Nutrient and Weed Management Strategies for Organic Wild Blueberry Growers

Progress report for LNE19-374

Project Type: Research and Education
Funds awarded in 2019: $199,828.00
Projected End Date: 11/30/2022
Grant Recipient: University of Maine Extension
Region: Northeast
State: Maine
Project Leader:
Dr. Lily Calderwood
University of Maine
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Project Information

Summary:

The price of conventional frozen wild blueberries reached a record low $0.27/lb in 2017, a price that does not justify crop maintenance. Meanwhile the crop grown organically sells for $5.00/lb. Small organic growers are stuck with low yields and large organic-transition farms will struggle with low prices until effective organic fertility and weed management strategies are developed and disseminated effectively. At a pH of 4.0, most soil applied fertility is not available for blueberry plants, yet these nutrients feed weed species. Foliar nutrient uptake is not well understood for this crop and increases the risk for disease. The weed management tools available for organic growers are limited to sulfur applications, weed whacking, and hand weeding. Furthermore, the shallow blueberry root system is susceptible to drought conditions that non-irrigated fields have experienced over the last three seasons. While applied research has been conducted on wild blueberry for many years, it is time to focus on soil and plant health for a new market. 

Performance Target:

Fifty blueberry growers in Maine will adopt at least one new weed, nutrient, or irrigation management practice on  a total of 500 acres. Among these growers, 5 managing certified organic farms will increase their average yield  by 500 lbs/acre on a total of 100 acres. Additionally, 500 acres of conventional blueberry land will adopt practices  necessary to transition to certified organic production. 

Introduction:

Project A: Nutrient Management

Given the significant market declines for wild blueberries in the U.S. conventional market (USDA NASS 2018), interest in organic production is growing. Growing wild blueberries under certified organic standards is challenging because there are a limited number of fertilizer and pest management tools approved for use.

The effects of various organic amendments applied in wild blueberry systems have been previously studied. These include manure (Warman 1987), papermill sludge (Gagnon et al. 2003), gypsum (Sanderson and Eaton 2004), biosolids (Lafond 2004), municipal solid waste (Warman et al. 2009) and seafood-waste compost (Mallory and Smagula 2014). However, these studies produced variable results regarding blueberry productivity and marketable yield with few significant effects on soil organic matter or leaf nutrient concentrations. These studies demonstrate the need to investigate other organic alternatives at different rates and timings to better understand their cost-effectiveness and ability to aid in water retention and nutrient availability.

Factors that affect nutrient uptake in wild blueberries include weed presence, soil pH, water availability, and the presence of soil nutrients (Drummond et al. 2009). Wild blueberries compete with weeds for space, water, and nutrients, which can result in reduced crop yields and limited blueberry spreading if left unmanaged. Insects and disease pests can also benefit from nutrients applied to wild blueberry and in turn increase damage caused in blueberry plants. The low soil pH (4.0-4.5) of commercial wild blueberry fields does not allow critical nutrients like nitrogen, phosphorus, and potassium to be readily available to wild blueberry plants (Peterson 1982). Therefore, organic growers must rely on soil biology to break down applied organic matter in order to increase nutrient availability in crop fields. This study aims to identify materials that improve soil water holding capacity and nutrient availability for wild blueberries.

In this study we evaluate the efficacy of four organic soil amendments and one foliar spray treatment for their impact on wild blueberry growth and pest presence. This study focuses primarily on enhancing nutrient availability in organic wild blueberry systems rather than applying methods to directly manage pest populations. Because the materials applied may benefit pests, pest monitoring is a key aspect of this study. We seek to develop a better understanding of the relationship between wild blueberry nutrient inputs and pest presence in order to aid future recommendations for organic wild blueberry growers.

Project B: Weed Management

Due to the low prices of conventional frozen wild blueberries (2014-2018 mean = $0.40/lb) and increasing demand for organic wild blueberries, there are now 52 certified organic wild blueberry farms in Maine. While this group only accounts for 11% of all Maine wild blueberry farms, they are able to sell frozen berries at a higher price ($5.00 - $19.80/lb). Finding cultural and mechanical methods of weed management is important for all wild blueberry growers whether they are considered small, large, organic or conventional. Small organic growers are stuck with low blueberry yields because they do not have effective OMRI approved herbicides. Large organic-transition and conventional farms are in search of transition methods and low residue practices due to market demand.

To date, the University of Maine has found that removing weeds from a wild blueberry field can double yield in the conventional system (Yarborough 1997). Applying sulfur to reduce soil pH to 4.0 in the wild blueberry system is a very effective way of culturally reducing grass species (Saunders 2016 and Yarborough 1997). Soil pH reduction is a slow process which takes 2-3 years and one that does not reduce woody weeds as well as grasses. Removing woody weeds three times per season via mowing, weed whacking, and/or hand pulling is the most effective method of mechanical weed management to date (Drummond et al. 2012).

This four-year study will explore tine weeding and winter-kill cover crops as mechanical and cultural weed management tools for the wild blueberry system. A flex-tine weeder is a tractor attachment with metal fingers called “tines” that drag through the top one inch of

soil dislodging weed seedlings (Figure 1). Tine weeding is used on vegetable and small grain farms in early spring just as the first winter annual weed seedlings emerge. The stiffness of tines allows them to break through the soil crust and the vibration of tines uproots weed seedlings (Bowman 1997). Flex-tine weeders are designed to dislodge white thread stage weeds when the machine is run at a “fast” speed.

Cover cropping is defined as the planting of another plant species among or alternating with the cash crop. There are numerous benefits of cover cropping, a few of which include weed suppression, erosion management, soil organic matter builds up, increased soil water holding capacity, and habitat for natural enemy and pollinating insects. Several species of cover crop have been explored to meet the needs of different cropping systems. In wild blueberry production, planting a cover crop that would then become a weed would not be wise. Therefore, we are interested in “winter-kill” cover crop species that are planted in the late summer and die over the winter such as common oat (Avena sativa) or sorghum-sudan grass (Sorghum × drummondii). As the cover crop species grows in late summer through early fall, organic matter is created. After the plant dies, it falls to the ground creating a vegetative mat with the potential to suppress weeds (Clark 2007).

