working Group, Vine and Berry Fruits Section of the International Society for Horticultural Science (ISHS), the conveners and organizing committee invite you to attend the10th International Vaccinium Symposium, to be held June 17-22, 2012 in Maastricht, Province of Limburg, The Netherlands. The meeting is being held in conjunction with the Floriade 2012 World Horticultural Expo: http://www.floriade.nl/
For more information or to contact the conveners, please visit the symposium website: http://www.vaccinium2012.com/
I look forward to seeing you in Maastricht!
Bill Cline, Chair
ISHS Vaccinium Working Group
For more information or to contact the conveners, please visit the symposium website: http://www.vaccinium2012.com/
I look forward to seeing you in Maastricht!
Bill Cline, Chair
ISHS Vaccinium Working Group
2012 Blueberry Open House and Trade Show
The 46th Annual Open House of the North Carolina Blueberry Council is coming up on January 10th and 11th, 2012. The meeting will be held at the Sampson Agri-Exposition Center in Clinton, NC at 414 Warsaw Road near the intersection of Hwy 24 and Hwy 701 business. For more information or to preregister, Contact Julie Woodcock at (910) 471-3193, or email ncblueberry@bellsouth.net
Thursday, October 6, 2011
Evaluating leafspot effects
Late September is a good time of year to evaluate the effects of leaf spot diseases. If most of your leaves are still attached to the bush at this time of year, then most likely flower bud formation has occurred and the crop potential for next year is good. If, however, your leaves have already detached by the end of September, then chances are that some flower buds did not form due to premature defoliation, and crop potential for next year has already been reduced.
The image below shows three twigs from the cultivar Star, collected on 30 Sep 2011. Star is susceptible to Septoria leaf spot caused by the fungus Septoria albopunctata. These are older twigs from the first flush of leafy growth in spring, and by now should have formed visible flower buds at the base of each leaf.
The shoot on the left is from a bush that was protected with a fungicide, retained its leaves, and has formed 5-6 flower buds. The unprotected shoot in the middle defoliated early, and by comparison formed only a couple of flower buds at the tip. The shoot on the far right was also defoliated early, not by leaf spots but by hurricane Irene. It too, has only one or two flower buds. Note that the shoot defoliated by hurricane winds still has the leaf petioles (bases) attached -- the leaves did not abscise normally, but were torn away: This also happens (leaves missing, but petioles still attached) with caterpillar feeding damage.
Regardless of the cause, when the leaves are taken away too early, flower buds do not form, and the potential crop is reduced for the following year -- because fewer flower buds means fewer berries.
The two main fungal leaf spot diseases that cause defoliation on blueberries in North Carolina are Septoria leaf spot caused by Septoria albopunctata, and Anthracnose leaf spot, caused by Gloeosporium minus. The two diseases have very different symptoms, as shown below:
Anthracnose leaf spot, shown above, consists of large lesions that often occur at the edge of the leaf. Examples of susceptible cultivars are Pender (shown) and Duke.
Septoria leaf spot, by comparison, produces dozens of small lesions on each leaf. The southern highbush cultivar Star (shown) is very susceptible.
By evaluating leaf drop at this time each year, growers can get a good idea of how much disease pressure they have on their farm, whether fungicide use is warranted, and which cultivars are susceptible.
The image below shows three twigs from the cultivar Star, collected on 30 Sep 2011. Star is susceptible to Septoria leaf spot caused by the fungus Septoria albopunctata. These are older twigs from the first flush of leafy growth in spring, and by now should have formed visible flower buds at the base of each leaf.
The shoot on the left is from a bush that was protected with a fungicide, retained its leaves, and has formed 5-6 flower buds. The unprotected shoot in the middle defoliated early, and by comparison formed only a couple of flower buds at the tip. The shoot on the far right was also defoliated early, not by leaf spots but by hurricane Irene. It too, has only one or two flower buds. Note that the shoot defoliated by hurricane winds still has the leaf petioles (bases) attached -- the leaves did not abscise normally, but were torn away: This also happens (leaves missing, but petioles still attached) with caterpillar feeding damage.
Regardless of the cause, when the leaves are taken away too early, flower buds do not form, and the potential crop is reduced for the following year -- because fewer flower buds means fewer berries.
