eOrganic authors:
Carl Rosato, Woodleaf Farm
Helen Atthowe, Woodleaf Farm
Alex Stone, Oregon State University
This article is part of the Woodleaf Farm Organic Systems Description.
- Introduction
- Outcomes
- Disease Incidence and Fruit Quality
- Pesticide Use
- Key Practices
- Mineral Mix Foliar Sprays
- Disease-Specific Practices
- High Carbon Soil Amendments and Soil-building
- Soil Mineral Balancing
- Analysis: Integrating Practice and Research
- Brown Rot
- Peach Leaf Curl
- Apple Scab
- Fireblight
- References and Citations
Introduction
Woodleaf Farm has evolved a system of disease management strategies that work in concert with soil-building and habitat-building strategies to collectively reduce disease risk and the need for pesticide applications (Table 1). Practices include:
- In-field and in-row mixtures of resistant and susceptible varieties of peaches and apples (since late 1980s). (Table 2)
- Resistant pear varieties (Since late 1990s) (Table 2)
- High-carbon/low-nitrogen organic soil amendments to build soil organic matter and maintain balanced tree growth (since 1992).
- Soil mineral balancing (since late 1980s).
- Bloom- and post-bloom application of foliar mineral mix sprays (including 6–10 lb/A sulfur) (since mid-1990s).
- Good cultural practices:
- Pruning in both fall and spring (since late 1990s).
- Selective mowing of the understory to maximize air flow and reduce disease infection (since early 2000s).
- Microirrigation to keep fruit and foliage dry (since early 1990s).
- Squashing diseased fruit into the soil/living mulch during harvest to enhance rapid decomposition (since early 1990s).
- Removal of diseased residues from trees in the fall to reduce overwintering disease inoculum (since mid-1990s).
The Mediterranean climate of Woodleaf Farm also contributes to low disease risk. Annual precipitation is only 35 inches and occurs mainly in winter, fall, and early spring.
Outcomes
Disease Incidence and Fruit Quality
According to Carl Rosato, fruit yield and quality losses to disease have declined over the past 30 years, especially those resulting from peach brown rot and apple scab. Field monitoring and harvest evaluation records support this observation.
Pear fireblight, peach brown rot, and peach leaf curl remain management challenges. Fireblight and peach leaf curl do not appear to be suppressed by Woodleaf's farm design and soil/habitat-building practices. Brown rot may be suppressed, however, since it now occurs at a relatively low level.
- Brown rot: In the 1980s and early 1990s, brown rot caused up to 30% damage on peaches in some years. Damage was even higher during rainy years on very susceptible varieties such as O'Henry and Royal Glo (Fig. 1 and Fig. 2). However in 2013, damage averaged 2% across all peach varieties; in 2014, it averaged 1.3%; and in 2015, 2.6%.
- Peach leaf curl: Damage to foliage averaged 5% across all peach varieties in 2013, 6% in 2014, and less than 1% in 2015. Higher rates of lime sulfur were applied in 2015.
- Apple scab: Scab occurs at a very low level; damaged fruit averaged 4% in 2013, 3.5% in 2014, and 1.8% in 2015. Most damage is observed early in the season and removed at thinning.
- Fireblight: This disease occurred at low levels during the 1990s and early 2000s, but has been a greater problem in the past few years on susceptible pear and apple varieties as trees have aged (15-20 years old in 2015), especially in 2014 and 2015.
Pesticide Use
Spray records indicate that pesticide applications for disease management have decreased at Woodleaf Farm since 1992, with the exception of materials applied to control fireblight on pears. In the 1990s, wettable sulfur was sprayed at 15–20 lb/A during bloom (two or three applications) for control of peach brown rot, and copper was applied pre-bloom to manage peach leaf curl. Woodleaf stopped using copper-based materials in the mid-1990s. Currently, the only sprays are dormant lime sulfur applications for peach leaf curl. However, Carl also applies mineral mix bloom sprays (with 6-10 lb/A rates of sulfur) for overall tree health and for peach brown rot (Table 3). Though not originally intended to target specific diseases, mineral mix bloom/post-bloom sprays on pears and apples may be helping to manage fireblight and apple scab.
Key Practices
Mineral Mix Foliar Sprays
Carl designed a mineral foliar mix spray based on the results of an on-farm brown rot study conducted in the early 1990s, and on concerns about rising soil copper levels due to copper applications for management of peach leaf curl (Fig. 1 and Fig. 2). He tested many materials and application timings; the system continues to evolve based on trial and error.
The mineral mix was designed to improve tree growth, fruit set, and fruit health. Carl also believes that the mix coats disease-susceptible blossoms and thereby suppresses infection. The recipe generally contains kelp, rock dusts, minerals, and micronized sulfur (6–10 lb/A) (Table 3).
