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Disease - 219-Disease Control Guide for Wild Blueberries

219-Disease Control Guide for Wild Blueberries

Fact Sheet No. 219, UMaine Extension No. 2000 219 

Prepared by Seanna Annis, Associate Professor of Mycology and David E. Yarborough, Extension Blueberry Specialist, The University of Maine, Orono, ME 04469. Revised February 2014.

NOTICE: It is unlawful to use any pesticide for other than the registered use. Read and follow the label on the product container. The user assumes all responsibility for use inconsistent with the label.

This fact sheet is to be used only during 2014. Use in subsequent years may lead to improper and illegal use of pesticides. If your version of the guide is out of date, please request an updated version from your Extension office or on the web at extension.umaine.edu/blueberries/

WARNING! Pesticides are potentially hazardous. Handle carefully! Read and follow all directions and precautions on the labels. Store in original labeled containers out of reach of children, pets and livestock. Dispose of empty containers at once in a safe manner and place. Do not contaminate forage, streams, ponds or groundwater recharge areas.

Groundwater is a major natural resource. Pesticides have been detected in the groundwater in all states. A sound pesticide application program including site-specific selection of pesticides, adherence to label directions, sprayer calibration and mixing accuracy, spill and back siphon prevention, proper waste disposal, integrated pest management and judicious pesticide use can prevent groundwater contamination.

Trade names are used for identification. No product endorsement is implied, nor is discrimination intended against similar materials. Cooperative Extension makes no warranty or guarantee of any kind concerning the use of these products.

Disease Management

Prevention is the key to effective disease management. Many management practices reduce the incidence of disease-causing organisms. These include regular fire pruning, efficient harvesting techniques to reduce the number of disease infected fruit left on the ground, disposal of winnower refuse by composting or burning, and good weed control.

When conditions might permit diseases to become a problem, fungicides should be used to protect plants from potential infection; they will not cure the diseased plants.

For additional information on the identification, life cycles and control of blueberry diseases, please refer to Wild Blueberry Fact Sheets No. 211, Blueberry Diseases 1 and No. 218,  The Influences of Pruning Method on Disease and Insect Control.

All publications may be found on the web at extension.umaine.edu/blueberries/

Fungicide Effectiveness

Not all fungicides are equally effective for all diseases. Compare results in Table 1 and 2 found at the end of this fact sheet.

Cultural Techniques to Reduce Diseases – Burning as a pruning technique may reduce disease inoculum but may not give sufficient control of many diseases. The use of fungicides may also be necessary to produce the desired level of control.

Blossom & Twig Blight, Botrytis

Blueberry blossoms, particularly after frost damage or during late-bloom, are the most susceptible part of the plant to Botrytis blossom blight. In severe outbreaks, leaves and stems also can become infected. An extended period of wet weather, whose length is dependent upon the temperature,  is required for infection to occur.  Fields with regular fog cover are more likely to be infected by Botrytis. Blossoms can also be killed by Monilinia (mummy berry disease) or frost, so determine the cause of blossom death before applying fungicide.   Protection of the blossoms is the greatest concern when fighting this disease. Refer to Wild Blueberry Fact Sheet No. 212, Botrytis Blight Control for Wild Blueberries for more information on controlling blossom blight.

Mummyberry, Monilinia

Primary infections of leaf and flower buds by Monilinia occur for several weeks following bud-break. The disease is then spread by secondary infections from the infected leaves and flowers to the developing fruit. Primary infections are the most damaging stage of this disease on wild blueberry. Pruning blueberries with fire, using efficient harvesting techniques to reduce the number of infected fruit on the ground, composting, and burning or disposing of winnower refuse can reduce the incidence of this disease.

Primary infections can be controlled by ground applications of a fungicide when greater than 40% of the flower buds are at the crown stage (stage 4:Inflorescence tip visible; in Wild Blueberry Factsheet No. 216, Flower Primordia Development Stage and mummy berry cups (apothecia) are present in the field. The mummy berry forecast method (refer to Wild Blueberry Fact Sheet No. 217, A Method to Control Monilinia Blight) can be used to predict when there has been an infection period for the fungus.  Fungicides (propiconazole or fenbuconazole ) applied within 72 hours of an infection period will kill off fungus that penetrated into the plant and prevent further infections for up to 7 to 10 days. Fungicides also can be applied by the calendar method at seven to ten day intervals until mummy berry cups are no longer present in the field. When compared to the calendar method in 2009 and 2010, the mummy berry forecast method required two fungicide applications to protect plants compared to three applications required for the calendar method to protect plants in the same field for the same length of time. Full coverage around the stems is essential.