The two main fungal leaf spot diseases that cause defoliation on blueberries in North Carolina are Septoria leaf spot caused by Septoria albopunctata, and Anthracnose leaf spot, caused by Gloeosporium minus. The two diseases have very different symptoms, as shown below:
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| Anthracnose leaf spot (Gloeosporium minus) |
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| Septoria leaf spot (Septoria albopunctata) |
By evaluating leaf drop at this time each year, growers can get a good idea of how much disease pressure they have on their farm, whether fungicide use is warranted, and which cultivars are susceptible.
Tuesday, September 27, 2011
Cylindrocladium blight
Cylindrocladium blight is a disease caused by a plant pathogenic fungus. Infection results in leaf spots, brown, dead stems, and often dead plants. On blueberry it is a disease of propagation and nursery beds, and is rarely seen on plants in the field. Symptoms commonly appear in blueberry rooting beds in the late summer and into fall. The disease may also occur in potted plants that are spaced too close together in pot yards. One species of this particular fungus also infects peanut plants in the field, so blueberry propagators in North Carolina often call the disease "peanut blight". There are many species of Cylindrocladium that infect plants, and there may be more than one species of this fungus causing disease in blueberry rooting beds. At present the only species reported on blueberry in North Carolina is now considered to be Cylindrocladium parasiticum, hence the common name of the disease, Cylindrocladium blight.
The disease is most often seen in propagation beds and pot yards that have grown vigorously and are too dense to allow proper air movement between plants. Spores of the fungus infect leaves and stems, and eventually kill entire plants. Often the root system is the last healthy part remaining. The phenomenon of plants dying in the center of a dense block, while those at the edge (with better air circulation) survive, is characteristic of this disease in dense beds of plants.
In pot yards and late-stage propagation beds where the plants have already formed roots, this disease is best managed by not over-watering or over-fertilizing plants, and by maintaining proper plant spacing so that the leaves and stems can dry between waterings. Cull to remove and discard any dead plants, and space the remaining plants out as much as possible so that there is good air movement between the bushes. Do not re-use any old used potting media, as this disease can carry over from one year to the next in contaminated soil or potting mix. Clean up as much debris as possible and sanitize the bed area and any pots that you plan to re-use.
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| Cylindrocladium blight in a bed of softwood cuttings in late fall. |
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| Closeup of orange fungal fruiting bodies on an infected cutting |
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| Irregular-shaped spots on lower leaves of older rooted cuttings |
The disease is most often seen in propagation beds and pot yards that have grown vigorously and are too dense to allow proper air movement between plants. Spores of the fungus infect leaves and stems, and eventually kill entire plants. Often the root system is the last healthy part remaining. The phenomenon of plants dying in the center of a dense block, while those at the edge (with better air circulation) survive, is characteristic of this disease in dense beds of plants.
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| Large area of dead plants in a propagation bed late in the season |
In pot yards and late-stage propagation beds where the plants have already formed roots, this disease is best managed by not over-watering or over-fertilizing plants, and by maintaining proper plant spacing so that the leaves and stems can dry between waterings. Cull to remove and discard any dead plants, and space the remaining plants out as much as possible so that there is good air movement between the bushes. Do not re-use any old used potting media, as this disease can carry over from one year to the next in contaminated soil or potting mix. Clean up as much debris as possible and sanitize the bed area and any pots that you plan to re-use.
Tuesday, August 23, 2011
Blueberry Stem Canker
Blueberry stem canker caused by the fungus Botryosphaeria corticis is common on cultivated and wild blueberries in North Carolina. The disease spreads by spores and through the use of infected cutting wood for propagation. Canker is important because it can weaken and kill susceptible or stressed bushes.
Symptoms: Cankers are noticeably thicker than adjacent portions of the stem, forming raised areas with deep cracks. Usually only short sections of the stem are affected, though canes of some very susceptible cultivars can have multiple infection points along their entire length.
Disease cycle: Infection of stems is by spores (ascospores and conidia) that are released during wet weather and disseminated by wind from April through September. Young, succulent, actively growing shoots are infected, and symptoms appear within 4 to 6 months after infection. As the fungus continues to grow and invade the wood, large cankers with deep fissures and cracks develop that girdle, weaken and kill the stem.