Cooperators

Click linked name(s) to expand
  • Dr. Yongjiang Zhang (Researcher)
  • Dr. Seanna Annis (Researcher)

Research

Hypothesis:

We hypothesize that the execution of timely organic nutrient and weed management strategies will increase wild blueberry yields. In turn, this will improve the economic and environmental sustainability of this native crop. We seek to build upon recent research conducted (FNE14-808, ONE14-222) and expand our knowledge of the organic wild blueberry system for the long-term benefit of all berry growers in the Northeast.

Materials and methods:

Project A: Nutrient Management

This project is replicated at three farm locations that were selected to represent three scales (small, medium, and large) and the three major wild blueberry growing regions (Mid-coast, Ellsworth, and Downeast) in Maine. The experimental design is a randomized complete block replicated six times. Each plot is 6’ by 30’ (180 ft2). A total of 54 plots and 9 treatments are located at each site (Table 1). The foliar fertilizer and chicken manure were applied at the recommended time and rate according to the label and company representative instructions. The Cobscook blend, mulch, and compost were applied according to recommendations from University of Maine Extension Educator Mark Hutchinson (personal communication, 2019). All products were applied one time except for the foliar fertilizer which was applied multiple times as recommended by the manufacturer.

All products were applied during the prune cycle of 2019. The foliar fertilizer was applied three times – once during the emergence, tip dieback, and bud development stages of wild blueberry growth at each site. It was applied on: June 19th, July 15th, and August 27th in Hope; June 24th, July 19th, and August 28th in Columbia Falls; and June 4th, July 18th, and August 30th in Surry. Chicken manure was applied on June 4th in Surry, June 5th in Hope, and June 12th in Columbia Falls. The Cobscook blend was applied on June 20th in Hope, June 24th in Columbia Falls, and June 26th in Surry. Mulch was applied on July 23rd and 24th in Columbia Falls and Surry, respectively. UMaine compost was only applied in Hope on June 19th. See Table 1 for product details. 

Table 1. Treatments tested at each of three organic farms in a randomized complete block design with 6 replicates.

 

Product

Rate

Rate Type

Crop Cycle

% NPK

Control

N/A

N/A

N/A

N/A

North American Kelp Co. Seacrop16 Foliar Fertilizer

1.2 L/242 gal. H2O/A

N/A

Prune

0.18% N

6.37% P

4.89% K

N/A

Crop

North Country Organics Cheep Cheep Chicken Manure 4-3-3

1089 lbs./A

Low

Prune

4% N

3% P

3% K

2178 lbs. /A

High

Prune

Coast of Maine Cobscook Blend Garden Soil

7.5 yd3/A

Low

Prune

0.4% N

0.14% P

0.12% K

15 yd3/A

High

Prune

*Mark Wright Disposal Dark Brown Mulch

7.5 yd3/A

Low

Prune

N/A

15 yd3/A

High

Prune

**University of Maine Compost

7.5 yd3/A

Low

Prune

0.41% N

0.11% P

0.10% K

15 yd3/A

High

Prune

*Only applied at Columbia Falls and Surry locations, % NPK analysis not completed

**Only applied at Appleton location

NPK represented as total nitrogen, phosphorus as P2O5, and potassium as K2O

Data Collection

Physiology

Two 0.37 m2 quadrats were placed in each plot to monitor percent tip-die back and physiological measures in the  vegetative year (2019). Within each plot, each of the two quadrats were placed in separate genets (plants). Six stems from each plot were randomly selected and marked to monitor stem length, chlorophyll content and anthocyanin content during June-October on a vegetative year (2019). Chlorophyll content was measured by a SPAD Chlorophyll Meter (SPAD 502; Minolta Corp, Osaka, Japan), anthocyanin content was measured by an ACM-200 anthocyanin meter (Opti-sciences, Hudson, USA). Photosynthetic electron transport rates were measured in leaves from 6 stems in each plot by a Y(II) meter (Opti-sciences, Hudson, USA) in August on a vegetative year (2019) between 10:00 and 14:00 h solar time. Ten random leaves from each genet in each plot (20 leaves as 2 samples in each plot) were collected in September of 2019 to measure leaf area and their dry biomass. Leaf area was determined using LI-3000A area meter (Li-Cor, Lincoln, NE, USA), then the leaves were oven-dried at 70ºC to constant mass and weighed.

Pest Pressure

Insects, weeds, and disease were monitored in the same 0.37 m2 quadrats (twice per plot) as pant physiology throughout the 2019, 2020 field seasons. In the 2019 prune-year pest scouting took place 3 times (once per month) from July to September at each of the three locations. In the following 2020 crop-year pest scouting took place 3 times May to July at each location. Pest severity (percent cover) for weeds, insect and disease were quantified using equal interval ranks between 0 and 6, where: 0 = not present, 1 = ≤1%-17%, 2 = 17%-33%, 3 = 33%-50%, 4 = 50%-67%, 5 = 67%-83% and 6 = 83%-100%. Weeds were identified into two groups in 2019 (grass and broadleaf) and in 2020 weeds were identified by genera and counted to obtain weed number per quadrat. In 2020 the number of wild blueberry stems with insect or disease damage were also identified and counted in addition to ranking.

Disease symptoms and leaf loss were rated in August and September using 0.25m2 quadrat in both 2019 and 2020.  Two quadrats were sampled per plot and percentages of blueberry cover, blueberry leaf loss, and blueberry leaf area with the following leaf spot diseases: Septoria leaf spot, powdery mildew, and leaf rust were estimated visually.  Symptoms of insect damage were also noted. August and September disease ratings were averaged across the 2 quadrats within the trial plot. 

Crop Productivity

Blueberry cover was quantified using the same equal interval ranking at the time of each pest scouting. Additionally, in the 2019 prune-year, stem heights and the number of buds per stem were recorded for 8 stems per plot at all locations late August to early Sept. In the following 2020 crop-year, fruit-set and fruit-drop were monitored with repeated measures on the same 4 stems per plot. Fruit-set measures included flower counts at peak bloom, green fruit counts prior to ripening, and blue fruit counts during ripening. Percent fruit-set was quantified by the number of green fruit relative to the number of flowers per stem, while fruit-drop was established through the number of blue fruit relative to the initial number of green fruit observed for each stem.

