How is your season going? Southern New England is having a hot, humid season with very little rainfall. Given the number of diseases that attack blueberries, I'm sure there are some that are doing quite well this season, if any blueberry plants have been left unprotected. So, if you're having disease problems here's what might be the cause: mummy berry or phomopsis canker, twig blight and fruit rot.
In order for disease to become a problem, three things must be present simultaneously:
Disease management practices involve the first two, and to a lesser degree the third. There are varieties with differing levels of resistance to these diseases. Growers can use cultural practices such as raking, mulching, pruning and fertilization to destroy disease causing organisms. Overhead irrigation, if done improperly, can create the favorable environment needed by the causal organism.
Mummy berry is a two-stage fungal disease of economic importance in New England on high and lowbush blueberries. The first stage is a blight of shoots and emerging leaves. The second is infection of flowers and subsequent fruit that becomes obvious only as the fruit begins to ripen.
The causal organism is Monilinia vaccinii-corymbosi.
A favorable environment for ascospores of the first stage includes wet, windy weather and 60oF between green tip and bloom. If foliage is wet for four to 12 hours after the spore lands, it will germinate. The conidia of the second stage also need wet, windy weather. Insects are involved in transferring this stage from flower to flower.
Susceptible hosts include varieties such as Blue Crop, Blare, Earliblue, Weymouth, Jersey and Berkeley.
Collins, Burlington, Darrow, Rubel, Bluetta and Dixi are more resistant.
Disease Cycle: The fungus overwinters in mummified berries.
In favorable spring weather, ascospores are released from the brown cup-shaped apothecia and blown onto emerging blueberry leaves and stems. Symptoms include new leaves and shoots wilting and quickly turning brown. If wet humid conditions persist, a light gray, powdery mold develops on blighted tissue.
In the second stage, conidia are produced on leaves and stems and blown onto flowers. Bees then transfer conidia to healthy flowers. If humidity remains high, germination will occur. The fungus grows through the style into the ovary of the developing berry. Infected berries turn white or salmon in color as other berries ripen. They shrivel, harden and fall to the ground prematurely. By spring they are pumpkin-shaped and a dark brown.
Control: Several cultural practices reduce the severity of this disease. Raking mummified berries just before bud break destroys ascospores as they are being produced. Covering the mummified berries with two inches of mulch before bud break will prevent light from reaching them and stop the formation of ascospores.
Fungicide sprays may also be necessary. If weather conditions are favorable for ascospores to develop, fungicidal sprays can be applied between bud break and bloom. When conditions are less favorable for disease, a single spray one to two weeks after bud break may provide adequate protection. Table 1 shows what fungicide to use at each stage.
Currently this may be the most prevalent canker disease in New England. It also causes twig blight and fruit rot in highbush blueberries. This disease occurs mainly in stressed plantings.
The causal organism is Phomopsis vaccinii.
A favorable environment for the disease is a 48-hour period of wet, windy weather with temperatures between 70 and 81oF.
Susceptible hosts include Murphy, Harrison, and Weymouth. Coville, Bluecrop, Blueray, Jersey and Berkeley are less susceptible. In New England Rancocas has shown some resistance to the canker stage.
Disease cycle: The fungus overwinters in diseased plant parts. Most conidia are splashed onto flowers, new leaves, and wounds during blossom and petal fall. If conditions remain humid, germination occurs and twig blight begins. The fungus moves from either flowers or leaves into the stem. Symptoms include red foliar lesions that progress to wilted stems, to dead stems with leaves attached. If a stem is infected at the crown because of winter injury, the entire stem will suddenly wilt and die. Infected fruits are soft and split easily.
Phomopsis canker infects one, two and three-year-old stems. Conidia are released during rainy periods from blossom bud swell thru late August. Cankers are brownish and may encircle the stem. As they progress downward, stems become flattened and turn gray. In the heat of summer these stems wilt. The reddened leaves remain attached.
Control: Culturally, keeping plantings healthy is the best disease prevention. Begin by planting varieties able to withstand the low temperatures in your location. Irrigate during hot, dry spells and avoid causing mechanical injury.
If Phomopsis is present, remove and destroy all infected plant parts to reduce the innoculum for next season.
Fungicides, if needed, should be applied at bud break and every 14 days thereafter thru late August. This will prevent fruit rot. Table 1 gives the fungicides labeled for use against Phomopsis.
Disease |
Spray Material |
Rate/A |
Comments |
|
Mummy berry Stage 1 (about March 20) |
Funginex 1.6 EC | 24 oz. | Apply at bud break and seven-to 10-day intervals till early bloom |
|
Mummy berry Stage 2 |
Captan 50 WP + Benlate 50 WP |
3 lb. 8 oz. |
Apply at mid-bloom and repeat in 10 days |
| Phomopsis twig blight and canker | lime sulfur | 5 gal. | Use only once in spring and again in fall if needed |
References
Caruso, F. L. and D. C. Ramsdell. 1995. Compendium of Blueberry and Cranberry Diseases. American Phytopathological Society. St. Paul, MN.
Pritts, M. P. and J. Hancock (eds). 1992. Highbush Blueberry Production Guide. Northeast Agricultural Engineering Service. Ithaca, NY.
Schloeman, S., D. Cooley, D. Handley, and R. Bonnano (eds). 1994. New England Small Fruit Pest Management Guide. University of Massachusetts. Amherst, MA.
The information in this material is for educational purposes. The recommendations contained are based on the best available knowledge at the time of printing. Any reference to commercial products, trade or brand names is for information only, and no endorsement or approval is intended. The Cooperative Extension system does not guarantee or warrant the standard of any product referenced or imply approval of the product to the exclusion of others which also may be available.All agrochemicals/pesticides listed are registered for suggested uses in accordance with federal and Connecticut state laws and regulations as of the date of printing. If the information does not agree with current labeling, follow the label instructions. The label is the law.Warning! Agrochemicals/pesticides are dangerous. Read and follow all instructions and safety precautions on labels. Carefully handle and store agrochemicals/pesticides in originally labeled containers immediately in a safe manner and place. Contact the Connecticut Department of Environmental Protection for current regulations.The user of this information assumes all risks for personal injury or property damage.Issued in furtherance of Cooperative Extension work, Acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture. Kirklyn M. Kerr, Director, Cooperative Extension System, The University of Connecticut, Storrs. The Connecticut Cooperative Extension System offers its programs to persons regardless of race, color, national origin, sex, age or disability and is an equal opportunity employer.