Pathologies

Chlorosis Issue -- Summer 2010

A few of the blueberry plants started developing yellowing of leaves that looked a lot like classic chlorosis.  In response I treated 10 affected plants with Espoma Soil Acidifier (sulfur to promote lowering the pH making iron more available) and Holly-tone (to provide any needed nutrients).

Above: Chlorosis in a Duke Blueberry Plant -- May 2010

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Defoliation Issue -- Late Summer/Fall 2010

Jersey 14G Blueberry Plant -- Defoliated.  Photograph taken 10/11/10

Invited a local horticultural consultant to analyze the situation.  Also whole plants were sent for analysis to two plant pathology laboratories -- first at Virginia Tech, Blacksburg, VA and then later to Michigan State University, Lansing, MI.  A soil sample taken from the root zone of two of the affected plants was sent to the Virginia Tech soil testing laboratory for analysis.

Subsequently, I received four responses:

Response #1.  Analysis by a local horticultural consultant (September 2010)

Found symptoms of root rot or Phytophthora or Phythium in the soil.  Drainage  is the main issue.  Secondary issue is iron deficiency; symptoms of defoliation and reddening of the leaves.

Response #2: VA Tech Plant Disease Clinic (Mary Ann Hansen)

Cultured from roots but no root pathogens were found; soil forwarded to Nematode Assay Lab to check for potentially damaging levels of plant parasitic nematodes. Found the fungus Botryospaeria sporulating on dying stems.  Botryospaeria is an opportunistic pathogen on stressed plants and unlikely to be the main problem �Predisposing stress factors could include drought, nutrient deficiency, improper pH, winter injury, soil compaction, etc.

Response #3.  Virginia Tech Soil Testing Laboratory

P (lb/A)	K (lb/A)	Ca (lb/A)	Mg (lb/A)	Zn (ppm)	Mn (ppm)
561	178	4646	533	14.7	19.9
VH	H	VH	VH	SUFF	SUFF
Cu (ppm)	Fe (ppm)	B (ppm)	pH	Est. CEC	Org Matter %
0.2	9.8	0.4	5.3	15.6	15.4
SUFF	SUFF	SUFF

Response #4: MSU Plant Disease Clinic (Jan Byrne & Dr. Schilder)

Found no indication of root rot.  Some twig blight/dieback due to Fusicoccum, a fungal pathogen.  We suspect compost amendments (horse manure-sawdust and sheep manure-hay) were rich enough to cause root damage; some nutrient levels in the soil analysis are very high or high �Images submitted are suggestive of a “burn” caused by high fertility or drought stress

I personally concur with response #4.  Actually about two months earlier, my wife had the same diagnosis based on her tuition and experiences.  So we are trying to modulate the soil conditions a bit with a few replacement plantings and allow time to mellow the richness of the compost amendments.

Pathology Issues Summer 2011

In the spring of 2011 I applied two treatments of Regalia, an organically approved fungicide produced by Marrone Bio Innovations, on the organic blueberries during the time they were in the bud and early flower stage.  For the conventional blueberries I applied two treatment s of Daconil, another fungicide (not approved for organic production).  I thought these applications might be prophylactic in preventing fungi stress on the blueberry bushes.

I again saw some selected examples of foliar discoloration (yellowing) and foliar and fruit dieback.  I again removed two entire bushes and sent them to Virginia Tech Plant Pathology Lab for diagnosis.  The one bush had an encircling root which they cited as the cause of the problem; their diagnosis was “girdling roots”; for the other samples their response was that no pathogens were found on the branches and leaf samples.  Their diagnosis for these samples were too “deep planting” and or a “cultural problem” that could not be diagnosed from the sample.

 

 

 

 

 

 

 

 

 

A July plant pathology example was discovered in which a portion of another Jersey bush in the Planters choice compost plot suddenly developed dead brown leaves with shriveled up fruit.  However the balance of the bush seemed healthy.  My “self-diagnosis” of this bush seemed to match the symptoms of Botryosphaeria stem blight.  See the photograph above which shows both the “brown” and “green” portions of this blueberry bush.  As with the other examples of stem blight that I have seen, I cut out and destroy the affected parts.  According to most things I have read, treatment of stem blights with fungicides are not very effective.  Rather the use of fungicides may be more preventive than curative in nature.

For the 2012 season, I intend to be more aggressive in the Organic plots with more Regalia treatments as well as to apply PlantShield, an organically approved biological foliar and root fungicide which uses Trichoderma harzianum as the active agent.  PlantShield is a product from BioWorks, Inc.  For the conventional (non-organic) plot I will probably use Daconil again.

 

 

 

Related resources

• Virginia Tech Plant Pathology Laboratory
  Plant Disease Clinic
  
• Virginia Tech Crop & Soil Environmental Sciences Testing Laboratory
  Soil Testing Lab
  
• Michigan State University Plant Pathology Laboratory
  Diagnostic Services
  
• Marrone Bio Innovations
  Develops and manufactures natural products for pest control for the horticultural industry.
  
• BioWorks
  Horticultural products, many are OMRI-listed