Control: Fungicides are partially effective but not practical. Control relies on maintaining general plant health,
pruning to remove canker-weakened canes,use of resistant cultivars, and use of disease-free planting stock. Cutting wood should be selected from undiseased plants, or the plants sourced from disease-free nurseries. In areas where canker is not present, the use of disease-free planting stock is critical to avoid introducing this pathogen to an new field.
Highbush blueberry: Among the popular southern highbush cultivars (Vaccinium corymbosum) grown in eastern NC, O'Neal, Blueridge and Legacy are susceptible -- however all three are successfully grown where plant health is maintained via proper site selection, fertility, pruning and irrigation.
Rabbiteye blueberry: Cankers can be numerous on rabbiteye blueberries (Vaccinium virgatum, synonym V. ashei) but generally do not cause yield loss on this vigorous blueberry species.
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| 'O'Neal' canes dying out due to canker infections |
Symptoms: Cankers are noticeably thicker than adjacent portions of the stem, forming raised areas with deep cracks. Usually only short sections of the stem are affected, though canes of some very susceptible cultivars can have multiple infection points along their entire length.
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| Swollen area (at center) with deep cracks is a fully developed canker |
Disease cycle: Infection of stems is by spores (ascospores and conidia) that are released during wet weather and disseminated by wind from April through September. Young, succulent, actively growing shoots are infected, and symptoms appear within 4 to 6 months after infection. As the fungus continues to grow and invade the wood, large cankers with deep fissures and cracks develop that girdle, weaken and kill the stem.
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| Cankers on a young stem, exuding spores |
Control: Fungicides are partially effective but not practical. Control relies on maintaining general plant health,
pruning to remove canker-weakened canes,use of resistant cultivars, and use of disease-free planting stock. Cutting wood should be selected from undiseased plants, or the plants sourced from disease-free nurseries. In areas where canker is not present, the use of disease-free planting stock is critical to avoid introducing this pathogen to an new field.
Highbush blueberry: Among the popular southern highbush cultivars (Vaccinium corymbosum) grown in eastern NC, O'Neal, Blueridge and Legacy are susceptible -- however all three are successfully grown where plant health is maintained via proper site selection, fertility, pruning and irrigation.
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| Cankers on a one-year-old 'Legacy' stem |
Rabbiteye blueberry: Cankers can be numerous on rabbiteye blueberries (Vaccinium virgatum, synonym V. ashei) but generally do not cause yield loss on this vigorous blueberry species.
Monday, August 22, 2011
Collecting softwood cuttings
As discussed in a previous post, blueberries can be easily propagated in summer from leafy softwood cuttings by using an intermittent mist system to keep the cuttings from drying out during the six- to eight-week rooting period. However, a specific stage of shoot growth must be selected for cuttings, because not all leafy shoots will root -- those that are too old will tend to form flower buds rather than roots, and cuttings from shoots that are too young and succulent will wilt before rooting can occur. The photos below illustrate when and how to collect and stick softwood cuttings.
Timing: Collect cuttings when shoots are 10-12 inches long and semi-hardened. In southeastern NC, this occurs in late May and again in late July or early August:
Age of cuttings: Select cuttings with leaves that are intermediate in color between the darkest older leaves and the palest young shoots. Softwood cuttings should be immature but not succulent. Cuttings that snap easily when bent are too young -- the cuttings should be bendable and becoming woody.
Handling: Collect cuttings early in the morning if possible, to minimize wilting. Once collected, cuttings are susceptible to wilting and must be kept moist and cool. Sprinkle with water and store in a cooler with ice until ready to stick the cuttings in the rooting bed. Caution -- direct contact with too much ice can damage cuttings -- keep them cool but not icy.
Sticking cuttings: Cuttings are stuck into six- to eight-inch deep rooting beds filled with aged milled pine bark. Stick the cuttings 1.5 to 2 inches apart in rows by cultivar. Approximately half the length of the cutting should be in the bark, with only the leafy section above the bark. The mist system should be running during this process so that the cuttings are never allowed to dry out.
Cuttings typically root within six to eight weeks. Once fully dormant, the cuttings can be dug and either potted, or planted directly into the field. Most nurseries and commercial growers pot rooted cuttings and grow them out for a year prior to selling or setting in the field.
