Disease - 219-Disease Control Guide for Wild Blueberries

Fact Sheet No. 219, UMaine Extension No. 2000

Prepared by Seanna Annis, Associate Professor of Mycology and David E. Yarborough, Extension Blueberry Specialist, The University of Maine, Orono, ME 04469. Revised March 2011.

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 2011. Use in subsequent years may lead to improper and illegal use of pesticides. When this guide is outdated, please request an updated version from you Extension office.  WARNING! Pesticides are potentially hazardous. Handle carefully! Read and follow all directions and precautions on 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 of all states. A sound application program including site-specific selection, adherence to label directions, sprayer calibration 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 (UMaine Extension No. 2015), Diseases 1, and No. 218 (UMaine Extension No. 2238), The Influences of Pruning Method on Disease and Insect Control.

All publications may be found on the web at http://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 (greater than 24 hours) 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 (UMaine Extension No. 2027), 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 greatly 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: Production – 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 got 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 ft of infected areas.

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

This leaf spot is often mistaken for Valdensinia leaf spot, but is wide spread in wild blueberries and causes defoliation of heavily infected leaves only 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, affected leaves will shrivel and dry up.  Few or no fruit develop on infected stems; some twigs may be killed. The disease over-winters 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 sometimes affects yield.  Some berries may also fall with severe infections and dry weather.  Leaf lesions are small water-soaked spots 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, 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 appear likely before harvest.

Stem Blight, Phomopsis or Godronia

Stem blights caused by Phomopsis or Godronia are common diseases found in blueberry and are more commonly associated with cultivated blueberries. However, in recent years a greater incidence of this disease has been seen in wild blueberries. The primary symptom is blighting of the first year growth stems.  This may occur sporadically. The infected stem tissue is reddish brown and killed leaves remain on the stems. The fungus over-winters in blueberry twigs infected 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.

Chemical Disease Control for Wild Blueberries
Disease	Material	Rate/a Product	Comments
Blossom and Twig Blight (Botrytis)	Captevate 68 WDG  (Captan & Fenhexamid)	3.5 – 4.7 lb.	Apply at pink bud. Repeat 7 to 10 days interval through petal fall.  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 lb/a/season.
	Elevate 50 WDG  (Fenhexamid)	1.5 lb.
	Switch 62.5 WG (Cyprodinil & Fludioxonil)	11 to 14 oz.	Make application prior to disease development. Additional applications may be applied at 7 to 14 day intervals, if conditions are favorable for disease. Switch: Do not apply more than 56 oz/a per year. Pristine: 0 day PHI Do not apply during bloom to prevent potential bee injury
	Pristine 38 WDG (Pyraclostrobin & Boscalid)	18.5 oz.
Mummyberry (Monilinia)  Primary Infection	Tilt (was Orbit) (Propiconazole)	6 oz.	Begin applications when greater than 40% of stems have blossoms at the crown stage.  Follow the mummy berry forecast method or calendar method to time applications.  Tilt/Bumper: Do not apply more than 30 oz/a/year or within 30 days of harvest. Indar: Do not apply more than 8 oz. WSP or 24 oz. 2F/a/year or within 30 days of harvest. Pristine: 0 day PHI. PHI Do not apply during bloom to prevent potential bee injury
	Bumper 41.8 EC  (Propiconazole)	6 oz.
	Indar 75 WSP  (Fenbuconazole)	2 oz. & 1% crop oil concentrate
	Indar 2F (Fenbuconazole)	6 oz. & 1% crop oil concentrate
	Pristine 38 WDG (Pyraclostrobin & Boscalid)	18.5 oz.
	Procidic  (citrus extract)	2 to 2.5 oz/10 gal water	Spray solution must be pH 5, low salt concentration, and not 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)	2 to 4 qts.	Apply at bud break and repeat every 7 to 10 days; can be tank mixed with registered fungicides. 0 day PHI.
	Serenade Max (Bacillus subtilis)	1 to 3 lb.	For suppression, begin application at the bud break stage of development and repeat on a 7 to 10 day interval or as needed.
Powdery Mildew (Microsphaera)	Captec 4L (Captan)	0.75-1 qt/100 gal water. Max 2.5 qts/a/application	Use only if substantial infection occurs prior to harvest.  Cabrio: 4 applications or 56 oz/a maxiumum per season 0 day PHI.
	Cabrio EG (Pyraclostrobin)	14 oz.
Leaf-spot (Septoria)	Bravo UltrexEquus DF (Chlorothalonil)	2.7 to 3.6 lb.	Apply before petal drop.
	Bravo Weather StikEquus 720 SST (Chlorothalonil)	3 to 4 pt. in 5 to 50 gal/acre water
	Cabrio EG (Pyraclostrobin)	(see rates above)	Cabrio: see comments above.
	Serenade Max (Bacillus subtilis)	(see rates above)	Begin application prior to disease development and repeat on a 7 to 10 day interval or as needed. Serenade Max may be applied to fruit up to and including the day of harvest.
NOTE: Not all fungicides are equally effective -  SEE TABLES.

