Developing pest management guidelines for organic production of highbush blueberries in the North Central Region

Final Report for LNC07-281

Project Type: Research and Education
Funds awarded in 2007: $149,991.00
Projected End Date: 12/31/2010
Region: North Central
State: Michigan
Project Coordinator:
Dr. Annemiek Schilder
Michigan State University
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Project Information

Summary:

The overall goal of this project is to facilitate organic blueberry production in the region by evaluating organic nutrient and soil health management, weed control, and disease and insect management practices. Organic management improves soil health and nutrient cycling in blueberry soils, but low soil pH may be limiting to beneficial microbes. Organic herbicides were mostly ineffective and mulches reduced the need for hand-weeding. Care must be taken to supply sufficient N when wood chips are use. Compost is a good source of nitrogen at the time the plant needs it but may raise soil pH. Insect and diseases can be managed with available organic products, but sprays may need to be applied more frequently.

Introduction:

High consumer demand for organically produced fruit, perceptions of increased marketability and value of organic blueberries, and concerns over the safety of conventional inputs have motivated Michigan highbush blueberry growers to consider organic production practices. Michigan growing conditions are perceived to be favorable for organic production as highbush blueberries are a native plant. Spodosols, acid sands, and mucks are present in several regions within the state and there are several major metropolitan areas in the region to provide a marketplace for organically produced berries (Chicago, Grand Rapids, Detroit, Lansing). However, despite Michigan being the number one blueberry production region, only 60 of Michigan’s over 19,500 acres (less than 0.3%) of blueberries were certified organic at the start of this project). Potential reasons for the low percentage of certified organic blueberry acreage in Michigan include a lack of knowledge and resources regarding organic production methods; challenges related to organic management of weeds, pests and nutrients; and lack of an established organic marketplace for wholesale organic blueberries.

Project Objectives:
  1. Evaluate and optimize organically acceptable cultural, chemical, and biological options for control of pests (insects, diseases, and weeds)

    Evaluate different cover crops in row middles for their effects on soil and plant nutrient status and pest pressure

    Evaluate organic fertilizer programs for their effects on soil and plant nutrient status and pest pressure

    Develop a guidebook on pest management in organic blueberries for the North Central Region.

Cooperators

Click linked name(s) to expand
  • Dr. Stuart Grandy
  • Dr. Matthew Grieshop
  • Dr. Eric Hanson
  • Dr. Rufus Isaacs
  • Dr. Hao Jianjun
  • Dale Mutch

Research

Materials and methods:
Cover Crops and Nutrition Experiment

An organic blueberry planting (cvs. Bluecrop and Elliott) located at the Michigan State University campus Horticulture Farm was established in 2007 and was organically certified in the fall of 2010. The specific research objectives for the planting were to monitor: (1) nutrient management practices and different cover crop plantings on soil and plant nutrition, (2) surface mulches for weed control, (3) disease and insect pest prevalence, and (4) soil biological characteristics. The organic cover crops and nutrient management experiment was initiated in 2008 in the ‘Bluecrop’ section to compare three cover crops (cereal rye, crimson clover, and alsike clover) and three fertility treatments: conventional fertilizers (ammonium sulfate and potassium sulfate); compost (dairy based, Morgan Composting, Evert, MI); and pelleted organic fertilizer (8-1-1, McGeary’s Organics, Lancaster, PA, USA). The experimental design was a split plot with main plots consisting of different cover crops and split plots consisting of nutrition treatments. Main plots were replicated four times in a randomized complete block design. Cover crop plots consisted of 16 bushes each, and nutrition split plots contain 5 bushes each. Rates of each material were adjusted to supply comparable amounts of available N as the conventional recommendations (20 lb N/acre for each year in the field, by assuming a 50% mineralization rate for the organic fertilizer and a 25% rate for the compost. The conventional and organic fertilizers were split into two applications (bud break, late bloom)whereas all compost was applied at budbreak. Row middles were maintained in fall-seeded annual rye, and the plots were weeded by hand and trickle irrigated as needed. Plant nutrient status was determined by leaf tissue analysis for N (Kjeldahl) and other nutrients (emission spectroscopy). Soil N (ammonium, nitrate) dynamics were monitored by soil sampling on five dates each year, between April and October. Each sample consisted of a composite of ten 20-cm-deep cores collected with a 2-cm-diameter soil probe. Soils were dried, homogenized, extracted with 1 M KCl, and analyzed for nitrate and ammonium by colorimetric methods. Soil quality parameters were assessed by collecting a composite soil sample from each plot in September of 2009. Data analysis was performed using Analysis of Variance and mean separation.

Using mulches for weed control

The mulch study at the MSU organic planting was initiated in 2008 to compare nine surface mulch materials spread beneath ‘Elliott’ bushes: – (1) hand weeded control, (2) perforated plastic, (3) woven black plastic weed ground cover, (4) chipped local landscape brush (2–4 inches deep), (5) fresh pine wood chips (2 inches deep), (6) pine bark nuggets (4 inches deep), (7) wheat straw (6 inches deep), (8) aged grass hay (6 inches deep), and (9) burlap coffee sacks from a local roaster, laid flat. The design was a randomized complete block with 5-bush plots and four replications. Mulches were put in place after planting in May 2008. Plots received surface applications of pelleted 8-1-1 fertilizer (McGeary’s Organics) each May at recommended rates. Additional materials were applied as needed to suppress weeds as well as weeded by hand. Total time spent weeding was recorded and a cost of $10 per hour assessed.