For further reading:
Krewer, G. K. and W. O.Cline. 2003. Blueberry Propagation Suggestions.
Bilderback, T. E., R. E. Bir and M. A. Powell 1993. A Simple Intermittent Mist System for Propagation.
Timing: Collect cuttings when shoots are 10-12 inches long and semi-hardened. In southeastern NC, this occurs in late May and again in late July or early August:
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| Blueberry bush in early August with suitable shoots for propagation |
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| Cuttings can be snapped off by hand or clipped with pruning shears |
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| Pinch off the top of the cutting and remove the lower leaves |
Age of cuttings: Select cuttings with leaves that are intermediate in color between the darkest older leaves and the palest young shoots. Softwood cuttings should be immature but not succulent. Cuttings that snap easily when bent are too young -- the cuttings should be bendable and becoming woody.
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| Leafy shoots from oldest to youngest. The two in the center are suitable for propagation. |
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| Softwood cuttings of the proper stage are bendable but do not snap |
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| Shoots that snap easily when bent are too succulent for outdoor propagation beds |
Handling: Collect cuttings early in the morning if possible, to minimize wilting. Once collected, cuttings are susceptible to wilting and must be kept moist and cool. Sprinkle with water and store in a cooler with ice until ready to stick the cuttings in the rooting bed. Caution -- direct contact with too much ice can damage cuttings -- keep them cool but not icy.
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| Take a cooler and water to the field to keep cuttings from wilting |
Sticking cuttings: Cuttings are stuck into six- to eight-inch deep rooting beds filled with aged milled pine bark. Stick the cuttings 1.5 to 2 inches apart in rows by cultivar. Approximately half the length of the cutting should be in the bark, with only the leafy section above the bark. The mist system should be running during this process so that the cuttings are never allowed to dry out.
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| A measuring stick is used to space the cuttings evenly across the bed. |
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| Cuttings are stuck approximately half their lengh in the bark |
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| A commercial rooting bed partially filled with cuttings |
Cuttings typically root within six to eight weeks. Once fully dormant, the cuttings can be dug and either potted, or planted directly into the field. Most nurseries and commercial growers pot rooted cuttings and grow them out for a year prior to selling or setting in the field.
For further reading:
Krewer, G. K. and W. O.Cline. 2003. Blueberry Propagation Suggestions.
Bilderback, T. E., R. E. Bir and M. A. Powell 1993. A Simple Intermittent Mist System for Propagation.
Wednesday, August 3, 2011
Blueberry cultivar 'LEGACY'
Released: 1993 (not patented)
Developed by: USDA and NJAES, Rutgers University
Selection number: G-290
Parentage: 'Elizabeth' x US75 (Vaccinium darrowi,'Florida 4B', x 'Bluecrop')
Species/Type: Vaccinium corymbosum (southern highbush)
Bloom date: April 1 in southeastern NC (approx 1 wk before 'Croatan')
Harvest season: First harvest around May 30 - June 3 in southeastern NC
Chill requirement: Estimated to be 700 to 800 hours below 45F
Description: Upright, open habit with flexible canes. Highly vigorous, forming an abundance of flower buds on both longer canes and lateral fruiting twigs. Often a few leaves from the previous season will overwinter, persisting until after bloom the following spring. Early-blooming with pure white,elongate flowers. Fruit light blue, firm, with excellent flavor; large berries becoming medium in size with successive harvests, small dry stem scar. Clusters are open and well suited to mechanical harvest. Berries maintain their quality even when slightly overripe, and are less prone to decay than other highbush cultivars.
Good Characteristics: Blooms exhibit cold hardiness during spring freezes. 'Legacy' is highly productive with high-quality fruit that can be hand- or machine-harvested for the fresh market. Widely adapted to different soil types, 'Legacy' is a good candidate for highbush production on pine-bark-amended soils in the piedmont.
Flaws: Early blooming may result in yield loss due to spring freezes. 'Legacy' ripens two to three weeks later than early cultivars like 'Star' and 'O'Neal'. 'Legacy' is susceptible to blueberry stem canker disease caused by the fungus Botryosphaeria corticis, and will require irrigation and selective pruning to manage this disease. Purchase of disease-free propagation stock will reduce or delay the effects of stem canker.