The first harvest of these plots took place on August 3rd, 6th and 11th, 2020 in Appleton, Surry and Columbia Falls, respectively. Harvest procedure included hand raking an exact quadrat in the flagged locations where repeated scouting had taken place, followed by hand raking the entire plot. Quality measures were also taken for each treatment including a 100-berry count to quantify average berry size and a brix measure of the relative sugar content.

Data Analysis

Physiology

The effects of the fertilizer treatments on chlorophyll concentration, leaf size, dry biomass per leaf of wild blueberry plants were statistically compared using a one-way analysis of variance (ANOVA) followed by a LSD (least significant difference) post-hoc test in SPSS software (α = 0.05). Each site (Appleton, Surry and Columbia Falls) was analyzed individually.

Pest Pressure & Productivity

Due to the nature of count data collected in the field (which often has a high number of zeros creating a skewed distribution) much of our data failed the assumptions of normality and equal variance often required to run parametric statistical tests. Therefore, all pest data was transformed with a square root transformation prior to any statistical testing. in the 2019 prune year, percent blueberry cover, grass cover, broadleaf cover, insect presence, and disease presence were statistically compared in JMP (JMP®, Version 14.3) across all treatments at the 0.05 level of significance. The effects of the treatments on blueberry health, evaluated as a function of stem height and number of buds per stem were statistically analyzed using a randomized block design where location was a random effect. For 2020 crop year data, single date measurements including: the counts of flowers, green fruit and blue fruit, percent fruit-set and fruit-drop, harvest yield, berry size, sugar content (brix) and leaf nutrients were evaluated using a generalized linear model (GLM), followed by a Tukey’s Pairwise comparison in JMP (JMP®, Version 14.3) across all treatments (α = 0.05). Ranked blueberry cover and pest data were transformed to their corresponding percent mid-point and compared across both years (2019 and 2020) using a full-factorial repeated-measures mixed model design in JMP. Here, the full factorial tested the effects of year, treatment, and any interaction between year and treatment for the ranked response variables. Pest count data collected in 2020 was tested using a linear repeated-measures mixed model design in JMP. Additionally, the effect of weed pressure (weed number/m2) on yield was investigated using a nonparametric Spearman ρ Correlation also in JMP.

Project B: Weed Management

In April 2019, the site location for this study was selected at Blueberry Hill Farm in Jonesboro, ME. This ongoing trial is a randomized complete block design replicated six times with 6’ by 30’ plots and 3’ wide buffers between plots. The trial is located on one acre that is now managed organically although it is not an organically certified piece of land. One soil sample was taken of the site location before the project began.

In March 2020 we conducted a lab experiment to test the ability of cereal cover crop species to germinate in acidic wild blueberry soil. The effects of low pH were tested using a water and buffer solution. In the lab, common oat (Avena sativa, Blue Seal) and pearl millet (Pennisetum glaucum F1, Johnny’s Selected Seeds) were germinated in petri dishes (100 seed/dish) with 4 watering treatments: a control using distilled water only (pH: 7.0) and 3 water/buffer solutions (pH: 4.0, 4.5 and 5.0) . Each watering treatment was replicated 3 times for each species. Seeds were sprayed daily using a spray bottle for 5 days. The number of seeds germinated per petri dish was recorded and average percent germination was calculated. Because successful germination occurred in the lab, common oat and pearl millet cover crop seed was planted via broadcast in the field on September 1st, 2020 after harvest. Four cover crop treatments were planted: common oat and pearl millet each at a low and a high rate (Table 1).

Treatments are listed in Table 1. Two controls were employed; no weeding and hand weeding on one date. On May 13th and June 12th prune year tine weeding treatments were completed. Tines on a Williams flex-tine weeder were set to have the greatest down pressure (setting 8)(Image 1). The tractor was run slower than recommended at 1 mph due to the bumpy field and our learning curve. The hand weeded treatment was completed on June 12th.

Table 1. Weed management treatments used in the 2019 prune-cycle and the 2020 crop-cycle. All tine weed treatments had 2-passes per date and cover crop seeds were planted on September 1, 2020 after harvest.
Williams flex-tine weeder at Blueberry Hill Farm, May 2019.

Measures of weed and blueberry crop growth were collected using two 0.5m x 0.5m quadrats per plot. Two quadrats were placed per plot and flagged for repeated measurements in the same locations throughout the study.

Weed control efficacy was evaluated within each quadrat by ranking overall weed cover using the Daubenmire scale of 0-6 (Table 2). In 2019, weeds were identified into two groups; grass and broadleaf, each of which were also given a severity rating on the same 0-6 scale and sampled twice throughout the season (June 27th and August 28). In 2020 we took a slightly different approach by counting the total number of weeds per quadrat with an overall rank of cover using the Daubenmire scale and listing the top three weeds that covered the most area within each quadrat. These measurements were taken three times throughout the 2020 crop-year (May 14th, May 27th and July 2nd).

The response of the blueberry plant to tine weeding in 2019 was monitored through repeated observations of blueberry cover as well as physical measures of stem height, bud number per stem and ramet density (Figure 2). In 2020, six random stems were flagged per treatment and monitored repeatedly for fruit-set and fruit-drop for the 3 tine weed treatments and the 2 controls. Fruit-set measures included bud counts in the late spring, flower counts at peak bloom, green fruit counts prior to ripening, and blue fruit counts during ripening. Percent fruit-set was calculated from the number of green fruit and the number of flowers per stem, while fruit-drop was calculated from the number of blue fruit and the original number of green fruit observed for each stem.

Harvest occurred on August 17th, 2020 for the tine weed treatments and both controls. Harvest procedure included hand raking exact quadrats in the flagged locations where repeated measurements were taken throughout the season. Then a walk behind harvester, harvested a 3ft strip down the center of each plot. The two modes of harvesting provided an ‘exact’ yield and a more ‘realistic’ yield (accounting for % loss that may occur with a mechanical harvester) for each treatment. Quality measures were also taken for each treatment including 100-berry weight to quantify average berry size and a brix measure of the relative sugar content using a hand-held Atago brix-acid meter.