Comparison of Organic and Conventional Blueberry Farms

We matched eight pairs of organic and conventionally managed fields by NRCS soil series, and plant age and cultivar where possible. The fields ranged from 10 to 65 years old and received annual inputs of organic or inorganic N fertilizers. All organic fields were managed with conventional practices prior to receiving organic certification. Roots and soil were collected at 0- to 30-cm depth below the canopy of eight bushes per site on July 6-7, August 21-22, and October 9-10, 2009. Hair roots were excised from root pieces of 5 to 20 cm in length, cleared and stained and inspected microscopically for evidence of root cell colonization by ericoid mycorrhizae (ERM) and dark septate endophytes (DSE). Mycorrhizae can be important for blueberry plants by breaking down organic forms of N which would otherwise not be available to the plant. In addition, they can increase root surface area for uptake of nitrate, ammonium and other mineral nutrients. The role of DSE is less clear but they are common in blueberry root cells. Fifty contiguous epidermal cells of 25 hair root segments per bush from four randomly selected bushes (eight bushes in July) were examined per field site. Hair root diameter was measured on the midpoint of root segments and was only assessed on samples collected in October 2009. Soil was passed through a 2-mm sieve and dried at 70.C within 3 days of collection. Ammonium and nitrate were extracted from dried soil in a 5:1 ratio (wt/wt) of 1 M KCl to soil and measured according to established protocols. Soil pH was measured with an electrode in a 1:1 mixture of soil and deionized water and soil carbon (C) and N were determined with an elemental analyzer (Costech ECS, Costech Analytical Technologies, Inc., Valencia, CA, USA). Information on the field history and cultural practices such as fertilizer type and rate and fungicide applications was provided by the owners of the blueberry fields. A repeated measures ANOVA of the effects of management practices, soil type (sand and muck), and sampling date was conducted using the LSMEANS option in SAS PROC GLIMMIX (SAS Institute, Cary, NC, USA) with field pairs specified as a random factor. The relationships between ERM and DSE and field variables across field sites was determined in SAS PROC CORR using the mean value of three sampling dates at each site. Correlations between measured variables were analyzed for all sampled sites (n = 16), and for sandy soils only (n = 12). Mucks were excluded in the latter case due to extreme values in soil C, soil N, and inorganic N. Ripe fruit samples were also collected in 2008 and incubated at 100% RH to determine fruit rot incidence in organic and conventional fields. The percentage anthracnose fruit rot (Colletotrichum acutatum), Alternaria fruit rot (Alternaria tenuissima) and marketable (sound) fruit were visually estimated after 7-10 days’ incubation.

Disease Management

Ten disease control efficacy trials were conducted between 2008 and 2010 in mature commercial blueberry plantings of disease-susceptible cultivars. Due to the inclusion of a conventional standard program and the need for sufficient disease pressure, trials were conducted in unsprayed conventional fields. Treatments were applied to 4-bush plots and were replicated four times in a randomized complete block design. In 2008 and 2009, sprays were applied using an R&D Research CO2 cart-styled sprayer equipped with six 0.8 gallon bottles, a twin gauge Norgren pressure regulator set at 55 psi, and a single SR TeeJet 8002VS nozzle on a 5-ft spray boom. In 2010, sprays were applied using a Farmco research skid-mounted sprayer equipped with six 5-gal tanks, a 12-volt 3.8-gpm diaphragm pump set at 55 psi, and an XR TeeJet 8002VS nozzle on a 5-ft spray boom. In all cases, disease evaluations were conducted on the two center bushes of each plot. Two harvests, spaced 10 to 14 days apart, were conducted. For evaluation of mummy berry (Monilinia vaccinii-corymbosi), the total number of shootstrikes per bush and total mummified fruit (on ground) were counted at peak disease levels. Phomopsis (Phomopsis vaccinii) infection was assessed as the number of blighted twigs or shoots per bush. For evaluation of anthracnose fruit rot (Colletotrichum acutatum), Botrytis fruit rot (Botrytis cinerea), Alternaria (Alternaria tenuissima), and Phomopsis fruit rot (Phomosis vaccinii), fifty ripe berries per subplot were removed at harvest and placed equidistantly on metal screens in aluminum trays covered with plastic wrap. Trays were incubated at room temperature and 100% relative humidity for ten to twelve days after which the berries were rated for fruit rots. Not all diseases were found at all trial sites. The following OMRI-listed and experimental products were tested for efficacy against disease in one or more years of the study: 1) Actinovate (Streptomyces lydicus); 2) B29 and 3) B109 and 4) Bacteria1A (experimental bacteria isolated from blueberry fruit); 5) Basic Copper (copper sulfate); 6) Blightban (Pseudomonas fluorescens A506); 7) BW240 (Trichoderma virens and T. harzianum); 8) Fungastop PC (citric acid and mint oil); 9) Gantec Gold (plant extract containing terpenoids and limonoids); 10) Lime Sulfur (calcium polysulfide); 11) MilStop (potassium bicarbonate); 12) Nordox (Cuprous oxide); 13) Nu-Film-P (poly-1-p-menthene spreader-sticker); 14) Organic Gemfish (fish fertilizer); 15) Oxidate (hydrogen dioxide); 16) Plantshield/Rootshield (Trichoderma hazianum Rifai strain KRL-AG2), 17) Polyversum (Pythium oligandrum), 18) Regalia (extract of Reynoutria sachalinensis, tested); 19) Serenade Max (Bacillus subtilis strain QST 713), 20) Sonata (Bacillus pumilus), 21) SPI Compost Tea (derived from compost extract, worm casting extract, plant and mineral extracts), 22) Sporan (rosemary, clove, and thyme oils), 23) Tetrasul (calcium polysulfide). Conventional products used for comparison were: Abound, (azoxystrobin); Pristine (pyraclostrobin and boscalid); Indar (fenbuconazole); Phostrol (mono- and dibasic sodium, potassium and ammonium phosphites); and Captec 4L (captan).

Insect Management

An efficacy trial was conducted in a mature ‘Jersey’ blueberry planting at the Trevor Nichols Research Complex in Fennville, Michigan to evaluate OMRI-listed insecticides against Japanese beetle, a serious pest of blueberries in the northcentral region. Sprays were applied to foliage of three-bush plots on September 24, 2009 using a CO2-powered backpack sprayer operating at 50 psi in a volume of water equivalent to 80 gallons of water per acre. Treatments included four replicates each of Aza-Direct (azadirachtin) at 16 oz per acre, Aza-Direct at 32 oz per acre, Pyganic 1.4EC (pyrethrins) at 32 oz per acre, Pyganic 1.4EC at 64 oz per acre, Surround WP (kaolin clay) at 25 lbs per acre, and an untreated control. Two mature shoots on the center bush of each plot were loosely bagged with a gallon ziplock one day after treatment (DAT) to eliminate chemical wash-off as a variable in this experiment. Bagged shoots (thinned down to 10 leaves per shoot) were taken off bushes at 1 day after treatment and 4 days after treatment and placed in a water pick (Aquapic® brand, #49-47, 41/2 length) that was inserted into a hole cut into the bottom of a 32 oz deli cup. One female Japanese beetle (collected from the field 2 weeks earlier and fed on a diet of sassafras leaves and apple slices until use in the experiments) was added to each cup and allowed to feed for 48 hr. At the 48-hr point, beetle health was assessed on a scale of 1 to 4 with 1 being dead, 2 being twitching and dead, 3 being twitching and alive, and 4 being alive. Those recorded as being twitching and alive were showing some signs of sublethal chemical poisoning (legs dragging, slow movements, etc.) but were still able to move around. Those recorded as twitching and dead were clearly close to death (on their backs on the bottom of the cup, legs curling up, etc.), but were still technically alive. After the initial beetle health assessment, the foliage was assessed for feeding damage beginning with trace feeding and increasing in 5% increments. Assessments were conducted by two observers with the average of these two assessments being used in data analyses. Percentage damage data were arcsine square root (p1/2) transformed before being subjected to ANOVA followed by Fisher’s Least Significant Difference test for post-hoc comparison of means (Statview, v. 5.0.1, Cary, NC, USA). Japanese beetle health assessment data were analyzed using ANOVA followed by Fisher’s Least Significant Difference test for post hoc comparisons.