Table 1: Fungicide trial results for Monilinia disease conducted by the University of Maine 2006-2010
2006 Treatment	Rate/a	Time Applied	Stems with Blight %
T-19
Untreated			25
Orbit	6 oz.	5/5, 5/15	14
Orbit (10 gal/a water)	6 oz.	5/5, 5/15	15
Indar	6 oz.	5/5, 5/15	11
Indar (with 1% COC)	6 oz.	5/5, 5/15	04
Pristine	18.5 oz.	5/5, 5/15	20
Serenade	3 lb.	5/5, 5/15	35
Serenade (with surfactant)	3 lb.	5/5, 5/15	25
Deblois
Untreated			16
Orbit	6 oz.	5/5, 5/15	03
Orbit (10 gal/a water)	6 oz.	5/5, 5/15	06
Indar	6 oz.	5/5, 5/15	12
Indar (with 1% COC)	6 oz.	5/5, 5/15	03
Pristine	18.5 oz.	5/5, 5/15	05
Serenade	3 lb.	5/5, 5/15	08
Serenade (with surfactant)	3 lb.	5/5, 5/15	19
2007 Treatment – heavy disease pressure	Rate/a	Time Applied	Stems with Blight %
T-19
Untreated			22
Orbit	6 oz.	5/8, 5/17	06
Indar (with 1% COC)	6 oz.	5/8, 5/17	01
Serenade	3 lb.	5/8, 5/17	13
Deblois
Untreated			36
Orbit	6 oz.	5/8, 5/17	15
Indar (with 1% COC)	6 oz.	5/8, 5/17	04
Serenade	3 lb.	5/8, 5/17	24
2010 Treatment – heavy disease pressure	Rate/a	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 lb. *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
Regalia	64 oz.	4/11, 4/20, 4/26	61
Regalia Max	16 oz.	4/11, 4/20,4/26	61
Serenade Max	8 lb. *higher than recommended rate	4/11, 4/20, 4/26	55

Table 2: Fungicide Trial Results for Septoria Leaf-Spot Conducted by The University of Maine 2008-2010
2008 Treatment	Rate/a	Time Applied	Leaf Drop %
Columbia
Untreated			10
Bravo	2 pt	5/20	6
Pristine	18 oz	5/20, 5/27	4
Serenade	3 lb	5/20, 5/27	11
Equus 720 SST	2 pt	5/20	6
Equus DF	1.5 lb	5/20	8
Deblois
Untreated			21
Bravo	2 pt	5/19	16
Pristine	18 oz	5/19, 5/27	13
Serenade	3 lb	5/19, 5/27	23
Equus 720 SST	2 pt	5/19	17
Equus DF	1.5lb	5/19	18
2009 Treatment	Rate/a	Time Applied	Leaf Drop %
Columbia
Untreated			12
Pristine	18 oz.	5/20, 6/2, 6/11	10
Serenade	3 lb.	5/20, 6/2, 6/11	14
Deblois
Untreated			21
Pristine	18 oz.	5/20, 6/2, 6/11	7
Serenade	3 lb.	5/20, 6/2, 6/11	10
2010 Treatment – heavy disease pressure	Rate/a	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

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