Potential: Rapidly becoming a leading cultivar in North Carolina due to high yields and excellent fruit quality, 'Legacy' is recommended for commercial planting on lowland blueberry soils in southeastern NC, and for trial plantings in amended upland soils in the coastal plain and piedmont.
Developed by: USDA and NJAES, Rutgers University
Selection number: G-290
Parentage: 'Elizabeth' x US75 (Vaccinium darrowi,'Florida 4B', x 'Bluecrop')
Species/Type: Vaccinium corymbosum (southern highbush)
Bloom date: April 1 in southeastern NC (approx 1 wk before 'Croatan')
Harvest season: First harvest around May 30 - June 3 in southeastern NC
Chill requirement: Estimated to be 700 to 800 hours below 45F
Description: Upright, open habit with flexible canes. Highly vigorous, forming an abundance of flower buds on both longer canes and lateral fruiting twigs. Often a few leaves from the previous season will overwinter, persisting until after bloom the following spring. Early-blooming with pure white,elongate flowers. Fruit light blue, firm, with excellent flavor; large berries becoming medium in size with successive harvests, small dry stem scar. Clusters are open and well suited to mechanical harvest. Berries maintain their quality even when slightly overripe, and are less prone to decay than other highbush cultivars.
Good Characteristics: Blooms exhibit cold hardiness during spring freezes. 'Legacy' is highly productive with high-quality fruit that can be hand- or machine-harvested for the fresh market. Widely adapted to different soil types, 'Legacy' is a good candidate for highbush production on pine-bark-amended soils in the piedmont.
Flaws: Early blooming may result in yield loss due to spring freezes. 'Legacy' ripens two to three weeks later than early cultivars like 'Star' and 'O'Neal'. 'Legacy' is susceptible to blueberry stem canker disease caused by the fungus Botryosphaeria corticis, and will require irrigation and selective pruning to manage this disease. Purchase of disease-free propagation stock will reduce or delay the effects of stem canker.
Potential: Rapidly becoming a leading cultivar in North Carolina due to high yields and excellent fruit quality, 'Legacy' is recommended for commercial planting on lowland blueberry soils in southeastern NC, and for trial plantings in amended upland soils in the coastal plain and piedmont.
Tuesday, August 2, 2011
Wind burn
Wind burn occurs when high winds coincide with the emergence of new, succulent leaf shoots. The symptoms can be mistaken for insect injury, disease, drought or chemical injury. Characteristics of wind burn are new shoots that first appear scorched and wilted, then become dried, dead and shriveled. Older leaves with wind damage have necrotic areas and cracks at the leaf margins. Symptoms appear immediately on new shoots in high winds. The first photo below was taken on the day that injury occurred, while the wind was still blowing. The second photo shows what the injury looked like one month later.
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| Browning of new shoots can occur very rapidly on a windy day |
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| Wind burn one month after the injury occurred |
Friday, July 29, 2011
Exobasidium fruit and leaf spot
Symptoms caused by the fungus Exobasidium vaccinii have occurred sporadically in individual fields for years, but have not posed an industry-wide threat to blueberry production in North Carolina. However, in 2011 we saw increased incidence of this disease, and symptoms on previously unaffected cultivars such as Legacy and Columbus. The fungus causes spots on both leaves and berries. Spots on fruit are especially problematic because it is impossible for pickers to avoid harvesting affected berries, and nearly impossible for color-sorters and packing-line inspectors to remove them during the sorting and packing process.
On berries, infection produces a green spot that fails to ripen normally. Affected berries do not leak or decay, but the green spot on an otherwise uniformly ripe berry is an unsightly defect that could lead buyers to reject the fruit when delivered. On leaves, spots are pale green on the upper surface but pure white below, with a thin, dense layer of fungal growth on the underside of the leaf. This fungal growth is most obvious on the underside of leaves, but can also occur on infected berries.
As spots on leaves age, they become brown and necrotic, although the white fungal layer is often still visible on the underside of the leaf.
Eventually, the unique symptoms fade and the spots become indistinguishable from many other leaf-infecting fungi.
The fungus produces spores on both leaves and berries. As shown below, they are often a distinctive 'musiform' or banana shape, may be divided (septate), and measure roughly 4.0 to 5.2 μm wide × 13 to 15 μm in length.