Organic Herbicide Evaluation

Efficacy trials were conducted with the following OMRI-approved herbicides: Nature’s Avenger (d-limonene 70%), Weed Zap (clove and cinnamon oil 90%), Matratec AG (clove oil 50% and others [wintergreen oil, butyl lactate, lecithin] 50%), Distilled White Vinegar Concentrate (Acetic acid 5%), Blackberry & Brush Block (citric acid 20%), and Worry Free Weed and Grass Killer Concentrate (d-limonene 70%). Products were compared to a non-approved herbicide, Scythe (pelargonic acid 57%, related fatty acids 3%). Treatments were applied at various concentrations in two trials in 2008. In Trial 1, the field was composed on young annual weeds, 2-3 cm high, primarily portulaca, pigsweed, and lambsquarters.

Clover seed germination in blueberry soils

In 2008, soil was collected from 16 blueberry fields (organic as well as conventional) and screened to break up the clods and get the rocks out. A 5-cm (2-inch) layer of soil was placed in 1 x 2-foot plastic trays with a divider. The trays had rather large drain holes in them, so a layer of paper towels was placed in the bottom to keep the soil in. Then 20 seeds (2 rows of 10 seeds) of six different types of clover (Alsike, Dixie Crimson, Crimson clover, Mammoth Red, Medium Red, and White Dutch) were planted in one half of three trays (3 replications). The seeds were covered with a little soil and kept moist. The trays were placed on a trailer so they could be moved inside the barn if the weather got bad. They were planted on September 2, 2008 and counts were taken on September 14th, 2008. Clover seedlings were observed for growth over a period of five weeks.

Effects of Fertilizers and Mulches on Soil Microbes

In the organic blueberry nutrition and mulch trial on the MSU Horticulture Farm, soil samples were collected on October 30, 2008 and on October 29, 2009. Eight soil cores were collected at 0–10 cm (0–4 in.) depth and 2.5 cm (1 in.) diameter, 20–30 cm apart within each plot. Soil was placed in plastic bags, transported in chilled coolers, and stored at 4°C for up to 10 days. Soil dilutions were prepared by adding 10 g field-moist soil to 90 mL phosphate-buffered saline and shaking for 30 min. Various differential and selective media were used to enumerate total cultivable fungi and bacteria as well as known beneficial fungi (Trichoderma spp.) and bacteria (Bacillus spp., Streptomyces spp., and fluorescent Pseudomonads). Plates were incubated in the dark at 22°C. Colony numbers were assessed after 3 days for bacteria and after 7–10 days for fungi. The prevalence of plant parasitic and free-living nematodes in soil samples was assessed in the nutrition trial in 2008 and 2009 by MSU Plant Diagnostic Services. The effects of cover crops, fertilizers, and interactions were analyzed as a split-plot design in the GLIMMIX procedure in SAS. Soil pH was determined in a 1:1 (m/v) deionized water:soil mixture and was included as a covariate to account for random field variability.

Effect of Fertilizers and Mulches on Disease and Insect Susceptibility

Plants were evaluated for diseases in the organic blueberry planting to determine whether soil-applied nutrition and mulch treatments affected disease susceptibility. The incidence and severity of foliar leaf spots, leaf rust and twig dieback were visually assessed in the fall of 2009 and 2010. Due to a lack of fruit in the first years of the planting, fruit rot incidence was not evaluated until 2011 (technically outside the duration of this grant). In July 2011, 50 ripe fruit were harvested from plots in the nutrition trial and incubated at 100% RH to assess fruit rot incidence; specific fruit rot pathogens were identified based on morphology. Data were analyzed by ANOVA and mean separation. In addition, during fall 2009, plants in the nutrition trial were also assessed for insect infestation. The main sources of infestation observed were the blueberry leafminer, Caloptilia porphyretica, and feeding from Japanese beetle, Popillia japonica. To assess their abundance in the different plots, three bushes per sub-plot were sampled, and the number of leaves infested with leafminer or damaged by Japanese beetle were counted. The number per sub-plot was averaged across the three bushes, and these counts were compared among cover crops and fertilization regimes using a two-way ANOVA.

Research results and discussion:
Cover Crops and Nutrition Experiment

Neither the crimson nor alsike clover established evenly across the experiment, which prevented us from analyzing cover crop effects, and in the fall of 2009 all rows were seeded to cereal rye. Cover crop failure resulted mostly from lack of moisture in the row middles, since irrigation was supplied with trickle only under the blueberry bushes. This emphasizes the need for irrigation to facilitate cover crop establishment, particularly on light soils. Once rye started to bloom, a roller crimper was used to flatten the rye which allowed more light to reach the small blueberry plants and also provided a fair amount of weed control in the row middles. Nitrate and ammonium levels in the organic blueberry planting varied considerably among the three nutrient management regimes. Compost maintained higher soil inorganic N levels than organic or conventional fertilizers early in the season, but all levels were similar after July. In 2008, plots receiving compost had approximately 8 ppm soil inorganic nitrogen content during May and early June, while the two fertilizer treatments averaged approximately 3 ppm during this same time frame all three treatments fell to approximately 1 ppm in late June. The low levels of nitrate and ammonium found in the two fertilizer regimes prompted us to double our fertilizer rates in 2009. Soil inorganic nitrogen content among nutrient treatments was somewhat more comparable in 2009 with approximately 10 ppm found in the compost treatment between April and early June and 6 ppm found in the other two treatments. Leaf nutrient analysis performed in 2009 showed a similar pattern with only the compost-amended plants showing a sufficient level of nitrogen. Thus, compost appears to provide the best levels of available nitrogen but may also raise soil pH, thereby necessitating additional sulfur applications.