Cover crop emergence was evaluated on October 9th, 2020 by counting the number of emerged plants within two quadrats/plot and measuring the heights of 6 random cover crop plants per plot.

Common oat (top) and pearl millet (bottom) cover crop seedlings at Blueberry Hill Farm in October.

Table 2. Daubenmire ranking scale (1-6).

 

Percent Coverage

Rank

Range

Midpoint

1

0-5%

2.5%

2

5-25%

15.0%

3

25-50%

37.5%

4

50-75%

62.5%

5

75-95%

85.0%

6

95-100%

97.5%

Data Analysis

Blueberry health and recovery after tine weeding were evaluated using blueberry stem height, bud counts (per stem), blueberry plant cover and number (ramets/m2). The continuous data (stem height, plant and bud number) were evaluated using a one-way ANOVA with a Tukey’s Pairwise comparison in JMP (JMP®, Version 14.3) across all weed management treatments (α = 0.05). Ranked (ordinal) data for blueberry plant cover and weed severity by type (broadleaf and grass) were compared using Chi-Squared test in JMP across all treatments (α = 0.05).

Research results and discussion:

Project A: Nutrient Management

Wild Blueberry Plant Physiology and Morphology

Overall, no significant differences were observed in the wild blueberry leaf sizes in any of the three organic wild blueberry fields. In the Appleton field, both low and high rates of coast of Maine cobscook blend treated plots and the control plot had comparatively higher leaf size than the other treatments. In the Surry field, the control plot, plots with the low rate of cobscook blend and chicken manure, and the SeaCrop16 treated plot in the prune year (2019) had higher leaf size compared to the other treated plots. In contrast to the leaf sizes observed in the Appleton and Surry fields, the high rate of chicken manure and SeaCrop16 in the crop year (2020) at Columbia Falls had higher mean leaf size compared to the control and other treatments.

Regarding the wild blueberry leaf dry biomass, significant differences were observed among the treatments in Appleton and Columbia Falls fields but not in the Surry field. In the Appleton field, higher leaf dry mass was observed in the control plot and the treated plots with both low and high rates of Coast of Maine Cobscook blend, SeaCrop16 applied in the prune year (2019), high rate of chicken manure compared to the other treated plots. In contrast, in the Surry field, the observed leaf dry mass was almost similar among the different treatments including the control plot. However, in the Columbia falls field, the high rate of chicken manure treated plot had significantly higher leaf dry mass compared to the control plot.

Effect of Organic Amendments on Leaf Nutrition – Preliminary Data

Here, nutrient availability is quantified through leaf nutrient content. Leaf samples were collected and analyzed in 2019 following all organic amendment applications and 2020 samples will be analyzed this winter. As expected, the macronutrients N, P and K were highest with the highest rate of chicken manure (4-3-3). Micronutrients (Ca, Mg, Mn, Al, B, Cu, Fe, Zn) did not exhibit significant treatments differences with the exception of magnesium (Mg) and boron (B) where mulch (high-rate) and University compost (low-rate) were significantly higher than the chicken manure (high-rate), respectively. We know wild blueberry responds slowly to the environment and different organic amendments release nutrients at different rates over time. Leaf nutrient analysis from 2020 is ongoing and crucial to observing micronutrient concentrations and slow-release amendments like compost and mulch.

Macronutrients: nitrogen (a), phosphorus (b) and potassium (c), leaf nutrient concentrations collected in 2019 around 1 month following organic amendment application. Letters indicate significance at the 0.05 level of significance. Error bars indicate the standard error of the mean.

Effect of Organic Amendments on Blueberry Cover and Pest Incidence, 2019 and 2020

Blueberry cover and pest pressure were ranked by treatment in both 2019 and 2020. In the 2019 prune-year, no significant differences were observed between treatments in blueberry cover or the incidence of insects or disease. Weed scouting in 2019, however, had revealed a significantly higher frequency of grasses in the chicken manure (Cheep Cheep) plots relative to the control. A greater frequency of broadleaf and grass weeds were observed in 2019 when compared to 2020. This difference could be due to the prune-vs. crop-year with greater opportunity for weed growth in the prune-year. However, slight changes in sampling technique and timing between the two years are likely the ultimate contributor. Overall, chicken manure had the highest occurrence of grasses in 2020 and 2019, and the greatest variety of weed species present in 2020. University Compost (high-rate) had grass present but no broadleaf weeds across both years. The top grass species observed in 2020 were poverty oat grass followed by witch grass for all treatments. The top broadleaf species varied by treatment.

Pest Incidence

Pest pressure identified in the 2019 and 2020 were divided into three categories: weeds, insects, and disease. Each category included several groups: two groups of weeds (grass and broadleaf), five groups of insects (tip midge, red-striped fireworm, flea beetle, gall wasp, and thrips), and two groups of disease (leaf spot and blight). Treatments did not significantly impact insect or disease pressures. However, incidence of grasses was significantly higher in both treatment rates of chicken manure than other treatments regarding weed pressure. More specifically on disease presence, there were no significant differences among the treatments in leaf loss, Sphaerulina leaf spot, powdery mildew, leaf rust or stem blights when each field was analyzed separately in July and August.  There was less than 10% leaf loss in July in all fields and the highest levels of Sphaerulina leaf spot (7 to 24%) in Columbia field compared to other fields (less than 10%).  Other diseases were less than 5% in July.  In August, leaf loss ranged from 20 to 55% and  leaves of powdery mildew and other leaf spots ranging from 10 to 25%. 

Weed severity (a), insect damage (b) and disease presence (c), measured across 3 locations (Hope, Surry and Columbia Falls) from May-July, 2020. Letters indicate significance at the 0.05 level of significance for weed intensity and insect damage. Treatment differences for disease presence (c) were nonsignificant. Error bars indicate the standard error of the mean.

