Labeled of late as one of the “super foods” for its antioxidant properties, blueberries have always been on my top ten list of favorite foods… blueberry pancakes, blueberry muffins, blueberry crumble. Ok, maybe that isn’t exactly how they want us to eat this power berry but, regardless, there is no end of good reasons to grow your own bush. So what happens when you see witches’ broom in the blueberry bush? Is that it for the blueberry pancakes? Let’s find out.
What is Witches’ Broom in Blueberry Bushes?
Witches’ broom on blueberry plants is caused by a rarely found fungal disease. This disease caused clusters of small branches to form at the base of the bush known as witches’ brooms. Although a fungal disease, the symptoms of blueberries with witches’ broom are more viral in nature than fungal.
The year after infection, blueberry bushes afflicted with witches’ broom produce a multitude of swollen, spongy shoots with tiny leaves and reddish bark rather than the green found on healthy young branches. This malformation is called a “broom” and they continue to appear year after year.
As the broom ages, it becomes progressively brown, shiny, and then dull, until eventually drying and cracking. Affected blueberries have multiple witches’ brooms on the plant. The plant will likely cease fruit production.
What Causes Witches’ Broom on Blueberry Plants?
Witches’ broom is caused by the rust fungus Pucciniastrum goeppertianum, which affects both blueberries and fir trees. When P. goeppertianum afflicts firs, it results in a yellowing and eventual needle drop. The spores of this fungus are produced on the fir needles and carried by the wind, infecting those blueberry plants that are in close proximity.
The fungal disease is found in North America, Europe, Siberia, and Japan and spends a part of its life on Highbush and Lowbush blueberry bushes. The rest of its life cycle is spent on fir trees, but both hosts must be present to ensure the survival of P. goeppertianum.
While the fungus attacks just the needles on firs, it grows into the bark of blueberry plants, affecting the entire plant. The fungus will live off the host blueberry plant for many years, continuing its life cycle by producing spores off the brooms, which will, in turn, infect balsam fir trees.
How to Combat Witches’ Broom on Blueberry Bushes
Because the fungus that causes blueberry bushes with witches’ broom is perennial and systemic in nature, the disease is hard to combat. Fungicides do not work when blueberries have witches’ broom nor can pruning remove the pathogen since it is infiltrating the entire plant.
The best defense is prevention. Do not plant blueberry bushes within 1,200 feet (366 m.) of balsam fir trees. Once the plant has the disease, there is nothing to be done about it. It is best to eradicate any diseased plants with an herbicide to prevent further spread.
Q. What are the seed looking things falling off my bush
I have a blueberry plant in a pot on my porch and these little black tiny balls are falling all over the cement. Are they seeds?
I would inspect your plant for caterpillars - I suspect it is caterpillar droppings.
Prune hard for better blueberries
OSU blueberry specialist urges deep pruning for sustainable quality.
Blueberries require constant renewal growth of vigorous, 1-year-old wood to sustainably produce good berries year-to-year. So, when winter pruning, growers should look beyond just the next summer crop and envision what wood will give them good growth — key to having flower buds and high-quality fruit the following summer.
That’s the recommendation from Bernadine Strik, Oregon State University horticulture professor and berry crop extension specialist at OSU’s North Willamette Research and Extension Center.
In other words: Prune hard, and prune aggressively.
Pruning hard does reduce yield, but pruning too little reduces shoot growth and increases competition among fruit, which reduces berry size, diminishes handpicking efficiency and delays harvest. Meanwhile, having too few shoots or shoots too short will leave little quality growth for the following year’s crop.
Strik honed her pruning approach over 35 years of working in berry crops and, in 2017, completed a 10-year, $890,000 research project on best practices for growing organic blueberries in the Northwest. She offers online classes in blueberry production through Oregon State University.
Oregon and Washington are the two largest blueberry production states in the United States, collectively producing between 40 percent and 50 percent of the country’s crop in 2018, according to the U.S. Department of Agriculture.
Growers may worry about overpruning, which can warrant expensive corrective measures, but Strik said she sees growers underprune far more often.
When winter pruning, remove the short, skinny, “twiggy” laterals and sections of unproductive growth, Strik told growers at a November pruning workshop in Prosser, Washington. Most of the growers who attended were from Eastern Washington.
Leave thicker and healthier laterals that are between 6 inches and 18 inches long with flower buds near the end. If a bush is stressed, or if it was insufficiently pruned the year before, prune it even harder, removing dead or diseased wood first.