Application timing has been relatively consistent for peaches over the past 10 years, but is still evolving for pears and apples. Peaches are sprayed during bloom for protection from brown rot. Through 2003, pears and apples were sprayed during bloom. Since then, they have been sprayed from petal fall through first fruit set. In 2015, Carl decided to return to the bloom timing of pear and apple sprays to provide protection from fireblight.
The mineral mix program (recipe, rates, and number of applications) changes each year based on the crop and on weather during bloom (Table 4).
Disease-Specific Practices
Woodleaf addresses specific disease problems with targeted crop and disease life-cycle-specific practices (Table 4):
- Brown rot on peach: Mineral mix is applied regularly at bloom. When weather conditions increase disease risk, micronized sulfur rates in the mineral mix are increased (up to 15 lb/A in the past), but the highest sulfur rates in the past 3 years have been 10 lb/A (Table 3).
- Peach leaf curl: One or two applications of lime sulfur are made during the dormant season. Lower lime sulfur rates were tried from 2012 to 2014, but did not seem to be as effective as the full rate (25 gal/A) applied in 2015.
- Apple scab: Mineral mix is applied from petal fall through first fruit set.
- Fireblight on pears and apples: Woodleaf Farm is continuously evolving its fireblight management system. Through 2003, mineral mix sprays were applied one to three times at bloom. From 2004 to 2014, the mineral mix was sprayed one to three times after bloom (petal fall through first fruit set) because Carl was experimenting with new materials at bloom.
At bloom, from 2004 through 2013, Woodleaf also regularly applied Serenade® (Bacillus subtilis) to apples and pears. In 2014, Serenade® and Blossom Protect™ (Aureobasidium pullulans) were applied three times at bloom. In 2015, Carl abandoned Serenade® and Blossom Protect™ and applied only the mineral mix (once at bloom and twice during petal fall through fruit set). He has decided to change the timing of the mineral mix spray back to bloom based on past results and evidence that products containing rock dust show some efficacy on fireblight when sprayed at bloom. See analysis below.
Susceptible pear varieties were removed and replaced with resistant varieties in 2014 (Table 2).
High Carbon Soil Amendments and Soil-building
Carl has been using high carbon/low nitrogen soil amendments since 1992 and soil test records indicate a rise in soil organic matter and a decreasing trend in soil nitrate-nitrogen. Some level of biological control may be generated by the farm's soil amendments and soil-building practices since damage from brown rot and pesticide applications for this disease have decreased over time.
Soil Mineral Balancing
Carl has been practicing soil mineral balancing since the late 1980s. He has worked particularly to optimize cation balance based on his targets for soil calcium, by applying gypsum annually at 250 lb/A. Soil test records indicate that calcium has increased from an average of 1202 to 1524 ppm and now averages 67% of base saturation across all Woodleaf fields . Carl's target for percent calcium is 68%.
Analysis: Integrating Practice and Research
Brown Rot
The low level of brown rot at Woodleaf is likely due partly to the dry climate as well as to system design and management. Likely contributing factors are row-by-row and in-row cultivar mixtures, as well as excellent sanitation, pruning, microirrigation, and harvest practices. Some level of biological control may be generated by the farm's soil-building practices.
Two bloom applications of a pesticide to reduce blossom and twig infection by the brown rot pathogen is the recommended practice for California peach growers (Adaskaveg, 2010). Woodleaf uses only the foliar mineral mix. The mix typically contains lower rates of sulfur (6–10 lb/A) than those used by neighboring organic growers (15–20 lb/A). According to Carl, micronized sulfur is more effective against brown rot compared to wettable sulfur and may be another reason that he has been able to reduce sulfur application rates. However, recent studies comparing the efficacy of wettable and micronized sulfur do not support this observation (Holb and Schnabel, 2005).
Woodleaf relies on a variety of high-carbon/low-nitrogen soil amendments instead of nitrogen fertilizer. There is some evidence that peaches fertilized with lower levels of nitrogen have fewer brown rot symptoms (Daane, 1995). Despite a downward trend in Woodleaf soil nitrate-nitrogen levels over time, soil total nitrogen levels, peach leaf tissue total nitrogen and fruit tissue total nitrogen were all above normal levels when tested in 2014.
Woodleaf removes fruit remaining on trees in the fall as they become mummies. According to the University of California Statewide Integrated Pest Management (IPM) Program, this practice helps prevent reinfection of blossoms the following season (Adaskaveg, 2010).