Effect of Organic Amendments on Harvest Yield and Quality

The 2020 harvest yield of the wild blueberry did not exhibit significant treatment differences across all three locations. Despite no statistical significance, every treatment that received organic amendments yielded higher than the control. Berry quality measures taken at the time of harvest included brix as a measure of berry sugar content and 100 berry weight as a measure of berry size. Berry sugar content was highest in the chicken manure treatments and lowest with University Compost, although treatment differences were nonsignificant. Berry size was significantly lower in both mulch treatments than the University compost (low-rate). All other treatments showed no significant differences from one another in berry size. It is worth noting that while University compost exhibited large berry size, it also had the lowest sugar content, suggesting the berries had a higher water content.

Project B: Weed Management 

Impact of Tine Weeding

Observationally, we saw that two tine weed passes were more effective than one pass per date at uprooting white thread stage weed seedlings. The first pass loosened up the soil required to then dislodge weeds in the second pass. Preliminarily, Canada mayflower, horse weed, and red sorrel were uprooted (Image 2). Loose and dead wild blueberry ramets were pulled up in some cases. The most damage to wild blueberry occurred from driving over the field on the second tine weed date, June 12th (Image 3). On the first tine weed date, May 13th, wild blueberry leaves were not out yet and therefore less damage to wild blueberry from tractor tracks was observed.

Canada mayflower uprooted from tine weeding on May 13, 2019.
The late tine weeding date damaged wild blueberry under tractor tracks and was not as effective at pulling weeds out.

Blueberry Health

In the 2019 prune-year blueberry health was quantified through blueberry cover, stem height, the number of buds per stem and ramet number relative to each treatment. In the prune-year we had observed a 15% increase in the number of ramets in the tine weed plots relative to the control, likely a result of the tine weeder’s capacity to disturb the rhizome and stimulate growth during the vegetative period. In the following crop-year, blueberry health was monitored through bud, flower and fruit development and subsequent fruit drop prior to harvest (Figures 4 & 5). Here, the number of buds and flowers formed per stem were significantly higher in the treatment tine weeded on a single date in the prune-year compared to the control and other treatments. While green fruit and blue fruit numbers were not significantly different between treatments, they followed a similar trend to the bud and flower counts, except blue fruit in the crop year where counts were lower.

Bud, flower and fruit counts by treatment measured in the 2020 crop-year. Treatment differences in green fruit and blue fruit counts were nonsignificant. Letters indicate significance at the 0.05 level of significance. Error bars indicate the standard error of the mean.

Effects of Tine Weeding on Blueberry Cover and Weeds

In 2019 we found no significant differences between weed management treatments and the presence of broadleaf or grass weeds. When combining weed cover over 2019 and 2020 the prune-tined treatment, tine weeded on only one date had significantly greater weed cover than the hand weeded treatment. Blueberry cover was not significantly different between treatments in 2019 or 2020, suggesting that either the blueberry recovered following tine weeding, or the two passes with the tine weeder were less destructive than anticipated.

In the 2020 crop year, the number of weeds (per quadrat) were counted as a measure of weed presence and coverage. Interestingly, the prune-tined treatments had a significantly higher number of weeds than the control and the crop-tined treatment had a significantly lower number of weeds than all other treatments (Figure 7). It’s important to keep in mind that weeds come in all shapes and sizes and the weed community changes over the course of the season. It was observed that small weeds such as bunchberry, red sorrel, or toadflax that remain below the blueberry canopy for much of the season often occurred in higher numbers. While large weeds such as bracken fern or dogbane usually occurred in smaller numbers (1-2 per plot).

Weed number and weed cover observed by treatment throughout the 2020 field season (measured 5/14/20, 5/27/20 and 7/02/20). Treatment differences in weed cover were nonsignificant. Letters indicate significance at the 0.05 level of significance for weed number. Error bars indicate the standard error of the mean.
Blueberry cover prior to tine weeding on May 11th and post-tine weeding (July 7th and Sept 9th). Treatment differences were not significant prior to tine weeding. Letters indicate significance at the 0.05 level of significance for blueberry cover post-tine weeding. Error bars indicate the standard error of the mean.

Preliminary results on cover crop establishment showed the oat outperformed the millet in height (for both rates) and germination (high rate only).

Germination and height of cover crops pearl millet and common oat at two seeding rates. Letters indicate significance at the 0.05 level of significance for germination and plant height, capital letters are to be compared separate from lowercase letters. Error bars indicate the standard error of the mean.
Research conclusions:

Project A: Nutrient Management

From the 2 years of data collected so far from this 4 year study, some soil amendments may be able to improve the condition of organic wild blueberry plants. The highest percent of grass was observed in both rates of chicken manure yet the low rate of chicken manure showed less grass and significantly higher blueberry cover. We also observed a significantly higher chlorophyll concentration in chicken manure treatments. This is most likely due to the higher nitrogen content of the chicken manure (Table 1). Nitrogen is the most important nutrient for building leaf chlorophyll which further helps to improve photosynthetic performance followed by better crop production (Taiz et al. 2015). The Cheep Cheep product has a high macro and micro-nutrient concentration where N-P-K is 4-3-3 and Fe, Cu, S, Ca, Mg, Zn, Mn are present. These nutrients make up 40% of the material. The remaining 60% is organic matter. This indicates that lower rates of chicken manure should be explored with continued monitoring of all pests.

Compost applications appear to have increased water holding capacity in the soil which led to significantly larger berry size. Increased soil water holding capacity allows the plant to move nutrients that fuel berry cell expansion.

SeaCrop16 applications in the prune year (2019) proved to more effective than other treatments yet this same trend was not observed in the 2020 crop year. Seacrop16 contains cytokinin, a plant growth hormone that can potentially protect plants from drought and frost damage and promote photosynthesis (Novakova et al. 2007). In 2020, wild blueberry experienced higher temperatures and drought conditions making plants stressed in these fields without irrigation. This may be why the 2019 SeaCrop16 application proved to be one of the efficient treatments compared to the 2020 SeaCrop16 application.