“If we don’t prune well, or if a plant is stressed for some other reason” then we have to prune it extremely hard to encourage vegetative growth, she said. Pruners sometimes have a tendency to leave a sick-looking plant alone, but “that’s the worst thing you can do,” she said.
Here are a few other key pruning tips from Strik:
—Leave no more than five or six strong fruiting laterals on a 2-year-old cane.
—Prune to open up the interior of the bush to sunlight and to remove low growth, forcing the bush upright.
—Thin to the most vigorous three or four whips (1-year-old canes) coming from the base. Remove older, unproductive canes entirely.
—Think about the picker or the machine harvester. Prune to a good picking height.
—Don’t be afraid to use your hand to strip and break away short, twiggy shoots.
—Don’t hedge postharvest. That may work in the climates in Georgia and Florida, but in the Northwest, it will reduce yields and cause “witches’ broom,” a structure of short twiggy growth. The Northwest growing season is too short for summer hedging.
—Experiment. Flag a few bushes and try different severities of pruning on them, leaving some bushes as control, and take note of their growth and production the following year or years.
Adam Waliser of Spokane, Washington, has attended several of Strik’s workshops over the years and gets better at finding the pruning severity sweet spot each year, he said. After first hearing her preach about aggressive pruning, he tried it on his 32 acres and thought it was too much. The next year, he finished pruning wishing he had pruned more.
“It’s one of the difficulties at farming you only get one chance a year,” he said.
He believes he’s got it down now. In November, he brought three of his full-time employees with him to Strik’s workshop.
Keith Oliver, a manager for Olsen Bros. Ranches, recalls the first time Strik visited his freshly pruned, Prosser-area blueberry field the first winter after it was planted in the spring of 2005. She recommended he send his crews back through the plot to reprune, removing twice as much vegetation.
He did — and liked what he saw. He has since compared his fields favorably to other lightly pruned plots, where the bush health seemed to wane over time.
“I learned that lesson early, it’s better to be aggressive,” Oliver said. He likens it to exercise. Pruning a plant invigorates it the way exercise invigorates people.
His crews do not count buds, however, as that would take too long, he said. Pruners are paid piece-rate per bush. Through experience, his managers have simply learned what a well-pruned bush should look like and they communicate that to pruners.
Yes, Oliver said. Pruning is a science.
“But sometimes the artwork is important, too,” he said. •
Fungal diseases above ground
Alternaria fruit rot
The fungus Alternaria tenuissima has caused severe losses in some Pacific Northwest fields, although it is not as common as ripe rot. The fungus overwinters as mycelium and spores in old, dried-up berries, dead twigs from the previous season’s crop and on other plant debris. Infections can occur any time between late bloom through fruit maturity.
Infections remain quiescent (latent) until fruit ripens. The disease often develops in storage or in transit to market. Damaged fruit may be covered with a blackish or dark greenish mass of spores that gives the surface of the berry a dull cast. Although berries may be dry in the field, the rot can become watery when harvested fruit is stored.
- Harvest promptly to prevent overripe fruit.
- Do not pick or handle fruit when it is wet.
- Hand harvesting results in less rot than machine harvesting.
- Avoid wounding or bruising fruit during harvest.
- Cool berries rapidly after harvest.
- Clean plant debris from picking buckets, packing lines and inspection belts frequently.
A wide variety of synthetic fungicides are registered for use after full bloom when berries are developing. Bloom applications have not been very effective.
The fungus Botrytis cinerea survives as sclerotia (resistant survival structure) and dormant mycelia on dead twigs of bushes and prunings. Spores spread primarily by wind but also by splashing water.
Susceptibility is highest during bloom and again near harvest. Cultivars that tend to retain floral structures over a long period are more susceptible. Also, branch tips killed by low winter temperatures are easily infected. Blueberry blossoms take on a brown, water-soaked appearance and die. Blossoms may be covered with dense grayish powdery masses of Botrytis spores. Infections may move through the blossoms rapidly and often destroy the entire floral structure. The disease also can move from blossoms back into fruit-producing wood.
Infected succulent twigs are at first brown to black and later bleach to tan or gray. Symptoms can be seen after winter injury or before floral bud break. When planting a new field, space plants for good air circulation and quick drying. Annually prune to remove infected twigs and to open the canopy for good air circulation. Adjust timing or frequency of overhead irrigation to keep aboveground portions of the plant dry. Drip irrigation will also keep flowers and above-ground portions of the plant dry. Pick fruit at correct stage of maturity and move harvested fruit to cold storage as soon as possible.