Using mulches for weed control

All mulches reduced hand-weeding costs compared to plots without mulch. Hours spent weeding per acre were estimated at 118 hours for the “no mulch” treatments with only 23 and 28 hours for the wheat straw and spoiled grass hay mulches. Fresh woodchips, bark chips, and burlap sacks performed similarly with 42, 45, and 46 hours spent weeding, respectively. Fifty-three and 74 hours/acre were spent weeding on white and black weed barriers, respectively. Bark nugget mulch plots were weeded for 61 hours/acre. The lower level of reduction in weeding time observed for the plastic mulches compared to the other mulches was somewhat surprising but this was likely due to a high level of weed root infiltration under the mulch. Other studies have shown that plastic mulches utilizing a machine that “tucks” the edges of mulches 2-3 inches into the soil can reduce this problem. The relative success of the hay-based mulches is encouraging as hay is widely available and reasonably priced. However, they may need to be reapplied more often, similar to pine straw mulch. A study completed in Georgia on rabbiteye blueberries indicated that pine straw mulches may need to be reapplied every 1 to 2 years, which would lessen the realized economic benefits. Several organic as well as conventional growers in Southwest Michigan established new plantings with black woven weed barrier, using wood chips around the planting hole. The longevity of the weed barrier may make it economical although care must be taken not to pull up blueberry roots when hand-pulling grasses and other weeds that spring up around the base of young plants. In some cases, young plants were partially pulled out of the soil and damaged. One feature that facilitates weedcontrol is a fairly flat application of the weed cloth (i.e., don’t use tall raised beds) such that a mower can easily move along the edges of the weed barrier.

Comparison of Organic and Conventional Farms

Organic and conventional blueberry soils do not differ significantly in labile C content but conventional management accelerates decomposition of labile C and tends to enrich slower cycling soil C pools. Although management did not affect the activity of individual soil enzymes, transition to organic management shifted N:P enzyme allocation towards acquisition of N and increased the rate potential N mineralization by two-fold. Microbial communities in organic and conventional fields tend to diverge with as biological activity increases. Patterns of specific C, N, and P enzyme activities between management types suggest alteration in soil organic matter quality and resource availability occurs following the transition to organic management.Ericoid mycorrhizal colonization is generally higher in organic fields, inversely related to field age and total soil N, and positively associated with soil pH and mean hair root diameter in commercial blueberry fields in Michigan. The causative factors underlying these relationships are not completely understood and need further study. These findings suggest that organic management results in more microbial activity, a measure of soil health, in blueberry soils. However, a higher incidence of anthracnose fruit rot in organically grown blueberries indicates that effective organic strategies for management of fruit rot diseases are needed in organic blueberry production in Michigan.

Disease Management

Disease control options are more limited for organic than conventional blueberry growers. The efficacy of various OMRI-approved and experimental fungicides was evaluated in small plot trials in commercial blueberry fields in Michigan in 2008 and 2009. Nu-Film-P (an adjuvant) was added to all products. All treatments reduced mummy berry shoot strikes significantly compared to the untreated control. In 2008, Serenade Max (Bacillus subtilis) reduced mummy berry shoot strikes by 95%, and Polyversum (Pythium oligandrum) and Actinovate (Streptomyces lydicus) reduced shoot strikes by 45% and 60%, respectively. The number of mummified berries was also significantly reduced, but less effectively than shoot strikes. Phomopsis fruit infection was reduced by 82, 55, and 86% by Serenade, Polyversum, and Actinovate, respectively. In 2009, Serenade and Regalia (giant knotweed extract) provided 78 and 76% control of mummy berry shoot strikes, and 84 and 89% of mummified fruit, respectively. While a standard conventional fungicide program (Indar/Captec/Pristine) provided the best numerical control, Serenade and Regalia performance was not statistically different. However, for anthracnose fruit rot, these products provided only moderate control and in past trials. These results indicate that organic growers have good options for control of mummy berry. However, more trials are needed to find effective fungicides for control of anthracnose fruit rot and Phomopsis twig blight and canker in organic blueberries.

Insect Management

While there were visual differences in feeding damage by Japanese beetle among the treatments at 1 day after treatment, these differences were not significant due to high variability in the untreated controls. At 4 days after treatment, there were significant differences among the treatments with both Aza-Direct treatments and the Pyganic 64 oz treatment showing significantly lower feeding damage on leaves than the untreated controls (P = 0.025). There were no significant differences in Japanese beetle health at 1 day after treatment, but after 4 days, there were significant differences (P < 0.01). Beetles in the Pyganic 32 oz treatment had an average health rating of 1.75, which was significantly lower than the Aza-Direct 16 oz, Pyganic 64 oz, Surround, and untreated treatments (all having health ratings of 4.0). Beetles in the Aza-Direct 32 oz treatment had an average health rating of 3.0, a value that was not significantly different from any other treatments, despite the effect on feeding damage. This is highly suggestive of an antifeedant effect from this insecticide, which may have been better observed in situations without beetle enclosure on treated shoots. Results from this trial support the grower use of Pyganic to “knock down” Japanese beetles just prior to harvest. Furthermore, Pyganic appears to kill beetles when applied at the higher rate as evidenced by a beetle health score of under 2, indicating a high level of beetle mortality. Numerically reduced feeding by Aza-Direct and Surround is also encouraging although residues from these two products have been known to temporarily remove the wax bloom after treatment (Aza-Direct) or leave white residues (Surround), making them less acceptable for growers, particularly in the fresh berry market

Organic herbicide evaluation

Efficacy trials with six OMRI–approved herbicides and Scythe (not approved showed that the only herbicide providing effective burndown of weeds was non-approved Scythe. Nature’s Avenger was partly effective, and the other materials were non-effective. This suggests that growers cannot rely on burn-down herbicides for effective weed control and must use other means, such as mulch, hand-weeding and/or mowing. Within-row cultivation is not very suitable for blueberries due to the shallow rooting of the bushes.

Clover seed germination in blueberry soils

Seed of all clover types germinated well in the acidic blueberry soils, although there was some variation between soils and clover types that did not seem to be related to the type of management. A few soils from conventional farms had white seedlings that grew poorly and showed evidence of herbicide damage. However, despite their smaller size, they had similar germination rates as healthy seedlings and kept growing, even after 5 weeks. While germination rates did not differ greatly between clover varieties, Dixie Crimson and White Dutch had the highest germination rates overall.