Little is known about the life cycle of this fungus on blueberry. Infections appear in the spring on developing leaves and berries, but the fungus does not appear to infect later flushes of leaf growth. Lesions have not been observed on other plant parts (stems, buds) and it is not known how this pathogen overwinters. Visually, infections appear to be localized, distinct and limited to the affected berry or leaf, rather than systemic in the plant. Since blueberries drop their leaves each winter, there may be some quiescent infection stage on or in the remaining, bare dormant stems or buds that serves as the overwintering mechanism.
Fungicides have been shown to be at least partially effective in controlling this disease. A study by David Ingram and John Braswell at Mississippi State University achieved measurable control on rabbiteye blueberries. The combination of pyraclostrobin + boscalid (Pristine) was most effective in their tests.
Why is this disease becoming more prevalent? It may be due to changes in the cultivars we grow, the loss of key fungicides in recent years, or to changes in cultural practices such as the increased use of irrigation. If you are experiencing problems with this disease, I would like to know about it. It appears to be an emerging problem not only in North Carolina, but in other southern states as well. The more we know about it, the sooner we will learn to manage it -- thanks for your help!
REFERENCES:
W.O. Cline, 1998. An Exobasidium disease of fruit and leaves of highbush blueberry.
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| Green spots caused by Exobasidium on 'Legacy', 1 June 2011 |
On berries, infection produces a green spot that fails to ripen normally. Affected berries do not leak or decay, but the green spot on an otherwise uniformly ripe berry is an unsightly defect that could lead buyers to reject the fruit when delivered. On leaves, spots are pale green on the upper surface but pure white below, with a thin, dense layer of fungal growth on the underside of the leaf. This fungal growth is most obvious on the underside of leaves, but can also occur on infected berries.
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| Exobasidium leaf spot -- upper surface |
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| Exobasidium leaf spot -- underside of leaves showing fungal growth |
As spots on leaves age, they become brown and necrotic, although the white fungal layer is often still visible on the underside of the leaf.
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| Exobasidium on 'Legacy' leaves and fruit 7 Jun 2011 |
Eventually, the unique symptoms fade and the spots become indistinguishable from many other leaf-infecting fungi.
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| Symptoms on 'Legacy' upper leaf surface 20 Jul 2011 |
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| Symptoms on the lower leaf surface 20 Jul 2011 |
The fungus produces spores on both leaves and berries. As shown below, they are often a distinctive 'musiform' or banana shape, may be divided (septate), and measure roughly 4.0 to 5.2 μm wide × 13 to 15 μm in length.
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| Drawing of characteristic spores as seen under a microscope |
Little is known about the life cycle of this fungus on blueberry. Infections appear in the spring on developing leaves and berries, but the fungus does not appear to infect later flushes of leaf growth. Lesions have not been observed on other plant parts (stems, buds) and it is not known how this pathogen overwinters. Visually, infections appear to be localized, distinct and limited to the affected berry or leaf, rather than systemic in the plant. Since blueberries drop their leaves each winter, there may be some quiescent infection stage on or in the remaining, bare dormant stems or buds that serves as the overwintering mechanism.
Fungicides have been shown to be at least partially effective in controlling this disease. A study by David Ingram and John Braswell at Mississippi State University achieved measurable control on rabbiteye blueberries. The combination of pyraclostrobin + boscalid (Pristine) was most effective in their tests.
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| Infections on the rabbiteye cultivar Premier, 13 Jun 2008 |
Why is this disease becoming more prevalent? It may be due to changes in the cultivars we grow, the loss of key fungicides in recent years, or to changes in cultural practices such as the increased use of irrigation. If you are experiencing problems with this disease, I would like to know about it. It appears to be an emerging problem not only in North Carolina, but in other southern states as well. The more we know about it, the sooner we will learn to manage it -- thanks for your help!
REFERENCES:
W.O. Cline, 1998. An Exobasidium disease of fruit and leaves of highbush blueberry.