Cost of Products

The cost of products used plays a critical role in implementation by wild blueberry growers (Table 2). The Coast of Maine Cobscook Blend was the most expensive product, followed by North Country Organics Cheep Cheep. Both the North American Kelp Seacrop 16 foliar fertilizer and Mark Wright Disposal mulch had lower costs per unit and were also applied at lower rates compared to the chicken manure, thus resulting in overall lower costs compared to all other treatments. No cost was given for compost because it was donated by the University of Maine for this study.

Table 2. Cost comparison of 2019 prune-cycle treatments. Cost is based on one application. Prices may vary based on quantity purchased, grower size, and retailer.

Product

Rate

Cost ($/acre)

Cost/unit

 

Control

N/A

N/A

 

 

N/A

 

North American Kelp Co. Seacrop16

Foliar Fertilizer

1.2 L/242 gal. H2O/A

$14.70

 

$245/5 gal.

 
 

North Country Organics Cheep Cheep

Chicken Manure 4-3-3

1089 lbs./A

$814

$37/50 lb.

 

2178 lbs. /A

$1628

 

Coast of Maine

Cobscook Blend Garden Soil

7.5 yd3/A

$2025

$270/yd3

 

15 yd3/A

$4050

 

Mark Wright Disposal

Dark Brown Mulch

7.5 yd3/A

$240

$32/yd3

 

15 yd3/A

$480

 

*University of Maine Compost

7.5 yd3/A

N/A

N/A

 

15 yd3/A

N/A

 

Project B: Weed Management 

Blueberry Health

In the initial two years of this trial, the greatest response from the wild blueberry to tine weeding has been through the formation of buds, flowers and subsequent berry size. In prune-tined treatments the number of buds per stem were significantly higher, as well as the number of flowers per stem for one of the two treatments (Figure 3). This increase in vegetative and reproductive growth may be a positive response from the blueberry to the physical disturbance of the tine weeding. Similar mechanical stimulus (i.e. pruning, burning and the cutting of rhizomes) has been observed to benefit wild blueberry (Libby 2011). The crop-tined treatment had a high bud count per stem, but a relatively low flower and fruit count suggesting the buds may have been damaged from tine disturbance in the crop-year. These differences in bud and fruit development suggest the plant couldn’t support the number of buds formed, fertilizing the wild blueberry in addition to tine weeding could mitigate this effect.

Weed Control

As a very direct and physically aggressive mode of weed management, we anticipated a decrease in the number of weeds and overall weed cover in the tine weeded plots. Interestingly, the treatments tine weeded in the 2019 prune-year, exhibited a greater number of weeds and weed cover in 2020 relative to the control and crop-tined treatments (Figure 7). This increase in weed pressure in the prune-tined plots could be due to a variety of factors.

First, the field where this trial is located is in organic transition and was last sprayed with herbicide in 2017. As the effect of the herbicide applied in the past wares off, we expect weed pressure to increase. However, as shown in Table 3, the top weeds in these plots shifted from bunch berry in 2019 to red sorrel (which typically occurs in higher numbers) in 2020. A successional shift in weed type and the presence of opportunist weeds in an organically managed field may be a driving factor in these prune-tined treatments. Similar to burn pruning, tine weeding may be more effective on certain types of weeds provide an opportunity for other species to emerge after the disturbance (Jensen and Yarborough 2004). 

An alternative theory is that the mechanism of tine weeding may have facilitated the gemination of these weeds. The organic field where this trial took place is primarily flail-mowed which is known to increase seed deposition and seed banks over time (Jensen and Yarborough 2004).  There may have been dormant seed banks stored on top of or below the surface in the organic pad that were “planted” by the tine weeder, providing weed seeds the resources they needed for establishment. Tine weeding in the prune-year may have been effective in the long-term in a burn field with smaller seedbanks from year-to-year.

The treatment tine weeded in the 2020 crop-year exhibited the least weed pressure showing that the tine weeder can be effective in the short-term. The efficacy of this method applied in the crop-cycle may be a tradeoff as these treatments also experienced poor fruit-set and yield. These results are interesting but still preliminary as this was year two of a four-year trial. Repeated measures throughout the 2021 prune-year and 2022 crop-year should help us to identify the true potential of tine weeding on the weed community and wild blueberry plant stimulation.

Yield and Quality

The 2020 harvest yield did not present significant treatment differences. It is worth noting, that there were patches of leaf spot disease in this field which may have impacted yield in 2020. While the control yielded highest with an average 4400 lbs/A, the hand weed treatment averaged 3300 lbs/A, which is 1100lbs/A less than the control and 100-500 lbs/A less than the prune-tined treatments. The prune-tined treatments averaged 3400 and 3900 lbs/A for the single date and double-date tine weed, respectively. The crop-tined treatment was the lowest at 2200 lbs/A, half that of the control. While a greater number of buds and flowers formed on the prune-tined treatments, this appeared to be a tradeoff for significantly smaller fruit. This further reinforces the plants ability to support the number of buds formed, as generating more fruit requires more resources. Slight treatment differences observed in berry sugar content may be a function of development rate or clonal differences.

Cover Crop Establishment

With successful cover crop establishment in September 2020, follow-up measures will be taken in the spring of 2021 to ensure winter kill of the cover crops and cover crops will be replanted the following fall. Because the coverage of cover crop seed in 2020 was low, a higher seeding rate will be planted in 2022 and cover crop seed will be planted earlier (right after harvest) to allow for more above ground cover crop growth before frosts occur.  

Participation Summary
5 Farmers participating in research

Education

Educational approach:

A collaborative research and outreach program continues to reach both organic and conventional wild blueberry growers. In the first year of this project, the research team worked with collaborating farmers to finalize treatments and set up research trials on three farms. We shared this project at the Annual Wild Blueberry Field Day held in Jonesboro ME (91 attendees), Organic Wild Blueberry Growers Field Day in Dresden ME (20 attendees), and Western Maine Wild Blueberry Field Meeting in Otisfield ME (14 attendees).  First year results were presented at the 2020 Wild Blueberry Conference which will be held in Bangor ME on February 22 which had 90 attendees, 45% of which identified as organic. Throughout the rest of 2020 education and outreach related to this project had to be conducted virtually due to the Covid-19 pandemic. From April through June on Friday mornings "Wild Blueberry Coffee Hours" were held as a way to engage growers and allow for further education as the season began (34 total attendees). Four virtual field days were held in July 2020 that covered disease, insect, weed, and nutrient management for both organic and conventional growers (61 total attendees). In September 2020 we were able to hold 2 in-person field meetings that were socially distanced and with masks where results from this project were shared on big posters outside (24 total attendees). In 2020 our wild blueberry newsletter reached 735 recipients (486 online and 249 in print) where important project updates are shared. The project team looks forward to hopefully holding in-person events in 2021. 