Valdensinia leaf spot, Valdensinia

Leaf spots caused by this fungus are usually round, large (>1/4 inch) brown spots with black margins. Young leaves with a single spot may fall off the plant while still green.  Heavy infections can cause complete defoliation which can decrease flower bud formation and yield.  Older leaves do not fall off of the plant and will show more leaf spots.  This fungus overwinters in veins of infected leaves from the previous year and will first produce spores after a 3 to 4 day wet period during bloom.  Fallen infected leaves will produce new spores after a couple of days of wetness throughout the growing season.  The spores are not carried by wind or water, but can be easily carried on leaf contaminated equipment, clothing or shoes.   There are no registered fungicides for this disease.  The recommended method of control is eradication by a hard burn to destroy all leaf litter of infected plants and all plants within 10 feet of infected areas.

“False Valdensinia” leaf spot (fungus not yet identified)

Leaf spots caused by this fungus are usually round, large (>1/4 inch) brown spots with black margins. Young leaves with a single spot may fall off the plant while still green. Heavy infections can cause complete defoliation which can decrease flower bud formation and yield. Older leaves do not fall off of the plant and will show more leaf spots. This fungus overwinters in veins of infected leaves from the previous year and will first produce spores after a 3 to 4 day wet period during bloom. Fallen infected leaves will produce new spores after a couple of days of wetness throughout the growing season. The spores are not carried by wind or water, but can be transported on leaf contaminated equipment, clothing or shoes. There are no registered fungicides for this disease. The recommended method of control is eradication by a hard burn to destroy all leaf litter of infected plants and all plants within 10 ft of infected areas.

“False Valdensinia” (fungus not yet identified)

This leaf spot is often mistaken for Valdensinia leaf spot, and can cause defoliation of heavily infected leaves in some clones in July and August with dry weather. Symptoms start to appear after bloom and appear as large brown patches (1/8 to ½ inch) on the lower and upper surfaces of leaves that may continue to expand during the season. Applications of fungicides after bloom will decrease incidence of this disease and defoliation but do not have a consistent effect upon yield.

Red-Leaf, Exobasidium

Plants with red-leaf disease occur singly, in scattered clumps, or in patches. Infected plants are recognizable by the bright red color in irregular blotches on partially affected leaves. In late June and July, the underside of diseased leaves turn white when spores are produced. In August, infected leaves will shrivel and dry up. Few or no fruit develop on infected stems; some twigs may be killed. The disease overwinters in stems and rhizomes. No fungicides adequately control this disease, but it does not seem to be increasing in importance. The only control recommendation is not to spread spores by walking through diseased areas when spores are being produced. Removing infected plants by directed spraying with an herbicide may kill infected stems but may also kill surrounding unaffected plants by transference of herbicide through rhizome connections.

Septoria Leaf-Spot, Septoria

Leaves and stems become infected during bloom in wet weather. Severe spotting can cause defoliation of some clones in dry weather in July and August, which may result in reduced vigor and decreased yield. Some berries may also fall with severe infections and dry weather. Leaf lesions are small (pin-prick) water-soaked spots on the underside of leaves in mid-June, and the spots become necrotic and appear as small red to brown spots on the top of the leaf by July. If excessive leaf drop has occurred in the past, then fungicide applications during bloom may be used to reduce the incidence of this disease.

Powdery Mildew, Microsphaera

In most years, powdery mildew appears near harvest time in both crop and prune fields and is not known to affect yield. Diseased leaves range in appearance from those covered with a white mildew to those showing little or no mildew in the center of large red spots or rings. When the disease is severe, leaves are shed prematurely. Fungicide treatments may reduce powdery mildew, but treatment is seldom necessary unless substantial amounts of disease and leaf loss have occurred in the past.