A wide variety of synthetic and some organic fungicides are registered for use from prebloom through the end of bloom. A preharvest application is useful to control fruit rot after harvest.
Fusicoccum canker (or sometimes still called Godronia canker)
The fungus, Fusicoccum putrefaciens, can interfere with new plantings in British Columbia and Washington. It is less serious in established fields because only new wood can be infected. However, disease incidence has been increasing in older fields since the late 1980s.
The fungus overwinters in cankers on stems and crowns of infected plants. Conidia are released from pycnidia in wet weather and disperse by splashing rain. Conidia infect stems primarily at leaf scars from March through June. Natural openings in the bark also may serve as infection sites. Infections appear on current-year stems at bud sites or wounded areas as small reddish-brown lesions in early spring. As these cankers enlarge, the centers usually become gray and the margins turn reddish brown or dark brown, giving the canker a bulls-eye appearance.
Small, dark, pimple-like pycnidia can frequently be found in the canker. Purchase healthy, certified planting material and do not use plants with injured branches. Sanitation is critical for successful management. If cankers are found, prune out and destroy cankered branches. Avoid overhead irrigation, using drip if possible. No fungicides are registered for control. Research in British Columbia indicates that broad-spectrum fungicides with multi-site modes of action used for control of other diseases are effective. Management of other diseases in the spring may indirectly be controlling this disease.
The fungus Monilinia vaccinii-corymbosi overwinters in mummified fruit (sclerotia) on the ground. In early spring, about the time buds begin to break, fungal fruiting cups (apothecia) grow from overwintering mummies in or near the soil surface. Ascospores from apothecia infect leaves and flowers shortly after buds open.
Infected flowers turn brown and wither as if they had been frosted. Leaf and shoot growth expanding from newly opened leaf buds are blackened in the center and eventually wilt and die. About three weeks after primary infection, a brownish gray mass of spores develops on blighted flower stalks and leaves. These spores are spread by wind, rain, and various insect pollinators to healthy flowers.
Flowers are most susceptible just as they open. During early berry development, diseased fruits look like healthy ones if cut open, however, the spongy white fungal growth can be seen within the carpels. As berries approach maturity, infected berries become a reddish buff or tan color in contrast to the waxy green of healthy fruits. Many of the diseased berries fall before healthy berries are harvested. Mature mummified berries are gray, shriveled, and hard.
Plant resistant cultivars and remove susceptible cultivars such as ‘Berkeley’ from mixed plantings. Disruption of the developing apothecia with physical or chemical tactics can help the overall management of mummy berry. In fall, before leaf drop, shallowly cultivate to bury mummies. In early spring between bud break and bloom, destroy developing apothecia by disrupting the soil under plants or in alleyways by raking or cultivating the soil. Some growers drag chains along the ground to disrupt the developing apothecia.
Harvest and destroy mummified fruit from bushes before they drop to the ground. This practice may take several years before a benefit can be realized but has been effectively used by some organic growers. Before moving to a new field, remove and destroy plant debris that accumulates on harvester machines. Also in spring, destroy any cull piles near packing houses. A wide variety of synthetic and some organic fungicides are registered for use to protect blossoms and foliage from bud break to end of flowering.
Ripe rot (sometimes still called anthracnose)
The fungus Colletotrichum acutatum can appear on fruit before harvest (ripe rot), but more often appears as a post-harvest fruit rot. Warm, wet conditions favor disease spread and buildup. Spores are dispersed by splashing rain or irrigation.
Infection can occur at any time during bloom and berry development. Berry infections remain quiescent (latent) until fruit is nearly mature. Blighting of shoot tips may be observed first. Then, a few flowers turn brown or black.
As infected berries ripen, the flower end may soften and pucker. Under warm and rainy conditions, salmon-colored spore masses form on infected berries. However, there may also be no indication of disease prior to harvest. After harvest, spore masses form rapidly on infected fruit when in cellophane-covered baskets or in plastic clamshell packs.
A combination of cultural and chemical practices combats losses from this disease. Prune bushes for adequate airflow and to reduce drying time after becoming wet. Avoid overhead irrigation or apply such that plants are not wet for extended periods of time. Lower the temperature of harvested fruit as soon as possible after picking. A variety of synthetic fungicides are registered for use during bloom. Applications may be needed after bloom in, especially wet years.
Silver leaf was confirmed for the first time in 2014 on ‘Draper’ and ‘Liberty’ blueberry, although samples with these symptoms had been noted since 2009. The fungus (Chondrostereum purpureum) invades cut or wounded stems and limbs of a wide variety of plants including blueberry.