Lily Calderwood presenting the tine weeding trial at the 2019 Maine Wild Blueberry Field Day in Jonesboro, ME.
Co-PI Seanna Annis explaining how to identify leaf spots on wild blueberry at the 2019 Organic Wild Blueberry Growers Meeting in Dresden, ME.
Calderwood and growers learning about organic weed management during an outdoor 2020 field meeting.

Milestones

Milestone #1 (click to expand/collapse)
What beneficiaries do and learn:

1. Four farmers give feedback on research trial design and treatments.

Proposed number of farmer beneficiaries who will participate:
4
Actual number of farmer beneficiaries who participated:
4
Actual number of agriculture service provider beneficiaries who participated:
5
Proposed Completion Date:
July 31, 2019
Status:
In Progress
Accomplishments:

From discussion with members of the advisory group the chicken manure treatments of the fertility trial are of interest and further study was suggested to look at lower rates of chicken manure which may cause less of a weed problem. Mulch is also a material of great interest after the 2020 drought conditions. Without water, plants can't take up the nutrients they need. 

Milestone #2 (click to expand/collapse)
What beneficiaries do and learn:

2. Three farmers host the three replications of the nutrient research trial on their farm.

Proposed number of farmer beneficiaries who will participate:
3
Actual number of farmer beneficiaries who participated:
3
Proposed Completion Date:
August 31, 2019
Status:
In Progress
Accomplishments:

Trials are in place and will continue next year. 

Milestone #3 (click to expand/collapse)
What beneficiaries do and learn:

3. One farmer hosts the irrigation demonstration.

Proposed number of farmer beneficiaries who will participate:
1
Proposed Completion Date:
September 30, 2021
Status:
In Progress
Accomplishments:

We attempted to set up an irrigation demonstration this year but the well at Blueberry Hill farm was in disrepair and farmers would not have been able to come to an in-person demo so this has been put off until next year. 

Milestone #4 (click to expand/collapse)
What beneficiaries do and learn:

4. Four trial host farmers collect production and sales data and report their 2018 and 2019 average blueberry yield and average price.

Proposed number of farmer beneficiaries who will participate:
4
Proposed Completion Date:
November 30, 2019
Status:
In Progress
Accomplishments:

Yield has been reported for 3 of the farms for the 2020 harvest and we will need to compare this to the next crop year which is 2024.

Organic wild blueberries are sold for $13.00/lb fresh and $5.00/lb frozen (average market values) and it costs approximately $3.00 to produce each pound with an average yield of 2,000lbs/acre.

For organic growers who sell their berries to the organic frozen commodity market in Maine, prices were $1.64/lb in 2017 and are now $1.04/lb due to the lack of marketing. However, demand for organic blueberries (both wild and cultivated) increased 12.6% (USHBC 2018). This trend is prominent in the Northeast and relevant to local businesses and the wild blueberry industry. RAS Wines, a large local purchaser of lowbush blueberries, has indicated that they plan to increase their annual purchase of organic lowbush blueberries from 18,000 lbs in 2020 to 32,000-40,000 lbs in 2021. Three prominent organic farms in Maine have already begun to engage with the trend, making online sales of organic lowbush frozen berries, powder, chips, and tea, where 12oz of powder is sold for $64.00 ($5.30/oz).

The number of certified organic wild blueberry acres in Maine has increased from 1,800 acres in 2018 to 2,635 acres in 2020, with current production of approximately 5 million lbs (2,000lbs/acre) of berries per year. 

Milestone #5 (click to expand/collapse)
What beneficiaries do and learn:

5. Ten farmers receive individual assistance with adoption of a new management practice through phone
consultations and/or site visits.

Proposed number of farmer beneficiaries who will participate:
10
Actual number of farmer beneficiaries who participated:
14
Actual number of agriculture service provider beneficiaries who participated:
1
Proposed Completion Date:
December 31, 2019
Status:
In Progress
Accomplishments:

Calderwood has documented individual consultations with 14 organic growers or interested-in-organic growers in the first 2 years. Communicating best organic management practices with these 14 producers impacts the management of 346 wild blueberry acres in Maine.

Milestone #6 (click to expand/collapse)
What beneficiaries do and learn:

6. 200 blueberry farmers attend the Maine Wild Blueberry Conference.

Proposed number of farmer beneficiaries who will participate:
200
Actual number of agriculture service provider beneficiaries who participated:
15
Proposed Completion Date:
March 31, 2022
Status:
In Progress
Accomplishments:

In 2019 there were 160 attendees at the UMaine Wild Blueberry Conference. 

In 2020 there were 90 attendees at the UMaine Wild Blueberry Conference. 

In 2021, the conference is planned to occur virtually for two hours on Wednesdays and Fridays from January-March. Organic pest and crop management is one of the sessions while others are not exclusively organic, will cover many organic crop and pest management topics related to this project. The full agenda can be found here: https://extension.umaine.edu/blueberries/calendar-of-events/umaine-wild-blueberry-conference/#agenda. 

 

Milestone #7 (click to expand/collapse)
What beneficiaries do and learn:

7. 40 blueberry farmers attend at least one of two field days held in 2020 and report learning about a new management practice.

Proposed number of farmer beneficiaries who will participate:
40
Actual number of farmer beneficiaries who participated:
172
Actual number of agriculture service provider beneficiaries who participated:
10
Proposed Completion Date:
December 31, 2020
Status:
In Progress
Accomplishments:

20 organic growers attended the 2019 Organic Field Day in Dresden ME. 