Stem Blight, Phomopsis or Godronia

Stem blights caused by Phomopsis or Godronia are common diseases found in blueberry. The primary symptom is blighting of the first year’s stems. Death of stems usually occurs scattered in patches of one to a few stems. The infected stem tissue is reddish brown and dead reddish brown leaves remain attached to the stem for some time. The fungus over-winters in blueberry stems infected in the previous year. Conidia are released during rainy periods and are spread by splashing raindrops. Disease levels have not been high enough to require control.

Leaf Rust, Thekopsora also called Pucciniastrum 

Leaf rust has a complex life cycle that includes several different spore types and the infection of both blueberry and an alternate host, hemlock in one year’s life cycle.  Rust infections are typically not evident until mid-July or later, so  rust has a minimal effect on cropping fields which are typically harvested in August. It can cause be a major problem in non-bearing fields by causing extensive leaf spotting that results in excessive leaf drop. Leaf rust symptoms are consist of small spots with brown centers and diffuse red margins  that can be easily distinguished from other diseases by raised yellow to rust colored pustules on the lower leaf surface. Leaf drop can be extensive by early September and production of fruit buds in severely affected fields may be reduced by 30 percent or more. A single application of fungicide in late July will suppress both leaf infection and leaf drop. There has been no evidence that pruning by burning decreases disease and even fields which do not have hemlock on their perimeter can still be severely affected by rust since the spores can travel for miles by wind.

Chemical Disease Control for Wild Blueberries

Disease Material Rate / acre Product Comments
Mummyberry (Monilinia)
Primary Infection

 

   

 

Tilt / Bumper / Propimax (propiconazole) 6 oz. For the following fungicides, begin applications when greater than 40% of stems have blossoms at the crown stage. Follow the mummy berry forecast method to time applications or apply every 7 to 10 days following the calendar method.

Tilt/Bumper/Propimax: Do not apply more than 2 sequential applications. Do not apply more than 30 oz./acre per year or within 30 days of harvest.

Fontelis: Do not make more than 2 sequential applications or exceed 72 oz. per year.

Indar: Do not apply more than 24 oz. of 2F / acre per year or within 30 days of harvest.

Quilt: Do not apply more than 2 consecutive applications before alternating to a non-Group 11 containing fungicide.

Pristine: New Label indicates for use only when mixed with water. Do not apply more than 2 sequential applications.

Proline: Do not apply more than 2 applications per year. Do not apply within 7 days of harvest.

Fontelis (penthiopyrad) 16-24 oz.
Indar 2F (fenbuconazole) 6 oz. & 1% crop oil concentrate
Quilt Xcel (azoxystrobin & propiconazole) 14-21 oz.
Pristine (pyraclostrobin & boscalid) 18.5 oz.
Proline (prothioconazole) 5.7 oz.
Organic materials   
Procidic (citrus extract) 2 to 2.5 oz. / 10 gal. water Apply at bud break and repeat every 7 to 10 days, Spray solution must be pH 5, low salt concentration and un-chlorinated. Use higher rate during high humidity. Do not mix with salt based or high alkali reaction products. Also bactericidal and may be used post-harvest. 0 day PHI.
Regalia (extract of Reynoutria sachalinensis) 1-4 qt. Apply in 50 to 100 gallons of water per acre. Apply at bud break and repeat every 7 to 10 days. 0 day PHI.
Serenade Max (Bacillus subtilis) 1 to 3 lbs. For suppression, begin application at bud break and repeat every 7 to 10 days as needed.
Blossom and Twig Blight (Botrytis)  Captevate 68 WDG
(captan & fenhexamid)
3.5 – 4.7 lbs. Captevate: Apply at 10% bloom, repeat every 7-10 days through petal fall. Do not apply more than 2 consecutive applications or apply greater than 21 lbs. /acre per season.
Elevate 50 WDG
(fenhexamid)
1.5 lbs. Elevate: Begin application at 10% bloom, continue every 7-10 days, when conditions favor disease development. Do not make more than 2 consecutive applications or apply more than 6 lbs./ acre per season.
Switch 62.5 WG (cyprodinil & fludioxonil) 11 to 14 oz. Switch:Make application prior to disease development. Additional applications may be applied at 7 to 10 day intervals, if conditions are favorable for disease.