Thursday, July 21, 2011
Leaf Disease Symptoms
Leaf spot diseases caused by fungi are apparent in some fields this week. Septoria leaf spot is a disease caused by the fungus Septoria albopunctata. Infection results in small circular spots with dead gray centers. Often fungal fruiting bodies are visible as tiny black specks in the dead gray area at the center of each spot, as in the photo below. Spots first appear on oldest leaves near the ground. The cultivar Star is very susceptible
Another leaf symptom that is evident this week (21jul2011) is premature drop of yellowing older leaves. The cause is unknown but is suspected to be a form of blueberry leaf rust. Rust fungi cause yellowing and premature drop of leaves, and a characteristic symptom is the appearance of green spots on otherwise yellow leaves, consistent with the image below. This symptom is especially noticeable on the southern highbush cultivar Legacy and on the rabbiteye Premier. Rust diseases get their name from the appearance of orange spore masses on the underside of infected leaves, but so far we have not seen spore production on these yellowed leaves. When viewed from the underside of the leaf, the symptoms resemble edema, so there may be some environmental stress, perhaps related to the drought, that is causing or contributing to the problem.
Leaf drop is a serious problem because it can severely reduce yield for the coming year. Twigs that defoliate prematurely will not set flower buds, and so will not bear fruit the following year. There are several fungicides that can be used to control leaf diseases; also, summer pruning immediately after harvest removes old infected leaves and forces clean new growth, greatly reducing the effects of leaf diseases.
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| Septoria leaf spot on 'Star' |
Another leaf symptom that is evident this week (21jul2011) is premature drop of yellowing older leaves. The cause is unknown but is suspected to be a form of blueberry leaf rust. Rust fungi cause yellowing and premature drop of leaves, and a characteristic symptom is the appearance of green spots on otherwise yellow leaves, consistent with the image below. This symptom is especially noticeable on the southern highbush cultivar Legacy and on the rabbiteye Premier. Rust diseases get their name from the appearance of orange spore masses on the underside of infected leaves, but so far we have not seen spore production on these yellowed leaves. When viewed from the underside of the leaf, the symptoms resemble edema, so there may be some environmental stress, perhaps related to the drought, that is causing or contributing to the problem.
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| Yellowing and premature drop of 'Legacy' leaves on 20 Jul 2011 |
Leaf drop is a serious problem because it can severely reduce yield for the coming year. Twigs that defoliate prematurely will not set flower buds, and so will not bear fruit the following year. There are several fungicides that can be used to control leaf diseases; also, summer pruning immediately after harvest removes old infected leaves and forces clean new growth, greatly reducing the effects of leaf diseases.
New OSU budget for Oregon growers
Researchers James Julian, Bernadine Strik, and Wei Yang at Oregon State University have developed a new budget (April 2011) for blueberry growers in their state entitled: "Blueberry Economics: The Costs of Establishing and Producing Blueberries in the Willamette Valley". While North Carolina growers cannot use this budget "as is" due to the many differences in our establishment and production practices, this is an excellent budget and it is interesting to see their budget assumptions, costs, and especially conclusions regarding economy of scale.
Wednesday, July 20, 2011
Pruning Young Blueberry Plants
Young blueberry bushes are usually planted in late winter while fully dormant and leafless. In North Carolina, this translates to February or early March. During the first year, flower buds are removed by pruning, or by stripping off flowers by hand after the blooms emerge. In subsequent years, flower buds must be thinned to prevent overcropping and to promote the vegetative growth so vital to the establishment of a full-sized bush.
The diagrams below show growth of a single blueberry bush for the first three years, with "before" and "after" pruning comparisons each February. The color red is used to represent one-year-old growth and dormant flower buds. Click on each image to enlarge.
Tuesday, July 19, 2011
Blueberry Necrotic Ring Blotch
Blueberry necrotic ring blotch symptoms were evident in some 'Star' fields visited this week. The cause of this disorder is unknown, but a virus is suspected. It seems likely that this disease was introduced, and is spreading, via propagation from infected plants.
Symptoms are round to irregular, brown to black spots or blotches. Unlike the rings caused by blueberry red ringspot virus, these rings are visible on both the upper and lower surfaces of the leaf, as shown above. As with other leaf diseases, affected bushes tend to drop leaves earlier in the fall of the year, and this can translate to fewer flower buds the following year.
Symptoms usually appear on the oldest leaves first, with younger leaves progressively less affected. These leaf spots might be confused with fungal leaf diseases, but unlike fungal spots that have dead centers, most of these spots remain green in the center.