Effects of Mulches and Fertilizers on Soil Microbes

Nutritional amendments and mulches had a significant effect on soil microbial populations. Compost application generally resulted in higher populations of Streptomycetes. The protein meal fertilizer treatment had higher fungal populations than the synthetic fertilizer treatment by the second year of the study. Organic mulches increased populations of total and beneficial bacteria and Trichoderma spp. fungi but did not affect total fungal populations. The cereal rye cover crop enhanced bacterial populations compared to alsike clover in the first but not second year of the study. Significant positive correlations in population sizes were observed among many of the microbial groups assessed. However, fluorescent pseudomonads and Streptomycetes were negatively correlated in the cover crop and fertilizer trial but not in the mulch trial. Organic mulches increased populations of total and beneficial bacteria and Trichoderma spp. fungi but did not affect total fungal populations. Populations of cultivable microbes were often positively correlated with soil pH, and appeared to be limited at the lower range of soil pH tolerated by blueberries. This finding suggests use of cultivable microorganism populations as a criterion of soil health may be at odds with nutritional requirements of blueberries where sulfur is continuously applied to maintain an acidic soil pH.

Effects of Mulches and Fertilizers on Disease and Insect Incidence

Foliar feeding insects were not observed at a significantly higher frequency in any of the three nutrient management treatments. Blueberry leafminer and Japanese beetle abundance was variable across the planting, with some bushes having low infestation, whereas others had high levels, especially of the leafminer. Despite this, there was no significant difference among any of the treatments. Leafminer infestation was numerically higher in the compost blend treatment than the other treatments but there was no significant difference among these three treatments (P = 0.09). Low levels of infestation by Japanese beetles were observed at this planting, with an average of 2–3 injured leaves per bush, and observations of higher leaf feeding at the edges of the planting. There was no significant difference among cover crops or among fertilization treatments in the level of Japanese beetle feeding injury (P = 0.82). The numerically higher number of leafminers detected on blueberries fertilized with compost blend suggests that the leafminers may do better on plants with higher leaf nitrogen levels. The lack of observable differences in Japanese beetle feeding was not overly surprising given the small size of the experimental plots and that insect’s extremely mobile nature.

Research conclusions:

Michigan and Great Lakes Region organic blueberry production may be at a major juncture in its development.The acreage, though still small, has doubled in the last three years and has the potential to increase much more. At present, it appears that most growers are focusing on local markets and on-farm sales as evidenced by the relatively small size of organic plantings. However, if the organic marketplace continues to grow at its current pace, it is likely that Michigan growers will seek to penetrate the wholesale organic marketplace. However, growers will likely need better described and economically vetted organic production practices before a noticeable expansion of wholesale marketing is likely. Nutrient and weed management are two important challenges for North Central region organic blueberry growers with insect and disease management close behind. Organic nutrient management research is underway across all major United States blueberry growing regions and will continue for the foreseeable future. The development of a better understanding of how to best manipulate nutrient inputs so that high levels of ammonium and micronutrients are available during the early spring and summer but less available in the fall continues to be an important challenge for organic blueberry production. It is likely that nutrient management practices will likely vary widely for specific Michigan and Great Lakes region organic blueberry plantings depending on whether they are on native blueberry soils (acid muck or peat bog) or on acidified sands or loams. All of the mulches tested at the MSU organic blueberry planting reduced the need for hand weeding but none of them completely eliminated it. Thus, organic weed management will likely be best accomplished by combining mulch with hand weeding and/or mowing. Growers also indicate a need for improved insect and pathogen management. At present, our focus has been the development of pest management tactics that replace conventional approaches. Our work with available OMRI-approved insecticides and fungicides indicate that these compounds can approach the efficacy of their conventional counterparts. However, effective use of these compounds requires careful timing and application, and reapplication due to the much shorter residual control they provide. Furthermore, while this approach has yielded early success it is our hope that as Michigan organic blueberry acreage increases we will increasingly shift attention to the development of a better understanding of the population and community dynamics driving pest and disease outbreaks with the objective of the development of pest management tactics that rely less on costly off-farm inputs and provide minimal system disturbance. The current report covers the establishment phase of the MSU campus organic blueberry planting, and as such has little information on fruit-related challenges. As the planting matures we intend to continue sampling, with greater emphasis on fruit quality.

This project has yielded valuable information on organic production methods and has also exposed problems that organic growers may encounter when starting new organic plantings, particularly nutrient deficiencies and weed competition. Perhaps transitioning older plantings would be easier, as the plants have already established and suffer less from weed pressure. The project also has led to improved communication between organic growers, university specialists and extension personnel, as well as amongst organic growers. An “Organic Pest and Nutrient Management Guide for Organic Blueberries” is being produced and will be available on-line later in 2012.

Farmer Adoption

General trends

Multiple small- to medium-scale blueberry growers in Michigan and the North Central Region are in the process of transitioning to certified organic production. Others, who already were growing organic blueberries, are expanding their acreage, as the demand for organic blueberries is still increasing. By 2011, the certified organic blueberry acreage had more than doubled (about 130 acres) compared to 2006. In the next 5 years, we anticipate that between 1 and 2% of the Michigan blueberry acreage will be organic. Grower-to-grower information shared at the organic blueberry meetings we organized has been important for novice as well as more experience organic blueberry growers. Novice blueberry growers in the region tend to be more interested in organic production than large-scale established blueberry growers.

We were able to reach at least 500 growers, consultants and extension educators in Michigan and other states through the many extension and commodity-specific meetings. A certain amount of technical and moral support while the grower experiments with a new system seems to facilitate successful adoption of organic practices. In the organic-conventional farm survey, Jesse Sadowsky often met up and talked with growers about what he saw in their fields; he also provided each grower with a detailed report on the health status of their soil and plants. Based on this interaction, at least one grower altered his practices to lessen use of in-row tillage and use more mulching to increase soil health. In many cases, problems experienced in young plantings are due to improper horticultural practices or extreme weather events, but pests and diseases could also play a role. The personal interaction of the PIs with growers while making diagnostic visits and setting up field experiments also led to individual changes in management practices. For instance, one grower modified nutrient applications when a nutrient deficiency was diagnosed rather than a disease. Another grower found out that extensive dieback in a new organic planting was not caused by a disease and was able to adjust his field establishment practices accordingly. Another (minority) grower was able to use information on managing mummy berry to become a successful organic fruit supplier to a local market in the South Haven/Covert area. We believe our project has contributed directly or indirectly to increased grower confidence in organic production techniques and has helped growers better manage soil and plant health on their farms. We feel that those Michigan growers that are interested in organic production are able to adapt and occupy this niche and thereby supply Michigan demand for organic fruit.