91 growers attended the 2019 Annual Wild Blueberry Field Day in Jonesboro ME (approximately 20% were organic)

61 growers attended the 2020 Virtual Wild Blueberry Field Meetings (approximately 30% were organic)

 

Milestone #8 (click to expand/collapse)
What beneficiaries do and learn:

8. Ten farmers receive individual assistance with adoption of a new management practice through phone consultations and/or site visits.

Proposed number of farmer beneficiaries who will participate:
10
Proposed Completion Date:
December 31, 2020
Status:
In Progress
Accomplishments:

Calderwood has documented individual consultations with 14 organic growers or interested-in-organic growers in the first 2 years. Communicating best organic management practices with these 14 producers impacts the management of 346 wild blueberry acres in Maine.

Milestone #9 (click to expand/collapse)
What beneficiaries do and learn:

9. 400 blueberry farmers attend the Maine Wild Blueberry Conference.

Proposed number of farmer beneficiaries who will participate:
400
Proposed Completion Date:
March 31, 2021
Status:
In Progress
Milestone #10 (click to expand/collapse)
What beneficiaries do and learn:

10. 1000 Northeast (ME, NH, MA, and Canadian provinces) blueberry farmers receive blueberry newsletter and factsheets.

Proposed number of farmer beneficiaries who will participate:
1000
Proposed Completion Date:
March 31, 2021
Status:
In Progress
Milestone #11 (click to expand/collapse)
What beneficiaries do and learn:

11. 40 blueberry farmers attend at least one of two field days held in 2021 and report learning about a new management practice.

Proposed number of farmer beneficiaries who will participate:
40
Proposed Completion Date:
September 30, 2022
Status:
In Progress
Milestone #12 (click to expand/collapse)
What beneficiaries do and learn:

12. 30 blueberry farmers from ME, NH, MA, and Canadian provinces attend some or all of three webinars and report learning about a new management practice

Proposed number of farmer beneficiaries who will participate:
30
Proposed Completion Date:
December 31, 2021
Status:
In Progress
Milestone #13 (click to expand/collapse)
What beneficiaries do and learn:

13. Ten farmers receive individual assistance with adoption of a new management practice through phone consultations and/or site visits.

Proposed number of farmer beneficiaries who will participate:
10
Proposed Completion Date:
December 31, 2021
Status:
In Progress
Milestone #14 (click to expand/collapse)
What beneficiaries do and learn:

14. 30 blueberry farmers attending at least one of two field days held in 2022 report learning about a new management practice.

Proposed number of farmer beneficiaries who will participate:
30
Proposed Completion Date:
November 30, 2022
Status:
In Progress
Milestone #15 (click to expand/collapse)
What beneficiaries do and learn:

15. 30 blueberry farmers ME, NH, MA, and Canadian provinces attend some or all of three webinars and report learning about a new management practice.

Proposed number of farmer beneficiaries who will participate:
30
Proposed Completion Date:
November 30, 2022
Status:
In Progress
Milestone #16 (click to expand/collapse)
What beneficiaries do and learn:

16. 200 blueberry farmers from ME, NH, MA, and Canadian provinces watch at least one of 6 webinar videos posted to our YouTube channel.

Proposed number of farmer beneficiaries who will participate:
200
Proposed Completion Date:
November 30, 2022
Status:
In Progress
Milestone #17 (click to expand/collapse)
What beneficiaries do and learn:

17. Three trial host farmers collect and submit their 2020, 2021, and 2022 average blueberry yield and average price data, excluding trial plots

Proposed number of farmer beneficiaries who will participate:
3
Proposed Completion Date:
November 30, 2022
Status:
In Progress
Milestone #18 (click to expand/collapse)
What beneficiaries do and learn:

18. 600 Northeast (ME, NH, MA, and Canadian provinces) blueberry farmers receive the Lowbush Blueberry Management Guide.

Proposed number of farmer beneficiaries who will participate:
600
Proposed Completion Date:
November 30, 2022
Status:
In Progress
Milestone #19 (click to expand/collapse)
What beneficiaries do and learn:

19. Ten farmers receive individual assistance with adoption of a new management practice through phone consultations and/or site visits.

Proposed number of farmer beneficiaries who will participate:
10
Proposed Completion Date:
November 30, 2022
Status:
In Progress

Milestone Activities and Participation Summary

Educational activities:

89 Consultations
1 Curricula, factsheets or educational tools
4 On-farm demonstrations
5 Online trainings
3 Published press articles, newsletters
1 Tours
2 Webinars / talks / presentations
9 Workshop field days

Participation Summary:

150 Farmers
35 Number of agricultural educator or service providers reached through education and outreach activities

Learning Outcomes

70 Farmers reported changes in knowledge, attitudes, skills and/or awareness as a result of their participation
3 Agricultural service providers reported changes in knowledge, skills, and/or attitudes as a result of their participation
Key areas in which farmers reported changes in knowledge, attitude, skills and/or awareness:

Six new and transitioning growers asked about managing wild blueberry organically in 2019 and 2020. 

Three organic growers let me know that they are taking on new organic acreage. The only wild blueberry growers buying land are currently organically certified. 

One wild blueberry grower wanted to discuss the difficulty in getting a farm loan for wild blueberry due to the lack of market for wild blueberry in general. 

One grower wanted to learn more about managing pollinator habitat on organic wild blueberry land.

Service providers ask about mulching, applying sulfur for weed management, and if burning actually helps to manage mummy berry. 

Performance Target Outcomes

Target #1

Target: number of farmers:
50
Target: change/adoption:

adopt at least one new weed, nutrient, or irrigation management practice

Target: amount of production affected:

500

Target: quantified benefit(s):

5 managing certified organic farms will increase their average yield by 500 lbs/acre on a total of 100 acres

Actual: number of farmers:
7
Actual: change/adoption:

Adopted weed management especially, how and when to apply sulfur to reduce soil pH which is a known grass management tool. Adopted different burn-pruning practices that allow for mummy berry management while saving organic matter.

Actual: amount of production affected:

330

Actual: quantified benefit(s):

Working on that...

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.