There are no control measures known for this disease, although some cultivars are more affected than others. Cultivars most affected include V-1, Star and O'Neal. The disease is present in Florida, Georgia, North Carolina and South Carolina. The vector, if any, is unknown.
Growers should be advised not to propagate from visibly infected bushes, and to buy plants from tissue culture or other sources known to be free of symptoms.
Symptoms are round to irregular, brown to black spots or blotches. Unlike the rings caused by blueberry red ringspot virus, these rings are visible on both the upper and lower surfaces of the leaf, as shown above. As with other leaf diseases, affected bushes tend to drop leaves earlier in the fall of the year, and this can translate to fewer flower buds the following year.
Symptoms usually appear on the oldest leaves first, with younger leaves progressively less affected. These leaf spots might be confused with fungal leaf diseases, but unlike fungal spots that have dead centers, most of these spots remain green in the center.
There are no control measures known for this disease, although some cultivars are more affected than others. Cultivars most affected include V-1, Star and O'Neal. The disease is present in Florida, Georgia, North Carolina and South Carolina. The vector, if any, is unknown.
Growers should be advised not to propagate from visibly infected bushes, and to buy plants from tissue culture or other sources known to be free of symptoms.
Saturday, July 16, 2011
Blueberry cultivar ‘NEW HANOVER’
Released: 2007 (Patent date 12 May 2009)
Developed by: Jim Ballington and Susan Rooks, NCSU
Selection Number: NC 3103
Parentage: NC 1522 × 'O’Neal'
Species/type: Vaccinium corymbosum (Southern highbush blueberry)
Bloom Date: April 1 (or approximately 1 week before ‘Croatan’)*
Harvest Season: Begins May 25 (3-4 days later than ‘Croatan’)*
Parentage: NC 1522 × 'O’Neal'
Species/type: Vaccinium corymbosum (Southern highbush blueberry)
Bloom Date: April 1 (or approximately 1 week before ‘Croatan’)*
Harvest Season: Begins May 25 (3-4 days later than ‘Croatan’)*
Chill Requirement: Unknown; likely 800+ hours based on observations of leafing at the NCSU Ideal Tract farm in Castle Hayne.
Description: Moderately upright, sturdy, vigorous bush, flowers white, new leaf growth with reddish-orange tinge. Self-fruitful and very high yielding. Developed for hand harvest. Large, light blue fruit.
Description: Moderately upright, sturdy, vigorous bush, flowers white, new leaf growth with reddish-orange tinge. Self-fruitful and very high yielding. Developed for hand harvest. Large, light blue fruit.
Good Characteristics: Excellent flavor, large, light blue fruit. Vigorous, very high-yielding and early ripening; easily propagated from cuttings.
Flaws: Low spreading branches require aggressive pruning as a young bush to force upright growth. Tearing of the berry skin around the stem scar at harvest (torn scars) has been observed on as much as 5% of the fruit. This tendency is worse on young bushes and when berries are overripe.
Potential: Released for hand harvest, not considered suitable for machine harvest due to wide growth habit, rigid, non-bending canes and large berry size. Though slightly later ripening, 'New Hanover' is recommended as a replacement for 'Croatan' on lowland blueberry soils in the southeastern coastal plain of NC. Not currently recommended for upland, piedmont or mountain sites.
*Dates are for southeastern NC
Scouting fields for blueberry red ringspot virus
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| Red rings on stems are diagnostic for BRRV |
Unlike fungal leaf spots, the rings caused by BRRV have green centers or pale centers, and usually do not show through to the underside of the leaf. Rabbiteye cultivars appear to be resistant to the virus, while highbush and southern highbush cultivars are more susceptible. Plants are infected for life, and cuttings taken from infected plants will also have the disease – so it is very important to scout fields that will be used for cuttings, and avoid or remove any suspicious plants before they are propagated. The vector (carrier) is not known, so the only control for this disease is to look for it in July-Sept and isolate or remove any infected bushes.
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| Spots on leaves are usually only visible on the upper surface. spots are red rings with green centers, unlike fungal leaf spots that have dead centers. |
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| Infected plants may exhibit faint rings on ripening fruit that disappear when the fruit is fully blue. |