Grower questionnaire at the Great Lakes Fruit and Vegetable Expo in 2007

A four-question survey was distributed to audience members during the “Organic Blueberry Production: What We Know and Need to Learn” presentation at the 2007 Great Lakes Fruit, Vegetable, and Farm Market Expo in Grand Rapids, MI. Thirty-three completed surveys were collected. Eleven of fifteen respondents who included contact information were from Michigan, with the remaining respondents hailing from Wisconsin, Iowa, Illinois, or Ohio. This report summarizes the data and comments collected in this survey.

Of the 33 responses to question one, “What is your interest level in organic blueberry production?”, 25 respondents indicated they were considering organic blueberry production, two respondents indicated no interest, and one respondent indicated current organic-certified blueberry acreage in production.
Of the 25 respondents considering organic blueberry production, 17 indicated an interest in establishing new blueberry plantings, three had an interest in both new and established plantings, and six were interested in transitioning mature plantings to organic production.

Approximately three-quarters of those surveyed regarded aspects of cultural management as major concerns. Responses included insect pest management (27 responses, 82%), nutrition (26 responses, 79%), weed control (26 responses, 79%), and disease management (25 responses, 76%). Slightly less than half of respondents indicated marketing (13 responses, 39%) or labor (13 responses, 39%) as major concerns.

Six respondents indicated that they were willing to serve as research grower cooperators in 2008; five of these resided in Michigan. Four potential grower cooperators reported that they were most interested in establishment of new plantings, while the other two potential grower-cooperators had an interest in research in both established plantings and new plantings. Many respondents included additional comments at the end of the survey. Four respondents offered concerns regarding cost of production and marketing. Four other respondents questioned the reliability of organic production inputs. Concerns about management of pests were noted by four respondents. Three respondents commented on nutrient management. Finally, two respondents voiced concerns about E. coli contamination stemming from the use of animal manures.

Overall, the results of this survey indicated a significant interest in organic production of blueberries in Michigan and other Midwest states. However, results of this survey may not be an accurate representation of the opinions of all blueberry producers in Michigan, as indicated by the relatively small number of surveys collected. This survey nonetheless enhanced our awareness of concerns of prospective and current organic blueberry growers. While production-related issues ranked highest among respondents, economics (labor cost and marketing) were also a significant concern. Both of these aspects of organic blueberry production need to be addressed in future research at Michigan State University.

Grower questionnaire at MSU Organic Blueberry Meeting in 2009

We distributed an informal grower questionnaire at the MSU Organic Blueberry Meeting on December 18, 2009. Attendees were asked whether they produced organic blueberries or were interested in organic production. Also they were polled concerning their current blueberry acreage under organic transition or certification.

Respondents were also asked to rank the following areas of organic production in the order of which should receive the most needed research and extension attention: nutrient management, weed management, insect pest management, vertebrate pest management, compost and/or compost tea production, food safety, marketing/economics, labor, or other.

We had 11 respondents to our questionnaire, 9 of whom indicated that they had either transitional or certified organic acreage and one who indicated that they were considering growing organic blueberries. Respondents indicated that they had a total of 33.5 acres of new blueberry plantings and 33.5 acres of mature blueberry plantings in transition with an additional 14 acres of new plantings and 2 acres of mature plantings already certified. The average new planting in transition, new certified planting, mature planting in transition, and mature certified planting were 8.4 (n = 4), 4.6 (n = 3), 11.2 (n = 3), and 2 (n = 1) acres, respectively. Weed and nutrient management were indicated as the top grower priorities for future research and extension with both categories indicated as having being a top three priority in seven instances. Insect and pathogen management received six “top three” spots, followed by vertebrate management and compost and compost tea production, marketing, food safety, and labor, which received five, five, four, three, and three top three priority rankings, respectively. Two of the respondents did not respond to this question, three did not rank all of the categories, and two simply indicated the categories of interest. One grower indicated that
alternative sources of pollinators should be a top research priority.

Results of this survey indicated that the amount of known certified organic acreage in Michigan will more than double within the next 3 years. Grower concerns with nutrient management, weeds, insect pests, and pathogens were consistent with personal communications among extension staff and individual growers. The apparent grower interest in compost teas was an interesting development and suggests that more research is needed in this area, especially considering the variable results reported in trials utilizing compost teas. Research and extension on food safety was the lowest grower priority and marketing was also surprisingly low. This may be attributable to the relatively small size of the organic plantings maintained by the respondents, which likely results in a marketing plan based on selling directly to consumers rather than one dependent on wholesalers requiring Good Agricultural Practices (GAP) certification.

Participation Summary

Educational & Outreach Activities

Participation Summary

Education/outreach description:
Organic Grower Meetings held
  • 2007 MSU Organic Blueberry Discussion Meeting, August 16, 2007, Trevor Nichols Research Complex, Fennville, MI (attended by 20 regional growers, commodity group representatives, and extension personnel) to present the NC SARE project objectives and obtain input from growers on directions.

    2009 MSU Organic Blueberry Meeting, December 18, 2009, Trevor Nichols Research Complex, Fennville, MI (attended by 50+ regional growers). Purpose: to share results from organic blueberry trials in Michigan and to obtain grower input in setting organic research and extension priorities for 2010 and beyond.

    2011 MSU AG EXPO, Horticulture Farm Tour. Demonstration of Organic Blueberry Trial; July 20, 2011 (attended by about 20 growers and consultants).

Publications and Meeting abstracts
  • Sadowsky, J. J., Hanson, E. J., Grandy, A. S., Hao, J. J., and Schilder, A. M. C. 2012. Soil biology in mature Michigan blueberry fields following transition from conventional to organic management. Soil Biology and Biochemistry (in preparation).

    Sadowsky, J. J., Schilder, A. M. C., and Hanson, E. J. 2012. Root colonization by ericoid mycorrhizae and dark septate endophytes in organic and conventional blueberry fields in Michigan. International Journal of Fruit Science, 12:169–187.