Small bracket-like fruiting bodies are produced in the fall and winter during moist weather. Spores are blown for miles, germinate and enter fresh surface wounds such as pruning cuts, mechanical injury, winter injury or insect damage. Pruning cuts are most susceptible within a week of wounding.
After infection, fungus growth is systemic into the root crown of the bush. During the summer the top surface of young leaves turns silvery. Symptoms may start on one of two branches, which show reduced growth and die in two or three seasons. New branches on the same plant continue to develop symptoms until the whole bush is affected.
The heartwood of infected stems may turn brown or exhibit purple to brown concentric rings of discoloration. This discoloration is more accentuated at the base of bushes and branches. Rogue out and destroy symptomatic plants. Destroy all dead wood removed from 'Draper' fields. Burn prunings because the fungus will fruit only on dead wood and pruning piles are often the source of reinfection in other fruit systems.
The fungus Phomopsis vaccinii overwinters in infected plant debris. In the spring, spores are dispersed from fruiting bodies (pycnidia) embedded in diseased tissue by rain splash and irrigation water. Infection occurs through flower buds from bud break to bloom.
The disease spreads from flowers into shoots and twigs. The fungus can also infect through injuries such as wounds from pruning, harvest equipment, frost cracks, and herbicide injury and produces girdling cankers. Cankers may be present at the base of infected canes. Cankers are seen as elongated, flattened areas that become covered with small, pinpoint-sized fruiting bodies (pycnidia) that produce spores.
Infected stems wilt during the summer and the leaves turn color earlier, causing a red flagging. Purchase healthy planting material and do not use plants with injured branches. Provide adequate plant spacing and manage canopy size to promote good air circulation. Prune out, remove, and destroy infected and dead branches. Avoid wounding or injuring plants. Encourage plants to harden off in winter to avoid frost damage. A variety of synthetic fungicides are registered for use during bloom. The fungus may be active anytime it rains in the spring from bud break to harvest but focus applications during bloom.
How to Start Blueberry Plants From Another Grown Plant
Blueberries (Vaccinium corymbosum) appeal to gardeners seeking a compact fruit-bearing shrub with a high yield and ornamental appeal. Cultivars such as Coville (V. corymbosum "Coville") and Jersey (V. corymbosum "Jersey") are particularly popular in warmer areas since they thrive within U.S. Department of Agriculture plant hardiness zone 8, where few other blueberry cultivars will grow. Blueberries start easily from cuttings taken from a mature, well-established plant. The cuttings will root in two to three months if kept in a warm, moist environment however, they must be treated with rooting hormone to ensure successful rooting.
Start blueberry cuttings in summer when the plant is actively growing. Water the plant to a 4-inch depth the night before gathering the cuttings to ensure the stems and foliage are hydrated.
Fill 4-inch plastic pots with a mix of half coarse sand and half milled peat moss that has been soaked in water until plump. Firm the mixture, and poke a 3-inch-deep hole in the center.
Gather a 6-inch-long cutting from the tip of a healthy, vigorous blueberry stem. Avoid stems with active flowers or fruit since both will divert the cutting's energy away from root production.
Sever the cutting 1/8-inch below a set of leaves, using very sharp, clean shears. Make the cut at a slight angle. Pull off and throw away all of the leaves along the lower half of the stem.
Measure out 1 tablespoon of 0.8-percent IBA (indolebutyric acid) rooting talc and pour it onto a sheet of newspaper. Dab the severed end of the blueberry cutting into the talc. Gently flick the stem to knock off the excess powder. Discard the remaining powder.
Pot the blueberry cutting in the prepared rooting container. Insert the stem into the hole, and press the sand and peat mixture snugly against the stem. Drizzle water around the base of the stem to settle the sand.
Place the potted blueberry cutting in a lightly shaded, ventilated cold frame. Warm the pot to 70 F, using a propagation mat, if daytime temperatures are consistently below 65 F.
Water the blueberry cutting whenever the sand dries out in the top inch. Add water until the sand feels moderately moist but not sopping wet in the top 2 inches. Gently press the sand to release the excess moisture.
Check for roots in two to three months by lightly tugging on the base of the stem. Feel if the stem is firmly affixed to the sand by roots. Transplant the blueberry into a 6-inch container filled with acidic potting mix, such as those formulated for roses or azaleas.
Grow the blueberry plant under light shade during the summer months. Provide water whenever the soil feels dry in the top inch. Acclimate the blueberry to direct sun over the course of one week. Transplant into a permanent bed in autumn after the first rain.
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