Peach Leaf Curl
For organic growers, the University of California Statewide IPM Program recommends dormant sprays of Bordeaux mixture or copper for peach leaf curl (Adaskaveg, 2010). Woodleaf uses lime sulfur as a dormant spray. Peach leaf curl currently occurs at a fairly low level at Woodleaf, likely due to the dry climate and regular dormant spraying.
Apple Scab
There is evidence that sulfur is effective on apple scab when disease pressure is relatively low (Holb, 2001). For organic growers, the University of California Statewide IPM Program recommends treatments with lime and sulfur, sulfur alone, or with fixed copper products when temperature and precipitation are favorable to scab infection (Gubler, 2009). Woodleaf's organic apple-growing neighbors spray sulfur and lime sulfur regularly throughout the growing season.
Woodleaf relies on the mineral mix alone. The micronized sulfur in Woodleaf's mineral mix may help manage apple scab and powdery mildew (Podosphaera leucotricha), which is seen rarely on new growth in the spring. The low level of apple scab at Woodleaf likely is partly due to the dry climate, as well as to system design and management.
Fireblight
For organic growers, the University of California Statewide IPM Program recommends spraying copper at bloom when mean temperatures reach 62°F in March, 60°F in April, or 58°F in May. This model recommends treating every three to five days until the end of bloom (Gubler, 2009). There is some evidence that Blossom Protect™ bloom sprays are effective in managing fireblight (Kunz, 2012)
For Woodleaf, fireblight is consistently a challenge on pears and occasionally on more susceptible apple varieties (Table 2). Carl had unsatisfactory results from Blossom Protect™ bloom sprays in 2014, and now relies on the mineral mix spray alone. Carl feels that the mineral mix sprays resulted in lower levels of fireblight infection, but he never tested Blossom Protect™ and mineral mix sprayed together during bloom. Carl was worried that the mineral mix would kill the biological organisms present in Blossom Protect™. The mineral mix contains both rock dust and boron. There is some evidence that products containing rock dust may reduce fireblight when sprayed at bloom (Kunz, 2012). Boron has been shown to increase fruit set of pear (Thompson, 1950).
This article was developed with support from USDA's National Institute of Food and Agriculture through the Western Sustainable Agriculture Research and Education program under grant number SW13-017.
References and Citations
- Adaskaveg, J. E., R. A. Duncan, J. K. Hasey, and K. R. Day. 2010. University of California IPM pest management guidelines: Peach. University of California ANR Publication 3454. (Available online at: http://www.ipm.ucdavis.edu/PMG/r602100111.html#MANAGEMENT) (verified 23 Dec 2015)
- Gubler W. D. 2009. University of California IPM pest management guidelines: Apple. University of California ANR Publication 3432. (Available online at: http://www.ipm.ucdavis.edu/PMG/selectnewpest.apples.html) (verified 23 Dec 2015)
- Kent, M., K. M. Daane, R. S. Johnson, T. J. Michailides, C. H. Crisosto, J. W. Dlott, H. T. Ramirez, G. Yokota, and D. Morgan. 1995. Excess nitrogen raises nectarine susceptibility to disease and insects. California Agriculture 49: 13–18. doi: 10.3733/ca.v049n04p13. (Available online at: http://californiaagriculture.ucanr.org/landingpage.cfm?article=ca.v049n04p13&fulltext=yes) (verified 23 Dec 2015)
- Holb, I. J., and B. Heijne. 2001. Evaluating primary scab control in organic apple production. Gartenbauwissenschaft 66: 254–261. ISSN 0016–478X
- Holb, I. J., and Schnabel, G. 2005. Effect of fungicide treatments and sanitation practices on brown rot blossom blight incidence, phytotoxicity, and yield for organic sour cherry production. Plant Disease. 89:1164-1170. (Available online at: http://apsjournals.apsnet.org/doi/pdf/10.1094/PD-89-1164) (verified 23 Dec 2015)
- Kunz, S., A. Schmitt and P. Haug. 2012. Development of strategies for fireblight control in organic fruit growing. p. 71–78. In Integrated plant protection in fruit crops, subgroup "pome fruit diseases." IOBC-WPRS Bulletin, volume 84. (Available online at: http://www.bio-protect.de/fileadmin/bio-protect/Public/Content/Images/Content/PDFs/Feuerbrand/2012_Kunz__S_-_Development_strategies_fire_blight_organic_fruit_growing.pdf) (verified 16 Dec 2017)
- Thompson, A. H. and L. P. Batjer. 1950. The effect of boron in the germination medium on pollen germination and pollen tube growth of several deciduous tree fruits. Proceedings of the American Society for Horticultural Science 56:227-230.
This article is part of the Woodleaf Farm Organic Systems Description.
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