Do not make more than 2 consecutive applications or apply more than 56 oz./ acre per year.

Organic materials
Procidic (citrus extract) 2 to 2.5 oz. / 10 gal. water Repeat every 5 to 7 days as needed.
Serenade Max (Bacillus subtilis) 1-3 lb. Begin application prior to disease development and repeat on a 2 to 10 day interval or as needed.
Leaf-spot (Septoria)

Leaf Rust (hekipsora)

 

Equus DF (chlorothalonil) 2.7 to 3.6 lbs.

 

Equus: Do not apply more than 10.9 lbs. of DF or 12 pt. / acre per season of 720 SST.  Minimum interval is 10 days. Apply only in prune year for these diseases.

Bravo: Maximum of 12 pt./acre per year (or 9 lbs. active ingredient).  Minimum interval is 10 days. Apply only in prune year for these diseases.

Proline: Do not apply more than 2 applications per year. Do not apply within 7 days of harvest.

Equus 720 SST (chlorothalonil) 3 to 4 pt. in 20 to 100 gal. water / acre
Bravo Weather Stik (chlorothalonil) 3 to 4 pt. in 20 to 100 gal. water / acre
Proline (prothioconazole) 5.7 oz.
Valdensinia Leaf Spot (Valdensinia) Proline (prothioconazole)  5.7 oz. Eradication by hard burn of all leaf litter and infected plants is the preferred method of control of this disease. NOTE: Valdensinia control is not longer listed on the Pristine label. 

Proline: For suppression ONLY. Do not apply more than 2 applications per year. Do not apply within 7 days of harvest.

NOTE: Not all fungicides are equally effective. See the following trial result tables.

 

Table 1: Fungicide trial results for Monilinia disease conducted by the University of Maine 2010-2013

2010 Treatment
(heavy disease pressure)
Rate / acre Time Applied % Stems with Blight
Deblois      
Untreated     43
Bumper 6 oz. 4/13, 4/21, 4/26, 5/3 8
Procidic 20.5  oz. 4/13, 4/21, 4/26, 5/3 18
Regalia 64  oz. 4/13, 4/21, 4/26, 5/3 18
Regalia Max 16  oz. 4/13, 4/21, 4/26, 5/3 19
Serenade Max 8 lbs. (higher than
recommended rate)
4/13, 4/21, 4/26, 5/3 27
East Palermo
     
