Fish extracts for integrated disease, insect and fertility management in organic blueberries

Fish extracts for integrated disease, insect and fertility management in organic blueberries

Summary

Two on-farm trials (one each on rabbiteye and southern highbush blueberry cultivars) were conducted in 2009 in southern Georgia to evaluate an integrated system for improved disease, insect, and nutrient management in organic blueberries based on foliar applications of fish byproducts. Six spray applications of four different fish formulations (Omega Grow, Organic Gem, Organocide, and SeaCide) were made during summer and early fall at each site and compared with an untreated check, an organic standard fungicide (Serenade Max), and a plant oil-based biofungicide (Sporan). Although disease and insect pressures were only low to moderate, several preliminary conclusions could be drawn from the first year of this project. Two different foliar diseases, Septoria leaf spot (on rabbiteye) and leaf rust (on southern highbush), were suppressed successfully. Among the four tested fish formulations, Omega Grow (which reduced Septoria leaf spot severity to less than one-third of the untreated plots) and SeaCide appeared most effective. Two of the four products, Organocide and SeaCide, were effective in maintaining plant vigor and reducing defoliation into late fall. For example, by early December in the rabbiteye trial, the SeaCide-treated plants had retained three times more leaves than the untreated check. Leaf beetle damage differed among treatments in the southern highbush trial, with SeaCide, Serenade Max, and Sporan having lower damage levels than the untreated plots. Some changes in leaf nutrient concentrations were observed in response to treatment, including an increase in foliar Na in Omega Grow-treated plants in both trials and an increase in leaf P following applications of Organic Gem and Organocide in the southern highbush trial.

Objectives/Performance Targets

Overall aim: develop an integrated approach for disease, insect, and nutrient management in organic blueberries centered around foliar applications of fish byproducts.

Specific objectives:
(1) compare and demonstrate the efficacy of several fish extracts against foliar diseases of blueberry;
(2) evaluate leaf beetle suppression in fish extract-treated plots; and
(3) determine the nutritional benefits of fish extracts applications by measuring foliar nutrient status as well as plant growth and yield parameters in treated plots.

Accomplishments/Milestones

Two on-farm trials were conducted during summer and fall 2009 on commercial blueberry farms in southern Georgia. Site 1 was a certified organic farm in Appling County, where the trial was conducted in mature bushes of Brightwell rabbiteye blueberry. Site 2 was a commercial farm located in neighboring Bacon County, where mature bushes of Bluecrisp southern highbush blueberry were utilized for the trial.

Six foliar spray applications of four fish product formulations were made between late July and early October (site 1) or mid-July and late September (site 2): (1) Omega Grow, 2% (Omega Protein, Houston, TX); (2) Organic Gem, 2% (Advanced Marine Technologies, New Bedford, MA); (3) SeaCide, 1% (Omega Protein, Houston, TX); and (4) Organocide, 2% (Organic Laboratories, Stuart, FL). The latter product contains sesame oil in addition to fish oil. As the fifth treatment, Sporan at 2.5 pt/acre (EcoSMART Technologies, Franklin, TN), a plant-derived biofungicide containing rosemary and wintergreen oils, was included. Furthermore, (6) an untreated check and (7) an organic standard treatment of the biofungicide Serenade Max at 1.5 lb/acre (AgraQuest, Davis, CA) were included. All products are OMRI-listed. Applications were made with backpack sprayers calibrated to deliver the equivalent of 60-75 gal/acre. At both sites, treatment plots were arranged in a randomized complete block design with four replicates. Individual plots were four (site 1) or between two and four (site 2) bushes long and separated by untreated buffers.