    Grieshop, M., Hanson, E., Schilder, A., Isaacs, R., Mutch, D., Garcia-Salazar, C., Longstroth, M., Sadowsky, J. 2012. Status update on organic blueberries in Michigan. International Journal of Fruit Science 12:232–245.

    Sadowsky, J. J., Schilder, A. M. C., Hanson, E. J., Grandy, A. S., and Hao, J. J. 2011. Carbon and nutrient cycling and beneficial microorganisms in organic and conventionally managed blueberry soils in Michigan, USA. Page 279 in: FEMS Conference: Ecology of Soil Microorganisms, April 27-May 1 2011, Prague, Czech Republic (abstract).

    Sadowsky, J. and Schilder, A. 2011. Carbon and nutrient cycling and beneficial microorganisms in organic and conventionally managed blueberry soils in Michigan. Pages 3-4 in Michigan Organic Food & Farming Reporting Session. http://www.michiganorganic.msu.edu/uploads/files/31/Compiled%20Abstracts.pdf.

    Sadowsky, J. J. 2010. Effects of organic and conventional management on plant health and soil biology in blueberries. M.S. Thesis, Michigan State University, East Lansing, MI.

    Sadowsky, J. J., Schilder, A. M. C., Hanson, E. J., Grandy, A. S., and Hao, J. J. 2010. Effects of organic and conventional management on plant health and soil biology in Michigan blueberries. Page 34 in: North American Blueberry Research and Extension Workers meeting (abstract).

    Schilder, A. M. C., Gillett, J. M., Sysak, R. W. 2010. Disease control options for organic blueberries.North American Blueberry Research and Extension Workers meeting (abstract).

    Hanson, E., Schilder, A., and Sadowsky, J. 2010. Nitrogen release patterns from organic nutrient sources. Page 34 in: North American Blueberry Research and Extension Workers meeting (abstract).

    Sadowsky, J. J., Schilder, A. M. C., Hanson, E. J., Grandy, A. S., and Hao, J. J. 2010. Effects of organic and conventional management on plant health and soil biology in Michigan blueberries. Page 10 in: Michigan Organic Food & Farming Reporting Session. http://www.michiganorganic.msu.edu/uploads/files/31/Abstract%20compiled%202010.pdf.

    Sadowsky, J. 2009. Current Organic Blueberry Research at Michigan State University: What we have learned so far. Michigan’s Organic Research Reporting Session (abstract). http://www.michiganorganic.msu.edu/uploads/files/31/Organic%20Blueberry%20Research%20at%20MSU.pdf

    Sadowsky, J. and Schilder, A. Organic Blueberry Production: What we know and need to learn. Proceedings of the 2007 Great Lakes Fruit, Vegetable, and Farm Market Expo. http://www.glexpo.com/summaries/2007summaries/blueberry_I_2007.pdf.

Extension Publications
  • Schilder, A. M. C., Isaacs, R., Hanson, E., Grieshop, M., and Landis, J. 2012. Organic Blueberry Pest And Nutrient Management Guide For The North Central Region. Michigan State University Extension Bulletin (will be co-published with the Integrated Pest Management Guide for Blueberries) (in preparation, to be published in 2012).

    Wise, J. C., Gut, L. J., Isaacs, R., Schilder, A. M. C., Sundin, G. W., Zandstra, B., Hanson, E., and Shane, B. 2011. Michigan Fruit Management Guide 2012. Extension Bulletin E-154. Michigan State University, East Lansing, MI. Schilder, A. 2011. Fungicide update for blueberries. MSU Extension News for Agriculture (http://news.msue.msu.edu/news/category/fruit). Posted on 3 May 2011.

    Schilder, A. 2011. Scouting and management of mummy berry in blueberries. MSU Extension News for Agriculture (http://news.msue.msu.edu/news/category/fruit). Posted on 12 April 2011.

    Wise, J. C., Gut, L. J., Isaacs, R., Schilder, A. M. C., Sundin, G. W., Zandstra, B., Hanson, E., and Shane, B. 2010. Michigan Fruit Management Guide 2011. Extension Bulletin E-154. Michigan State University, East Lansing, MI.

    Wise, J. C., Gut, L. J., Isaacs, R., Schilder, A. M. C., Sundin, G. W., Zandstra, B., Hanson, E., and Shane, B. 2009. Michigan Fruit Management Guide 2010. Extension Bulletin E-154. Michigan State University, East Lansing, MI.

    Wise, J. C., Gut, L. J., Isaacs, R., Schilder, A. M. C., Sundin, G. W., Zandstra, B., Hanson, E., and Shane, B. 2008. Michigan Fruit Management Guide 2009. Extension Bulletin E-154. Michigan State University, East Lansing, MI.

    Schilder, A., and Miles, T. 2008. Anthracnose Fruit Rot (Ripe Rot). Michigan Blueberry Facts. Michigan State University Extension Bulletin E-3039.

    Schilder, A., Wharton, P., and Miles, T. 2008. Mummy Berry. Michigan Blueberry Facts. Michigan State University Extension Bulletin E-2846.

Oral Presentations at Meetings
  • Schilder, A. M. C. Management of diseases in organic blueberries. South East Regional Fruit and Vegetable Conference. Savannah, Georgia, 6-7 Jan, 2011.

    Schilder, A. M. C. Blueberry disease control in Michigan. Great Lakes Expo, 6-8 Dec, 2011.

    Schilder, A. M. C., Gillett, J. M., Sysak, R. W. Disease control options for organic blueberries. North American Blueberry Research and Extension Workers meeting, Kalamazoo, MI, July 25-28, 2010.

    Sadowsky, J. J. 2011. Effects of organic and conventional management on plant health and soil biology in highbush blueberries in Michigan, USA. 2011. Seminá? Mykosymu (Department of Mycorrhizal Symbioses Seminar Series), March 2, 2011, Institute of Botany, Academy of Sciences of the Czech Republic, Pr?honice, Czech Republic.

    Sadowsky, J. J. Effects of organic and conventional management on plant health and soil biology in blueberries. 2010. North American Blueberry Research and Extension Workers meeting, Kalamazoo, MI, July 25-28, 2010.

    Sadowsky, J. J. Effects of conventional and organic management on plant health and soil biology in blueberries. 2010. MSU Department of Plant Pathology Master’s defense seminar, East Lansing, MI.

    Sadowsky, J. Soil biology and diseases in Michigan blueberries. 2009. MSU Organic Blueberry Meeting, Trevor Nichols Research Complex, Fennville, MI, December 18, 2009.