Untreated     75
Bumper 6 oz. 4/11, 4/20, 4/26 16
Procidic 20.5 oz. 4/11, 4/20, 4/26 55
Regali 64 oz. 4/11, 4/20, 4/26 61
Regalia Max 16 oz. 4/11, 4/20, 4/26 61
Serenade Max 8 lbs. (higher than
recommended rate)
4/11, 4/20, 4/26 55
2011 Treatment  Rate / acre Time Applied % Stems with Blight
Township-19      
Untreated     42
Fontelis 24 oz. 5/2, 5/13 19
Indar 2F (with 1% crop oil concentrate) 6 oz. 5/2, 5/13 19
Procidic 20.5 oz. 5/2, 5/13 33
Propimax EC 6 oz. 5/2, 5/13 13
Quilt Xcel 14 oz. 5/2, 5/13 19
Quilt Xcel 17.5 oz. 5/2, 5/13 12
Regalia 1 qt. 5/2, 5/13 43
Regalia 2 qt. 5/2, 5/13 36
Serenade Max (with NufilmP surfactant at 39.5 oz./acre) 3 lbs. 5/2, 5/13 41
Tilt 6 oz. 5/2, 5/13 27
2012 Treatment Rate / acre Time Applied % Stems with Blight
Deblois      
Untreated     23
Tilt 6 oz. 4/19, 5/3, 5/13 1
Fontelis (with 0.25% v/v Silwet 77 surfactant) 24 oz. 4/19, 5/3, 5/13 3
Indar 2F (with 1% crop oil concentrate) 6 oz. 4/19, 5/3, 5/13 0
Propimax 6 oz. 4/19, 5/3, 5/13 4
Quilt Xcel 14 oz.
17.5 oz.
4/19, 5/3, 5/13 5
4
2012 Treatment Rate / acre Time Applied % Stems with Blight
Township-19      
Untreated     16
Tilt 6 oz. 4/19, 5/3, 5/13 5
Fontelis (with 0.25% v/v Silwet 77 surfactant) 24 oz. 4/19, 5/3, 5/13 4
Indar (with 1% crop oil concentrate) 6 oz. 4/19, 5/3, 5/13 2
Propimax 6 oz. 4/19, 5/3, 5/13 2
Quilt Xcel 14 oz.
17.5 oz.
4/19, 5/3, 5/13 3
3
2013 Treatment
(very low disease pressure)
Rate / acre Time Applied % Stems with Blight
Township-19      
Untreated     8.8 
Tilt   6 oz.  5/7  1.6
Fontelis (with 0.25% v/v Silwet 77 surfactant)  16 oz.
24 oz.
5/7 2.2
0.9 
Proline (with 0.25% v/v Silwet 77 surfactant)  5 oz.
5.7 oz.
 5/7 1.9
1.0 
Quash 2.5 oz.    5/7  1.6
Deblois      
Untreated     2.8  
Tilt  6 oz.   5/7  4.2
Fontelis (with 0.25% v/v Silwet 77 surfactant)   16 oz.
24 oz.
  5/7  3.2
5.6
Proline (with 0.25% v/v Silwet 77 surfactant)   5 oz.
5.7 oz.
  5/7  1.9
3.8
Quash  2.5 oz.    5/7  0.9

 

Table 2: Fungicide Trial Results for Septoria Leaf-Spot Conducted by The University of Maine 2008-2010

2008 Treatment Rate / acre Time Applied % Leaf Drop
Columbia      
Untreated     10
Bravo 2 pts. 5/20 6
Pristine 18 oz. 5/20, 5/27 4
Serenade 3 lbs. 5/20, 5/27 11
Equus 720 SST 2 pts. 5/20 6
Equus DF 1.5 lbs. 5/20 8
Deblois      
Untreated     21
Bravo 2 pts. 5/19 16
Pristine 18 oz. 5/19, 5/27 13
Serenade 3 lbs. 5/19, 5/27 23
Equus 720 SST 2 pts. 5/19 17
Equus DF 1.5 lbs. 5/19 18
2009 Treatment Rate / acre Time Applied % Leaf Drop
Columbia      
Untreated     12
Pristine 18 oz. 5/20, 6/2, 6/11 10
Serenade 3 lbs. 5/20, 6/2, 6/11 14
Deblois      
Untreated     21
Pristine 18 oz. 5/20, 6/2, 6/11 7
Serenade 3 lbs. 5/20, 6/2, 6/11 10
2010 Treatment
(heavy disease pressure)
Rate/acre Time Applied %Leaf Drop
Columbia      
Untreated     39
Pristine WG 18.5 oz. 5/12, 5/21 33
Deblois      
Untreated     35
Pristine WG 18.5 oz. 5/12, 5/21 32

 Information in this publication is provided purely for educational purposes. No responsibility is assumed for any problems associated with the use of products or services mentioned. No endorsement of products or companies is intended, nor is criticism of unnamed products or companies implied.

© 2014

Published and distributed in furtherance of Cooperative Extension work, Acts of Congress of May 8 and June 30, 1914, by the University of Maine and the U.S. Department of Agriculture cooperating. Cooperative Extension and other agencies of the USDA provide equal opportunities in programs and employment. Call 800.287.0274 or TDD 800.287.8957 (in Maine), or 207.581.3188, for information on publications and program offerings from University of Maine Cooperative Extension, or visit extension.umaine.edu.

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Contact Information

Cooperative Extension: Maine Wild Blueberries
5741 Libby Hall
Orono, Maine 04469-5741
Phone: 207.581.3188, 800.287.0274 (in Maine) or 800.287.8957 (TDD)E-mail: extension@maine.edu
The University of Maine
Orono, Maine 04469
207.581.1110
A Member of the University of Maine System