LEAF DISEASE SUPPRESSION
At site 1, Septoria leaf spot (caused by the fungus Septoria albopunctata) was the dominant foliar disease. Disease severity was determined in late August and late October by counting the number of spots on a sample of 40 leaves per plot. Disease levels remained low during the early fall, with an average of 2.4 spots per leaf in the untreated check during the late-August assessment; because of the low leaf spot levels, no biofungicide effects on disease severity were apparent for this assessment date. During the next 2 months, Septoria leaf spot increased to moderate levels, reaching an average of about 10 spots per leaf in the untreated plots during the late-October assessment (Table 1). There was a trend (P = 0.0647) for differences among biofungicide treatments, with all fish products (Omega Grow, Organic Gem, Organocide, SeaCide) as well as Sporan having less severe disease than the untreated check. Leaf spot severity was lowest for Omega Grow (less than one-third of untreated).

Septoria leaf spot was all but absent at site 2, with <0.2 spots per leaf in the untreated plots during the late-October assessment. However, late-season leaf rust (caused by the fungus Thekopsora minima) developed at this site and was assessed by visually estimating the percentage of leaf area covered with rust pustules on a sample of 25 leaves per plot. Due to high variation among replicates, no significant treatment effects on rust severity were observed; however, Omega Grow and SeaCide-treated plots consistently had very low rust severities (Table 1).

LEAF BEETLE SUPPRESSION
No leaf beetle populations built up at site 1, hence only results from site 2 are shown here. At the latter site damage assessments were made in early and late October using a rating scale from 0 (no damage) to 4 (severe damage). On average, about 20% of the leaves inspected during the late-October assessment showed symptoms of leaf beetle damage. Beetle damage differed among biofungicide treatments at a trend level of P = 0.0641, with SeaCide, Serenade Max, and Sporan having lower damage scores than the untreated plots (Table 1).

PLANT VIGOR AND LEAF NUTRIENT LEVELS
A plant vigor rating was conducted at site 1 in late October using a rating scale from 1 (poor) to 5 (excellent). At the same time, a random sample of spring leaves from each plot was submitted for tissue nutrient analysis. In early December defoliation and flower bud set were determined by counting the leaves missing and the flower buds present on a sample of ten shoots per plot. No such assessments were made at site 2 due to confounding effects of infections with bacterial leaf scorch (caused by Xylella fastidiosa), a systemic disease of southern highbush blueberry affecting plant vigor, leaf retention, and flower bud set.

When plant vigor was assessed at site 1, biofungicide treatment effects were highly significant (P = 0.0011). Vigor was increased by all treatments relative to untreated, except by Organic Gem (Table 2). Ratings were highest for Serenade Max, Organocide, and SeaCide. The latter two fish products also increased leaf retention (assessed separately in early December) significantly compared with the untreated plots (Table 2). For example, the SeaCide-treated plants retained three times more leaves than their untreated counterparts. Flower bud set (also assessed in early December) was very low overall and was not significantly affected by treatment (Table 2).

No pronounced treatments effects on foliar nutrient levels were found at site 1, except for a highly significant (P < 0.0001) increase in leaf Na concentrations following application of Omega Grow and, to a lesser degree, Serenade Max (Table 3). The impact of such drastically increased Na levels on the physiology of the plant remains to be determined. A less pronounced (P = 0.0643) increase in leaf Na concentrations following the application of Omega Grow was also observed at site 2. At the latter site, applications of Organic Gem and Organocide had the beneficial effect of increasing leaf P levels compared with the untreated check (P = 0.0510; Table 3).

• Tables 1 through 3

Impacts and Contributions/Outcomes

• Both Septoria leaf spot and leaf rust were suppressed successfully with fish products. Among the four tested formulations, Omega Grow and SeaCide appeared most effective.
  Two of the four fish products evaluated, Organocide and SeaCide, were effective in maintaining plant vigor and improving leaf retention into the late fall. However, under the conditions of this test, flower bud set (the foundations of next year’s yield) was not enhanced.
  Some changes in leaf nutrient concentrations were observed in response to treatment, the most pronounced of which was the considerable increase in foliar Na concentrations in Omega Grow-treated plants; this effect could be undesirable if it interferes with K uptake and/or metabolism in the cell. Although only significant at one of the two sites, the increase in foliar P concentrations following application of Organic Gem and Organocide could be very positive and should be explored further.

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