    Schilder, A. Organic Disease Management Trials. MSU Organic Blueberry Meeting, Trevor Nichols Research Complex, Fennville, MI, December 18, 2009.

    Grieshop, M. Video-monitoring for studying insect and pathogen ecology. MSU Organic Blueberry Meeting, Trevor Nichols Research Complex, Fennville, MI, December 18, 2009.

    Hanson, E. Organic blueberry nutrition, weed control, cover crops. MSU Organic Blueberry Meeting, Trevor Nichols Research Complex, Fennville, MI, December 18, 2009.

    Blaauw, B., and Isaacs, R. Organic insect management trials. MSU Organic Blueberry Meeting, Trevor Nichols Research Complex, Fennville, MI, December 18, 2009.

    Sadowsky, J. J. Hanson, E., Hao, J., Isaacs, R., Mutch, D. Schilder, A., Grandy, S. Organic blueberry research at Michigan State University: What we have learned so far. Michigan’s Organic Agriculture Research Reporting Session, March 6, 2009, East Lansing, MI.

    Sadowsky, J. J. Organic blueberry production: Shifting the biological balance. 2008. Michigan State University Department of Plant Pathology graduate seminar, March 17, 2008, East Lansing, MI.

    Schilder, A. and Sadowsky, J. Organic blueberry production: Challenges and opportunities. Michigan Organic Conference, 1 March, 2008.

    Sadowsky, J. J. Organic blueberry research at Michigan State University. 2008. Michigan’s Organic Agriculture Research Reporting Session, March 5, 2008, East Lansing, MI.

    Sadowsky, J. J. 2007. Organic blueberry production: What we know and need to learn. Great Lakes Fruit and Vegetable Expo, December 5, 2007, Grand Rapids, MI.

    Schilder, A., and Bingen, J. Organic training and research at Michigan State University. June 18, 2007, Faculty of Life Sciences, University of Kopenhagen, Denmark.

    Schilder, A., and Bingen, J. Organic training and research at Michigan State University June 28, 2007, Faculty of Human Nutrition and Consumer Sciences, Warsaw Agricultural University, Warsaw, Poland.

Poster Presentations at Meetings
  • Sadowsky, J., Schilder, A. M. C., Hanson, E. J., Grandy, A. S., and Hao, J. J. 2011. Carbon and nutrient cycling and beneficial microorganisms in organic and conventionally managed blueberry soils in Michigan, USA. FEMS Conference: Ecology of Soil Microorganisms, April 27-May 1 2011, Prague, Czech Republic.

    Sadowsky, J., Schilder, A. M. C., Hanson, E. J., Grandy, A. S., and Hao, J. J. 2011. Effects of conventional and organic management on plant health and soil biology in blueberries. 2010. Michigan’s Organic Agriculture Research Reporting Session, March 5, 2010, East Lansing, MI.

    Sadowsky, J., Schilder, A. M. C., Hanson, E. J., Grandy, A. S., and Hao, J. J. 2010. Effects of conventional and organic management on plant health and soil biology in blueberries. 2010. Upper Midwest Organic Farming Conference, February 25-27, 2010, La Crosse, WI.

    Sadowsky, J., Schilder, A. M. C., Hanson, E. J., Grandy, A. S., and Hao, J. J. 2010. Effects of conventional and organic management on plant health and soil biology in blueberries. Michigan State University Plant Science Graduate Symposium, March 30, 2010, East Lansing, MI.

    Schilder, A. M. C., Evaluation of organic fungicides for control of fruit rot diseases in Michigan blueberries. 2009. Great Lakes Fruit and Vegetable Expo, December 8-10, 2009, Grand Rapids, MI.

    Sadowsky, J. Determination of the relationship between soil nutrients, mycorrhizae, and plant health in Michigan blueberries. 2009. Michigan State University Department of Plant Pathology Graduate Symposium, September 18, 2009, East Lansing, MI.

    Sadowsky, J., Schilder, A. M. C., Hanson, E. J., Grandy, A. S., and Hao, J. J. 2009. Management system influence on mycorrhizal colonization, soil biology, and disease incidence in Michigan blueberries. Michigan State University Plant Science Graduate Symposium. March 25, 2009, East Lansing, MI.

Features and Awards

Student studies soil management and organic blueberry production in Michigan. North Central Region Sustainable Agriculture Research & Extension Field Notes, Winter/Spring 2011, http://www.northcentralsare.org/content/download/61604/839795/102306_Hi_res.pdf.

Fulbright Student Scholarship
Based on research conducted in NC SARE projects, Jesse Sadowsky (MSU Graduate Student in Plant Pathology) received a Fulbright Student Scholarship to work on “Ericoid mycorrhizae as a model system for plant-soil-microbe feedbacks” with Dr. Martin Vohník at the Institute of Botany of the Academy of Sciences in the Czech Republic in the Czech Republic (2010-2011).

PhD Assistantship, University of New Hampshire.
In 2011, Jesse received a Graduate Research Assistantship at the University of New Hampshire, where he is pursuing a PhD in Soil Microbial Ecology with Dr. Serita Frey.

Project Outcomes

Recommendations:

Areas needing additional study

While this study has answered many basic questions about the nutrition and pest management in organic blueberries, it has also revealed a need for further research. It would be interesting to study the organic transition process on different soil types to better understand nutrient dynamics and the functional significance of higher mycorrhizal colonization of roots and microbial activity in the soil. This may also reveal horticultural practices that could favor beneficial microbes and plant health. A question that has not been fully elucidated is whether a “healthy” soil automatically leads to healthy plants that are naturally less prone to attack by foliar pathogens and insects, i.e. the correlation between organic production practices and natural plant defenses. With new, invasive pests and pathogens appearing on the scene (e.g., spotted wing Drosophila), more research will also be needed on management tactics for these pests in organic fields. Furthermore, it would be helpful to evaluate newer cultivars under organic management for a number of years, as cultivars may differ in their response to organic practices. Presumably, newer cultivars have been bred under conventional conditions with synthetic fertilizers and there is a possibility that they may not adapt as well to an organic system. A goal of a future project could be to devise an organic system that is less reliant on off-farm inputs and labor, for instance by the use of disease- and insect-resistant cultivars, composts and compost teas made on-farm, using local mulches), which may especially benefit small-scale farmers. A detailed economic analysis of organic production systems would be useful.

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.